Description

APPARATUS FOR COMBINING AND SPLITTING WAVELENGTH BAND HAVING FOUR INPUT AND OUTPUT

PORTS

Technical Field

[1] The present invention relates to an apparatus for combining and splitting wavelength bands having four input and output ports for bi-directional transmission. More specifically, the present invention relates to an apparatus for combining and splitting wavelength bands having four input and output ports, which is capable of adding a new wavelength band for new bi-directional transmission and a new wavelength band for new uni-directional transmission, and is necessary for combining the new wavelength bands with an existing wavelength band being transmitted bi-directionally through a one-line transmission path or for splitting the new wavelength bands from the existing wavelength band, while accommodating the existing wavelength band as it is. Background Art

[2] A need for broadband services is increased rapidly since the use of Internet has been increased and image and video oriented services have been generally used, and thus an interest has been focused on a metro/access network which connects a remote node to subscribers. In order for the metro/access network to meet the need of the subscribers for high-speed services, a method of accomplishing a high-speed must be done easily and at low costs to accommodate many subscribers. Thus, it is possible to make effectively a network to have a high-speed and to provide broadband services if a wavelength division multiplexing technology is applied to the metro/access network, because such technology is possible to transmit wavelength division multiplexed optical signals using a plurality of wavelengths, with the transparency of transmission methods and bit rate. As a one method of expanding the existing metro/access network, a new wavelength band may be added as a transmission wavelength band, in addition to an existing wavelength band which has already been used. For doing so, a new wavelength band should be combined with or split from the existing wavelength band so that an apparatus for combining and splitting wavelength bands is required.

[3] An element such as add/drop multiplexers having a function of combining a signal with or splitting the signal from a predetermined wavelength in a transmission band has been used in the existing metro/access network. However, each add/drop multiplexer is required to be equipped with per each wavelength to be used for combining a signal having a new wavelength or splitting an existing signal in a prior art. Thus, such a requirement relating to add/drop multiplexers has a problem that it is

cumbersome in terms of installation and costs should be necessarily increased due to the use of a plurality of add/drop multiplexers.

[4] In addition, the add/drop multiplexers of the prior art may combine and split only a signal having a predetermined specific wavelength. Thus, there is a problem that usability of the add/drop multiplexers has a certain limitation. Disclosure of Invention Technical Problem

[5] The object of the present invention is to solve the prior art problems and provide an optical passive element, which is capable of adding a new wavelength band for new bidirectional transmission and a new wavelength band for new uni-directional transmission, and is necessary for combining the new wavelength bands with an existing wavelength band being transmitted bi-directionally through a one-line transmission path or for splitting the new wavelength bands from the existing wavelength band, while accommodating the existing wavelength band as it is. Technical Solution

[6] More specifically, according to a first aspect of the present invention, the present invention provides an apparatus for combining and splitting wavelength bands having four input and output ports for bi-directional transmission comprising: a first wavelength division multiplexing (WDM) filter for splitting X-band having a range of a first wavelength or less and Y-band having a range of a second wavelength or more from a wavelength band of light being transmitted though the four input and output ports; a second WDM filter for splitting X-band having a range of a first wavelength or less and Y-band having a range of a second wavelength or more from the wavelength band of light being transmitted though the four input and output ports; a third WDM filter for splitting Zl -band having a range of a third wavelength within Y-band having the range of the second wavelength or more; and a fourth WDM filter for splitting Z2-band having a range of a fourth wavelength within Y-band having the range of the second wavelength or more.

[7] According to a second aspect of the present invention, the present invention provides an apparatus for combining and splitting wavelength bands having four input and output ports for bi-directional transmission comprising: a first wavelength division multiplexing (WDM) filter for splitting X-band having a range of a first wavelength or less and Y-band having a range of a second wavelength or more from a wavelength band of light being transmitted though the four input and output ports; a second WDM filter for splitting Zl -band having a range of a third wavelength within Y-band having the range of the second wavelength or more; a third WDM filter for splitting Zl-band having the range of the third wavelength within Y-band having the range of the second

wavelength or more; and a fourth WDM filter for splitting Z2-band having a range of a fourth wavelength within Y-band having the range of the second wavelength or more.

[8] According to a third aspect of the present invention, the present invention provides an apparatus for combining and splitting wavelength bands having four input and output ports for bi-directional transmission comprising: a first wavelength division multiplexing (WDM) filter for splitting X-band having a range of a first wavelength or less and Y-band having a range of a second wavelength or more from a wavelength band of light being transmitted though the four input and output ports; s second WDM filter for splitting X-band having a range of a first wavelength or less and Y-band having a range of a second wavelength or more from the wavelength band of light being transmitted though the four input and output ports; a third WDM filter for splitting Zl -band having a range of a third wavelength within X-band having the range of the first wavelength or less; and a fourth WDM filter for splitting Z2-band having a range of a fourth wavelength within X-band having the range of the first wavelength or less.

[9] According to a fourth aspect of the present invention, the present invention provides an apparatus for combining and splitting wavelength bands having four input and output ports for bi-directional transmission comprising: a first wavelength division multiplexing (WDM) filter for splitting X-band having a range of a first wavelength or less and Y-band having a range of a second wavelength or more from a wavelength band of light being transmitted though the four input and output ports; a second WDM filter for splitting Zl -band having a range of a third wavelength within X-band having the range of the first wavelength or less; a third WDM filter for splitting Zl-band having the range of the third wavelength within X-band having the range of the first wavelength or less; and a fourth WDM filter for splitting Z2-band having a range of a fourth wavelength within X-band having the range of the first wavelength or less.

[10] According to a fifth aspect of the present invention, the present invention provides an apparatus for combining and splitting wavelength bands having four input and output ports for bi-directional transmission comprising: a first wavelength division multiplexing (WDM) filter for splitting X-band having a range of a first wavelength or less and Y-band having a range of a second wavelength or more from a wavelength band of light being transmitted though the four input and output ports; a second WDM filter for splitting Zl-band having a range of a third wavelength within Y-band having the range of the second wavelength or more; a third WDM filter for splitting Z2-band having the range of the fourth wavelength within Y-band having the range of the second wavelength or more; and a fourth WDM filter for splitting Z3-band having a range of a fifth wavelength within X-band having the range of the first wavelength or less.

[11] Further features and advantages of the present invention can be obviously understood

with reference to the accompanying drawings where same or similar reference numerals indicate same components.

Advantageous Effects

[12] An apparatus for combining and splitting wavelength bands having four input and output ports according to the present invention has the following advantages: [13] 1. The present invention can be embodied at low costs and with a simple configuration so that it may function as the prior art add/drop multiplexers. [14] 2. Unlike the prior art add/drop multiplexers which can combine and split only a signal with a specific wavelength, the present invention may combine a wavelength band having a certain range with or split it from an existing signal band so that high usability can be accomplished in the present invention. [15] 3. The present invention may be utilized as an element for upgrading and expanding an existing metro network or an existing access network so that performance of an optical communications system can be enhanced at low costs. [16] 4. The present invention may increase flexibility and expansibility of an existing metro network or an existing access network.

Brief Description of the Drawings [17] Fig. 1 illustrates a first example of a general view of split bands and bi-directional wavelength bands of wavelength division multiplexing filters for bi-directional transmission. [18] Fig. 2 illustrates a second example of a general view of split bands and bi-directional wavelength bands of wavelength division multiplexing filters for bi-directional transmission. [19] Fig. 3 illustrates a third example of a general view of split bands and bi-directional wavelength bands of wavelength division multiplexing filters for bi-directional transmission. [20] Fig. 4 illustrates a first embodiment of an apparatus for combining and splitting wavelength bands for bi-directional transmission according to the present invention illustrated in Fig. 1. [21] Fig. 5 illustrates a first alternative embodiment of an apparatus for combining and splitting wavelength bands according to the first embodiment of the present invention illustrated in Fig. 4. [22] Fig. 6 illustrates a second alternative embodiment of an apparatus for combining and splitting wavelength bands according to the first embodiment of the present invention illustrated in Fig. 4. [23] Fig. 7 illustrates a third alternative embodiment of an apparatus for combining and splitting wavelength bands according to the first embodiment of the present invention

illustrated in Fig. 4. [24] Fig. 8 illustrates a second embodiment of an apparatus for combining and splitting wavelength bands for bi-directional transmission according to the present invention illustrated in Fig. 1. [25] Fig. 9 illustrates a first alternative embodiment of an apparatus for combining and splitting wavelength bands according to the second embodiment of the present invention illustrated in Fig. 8. [26] Fig. 10 illustrates a second alternative embodiment of an apparatus for combining and splitting wavelength bands according to the second embodiment of the present invention illustrated in Fig. 8. [27] Fig. 11 illustrates a third alternative embodiment of an apparatus for combining and splitting wavelength bands according to the second embodiment of the present invention illustrated in Fig. 8. [28] Fig. 12 illustrates a third embodiment of an apparatus for combining and splitting wavelength bands for bi-directional transmission according to the present invention illustrated in Fig. 1. [29] Fig. 13 illustrates a first alternative embodiment of an apparatus for combining and splitting wavelength bands according to the third embodiment of the present invention illustrated in Fig. 12. [30] Fig. 14 illustrates a second alternative embodiment of an apparatus for combining and splitting wavelength bands according to the third embodiment of the present invention illustrated in Fig. 12. [31] Fig. 15 illustrates a third alternative embodiment of an apparatus for combining and splitting wavelength bands according to the third embodiment of the present invention illustrated in Fig. 12. [32] Fig. 16 illustrates a fourth embodiment of an apparatus for combining and splitting wavelength bands for bi-directional transmission according to the present invention illustrated in Fig. 1. [33] Fig. 17 illustrates a first alternative embodiment of an apparatus for combining and splitting wavelength bands according to the fourth embodiment of the present invention illustrated in Fig. 16. [34] Fig. 18 illustrates a second alternative embodiment of an apparatus for combining and splitting wavelength bands according to the fourth embodiment of the present invention illustrated in Fig. 16. [35] Fig. 19 illustrates a third alternative embodiment of an apparatus for combining and splitting wavelength bands according to the fourth embodiment of the present invention illustrated in Fig. 16. [36] Fig. 20 illustrates a fifth embodiment of an apparatus for combining and splitting

wavelength bands for bi-directional transmission according to the present invention illustrated in Fig. 1. [37] Fig. 21 illustrates a first alternative embodiment of an apparatus for combining and splitting wavelength bands according to the fifth embodiment of the present invention illustrated in Fig. 20. [38] Fig. 22 illustrates a second alternative embodiment of an apparatus for combining and splitting wavelength bands according to the fifth embodiment of the present invention illustrated in Fig. 20. [39] Fig. 23 illustrates a third alternative embodiment of an apparatus for combining and splitting wavelength bands according to the fifth embodiment of the present invention illustrated in Fig. 20. [40] Fig. 24 illustrates a sixth embodiment of an apparatus for combining and splitting wavelength bands for bi-directional transmission according to the present invention illustrated in Fig. 1. [41] Fig. 25 illustrates a first alternative embodiment of an apparatus for combining and splitting wavelength bands according to the sixth embodiment of the present invention illustrated in Fig. 24. [42] Fig. 26 illustrates a second alternative embodiment of an apparatus for combining and splitting wavelength bands according to the sixth embodiment of the present invention illustrated in Fig. 24. [43] Fig. 27 illustrates a third alternative embodiment of an apparatus for combining and splitting wavelength bands according to the sixth embodiment of the present invention illustrated in Fig. 24. [44] Fig. 28 illustrates a seventh embodiment of an apparatus for combining and splitting wavelength bands for bi-directional transmission according to the present invention illustrated in Fig. 2. [45] Fig. 29 illustrates a first alternative embodiment of an apparatus for combining and splitting wavelength bands according to the seventh embodiment of the present invention illustrated in Fig. 28. [46] Fig. 30 illustrates a second alternative embodiment of an apparatus for combining and splitting wavelength bands according to the seventh embodiment of the present invention illustrated in Fig. 28. [47] Fig. 31 illustrates a third alternative embodiment of an apparatus for combining and splitting wavelength bands according to the seventh embodiment of the present invention illustrated in Fig. 28. [48] Fig. 32 illustrates an eighth embodiment of an apparatus for combining and splitting wavelength bands for bi-directional transmission according to the present invention illustrated in Fig. 2.

[49] Fig. 33 illustrates a first alternative embodiment of an apparatus for combining and splitting wavelength bands according to the eighth embodiment of the present invention illustrated in Fig. 32. [50] Fig. 34 illustrates a second alternative embodiment of an apparatus for combining and splitting wavelength bands according to the eighth embodiment of the present invention illustrated in Fig. 32. [51] Fig. 35 illustrates a third alternative embodiment of an apparatus for combining and splitting wavelength bands according to the eighth embodiment of the present invention illustrated in Fig. 32. [52] Fig. 36 illustrates a ninth embodiment of an apparatus for combining and splitting wavelength bands for bi-directional transmission according to the present invention illustrated in Fig. 2. [53] Fig. 37 illustrates a first alternative embodiment of an apparatus for combining and splitting wavelength bands according to the ninth embodiment of the present invention illustrated in Fig. 36. [54] Fig. 38 illustrates a second alternative embodiment of an apparatus for combining and splitting wavelength bands according to the ninth embodiment of the present invention illustrated in Fig. 36. [55] Fig. 39 illustrates a third alternative embodiment of an apparatus for combining and splitting wavelength bands according to the ninth embodiment of the present invention illustrated in Fig. 36. [56] Fig. 40 illustrates a tenth embodiment of an apparatus for combining and splitting wavelength bands for bi-directional transmission according to the present invention illustrated in Fig. 2. [57] Fig. 41 illustrates a first alternative embodiment of an apparatus for combining and splitting wavelength bands according to the tenth embodiment of the present invention illustrated in Fig. 40. [58] Fig. 42 illustrates a second alternative embodiment of an apparatus for combining and splitting wavelength bands according to the tenth embodiment of the present invention illustrated in Fig. 40. [59] Fig. 43 illustrates a third alternative embodiment of an apparatus for combining and splitting wavelength bands according to the tenth embodiment of the present invention illustrated in Fig. 40. [60] Fig. 44 illustrates an eleventh embodiment of an apparatus for combining and splitting wavelength bands for bi-directional transmission according to the present invention illustrated in Fig. 2. [61] Fig. 45 illustrates a first alternative embodiment of an apparatus for combining and splitting wavelength bands according to the eleventh embodiment of the present

invention illustrated in Fig. 44. [62] Fig. 46 illustrates a second alternative embodiment of an apparatus for combining and splitting wavelength bands according to the eleventh embodiment of the present invention illustrated in Fig. 44. [63] Fig. 47 illustrates a third alternative embodiment of an apparatus for combining and splitting wavelength bands according to the eleventh embodiment of the present invention illustrated in Fig. 44. [64] Fig. 48 illustrates a twelfth embodiment of an apparatus for combining and splitting wavelength bands for bi-directional transmission according to the present invention illustrated in Fig. 2. [65] Fig. 49 illustrates a first alternative embodiment of an apparatus for combining and splitting wavelength bands according to the twelfth embodiment of the present invention illustrated in Fig. 48. [66] Fig. 50 illustrates a second alternative embodiment of an apparatus for combining and splitting wavelength bands according to the twelfth embodiment of the present invention illustrated in Fig. 48. [67] Fig. 51 illustrates a third alternative embodiment of an apparatus for combining and splitting wavelength bands according to the twelfth embodiment of the present invention illustrated in Fig. 48. [68] Fig. 52 illustrates a thirteenth embodiment of an apparatus for combining and splitting wavelength bands for bi-directional transmission according to the present invention illustrated in Fig. 3. [69] Fig. 53 illustrates a first alternative embodiment of an apparatus for combining and splitting wavelength bands according to the thirteenth embodiment of the present invention illustrated in Fig. 52. [70] Fig. 54 illustrates a second alternative embodiment of an apparatus for combining and splitting wavelength bands according to the thirteenth embodiment of the present invention illustrated in Fig. 52. [71] Fig. 55 illustrates a third alternative embodiment of an apparatus for combining and splitting wavelength bands according to the thirteenth embodiment of the present invention illustrated in Fig. 52. [72] Fig. 56 illustrates a fourteenth embodiment of an apparatus for combining and splitting wavelength bands for bi-directional transmission according to the present invention illustrated in Fig. 3. [73] Fig. 57 illustrates a first alternative embodiment of an apparatus for combining and splitting wavelength bands according to the fourteenth embodiment of the present invention illustrated in Fig. 56. [74] Fig. 58 illustrates a second alternative embodiment of an apparatus for combining

and splitting wavelength bands according to the fourteenth embodiment of the present invention illustrated in Fig. 56.

[75] Fig. 59 illustrates a third alternative embodiment of an apparatus for combining and splitting wavelength bands according to the fourteenth embodiment of the present invention illustrated in Fig. 56. Mode for the Invention

[76] Hereinafter, structures and functions of preferred embodiments in accordance with the present invention are described in more detail with reference to the appended drawings.

[77] An apparatus for combining and splitting wavelength bands having four input and output ports according to the present invention is directed to an apparatus for combining and splitting wavelength bands having four input and output ports which comprises a combination of a first and a second wavelength division multiplexing (WDM) filters, each of which has a function of splitting X-band and Y-band, a third WDM filter having a function of splitting a Zl -band, which is a first sub-band, within either X-band or Y-band, and a fourth WDM filter having a function of splitting a Z2-band, which is a second sub-band, within either X-band or Y-band. More specifically, in the apparatus for combining and splitting wavelength bands according to the present invention described above, the first and the second WDM filters may be embodied by an edge-filter, respectively, and the third and the fourth WDM filters may be embodied by a coarse wavelength division multiplexing (CWDM) filter, respectively.

[78] In addition, an apparatus for combining and splitting wavelength bands having four input and output ports according to the present invention is directed to an apparatus for combining and splitting wavelength bands having four input and output ports which comprises a combination of a first WDM filter having a function of splitting X-band and Y-band, a second and a third WDM filters, each of which has a function of splitting a Zl -band, which is a first sub-band, within either X-band or Y-band, and a fourth WDM filter having a function of splitting a Z2-band, which is a second sub- band, within either X-band or Y-band. More specifically, in the apparatus for combining and splitting wavelength bands according to the present invention described above, the first WDM filter may be embodied by an edge-filter, and the second to the fourth WDM filters may be embodied by a CWDM filter, respectively.

[79] Further, an apparatus for combining and splitting wavelength bands having four input and output ports according to the present invention is directed to an apparatus for combining and splitting wavelength bands having four input and output ports which comprises a combination of a first WDM filter having a function of splitting X-band

and Y-band, a second WDM filter having a function of splitting a Zl -band, which is a first sub-band, within Y-band, a third WDM filter having a function of splitting a Z2-band, which is a second sub-band, within Y-band, and a fourth WDM filter having a function of splitting a Z3-band, which is a third sub-band, within X-band. More specifically, in the apparatus for combining and splitting wavelength bands according to the present invention described above, the first WDM filter may be embodied by an edge-filter, and the second to the fourth WDM filters may be embodied by a CWDM filter, respectively.

[80] Any of the four apparatus for combining and splitting wavelength bands having four input and output ports according to the present invention enables a bi-directional transmission at least within four bands (X-band; Zl -band, Z2-band; and at least two bands among Yl -band, Y2-band, and Y3-band, or Y-band; Zl -band, Z2-band; and at least two bands among Xl-band, X2-band, and X3-band).

[81] Fig. 1 illustrates a first example of a general view of split bands and bi-directional wavelength bands of wavelength division multiplexing filters for bi-directional transmission, Fig. 2 illustrates a second example of a general view of split bands and bi-directional wavelength bands of wavelength division multiplexing filters for bidirectional transmission, and Fig. 3 illustrates a third example of a general view of split bands and bi-directional wavelength bands of wavelength division multiplexing filters for bi-directional transmission.

[82] Referring to Fig. 1, a case of bi-directional transmission is illustrated where a bidirectional transmission is made by using X-band and Z-band(Zl-band and Z2-band), while Y-band is split into two bands (i.e., any two bands among Yl -band, Y2-band and Y3-band) with split bands and bi-directional transmission bands of WDM filters for bidirectional transmission in four bands. In addition, referring to Fig. 2, a case of bidirectional transmission is illustrated where a bi-directional transmission is made by using Y-band and Z-band(Zl-band and Z2-band), while X-band is split into two bands (i.e., any two bands among Xl-band, X2-band and X3-band) with split bands and bidirectional transmission bands of WDM filters for bi-directional transmission in four bands. Further, referring to Fig. 3, a case of bi-directional transmission is illustrated where a bi-directional transmission is made by using Z3-band, and Zl -band and Z2-band, while another bi-directional transmission is made by using at least two bands among Xl-band, X2-band, Yl -band and Y2-band in X-band and Y-band with split bands and bi-directional transmission bands of WDM filters for bi-directional transmission in four bands. In the bi-directional transmission from Figs. 1 to 3 described above, wavelength transmission and reflection characteristics of a WDM filter may be changed depending on the bands of bi-directional transmission which is desired to be used. Further, an edge-filter is used for a first and a second WDM filters,

respectively, each having a function of splitting X-band and Y-band, among WDM filters being used for bi-directional transmission from Figs. 1 and 2 described above, while a CWDM filter is used for a third and a fourth WDM filters, respectively, each having a function of splitting Z-bands, which are a sub-band, within either X-band or Y-band. Further, an edge-filter is used for a first WDM filter having a function of splitting X-band and Y-band, among WDM filters being used for bi-directional transmission from Figs. 1 and 2 described above, while a first to a third CWDM filters are used for a second to fourth WDM filters, respectively, each having a function of splitting Z-bands, which are a sub-band, within either X-band or Y-band. Further, an edge-filter is used for a first WDM filter having a function of splitting X-band and Y- band, among WDM filters being used for bi-directional transmission from Fig. 3 described above, while CWDM filters are used for a second and third WDM filters, respectively, each having a function of splitting Z-bands, which are a sub-band, within Y-band and a CWDM filter is used for a fourth WDM filter having a function of splitting Z-bands, which are a sub-band, within X-band.

[83] Fig. 4 illustrates a first embodiment of an apparatus for combining and splitting wavelength bands for bi-directional transmission according to the present invention illustrated in Fig. 1.

[84] Referring to Fig. 4, an apparatus for combining and splitting wavelength bands according to a first embodiment of the present invention comprises a combination of a first and second edge filters, each for splitting X-band and Y-band from a wavelength band of light being transmitted, a first CWDM filter for splitting Zl -band within Y- band, and a second CWDM filter for splitting Z2-band within Y-band. In a first embodiment of the present invention illustrated in Fig. 4, an upstream signal having a wavelength band with a range of 1260 ~ 1360 nm, which has already been used as a standard band in a time division multiplexing passive optical network (TDM-PON), is used as X-band, while a downstream signal having a wavelength band with the range of 1480 ~ 1500 nm within Y-band having a wavelength band of 1415 nm or more is used as Zl -band. In this case, a downstream signal having a wavelength band with a range of 1550 ~ 1560 nm within Y-band may be used as Z2-band. These bands described above are standardized bands in ITU-T (International Telecommunications Union-Telecommunication Standardization Sector).

[85] More specifically, an apparatus for combining and splitting wavelength bands according to a first embodiment of the present invention illustrated in Fig. 4 comprises a first edge filter for splitting X-band having 1360 nm or less and Y-band having 1415 nm or more from a wavelength band of light being transmitted; a second edge filter for splitting X-band having 1360 nm or less and Y-band having 1415 nm or more from the wavelength band of light being transmitted; a first CWDM filter for splitting Zl -band

having a range of 1480 ~ 1500 nm within Y-band having 1415 nm or more; and a second CWDM filter for splitting Z2-band having a range of 1550 ~ 1560 nm within Y-band having 1415 nm or more. In this first embodiment of the present invention, a reflection port of the first edge filter is connected to a reflection port of the first CWDM filter, while a pass port of the first edge filter is connected to a pass port of the second edge filter. A reflection port of the second edge filter is connected to a common port of the first CWDM filter. A pass port of the first CWDM filter is connected to a common port of the second CWDM filter. In this case, each of the first and the second edge filters has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into each common port, through each pass port, and has a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into each common port, through each reflection port. The first CWDM filter outputs a signal having a wavelength band (Zl -band) with the range of 1480 ~ 1500 nm through its reflection port, while outputting a signal having a remaining wavelength band except Zl -band through its pass port. The second CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1550 ~ 1560 nm through its reflection port, while outputting a signal having a remaining wavelength band except Z2-band through its pass port. All of the first and the second edge filters and the first and the second CDWM filters used in Fig. 4 are a passive device and have a reciprocal characteristic. Thus, a Zl-band signal with the rage of 1480 ~ 1500 nm is transmitted along a path ®, a Z2-band signal with the rage of 1550 ~ 1560 nm is transmitted along a path ®, and an X-band signal having 1360 nm or less is transmitted along a path ® so that both the Z-band signals and the X-band signal may be used as bands for bi-directional transmission. Because an insertion loss of a reflection port is generally less than that of a pass port in a WDM filter, the Zl-band signal with the rage of 1480 ~ 1500 nm is designed to pass the reflection port. Any two bands among Yl -band, Y2-band, and Y3-band which may be used as another band for bi-directional transmission, are transmitted along a path ©. In this case, Yl -band is defined as having a wavelength range of 1415 ~ 1470 nm, Y2-band is defined as having a wavelength range of 1510 ~ 1540 nm, and Y3-band is defined as having a wavelength range of 1570 or more, respectively. Here, it is assumed that a guard band for separating Y-band from Z-band is to be 10 nm. This guard band may be changed depending on a characteristic of the filters to be used. Thus, any existing bi-directional signal is inputted into and outputted from the number one port (1) of an apparatus for combining and splitting wavelength bands having four ports according to the present invention as illustrated in Fig. 4, while any newly added bi-directional signal is inputted into and outputted from the number three port (3) thereof, both any existing bi-directional signal and any newly added bi-

directional signal are inputted into and outputted from the number two port (2) thereof, and any newly added uni-directional signal is inputted into and outputted from the number four port (4) thereof. Further, because all of the first and the second edge filters and the first and the second CDWM filters illustrated in Fig. 4 are a passive device having a reciprocalcharacteristic, it should be fully understood by a skilled person in the art that the Zl -band signal with the rage of 1480 ~ 1500 nm may be transmitted along a reverse direction of the path ® and the X-band signal having 1360 nm or less is transmitted along a reverse direction of the path ® so that the Zl -band signal and the X-band signal may be used as bands for bi-directional transmission, while any two bands among Yl -band, Y2-band, and Y3-band are transmitted along a reverse direction of the path © and the Z2-band signal with the rage of 1550 ~ 1560 nm is transmitted along a reverse direction of the path ®.

[86] Fig. 4a illustrates a first alternative embodiment of an apparatus for combining and splitting wavelength bands according to the first embodiment of the present invention illustrated in Fig. 4.

[87] More specifically, an apparatus for combining and splitting wavelength bands according to the first alternative embodiment of the first embodiment as illustrated in Fig. 4a illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first and the second CWDM filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 4 so that each pass port of the first and the second CWDM filters in Fig. 4 is changed to a reflection port in Fig. 4a, while each reflection port of the first and the second CWDM filters in Fig. 4 is changed to a pass port in Fig. 4a. In this case, the first CWDM filter outputs a signal having a wavelength band (Zl -band) with the range of 1480 ~ 1500 nm through its pass port, while outputting a signal having a remaining wavelength band except Zl -band through its reflection port. Further, the second CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1550 ~ 1560 nm through its pass port, while outputting a signal having a remaining wavelength band except Z2-band through its reflection port.

[88] Fig. 4b illustrates a second alternative embodiment of an apparatus for combining and splitting wavelength bands according to the first embodiment of the present invention illustrated in Fig. 4.

[89] More specifically, an apparatus for combining and splitting wavelength bands according to the second alternative embodiment of the first embodiment as illustrated in Fig. 4b illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first and the second edge filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 4 so that each pass port of the first and the second edge filters in Fig. 4 is changed to a

reflection port in Fig. 4b, while each reflection port of the first and the second edge filters in Fig. 4 is changed to a pass port in Fig. 4b. In this case, each of the first and the second edge filters has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into each common port, through each reflection port, while having a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into each common port, through each pass port.

[90] Fig. 4c illustrates a third alternative embodiment of an apparatus for combining and splitting wavelength bands according to the first embodiment of the present invention illustrated in Fig. 4.

[91] More specifically, an apparatus for combining and splitting wavelength bands according to the third alternative embodiment of the first embodiment as illustrated in Fig. 4c illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first and the second edge filters and the first and the second CWDM filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 4 so that each pass port of the first and the second edge filters and the first and the second CWDM filters in Fig. 4 is changed to a reflection port in Fig. 4c, while each reflection port of the first and the second edge filters and the first and the second CWDM filters in Fig. 4 is changed to a pass port in Fig. 4c. In this case, each of the first and the second edge filters has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into each common port, through each reflection port, while having a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into each common port, through each pass port. The first CWDM filter outputs a signal having a wavelength band (Zl -band) with the range of 1480 ~ 1500 nm through its pass port, while outputting a signal having a remaining wavelength band except Zl -band through its reflection port. In addition, the second CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1550 ~ 1560 nm through its pass port, while outputting a signal having a remaining wavelength band except Z2-band through its reflection port.

[92] Fig. 5 illustrates a second embodiment of an apparatus for combining and splitting wavelength bands for bi-directional transmission according to the present invention illustrated in Fig. 1.

[93] Referring to Fig. 5, an apparatus for combining and splitting wavelength bands according to a second embodiment of the present invention comprises a combination of a first edge filter for splitting X-band and Y-band from a wavelength band of light being transmitted, a first and a second CWDM filters, each for splitting Zl-band within Y-band, and a third CWDM filter for splitting Z2-band within Y-band. In a second

embodiment of the present invention illustrated in Fig. 5, an upstream signal having a wavelength band with a range of 1260 ~ 1360 nm, which has already been used as a standard band in a time division multiplexing passive optical network (TDM-PON), is used as X-band, while a downstream signal having a wavelength band with the range of 1480 ~ 1500 nm within Y-band having a wavelength band of 1415 nm or more is used as Zl -band. In this case, a downstream signal having a wavelength band with a range of 1550 ~ 1560 nm within Y-band may be used as Z2-band.

[94] More specifically, an apparatus for combining and splitting wavelength bands according to a second embodiment of the present invention illustrated in Fig. 5 comprises a first edge filter for splitting X-band having 1360 nm or less and Y-band having 1415 nm or more from a wavelength band of light being transmitted; a first CWDM filter for splitting Zl -band having a range of 1480 ~ 1500 nm within Y-band having 1415 nm or more; a second CWDM filter for splitting Zl-band having a range of 1480 ~ 1500 nm within Y-band having 1415 nm or more; and a third CWDM filter for splitting Z2-band having a range of 1550 ~ 1560 nm within Y-band having 1415 nm or more. In this second embodiment of the present invention, a pass port of the first edge filter is connected to a pass port of the first CWDM filter, while a reflection port of the first edge filter is connected to a common port of the second CWDM filter. A reflection port of the second CWDM filter is connected to a reflection port of the first CWDM filter. A pass port of the second CWDM filter is connected to a common port of the third CWDM filter. In this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its pass port, and has a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its reflection port. Each of the first and the second CWDM filters outputs a signal having a wavelength band (Zl-band) with the range of 1480 ~ 1500 nm through each reflection port, while outputting a signal having a remaining wavelength band except Zl-band through each pass port. The third CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1550 ~ 1560 nm through its reflection port, while outputting a signal having a remaining wavelength band except Z2-band through its pass port. Referring to Fig. 5, an apparatus for combining and splitting wavelength bands according to a second embodiment of the present invention illustrated in Fig. 5 performs substantially the same function as that performed by an apparatus for combining and splitting wavelength bands according to a first embodiment of the present invention illustrated in Fig. 4.

[95] Fig. 5a illustrates a first alternative embodiment of an apparatus for combining and splitting wavelength bands according to the second embodiment of the present

invention illustrated in Fig. 5.

[96] More specifically, an apparatus for combining and splitting wavelength bands according to the first alternative embodiment of the second embodiment as illustrated in Fig. 5a illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first to the third CWDM filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 5 so that each pass port of the first to the third CWDM filters in Fig. 5 is changed to a reflection port in Fig. 5a, while each reflection port of the first to the third CWDM filters in Fig. 5 is changed to a pass port in Fig. 5a. In this case, each of the first and the second CWDM filters outputs a signal having a wavelength band (Zl -band) with the range of 1480 ~ 1500 nm through each pass port, while outputting a signal having a remaining wavelength band except Zl -band through each reflection port. Further, the third CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1550 ~ 1560 nm through its pass port, while outputting a signal having a remaining wavelength band except Z2-band through its reflection port.

[97] Fig. 5b illustrates a second alternative embodiment of an apparatus for combining and splitting wavelength bands according to the second embodiment of the present invention illustrated in Fig. 5.

[98] More specifically, an apparatus for combining and splitting wavelength bands according to the second alternative embodiment of the second embodiment as illustrated in Fig. 5b illustrates a case that the functions of the pass port and the reflection port of the first edge filter are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 5 so that the pass port of the first edge filter in Fig. 5 is changed to a reflection port in Fig. 5b, while the reflection port of the first edge filter in Fig. 5 is changed to a pass port in Fig. 5b. In this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its reflection port, while having a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its pass port.

[99] Fig. 5c illustrates a third alternative embodiment of an apparatus for combining and splitting wavelength bands according to the second embodiment of the present invention illustrated in Fig. 5.

[100] More specifically, an apparatus for combining and splitting wavelength bands according to the third alternative embodiment of the second embodiment as illustrated in Fig. 5c illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first edge filter and the first to the third CWDM filters are switched each other in an apparatus for combining and splitting wavelength bands

illustrated in Fig. 5 so that each pass port of the first edge filter and the first to the third CWDM filters in Fig. 5 is changed to a reflection port in Fig. 5c, while each reflection port of the first edge filter and the first to the third CWDM filters in Fig. 5 is changed to a pass port in Fig. 5c. In this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its reflection port, while having a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its pass port. Each of the first and the second CWDM filters outputs a signal having a wavelength band (Zl -band) with the range of 1480 ~ 1500 nm through each pass port, while outputting a signal having a remaining wavelength band except Zl -band through each reflection port. In addition, the second CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1550 ~ 1560 nm through its pass port, while outputting a signal having a remaining wavelength band except Z2-band through its reflection port.

[101] Fig. 6 illustrates a third embodiment of an apparatus for combining and splitting wavelength bands for bi-directional transmission according to the present invention illustrated in Fig. 1.

[102] Referring to Fig. 6, an apparatus for combining and splitting wavelength bands according to a third embodiment of the present invention comprises a combination of a first edge filter for splitting X-band and Y-band from a wavelength band of light being transmitted, a first and a second CWDM filters, each for splitting Zl -band within Y- band, and a third CWDM filter for splitting Z2-band within Y-band. In a third embodiment of the present invention illustrated in Fig. 6, an upstream signal having a wavelength band with a range of 1260 ~ 1360 nm, which has already been used as a standard band in a time division multiplexing passive optical network (TDM-PON), is used as X-band, while a downstream signal having a wavelength band with the range of 1480 ~ 1500 nm within Y-band having a wavelength band of 1415 nm or more is used as Zl -band. In this case, a downstream signal having a wavelength band with a range of 1550 ~ 1560 nm within Y-band may be used as Z2-band.

[103] More specifically, an apparatus for combining and splitting wavelength bands according to a third embodiment of the present invention illustrated in Fig. 6 comprises a first edge filter for splitting X-band having 1360 nm or less and Y-band having 1415 nm or more from a wavelength band of light being transmitted; a first CWDM filter for splitting Zl -band having a range of 1480 ~ 1500 nm within Y-band having 1415 nm or more; a second CWDM filter for splitting Zl-band having a range of 1480 ~ 1500 nm within Y-band having 1415 nm or more; and a third CWDM filter for splitting Z2-band having a range of 1550 ~ 1560 nm within Y-band having 1415 nm or more. In this third embodiment of the present invention, a pass port of the first edge filter is

connected to a pass port of the first CWDM filter, while a common port of the first edge filter is connected to a pass port of the second CWDM filter. A reflection port of the second CWDM filter is connected to a reflection port of the first CWDM filter. A reflection port of the first edge filter is connected to a common port of the third CWDM filter. In this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its pass port, and has a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its reflection port. Each of the first and the second CWDM filters outputs a signal having a wavelength band (Zl -band) with the range of 1480 ~ 1500 nm through each reflection port, while outputting a signal having a remaining wavelength band except Zl-band through each pass port. The third CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1550 ~ 1560 nm through its reflection port, while outputting a signal having a remaining wavelength band except Z2-band through its pass port. Referring to Fig. 6, an apparatus for combining and splitting wavelength bands according to a third embodiment of the present invention illustrated in Fig. 6 performs substantially the same function as that performed by an apparatus for combining and splitting wavelength bands according to a first embodiment of the present invention illustrated in Fig. 4.

[104] Fig. 6a illustrates a first alternative embodiment of an apparatus for combining and splitting wavelength bands according to the third embodiment of the present invention illustrated in Fig. 6.

[105] More specifically, an apparatus for combining and splitting wavelength bands according to the first alternative embodiment of the third embodiment as illustrated in Fig. 6a illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first to the third CWDM filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 6 so that each pass port of the first to the third CWDM filters in Fig. 6 is changed to a reflection port in Fig. 6a, while each reflection port of the first to the third CWDM filters in Fig. 6 is changed to a pass port in Fig. 6a. In this case, each of the first and the second CWDM filters outputs a signal having a wavelength band (Zl-band) with the range of 1480 ~ 1500 nm through each pass port, while outputting a signal having a remaining wavelength band except Zl-band through each reflection port. Further, the third CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1550 ~ 1560 nm through its pass port, while outputting a signal having a remaining wavelength band except Z2-band through its reflection port.

[106] Fig. 6b illustrates a second alternative embodiment of an apparatus for combining

and splitting wavelength bands according to the third embodiment of the present invention illustrated in Fig. 6.

[107] More specifically, an apparatus for combining and splitting wavelength bands according to the second alternative embodiment of the third embodiment as illustrated in Fig. 6b illustrates a case that the functions of the pass port and the reflection port of the first edge filter are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 6 so that the pass port of the first edge filter in Fig. 6 is changed to a reflection port in Fig. 6b, while the reflection port of the first edge filter in Fig. 6 is changed to a pass port in Fig. 6b. In this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its reflection port, while having a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its pass port.

[108] Fig. 6c illustrates a third alternative embodiment of an apparatus for combining and splitting wavelength bands according to the third embodiment of the present invention illustrated in Fig. 6.

[109] More specifically, an apparatus for combining and splitting wavelength bands according to the third alternative embodiment of the third embodiment as illustrated in Fig. 6c illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first edge filter and the first to the third CWDM filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 6 so that each pass port of the first edge filter and the first to the third CWDM filters in Fig. 6 is changed to a reflection port in Fig. 6c, while each reflection port of the first edge filter and the first to the third CWDM filters in Fig. 6 is changed to a pass port in Fig. 6c. In this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its reflection port, while having a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its pass port. Each of the first and the second CWDM filters outputs a signal having a wavelength band (Zl -band) with the range of 1480 ~ 1500 nm through each pass port, while outputting a signal having a remaining wavelength band except Zl -band through each reflection port. In addition, the second CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1550 ~ 1560 nm through its pass port, while outputting a signal having a remaining wavelength band except Z2-band through its reflection port.

[110] Fig. 7 illustrates a fourth embodiment of an apparatus for combining and splitting wavelength bands for bi-directional transmission according to the present invention il-

lustrated in Fig. 1. Referring to Fig. 7, an apparatus for combining and splitting wavelength bands according to a fourth embodiment of the present invention comprises a combination of a first and a second edge filters, each for splitting X-band and Y-band from a wavelength band of light being transmitted, a first CWDM filter for splitting Zl -band within Y-band, and a second CWDM filter for splitting Z2-band within Y-band. In a fourth embodiment of the present invention illustrated in Fig. 7, an upstream signal having a wavelength band with a range of 1260 ~ 1360 nm, which has already been used as a standard band in a time division multiplexing passive optical network (TDM-PON), is used as X-band, while a downstream signal having a wavelength band with the range of 1480 ~ 1500 nm within Y-band having a wavelength band of 1415 nm or more is used as Zl-band. In this case, a downstream signal having a wavelength band with a range of 1550 ~ 1560 nm within Y-band may be used as Z2-band. More specifically, an apparatus for combining and splitting wavelength bands according to a fourth embodiment of the present invention illustrated in Fig. 7 comprises a first edge filter for splitting X-band having 1360 nm or less and Y-band having 1415 nm or more from a wavelength band of light being transmitted; a second edge filter for splitting X-band having 1360 nm or less and Y-band having 1415 nm or more from the wavelength band of light being transmitted; a first CWDM filter for splitting Zl-band having a range of 1480 ~ 1500 nm within Y-band having 1415 nm or more; and a second CWDM filter splitting Z2-band having a range of 1550 ~ 1560 nm within Y-band having 1415 nm or more. In this fourth embodiment of the present invention, a reflection port of the first edge filter is connected to a reflection port of the first CWDM filter, while a pass port of the first edge filter is connected to a pass port of the second edge filter. A reflection port of the second edge filter is connected to a common port of the second CWDM filter. A common port of the first CWDM filter is connected to a pass port of the second CWDM filter. In this case, each of the first and the second edge filters has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into each common port, through each pass port, and has a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into each common port, through each reflection port. The first CWDM filter outputs a signal having a wavelength band (Zl-band) with the range of 1480 ~ 1500 nm through its reflection port, while outputting a signal having a remaining wavelength band except Zl-band through its pass port. The second CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1550 ~ 1560 nm through its reflection port, while outputting a signal having a remaining wavelength band except Z2-band through its pass port. Referring to Fig. 7, an apparatus for combining and splitting

wavelength bands according to a fourth embodiment of the present invention illustrated in Fig. 7 performs substantially the same function as that performed by an apparatus for combining and splitting wavelength bands according to a first em bodiment of the present invention illustrated in Fig. 4.

[113] Fig. 7a illustrates a first alternative embodiment of an apparatus for combining and splitting wavelength bands according to the fourth embodiment of the present invention illustrated in Fig. 7.

[114] More specifically, an apparatus for combining and splitting wavelength bands according to the first alternative embodiment of the fourth embodiment as illustrated in Fig. 7a illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first and the second CWDM filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 7 so that each pass port of the first and the second CWDM filters in Fig. 7 is changed to a reflection port in Fig. 7a, while each reflection port of the first and the second CWDM filters in Fig. 7 is changed to a pass port in Fig. 7a. In this case, the first CWDM filter outputs a signal having a wavelength band (Zl -band) with the range of 1480 ~ 1500 nm through its pass port, while outputting a signal having a remaining wavelength band except Zl -band through its reflection port. Further, the second CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1550 ~ 1560 nm through its pass port, while outputting a signal having a remaining wavelength band except Z2-band through its reflection port.

[115] Fig. 7b illustrates a second alternative embodiment of an apparatus for combining and splitting wavelength bands according to the fourth embodiment of the present invention illustrated in Fig. 7.

[116] More specifically, an apparatus for combining and splitting wavelength bands according to the second alternative embodiment of the fourth embodiment as illustrated in Fig. 7b illustrates a case that the functions of the pass port and the reflection port of the first and the second edge filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 7 so that each pass port of the first and the second edge filters in Fig. 7 is changed to a reflection port in Fig. 7b, while each reflection port of the first and the second edge filters in Fig. 7 is changed to a pass port in Fig. 7b. In this case, each of the first and the second edge filters has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into each common port, through each reflection port, while having a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into each common port, through each pass port.

[117] Fig. 7c illustrates a third alternative embodiment of an apparatus for combining and

splitting wavelength bands according to the fourth embodiment of the present invention illustrated in Fig. 7.

[118] More specifically, an apparatus for combining and splitting wavelength bands according to the third alternative embodiment of the fourth embodiment as illustrated in Fig. 7c illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first and the second edge filters and the first and the second CWDM filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 7 so that each pass port of the first and the second edge filters and the first and the second CWDM filters in Fig. 7 is changed to a reflection port in Fig. 7c, while each reflection port of the first and the second edge filters and the first and the second CWDM filters in Fig. 7 is changed to a pass port in Fig. 7c. In this case, each of the first and the second edge filters has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into each common port, through each reflection port, while having a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into each common port, through each pass port. The first CWDM filter outputs a signal having a wavelength band (Zl -band) with the range of 1480 ~ 1500 nm through its pass port, while outputting a signal having a remaining wavelength band except Zl -band through its reflection port. In addition, the second CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1550 ~ 1560 nm through its pass port, while outputting a signal having a remaining wavelength band except Z2-band through its reflection port.

[119] Fig. 8 illustrates a fifth embodiment of an apparatus for combining and splitting wavelength bands for bi-directional transmission according to the present invention illustrated in Fig. 1.

[120] Referring to Fig. 8, an apparatus for combining and splitting wavelength bands according to a fifth embodiment of the present invention comprises a combination of a first edge filter for splitting X-band and Y-band from a wavelength band of light being transmitted, a first and a second CWDM filters, each for splitting Zl -band within Y- band, and a third CWDM filter for splitting Z2-band within Y-band. In a fifth embodiment of the present invention illustrated in Fig. 8, an upstream signal having a wavelength band with a range of 1260 ~ 1360 nm, which has already been used as a standard band in a time division multiplexing passive optical network (TDM-PON), is used as X-band, while a downstream signal having a wavelength band with the range of 1480 ~ 1500 nm within Y-band having a wavelength band of 1415 nm or more is used as Zl -band. In this case, a downstream signal having a wavelength band with a range of 1550 ~ 1560 nm within Y-band may be used as Z2-band.

[121] More specifically, an apparatus for combining and splitting wavelength bands

according to a fifth embodiment of the present invention illustrated in Fig. 8 comprises a first edge filter for splitting X-band having 1360 nm or less and Y-band having 1415 nm or more from a wavelength band of light being transmitted; a first CWDM filter for splitting Zl -band having a range of 1480 ~ 1500 nm within Y-band having 1415 nm or more; a second CWDM filter for splitting Zl-band having a range of 1480 ~ 1500 nm within Y-band having 1415 nm or more; and a third CWDM filter for splitting Z2-band having a range of 1550 ~ 1560 nm within Y-band having 1415 nm or more. In this fifth embodiment of the present invention, a pass port of the first edge filter is connected to a pass port of the first CWDM filter, while a reflection port of the first edge filter is connected to a common port of the third CWDM filter. A reflection port of the second CWDM filter is connected to a reflection port of the first CWDM filter. A common port of the second CWDM filter is connected to a pass port of the third CWDM filter. In this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its pass port, and has a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its reflection port. Each of the first and the second CWDM filters outputs a signal having a wavelength band (Zl-band) with the range of 1480 ~ 1500 nm through each reflection port, while outputting a signal having a remaining wavelength band except Zl-band through each pass port. The third CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1550 ~ 1560 nm through its reflection port, while outputting a signal having a remaining wavelength band except Z2-band through its pass port. Referring to Fig. 8, an apparatus for combining and splitting wavelength bands according to a fifth embodiment of the present invention illustrated in Fig. 8 performs substantially the same function as that performed by an apparatus for combining and splitting wavelength bands according to a first embodiment of the present invention illustrated in Fig. 4.

[122] Fig. 8a illustrates a first alternative embodiment of an apparatus for combining and splitting wavelength bands according to the fifth embodiment of the present invention illustrated in Fig. 8.

[123] More specifically, an apparatus for combining and splitting wavelength bands according to the first alternative embodiment of the fifth embodiment as illustrated in Fig. 8a illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first to the third CWDM filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 8 so that each pass port of the first to the third CWDM filters in Fig. 8 is changed to a reflection port in Fig. 8a, while each reflection port of the first to the third CWDM

filters in Fig. 8 is changed to a pass port in Fig. 8a. In this case, each of the first and the second CWDM filters outputs a signal having a wavelength band (Zl -band) with the range of 1480 ~ 1500 nm through each pass port, while outputting a signal having a remaining wavelength band except Zl -band through each reflection port. Further, the third CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1550 ~ 1560 nm through its pass port, while outputting a signal having a remaining wavelength band except Z2-band through its reflection port.

[124] Fig. 8b illustrates a second alternative embodiment of an apparatus for combining and splitting wavelength bands according to the fifth embodiment of the present invention illustrated in Fig. 8.

[125] More specifically, an apparatus for combining and splitting wavelength bands according to the second alternative embodiment of the fifth embodiment as illustrated in Fig. 8b illustrates a case that the functions of the pass port and the reflection port of the first edge filter are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 8 so that the pass port of the first edge filter in Fig. 8 is changed to a reflection port in Fig. 8b, while the reflection port of the first edge filter in Fig. 8 is changed to a pass port in Fig. 8b. In this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its reflection port, while having a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its pass port.

[126] Fig. 8c illustrates a third alternative embodiment of an apparatus for combining and splitting wavelength bands according to the fifth embodiment of the present invention illustrated in Fig. 8.

[127] More specifically, an apparatus for combining and splitting wavelength bands according to the third alternative embodiment of the fifth embodiment as illustrated in Fig. 8c illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first edge filter and the first to the third CWDM filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 8 so that each pass port of the first edge filter and the first to the third CWDM filters in Fig. 8 is changed to a reflection port in Fig. 8c, while each reflection port of the first edge filter and the first to the third CWDM filters in Fig. 8 is changed to a pass port in Fig. 8c. In this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its reflection port, while having a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its pass port. Each of the first and

the second CWDM filters outputs a signal having a wavelength band (Zl -band) with t he range of 1480 ~ 1500 nm through each pass port, while outputting a signal having a remaining wavelength band except Zl -band through each reflection port. In addition, the second CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1550 ~ 1560 nm through its pass port, while outputting a signal having a remaining wavelength band except Z2-band through its reflection port.

[128] Fig. 9 illustrates a sixth embodiment of an apparatus for combining and splitting wavelength bands for bi-directional transmission according to the present invention illustrated in Fig. 1.

[129] Referring to Fig. 9, an apparatus for combining and splitting wavelength bands according to a third embodiment of the present invention comprises a combination of a first edge filter for splitting X-band and Y-band from a wavelength band of light being transmitted, a first and a second CWDM filters, each for splitting Zl -band within Y- band, and a third CWDM filter for splitting Z2-band within Y-band. In a sixth embodiment of the present invention illustrated in Fig. 9, an upstream signal having a wavelength band with a range of 1260 ~ 1360 nm, which has already been used as a standard band in a time division multiplexing passive optical network (TDM-PON), is used as X-band, while a downstream signal having a wavelength band with the range of 1480 ~ 1500 nm within Y-band having a wavelength band of 1415 nm or more is used as Zl -band. In this case, a downstream signal having a wavelength band with a range of 1550 ~ 1560 nm within Y-band may be used as Z2-band.

[130] More specifically, an apparatus for combining and splitting wavelength bands according to a sixth embodiment of the present invention illustrated in Fig. 9 comprises a first edge filter for splitting X-band having 1360 nm or less and Y-band having 1415 nm or more from a wavelength band of light being transmitted; a first CWDM filter for splitting Zl -band having a range of 1480 ~ 1500 nm within Y-band having 1415 nm or more; a second CWDM filter for splitting Zl-band having a range of 1480 ~ 1500 nm within Y-band having 1415 nm or more; and a third CWDM filter for splitting Z2-band having a range of 1550 ~ 1560 nm within Y-band having 1415 nm or more. In this sixth embodiment of the present invention, a pass port of the first edge filter is connected to a pass port of the first CWDM filter, while a common port of the first edge filter is connected to a pass port of the third CWDM filter. A reflection port of the first CWDM filter is connected to a reflection port of the second CWDM filter. A pass port of the second CWDM filter is connected to a common port of the third CWDM filter. In this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its pass port, and has a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted

into its common port, through its reflection port. Each of the first and the second CWDM filters outputs a signal having a wavelength band (Zl -band) with the range of 1480 ~ 1500 nm through each reflection port, while outputting a signal having a remaining wavelength band except Zl-band through each pass port. The third CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1550 ~ 1560 nm through its reflection port, while outputting a signal having a remaining wavelength band except Z2-band through its pass port. Referring to Fig. 9, an apparatus for combining and splitting wavelength bands according to a sixth embodiment of the present invention illustrated in Fig. 9 performs substantially the same function as that performed by an apparatus for combining and splitting wavelength bands according to a first embodiment of the present invention illustrated in Fig. 4.

[131] Fig. 9a illustrates a first alternative embodiment of an apparatus for combining and splitting wavelength bands according to the sixth embodiment of the present invention illustrated in Fig. 9.

[132] More specifically, an apparatus for combining and splitting wavelength bands according to the first alternative embodiment of the sixth embodiment as illustrated in Fig. 9a illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first to the third CWDM filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 8 so that each pass port of the first to the third CWDM filters in Fig. 9 is changed to a reflection port in Fig. 9a, while each reflection port of the first to the third CWDM filters in Fig. 9 is changed to a pass port in Fig. 9a. In this case, each of the first and the second CWDM filters outputs a signal having a wavelength band (Zl-band) with the range of 1480 ~ 1500 nm through each pass port, while outputting a signal having a remaining wavelength band except Zl-band through each reflection port. Further, the third CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1550 ~ 1560 nm through its pass port, while outputting a signal having a remaining wavelength band except Z2-band through its reflection port.

[133] Fig. 9b illustrates a second alternative embodiment of an apparatus for combining and splitting wavelength bands according to the sixth embodiment of the present invention illustrated in Fig. 9.

[134] More specifically, an apparatus for combining and splitting wavelength bands according to the second alternative embodiment of the sixth embodiment as illustrated in Fig. 9b illustrates a case that the functions of the pass port and the reflection port of the first edge filter are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 9 so that the pass port of the first edge filter in Fig. 9 is changed to a reflection port in Fig. 9b, while the reflection port of the first edge

filter in Fig. 9 is changed to a pass port in Fig. 9b. In this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its reflection port, while having a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its pass port.

[135] Fig. 9c illustrates a third alternative embodiment of an apparatus for combining and splitting wavelength bands according to the sixth embodiment of the present invention illustrated in Fig. 9.

[136] More specifically, an apparatus for combining and splitting wavelength bands according to the third alternative embodiment of the sixth embodiment as illustrated in Fig. 9c illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first edge filter and the first to the third CWDM filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 9 so that each pass port of the first edge filter and the first to the third CWDM filters in Fig. 9 is changed to a reflection port in Fig. 9c, while each reflection port of the first edge filter and the first to the third CWDM filters in Fig. 9 is changed to a pass port in Fig. 9c. In this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its reflection port, while having a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its pass port. Each of the first and the second CWDM filters outputs a signal having a wavelength band (Zl -band) with the range of 1480 ~ 1500 nm through each pass port, while outputting a signal having a remaining wavelength band except Zl -band through each reflection port. In addition, the third CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1550 ~ 1560 nm through its pass port, while outputting a signal having a remaining wavelength band except Z2-band through its reflection port.

[137] Fig. 10 illustrates a seventh embodiment of an apparatus for combining and splitting wavelength bands for bi-directional transmission according to the present invention illustrated in Fig. 2.

[138] Referring to Fig. 10, an apparatus for combining and splitting wavelength bands according to a seventh embodiment of the present invention comprises a combination of a first and a second edge filters, each for splitting X-band and Y-band from a wavelength band of light being transmitted, a first CWDM filter for splitting Zl -band within X-band, and a second CWDM filter for splitting Z2-band within X-band. In a seventh embodiment of the present invention illustrated in Fig. 10, an upstream signal having a wavelength band with a range of 1260 ~ 1360 nm, which has already been

used as a standard band in a time division multiplexing passive optical network (TDM-PON), is used as Y-band, while a downstream signal having a wavelength band with the range of 1300 ~ 1320 nm within X-band having a wavelength band of 1360 nm or less is used as Zl -band. In this case, a downstream signal having a wavelength band with a range of 1260 ~ 1280 nm within X-band may be used as Z2-band. Here, the ranges of Zl -band and Z2-band are illustrative and may be changed depending on their use purpose and thus the scope of the present invention is not intended to be limited to the specific ranges thereof. More specifically, an apparatus for combining and splitting wavelength bands according to a seventh embodiment of the present invention illustrated in Fig. 10 comprises a first edge filter for splitting X-band having 1360 nm or less and Y-band having 1415 nm or more from a wavelength band of light being transmitted; a second edge filter for splitting X-band having 1360 nm or less and Y-band having 1415 nm or more from the wavelength band of light being transmitted; a first CWDM filter for splitting Zl-band having a range of 1300 ~ 1320 nm within X-band having 1360 nm or less; and a second CWDM filter splitting Z2-band having a range of 1260 ~ 1280 nm within X-band having 1360 nm or less. In this seventh embodiment of the present invention, a reflection port of the first edge filter is connected to a reflection port of the first CWDM filter, while a pass port of the first edge filter is connected to a pass port of the second edge filter. A reflection port of the second edge filter is connected to a common port of the first CWDM filter. A pass port of the first CWDM filter is connected to a common port of the second CWDM filter. In this case, each of the first and the second edge filters has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into each common port, through each pass port, and has a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into each common port, through each reflection port. The first CWDM filter outputs a signal having a wavelength band (Zl-band) with the range of 1300 ~ 1320 nm through its reflection port, while outputting a signal having a remaining wavelength band except Zl-band through its pass port. The second CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1260 ~ 1280 nm through its reflection port, while outputting a signal having a remaining wavelength band except Z2-band through its pass port. All of the first and the second edge filters and the first and the second CDWM filters used in Fig. 10 are a passive device and have a reciprocal characteristic. Thus, a Zl-band signal with the rage of 1300 ~ 1320 nm is transmitted along a path ®, a Z2-band signal with the rage of 1260 ~ 1280 nm is transmitted along a path ®, and a Y-band signal having 1415 nm or more is transmitted along a path ® so that both the Z-band signals and the Y-band signal may be used as bands for bi-directional

transmission. Because an insertion loss of a reflection port is generally less than that of a pass port in a WDM filter, the Zl-band signal with the rage of 1300 ~ 1320 nm is designed to pass the reflection port. Any two bands among Xl -band, X2-band, and X3-band which may be used as another band for bi-directional transmission, are transmitted along a path ©. In this case, Xl -band is defined as having a wavelength range of 1320 ~ 1360 nm, X2-band is defined as having a wavelength range of 1280 ~ 1300 nm, and X3-band is defined as having a wavelength range of 1260 or less, respectively. Thus, any existing bi-directional signal is inputted into and outputted from the number one port (1) of an apparatus for combining and splitting wavelength bands having four ports according to the present invention as illustrated in Fig. 10, while any newly added bi-directional signal is inputted into and outputted from the number three port (3) thereof, both any existing bi-directional signal and any newly added bidirectional signal are inputted into and outputted from the number two port (2) thereof, and any newly added uni-directional signal is inputted into and outputted from the number four port (4) thereof. Further, because all of the first and the second edge filters and the first and the second CDWM filters illustrated in Fig. 10 are a passive device having a reciprocalcharacteristic, it should be fully understood by a skilled person in the art that the Zl-band signal with the rage of 1300 ~ 1320 nm may be transmitted along a reverse direction of the path ® and the Y-band signal having 1415 nm or more is transmitted along a reverse direction of the path ® so that the Zl-band signal and the Y-band signal may be used as bands for bi-directional transmission, while any two bands among Xl -band, X2-band, and X3-band are transmitted along a reverse direction of the path ©.

[140] Fig. 10a illustrates a first alternative embodiment of an apparatus for combining and splitting wavelength bands according to the seventh embodiment of the present invention illustrated in Fig. 10.

[141] More specifically, an apparatus for combining and splitting wavelength bands according to the first alternative embodiment of the seventh embodiment as illustrated in Fig. 10a illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first and the second CWDM filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 10a so that each pass port of the first and the second CWDM filters in Fig. 10 is changed to a reflection port in Fig. 10a, while each reflection port of the first and the second CWDM filters in Fig. 10 is changed to a pass port in Fig. 10a. In this case, the first CWDM filter outputs a signal having a wavelength band (Zl-band) with the range of 1300 ~ 1320 nm through its pass port, while outputting a signal having a remaining wavelength band except Zl-band through its reflection port. Further, the second CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of

1260 ~ 1280 nm through its pass port, while outputting a signal having a remaining wavelength band except Z2-band through its reflection port.

[142] Fig. 10b illustrates a second alternative embodiment of an apparatus for combining and splitting wavelength bands according to the seventh embodiment of the present invention illustrated in Fig. 10.

[143] More specifically, an apparatus for combining and splitting wavelength bands according to the second alternative embodiment of the first embodiment as illustrated in Fig. 10b illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first and the second edge filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 10 so that each pass port of the first and the second edge filters in Fig. 10 is changed to a reflection port in Fig. 10b, while each reflection port of the first and the second edge filters in Fig. 10 is changed to a pass port in Fig. 10b. In this case, each of the first and the second edge filters has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into each common port, through each reflection port, while having a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into each common port, through each pass port.

[144] Fig. 10c illustrates a third alternative embodiment of an apparatus for combining and splitting wavelength bands according to the seventh embodiment of the present invention illustrated in Fig. 10.

[145] More specifically, an apparatus for combining and splitting wavelength bands according to the third alternative embodiment of the seventh embodiment as illustrated in Fig. 10c illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first and the second edge filters and the first and the second CWDM filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 10 so that each pass port of the first and the second edge filters and the first and the second CWDM filters in Fig. 10 is changed to a reflection port in Fig. 10c, while each reflection port of the first and the second edge filters and the first and the second CWDM filters in Fig. 10 is changed to a pass port in Fig. 10c. In this case, each of the first and the second edge filters has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into each common port, through each reflection port, while having a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into each common port, through each pass port. The first CWDM filter outputs a signal having a wavelength band (Zl -band) with the range of 1300 ~ 1320 nm through its pass port, while outputting a signal having a remaining wavelength band except Zl -band through its reflection port. In

addition, the second CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1260 ~ 1280 nm through its pass port, while outputting a signal having a remaining wavelength band except Z2-band through its reflection port.

[146] Fig. 11 illustrates an eighth embodiment of an apparatus for combining and splitting wavelength bands for bi-directional transmission according to the present invention illustrated in Fig. 2.

[147] Referring to Fig. 11, an apparatus for combining and splitting wavelength bands according to an eighth embodiment of the present invention comprises a combination of a first edge filter for splitting X-band and Y-band from a wavelength band of light being transmitted, a first and a second CWDM filters, each for splitting Zl-band within X-band, and a third CWDM filter for splitting Z2-band within X-band. In an eighth embodiment of the present invention illustrated in Fig. 11, an upstream signal having a wavelength band with a range of 1260 ~ 1360 nm, which has already been used as a standard band in a time division multiplexing passive optical network (TDM-PON), is used as Y-band, while a downstream signal having a wavelength band with the range of 1300 ~ 1320 nm within X-band having a wavelength band of 1360 nm or less is used as Zl-band. In this case, a downstream signal having a wavelength band with a range of 1260 ~ 1280 nm within X-band may be used as Z2-band.

[148] More specifically, an apparatus for combining and splitting wavelength bands according to an eighth embodiment of the present invention illustrated in Fig. 11 comprises a first edge filter for splitting X-band having 1360 nm or less and Y-band having 1415 nm or more from a wavelength band of light being transmitted; a first CWDM filter for splitting Zl-band having a range of 1300 ~ 1320 nm within X-band having 1360 nm or less; a second CWDM filter for splitting Zl-band having a range of 1300 ~ 1320 nm within X-band having 1360 nm or less; and a third CWDM filter for splitting Z2-band having a range of 1260 ~ 1280 nm within X-band having 1360 nm or less. In this eighth embodiment of the present invention, a pass port of the first edge filter is connected to a pass port of the first CWDM filter, while a reflection port of the first edge filter is connected to a common port of the second CWDM filter. A reflection port of the second CWDM filter is connected to a reflection port of the first CWDM filter. A pass port of the second CWDM filter is connected to a common port of the third CWDM filter. In this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its pass port, and has a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its reflection port. Each of the first and the second CWDM filters outputs a signal having a wavelength band (Zl-band) with the range of 1300 ~ 1320 nm through each reflection port, while outputting a signal

having a remaining wavelength band except Zl-band through each pass port. The third CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1260 ~ 1280 nm through its reflection port, while outputting a signal having a remaining wavelength band except Z2-band through its pass port. Referring to Fig. 11, an apparatus for combining and splitting wavelength bands according to an eighth embodiment of the present invention illustrated in Fig. 11 performs substantially the same function as that performed by an apparatus for combining and splitting wavelength bands according to a seventh embodiment of the present invention illustrated in Fig. 10.

[149] Fig. 11a illustrates a first alternative embodiment of an apparatus for combining and splitting wavelength bands according to the eighth embodiment of the present invention illustrated in Fig. 11.

[150] More specifically, an apparatus for combining and splitting wavelength bands according to the first alternative embodiment of the eighth embodiment as illustrated in Fig. 11a illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first to the third CWDM filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 11 so that each pass port of the first to the third CWDM filters in Fig. 11 is changed to a reflection port in Fig. 11a, while each reflection port of the first to the third CWDM filters in Fig. 11 is changed to a pass port in Fig. 1 Ia. In this case, each of the first and the second CWDM filters outputs a signal having a wavelength band (Zl-band) with the range of 1300 ~ 1320 nm through each pass port, while outputting a signal having a remaining wavelength band except Zl-band through each reflection port. Further, the third CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1260 ~ 1280 nm through its pass port, while outputting a signal having a remaining wavelength band except Z2-band through its reflection port.

[151] Fig. 1 Ib illustrates a second alternative embodiment of an apparatus for combining and splitting wavelength bands according to the eighth embodiment of the present invention illustrated in Fig. 11.

[152] More specifically, an apparatus for combining and splitting wavelength bands according to the second alternative embodiment of the eighth embodiment as illustrated in Fig. 1 Ib illustrates a case that the functions of the pass port and the reflection port of the first edge filter are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 11 so that the pass port of the first edge filter in Fig. 11 is changed to a reflection port in Fig. 1 Ib, while the reflection port of the first edge filter in Fig. 11 is changed to a pass port in Fig. 1 Ib. In this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common

port, through its reflection port, while having a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its pass port.

[153] Fig. 1 Ic illustrates a third alternative embodiment of an apparatus for combining and splitting wavelength bands according to the eighth embodiment of the present invention illustrated in Fig. 11.

[154] More specifically, an apparatus for combining and splitting wavelength bands according to the third alternative embodiment of the eighth embodiment as illustrated in Fig. 1 Ic illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first edge filter and the first to the third CWDM filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 11 so that each pass port of the first edge filter and the first to the third CWDM filters in Fig. 11 is changed to a reflection port in Fig. l ie, while each reflection port of the first edge filter and the first to the third CWDM filters in Fig. 11 is changed to a pass port in Fig. 1 Ic. In this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its reflection port, while having a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its pass port. Each of the first and the second CWDM filters outputs a signal having a wavelength band (Zl-band) with the range of 1300 ~ 1320 nm through each pass port, while outputting a signal having a remaining wavelength band except Zl-band through each reflection port. In addition, the third CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1260 ~ 1280 nm through its pass port, while outputting a signal having a remaining wavelength band except Z2-band through its reflection port.

[155] Fig. 12 illustrates a ninth embodiment of an apparatus for combining and splitting wavelength bands for bi-directional transmission according to the present invention illustrated in Fig. 2.

[156] Referring to Fig. 12, an apparatus for combining and splitting wavelength bands according to a ninth embodiment of the present invention comprises a combination of a first edge filter for splitting X-band and Y-band from a wavelength band of light being transmitted, a first and a second CWDM filters, each for splitting Zl-band within X- band, and a third CWDM filter for splitting Z2-band within X-band. In a ninth embodiment of the present invention illustrated in Fig. 12, an upstream signal having a wavelength band with a range of 1260 ~ 1360 nm, which has already been used as a standard band in a time division multiplexing passive optical network (TDM-PON), is used as Y-band, while a downstream signal having a wavelength band with the range

of 1300 ~ 1320 nm within Y-band having a wavelength band of 1360 nm or less is used as Zl -band. In this case, a downstream signal having a wavelength band with a range of 1260 ~ 1280 nm within X-band may be used as Z2-band.

[157] More specifically, an apparatus for combining and splitting wavelength bands according to a ninth embodiment of the present invention illustrated in Fig. 12 comprises a first edge filter for splitting X-band having 1360 nm or less and Y-band having 1415 nm or more from a wavelength band of light being transmitted; a first CWDM filter for splitting Zl -band having a range of 1300 ~ 1320 nm within X-band having 1360 nm or less; a second CWDM filter for splitting Zl -band having a range of 1300 ~ 1320 nm within X-band having 1360 nm or less; and a third CWDM filter for splitting Z2-band having a range of 1260 ~ 1280 nm within X-band having 1360 nm or less. In this ninth embodiment of the present invention, a pass port of the first edge filter is connected to a pass port of the first CWDM filter, while a common port of the first edge filter is connected to a pass port of the third CWDM filter. A reflection port of the first CWDM filter is connected to a reflection port of the second CWDM filter. A pass port of the second CWDM filter is connected to a common port of the third CWDM filter. In this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its pass port, and has a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its reflection port. Each of the first and the second CWDM filters outputs a signal having a wavelength band (Zl -band) with the range of 1300 ~ 1320 nm through each reflection port, while outputting a signal having a remaining wavelength band except Zl-band through each pass port. The third CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1260 ~ 1280 nm through its reflection port, while outputting a signal having a remaining wavelength band except Z2-band through its pass port. Referring to Fig. 12, an apparatus for combining and splitting wavelength bands according to a ninth embodiment of the present invention illustrated in Fig. 12 performs substantially the same function as that performed by an apparatus for combining and splitting wavelength bands according to a seventh embodiment of the present invention illustrated in Fig. 10.

[158] Fig. 12a illustrates a first alternative embodiment of an apparatus for combining and splitting wavelength bands according to the ninth embodiment of the present invention illustrated in Fig. 12.

[159] More specifically, an apparatus for combining and splitting wavelength bands according to the first alternative embodiment of the ninth embodiment as illustrated in Fig. 12a illustrates a case that the functions of the respective pass ports and the

respective reflection ports of the first to the third CWDM filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 12 so that each pass port of the first to the third CWDM filters in Fig. 12 is changed to a reflection port in Fig. 12a, while each reflection port of the first to the third CWDM filters in Fig. 12 is changed to a pass port in Fig. 12a. In this case, each of the first and the second CWDM filters outputs a signal having a wavelength band (Zl -band) with the range of 1300 ~ 1320 nm through each pass port, while outputting a signal having a remaining wavelength band except Zl -band through each reflection port. Further, the third CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1260 ~ 1280 nm through its pass port, while outputting a signal having a remaining wavelength band except Z2-band through its reflection port.

[160] Fig. 12b illustrates a second alternative embodiment of an apparatus for combining and splitting wavelength bands according to the ninth embodiment of the present invention illustrated in Fig. 12.

[161] More specifically, an apparatus for combining and splitting wavelength bands according to the second alternative embodiment of the ninth embodiment as illustrated in Fig. 12b illustrates a case that the functions of the pass port and the reflection port of the first edge filter are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 12 so that the pass port of the first edge filter in Fig. 12 is changed to a reflection port in Fig. 12b, while the reflection port of the first edge filter in Fig. 12 is changed to a pass port in Fig. 12b. In this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its reflection port, while having a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its pass port.

[162] Fig. 12c illustrates a third alternative embodiment of an apparatus for combining and splitting wavelength bands according to the ninth embodiment of the present invention illustrated in Fig. 12.

[163] More specifically, an apparatus for combining and splitting wavelength bands according to the third alternative embodiment of the ninth embodiment as illustrated in Fig. 12c illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first edge filter and the first to the third CWDM filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 12 so that each pass port of the first edge filter and the first to the third CWDM filters in Fig. 12 is changed to a reflection port in Fig. 12c, while each reflection port of the first edge filter and the first to the third CWDM filters in Fig. 12 is changed to a pass port in Fig. 12c. In this case, the first edge filter has a function of

splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its reflection port, while having a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its pass port. Each of the first and the second CWDM filters outputs a signal having a wavelength band (Zl-band) with the range of 1300 ~ 1320 nm through each pass port, while outputting a signal having a remaining wavelength band except Zl-band through each reflection port. In addition, the third CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1260 ~ 1280 nm through its pass port, while outputting a signal having a remaining wavelength band except Z2-band through its reflection port.

[164] Fig. 13 illustrates a tenth embodiment of an apparatus for combining and splitting wavelength bands for bi-directional transmission according to the present invention illustrated in Fig. 2.

[165] Referring to Fig. 13, an apparatus for combining and splitting wavelength bands according to a tenth embodiment of the present invention comprises a combination of a first and a second edge filters, each for splitting X-band and Y-band from a wavelength band of light being transmitted, a first CWDM filter for splitting Zl-band within X- band, and a second CWDM filter for splitting Z2-band within X-band. In a tenth embodiment of the present invention illustrated in Fig. 13, an upstream signal having a wavelength band with a range of 1260 ~ 1360 nm, which has already been used as a standard band in a time division multiplexing passive optical network (TDM-PON), is used as Y-band, while a downstream signal having a wavelength band with the range of 1300 ~ 1320 nm within X-band having a wavelength band of 1360 nm or less is used as Zl-band. In this case, a downstream signal having a wavelength band with a range of 1260 ~ 1280 nm within X-band may be used as Z2-band.

[166] More specifically, an apparatus for combining and splitting wavelength bands according to a tenth embodiment of the present invention illustrated in Fig. 13 comprises a first edge filter for splitting X-band having 1360 nm or less and Y-band having 1415 nm or more from a wavelength band of light being transmitted; a second edge filter for splitting X-band having 1360 nm or less and Y-band having 1415 nm or more from the wavelength band of light being transmitted; a first CWDM filter for splitting Zl-band having a range of 1300 ~ 1320 nm within X-band having 1360 nm or less; and a second CWDM filter splitting Z2-band having a range of 1260 ~ 1280 nm within X-band having 1360 nm or less. In this tenth embodiment of the present invention, a reflection port of the first edge filter is connected to a reflection port of the first CWDM filter, while a pass port of the first edge filter is connected to a pass port of the second edge filter. A reflection port of the second edge filter is connected to a

common port of the second CWDM filter. In this case, each of the first and the second edge filters has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into each common port, through each pass port, and has a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into each common port, through each reflection port. The first CWDM filter outputs a signal having a wavelength band (Zl -band) with the range of 1300 ~ 1320 nm through its reflection port, while outputting a signal having a remaining wavelength band except Zl -band through its pass port. The second CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1260 ~ 1280 nm through its reflection port, while outputting a signal having a remaining wavelength band except Z2-band through its pass port. All of the first and the second edge filters and the first and the second CDWM filters used in Fig. 13 are a passive device and have a reciprocal characteristic. Thus, a Zl-band signal with the rage of 1300 ~ 1320 nm is transmitted along a path ®, a Z2-band signal with the rage of 1260 ~ 1280 nm is transmitted along a path ®, and a Y-band signal having 1415 nm or more is transmitted along a path ® so that both the Z-band signals and the Y-band signal may be used as bands for bi-directional transmission. Because an insertion loss of a reflection port is generally less than that of a pass port in a WDM filter, the Zl-band signal with the rage of 1300 ~ 1320 nm is designed to pass the reflection port. Any two bands among Xl -band, X2-band, and X3-band which may be used as another band for bi-directional transmission, are transmitted along a path ©. In this case, Xl -band is defined as having a wavelength range of 1320 ~ 1360 nm, X2-band is defined as having a wavelength range of 1280 ~ 1300 nm, and X3-band is defined as having a wavelength range of 1260 or less, respectively. Thus, any existing bi-directional signal is inputted into and outputted from the number one port (1) of an apparatus for combining and splitting wavelength bands having four ports according to the present invention as illustrated in Fig. 13, while any newly added bi-directional signal is inputted into and outputted from the number three port (3) thereof, both any existing bi-directional signal and any newly added bidirectional signal are inputted into and outputted from the number two port (2) thereof, and any newly added uni-directional signal is inputted into and outputted from the number four port (4) thereof. Further, because all of the first and the second edge filters and the first and the second CDWM filters illustrated in Fig. 13 are a passive device having a reciprocalcharacteristic, it should be fully understood by a skilled person in the art that the Zl-band signal with the rage of 1300 ~ 1320 nm may be transmitted along a reverse direction of the path ® and the Y-band signal having 1415 nm or more is transmitted along a reverse direction of the path ® so that the Zl-band signal and the Y-band signal may be used as bands for bi-directional transmission,

while any two bands among Xl -band, X2-band, and X3-band are transmitted along a reverse direction of the path ©.

[167] Fig. 13a illustrates a first alternative embodiment of an apparatus for combining and splitting wavelength bands according to the tenth embodiment of the present invention illustrated in Fig. 13.

[168] More specifically, an apparatus for combining and splitting wavelength bands according to the first alternative embodiment of the tenth embodiment as illustrated in Fig. 13a illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first and the second CWDM filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 13 so that each pass port of the first and the second CWDM filters in Fig. 13 is changed to a reflection port in Fig. 13a, while each reflection port of the first and the second CWDM filters in Fig. 13 is changed to a pass port in Fig. 13a. In this case, the first CWDM filter outputs a signal having a wavelength band (Zl -band) with the range of 1300 ~ 1320 nm through its pass port, while outputting a signal having a remaining wavelength band except Zl -band through its reflection port. Further, the second CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1260 ~ 1280 nm through its pass port, while outputting a signal having a remaining wavelength band except Z2-band through its reflection port.

[169] Fig. 13b illustrates a second alternative embodiment of an apparatus for combining and splitting wavelength bands according to the tenth embodiment of the present invention illustrated in Fig. 13.

[170] More specifically, an apparatus for combining and splitting wavelength bands according to the second alternative embodiment of the tenth embodiment as illustrated in Fig. 13b illustrates a case that the functions of the pass port and the reflection port of the first and the second edge filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 13 so that each pass port of the first and the second edge filters in Fig. 13 is changed to a reflection port in Fig. 13b, while each reflection port of the first and the second edge filters in Fig. 13 is changed to a pass port in Fig. 13b. In this case, each of the first and the second edge filters has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into each common port, through each reflection port, while having a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into each common port, through each pass port.

[171] Fig. 13c illustrates a third alternative embodiment of an apparatus for combining and splitting wavelength bands according to the tenth embodiment of the present invention illustrated in Fig. 13.

[172] More specifically, an apparatus for combining and splitting wavelength bands according to the third alternative embodiment of the tenth embodiment as illustrated in Fig. 13c illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first and the second edge filters and the first and the second CWDM filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 13 so that each pass port of the first and the second edge filters and the first and the second CWDM filters in Fig. 13 is changed to a reflection port in Fig. 13c, while each reflection port of the first and the second edge filters and the first and the second CWDM filters in Fig. 13 is changed to a pass port in Fig. 13c. In this case, each of the first and the second edge filters has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into each common port, through each reflection port, while having a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into each common port, through each pass port. The first CWDM filter outputs a signal having a wavelength band (Zl -band) with the range of 1300 ~ 1320 nm through its pass port, while outputting a signal having a remaining wavelength band except Zl -band through its reflection port. In addition, the second CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1260 ~ 1280 nm through its pass port, while outputting a signal having a remaining wavelength band except Z2-band through its reflection port.

[173] Fig. 14 illustrates an eleventh embodiment of an apparatus for combining and splitting wavelength bands for bi-directional transmission according to the present invention illustrated in Fig. 2.

[174] Referring to Fig. 14, an apparatus for combining and splitting wavelength bands according to an eleventh fifth embodiment of the present invention comprises a combination of a first edge filter for splitting X-band and Y-band from a wavelength band of light being transmitted, a first and a second CWDM filters, each for splitting Zl -band within X-band, and a third CWDM filter for splitting Z2-band within X-band. In an eleventh embodiment of the present invention illustrated in Fig. 14, an upstream signal having a wavelength band with a range of 1260 ~ 1360 nm, which has already been used as a standard band in a time division multiplexing passive optical network (TDM-PON), is used as Y-band, while a downstream signal having a wavelength band with the range of 1300 ~ 1320 nm within X-band having a wavelength band of 1360 nm or less is used as Zl -band. In this case, a downstream signal having a wavelength band with a range of 1260 ~ 1280 nm within X-band may be used as Z2-band.

[175] More specifically, an apparatus for combining and splitting wavelength bands according to an eleventh embodiment of the present invention illustrated in Fig. 14 comprises a first edge filter for splitting X-band having 1360 nm or less and Y-band

having 1415 nm or more from a wavelength band of light being transmitted; a first CWDM filter for splitting Zl -band having a range of 1300 ~ 1320 nm within X-band having 1360 nm or less; a second CWDM filter for splitting Zl -band having a range of 1300 ~ 1320 nm within X-band having 1360 nm or less; and a third CWDM filter for splitting Z2-band having a range of 1260 ~ 1280 nm within X-band having 1360 nm or less. In this eleventh embodiment of the present invention, a pass port of the first edge filter is connected to a pass port of the first CWDM filter, while a reflection port of the first edge filter is connected to a common port of the third CWDM filter. A reflection port of the second CWDM filter is connected to a reflection port of the first CWDM filter. A common port of the second CWDM filter is connected to a pass port of the third CWDM filter. In this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its pass port, and has a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its reflection port. Each of the first and the second CWDM filters outputs a signal having a wavelength band (Zl -band) with the range of 1300 ~ 1320 nm through each reflection port, while outputting a signal having a remaining wavelength band except Zl-band through each pass port. The third CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1260 ~ 1280 nm through its reflection port, while outputting a signal having a remaining wavelength band except Z2-band through its pass port. Referring to Fig. 14, an apparatus for combining and splitting wavelength bands according to an eleventh embodiment of the present invention illustrated in Fig. 14 performs substantially the same function as that performed by an apparatus for combining and splitting wavelength bands according to a seventh embodiment of the present invention illustrated in Fig. 10.

[176] Fig. 14a illustrates a first alternative embodiment of an apparatus for combining and splitting wavelength bands according to the eleventh embodiment of the present invention illustrated in Fig. 14.

[177] More specifically, an apparatus for combining and splitting wavelength bands according to the first alternative embodiment of the eleventh embodiment as illustrated in Fig. 14a illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first to the third CWDM filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 14 so that each pass port of the first to the third CWDM filters in Fig. 14 is changed to a reflection port in Fig. 14a, while each reflection port of the first to the third CWDM filters in Fig. 14 is changed to a pass port in Fig. 14a. In this case, each of the first and the second CWDM filters outputs a signal having a wavelength band (Zl-band) with

the range of 1300 ~ 1320 nm through each pass port, while outputting a signal having a remaining wavelength band except Zl -band through each reflection port. Further, the third CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1260 ~ 1280 nm through its pass port, while outputting a signal having a remaining wavelength band except Z2-band through its reflection port.

[178] Fig. 14b illustrates a second alternative embodiment of an apparatus for combining and splitting wavelength bands according to the eleventh embodiment of the present invention illustrated in Fig. 14.

[179] More specifically, an apparatus for combining and splitting wavelength bands according to the second alternative embodiment of the eleventh embodiment as illustrated in Fig. 14b illustrates a case that the functions of the pass port and the reflection port of the first edge filter are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 14 so that the pass port of the first edge filter in Fig. 14 is changed to a reflection port in Fig. 14b, while the reflection port of the first edge filter in Fig. 14 is changed to a pass port in Fig. 14b. In this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its reflection port, while having a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its pass port.

[180] Fig. 14c illustrates a third alternative embodiment of an apparatus for combining and splitting wavelength bands according to the eleventh embodiment of the present invention illustrated in Fig. 14.

[181] More specifically, an apparatus for combining and splitting wavelength bands according to the third alternative embodiment of the eleventh embodiment as illustrated in Fig. 14c illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first edge filter and the first to the third CWDM filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 14 so that each pass port of the first edge filter and the first to the third CWDM filters in Fig. 14 is changed to a reflection port in Fig. 14c, while each reflection port of the first edge filter and the first to the third CWDM filters in Fig. 14 is changed to a pass port in Fig. 14c. In this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its reflection port, while having a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its pass port. Each of the first and the second CWDM filters outputs a signal having a wavelength band (Zl -band) with the range of 1300 ~ 1320 nm through each pass port,

while outputting a signal having a remaining wavelength band except Zl -band through each reflection port. In addition, the third CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1260 ~ 1280 nm through its pass port, while outputting a signal having a remaining wavelength band except Z2-band through its reflection port.

[182] Fig. 15 illustrates a twelfth embodiment of an apparatus for combining and splitting wavelength bands for bi-directional transmission according to the present invention illustrated in Fig. 2.

[183] Referring to Fig. 15, an apparatus for combining and splitting wavelength bands according to a twelfth embodiment of the present invention comprises a combination of a first edge filter for splitting X-band and Y-band from a wavelength band of light being transmitted, a first and a second CWDM filters, each for splitting Zl-band within X-band, and a third CWDM filter for splitting Z2-band within X-band. In a twelfth embodiment of the present invention illustrated in Fig. 15, an upstream signal having a wavelength band with a range of 1260 ~ 1360 nm, which has already been used as a standard band in a time division multiplexing passive optical network (TDM-PON), is used as Y-band, while a downstream signal having a wavelength band with the range of 1300 ~ 1320 nm within X-band having a wavelength band of 1360 nm or less is used as Zl-band. In this case, a downstream signal having a wavelength band with a range of 1260 - 1580 nm within X-band may be used as Z2-band.

[184] More specifically, an apparatus for combining and splitting wavelength bands according to a twelfth embodiment of the present invention illustrated in Fig. 15 comprises a first edge filter for splitting X-band having 1360 nm or less and Y-band having 1415 nm or more from a wavelength band of light being transmitted; a first CWDM filter for splitting Zl-band having a range of 1300 ~ 1320 nm within X-band having 1360 nm or less; a second CWDM filter for splitting Zl-band having a range of 1300 ~ 1320 nm within X-band having 1360 nm or less; and a third CWDM filter for splitting Z2-band having a range of 1260 ~ 1280 nm within X-band having 1360 nm or less. In this twelfth embodiment of the present invention, a pass port of the first edge filter is connected to a pass port of the first CWDM filter, while a common port of the first edge filter is connected to a pass port of the third CWDM filter. A reflection port of the first CWDM filter is connected to a reflection port of the second CWDM filter. A pass port of the second CWDM filter is connected to a common port of the third CWDM filter. In this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its pass port, and has a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its reflection port. Each of the first and

the second CWDM filters outputs a signal having a wavelength band (Zl -band) with the range of 1300 ~ 1320 nm through each reflection port, while outputting a signal having a remaining wavelength band except Zl-band through each pass port. The third CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1260 ~ 1280 nm through its reflection port, while outputting a signal having a remaining wavelength band except Z2-band through its pass port. Referring to Fig. 15, an apparatus for combining and splitting wavelength bands according to a twelfth embodiment of the present invention illustrated in Fig. 15 performs substantially the same function as that performed by an apparatus for combining and splitting wavelength bands according to a seventh embodiment of the present invention illustrated in Fig. 10.

[185] Fig. 15a illustrates a first alternative embodiment of an apparatus for combining and splitting wavelength bands according to the twelfth embodiment of the present invention illustrated in Fig. 15.

[186] More specifically, an apparatus for combining and splitting wavelength bands according to the first alternative embodiment of the twelfth embodiment as illustrated in Fig. 15a illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first to the third CWDM filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 15 so that each pass port of the first to the third CWDM filters in Fig. 15 is changed to a reflection port in Fig. 15a, while each reflection port of the first to the third CWDM filters in Fig. 15 is changed to a pass port in Fig. 15a. In this case, each of the first and the second CWDM filters outputs a signal having a wavelength band (Zl-band) with the range of 1300 ~ 1320 nm through each pass port, while outputting a signal having a remaining wavelength band except Zl-band through each reflection port. Further, the third CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1260 ~ 1280 nm through its pass port, while outputting a signal having a remaining wavelength band except Z2-band through its reflection port.

[187] Fig. 15b illustrates a second alternative embodiment of an apparatus for combining and splitting wavelength bands according to the twelfth embodiment of the present invention illustrated in Fig. 15.

[188] More specifically, an apparatus for combining and splitting wavelength bands according to the second alternative embodiment of the twelfth embodiment as illustrated in Fig. 15b illustrates a case that the functions of the pass port and the reflection port of the first edge filter are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 15 so that the pass port of the first edge filter in Fig. 15 is changed to a reflection port in Fig. 15b, while the reflection port of the first edge filter in Fig. 15 is changed to a pass port in Fig. 15b. In

this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its reflection port, while having a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its pass port.

[189] Fig. 15c illustrates a third alternative embodiment of an apparatus for combining and splitting wavelength bands according to the twelfth embodiment of the present invention illustrated in Fig. 15.

[190] More specifically, an apparatus for combining and splitting wavelength bands according to the third alternative embodiment of the twelfth embodiment as illustrated in Fig. 15c illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first edge filter and the first to the third CWDM filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 15 so that each pass port of the first edge filter and the first to the third CWDM filters in Fig. 15 is changed to a reflection port in Fig. 15c, while each reflection port of the first edge filter and the first to the third CWDM filters in Fig. 15 is changed to a pass port in Fig. 15c. In this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its reflection port, while having a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its pass port. Each of the first and the second CWDM filters outputs a signal having a wavelength band (Zl-band) with the range of 1300 ~ 1320 nm through each pass port, while outputting a signal having a remaining wavelength band except Zl-band through each reflection port. In addition, the third CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1260 ~ 1280 nm through its pass port, while outputting a signal having a remaining wavelength band except Z2-band through its reflection port.

[191] Fig. 16 illustrates a thirteenth embodiment of an apparatus for combining and splitting wavelength bands for bi-directional transmission according to the present invention illustrated in Fig. 3.

[192] More specifically, an apparatus for combining and splitting wavelength bands according to a thirteenth embodiment of the present invention illustrated in Fig. 16 comprises a first edge filter for splitting X-band having 1360 nm or less and Y-band having 1415 nm or more from a wavelength band of light being transmitted; a first CWDM filter for splitting Zl-band having a range of 1480 ~ 1500 nm within Y-band having 1415 nm or more; a second CWDM filter for splitting Z2-band having a range of 1550 ~ 1560 nm within Y-band having 1415 nm or more; and a third CWDM filter

for splitting Z3-band having a range of 1300 ~ 1320 nm within X-band having 1360 nm or less. In this thirteenth embodiment of the present invention, a reflection port of the first edge filter is connected to a reflection port of the first CWDM filter, while a pass port of the first edge filter is connected to a reflection port of the third CWDM filter. A pass port of the third CWDM filter is connected to a common port of the first CWDM filter. A pass port of the first CWDM filter is connected to a common port of the second CWDM filter. In this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its pass port, and has a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its reflection port. The first CWDM filter outputs a signal having a wavelength band (Zl -band) with the range of 1480 ~ 1500 nm through its reflection port, while outputting a signal having a remaining wavelength band except Zl -band through its pass port. The second CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1550 ~ 1560 nm through its reflection port, while outputting a signal having a remaining wavelength band except Z2-band through its pass port. The third CWDM filter outputs a signal having a wavelength band (Z3-band) with the range of 1300 ~ 1320 nm through its reflection port, while outputting a signal having a remaining wavelength band except Z3-band through its pass port.

[193] Fig. 16a illustrates a first alternative embodiment of an apparatus for combining and splitting wavelength bands according to the thirteenth embodiment of the present invention illustrated in Fig. 16.

[194] More specifically, an apparatus for combining and splitting wavelength bands according to the first alternative embodiment of the thirteenth embodiment as illustrated in Fig. 16a illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first to the third CWDM filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 16 so that each pass port of the first to the third CWDM filters in Fig. 16 is changed to a reflection port in Fig. 16a, while each reflection port of the first to the third CWDM filters in Fig. 16 is changed to a pass port in Fig. 16a. In this case, the first CWDM filter outputs a signal having a wavelength band (Zl -band) with the range of 1480 ~ 1500 nm through each pass port, while outputting a signal having a remaining wavelength band except Zl -band through each reflection port. The second CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1550 ~ 1560 nm through each pass port, while outputting a signal having a remaining wavelength band except Z2-band through each reflection port. Further, the third CWDM filter outputs a signal having a wavelength band (Z3-band) with the range of

1300 ~ 1320 nm through its pass port, while outputting a signal having a remaining wavelength band except Z3-band through its reflection port.

[195] Fig. 16b illustrates a second alternative embodiment of an apparatus for combining and splitting wavelength bands according to the thirteenth embodiment of the present invention illustrated in Fig. 16.

[196] More specifically, an apparatus for combining and splitting wavelength bands according to the second alternative embodiment of the thirteenth embodiment as illustrated in Fig. 16b illustrates a case that the functions of the pass port and the reflection port of the first edge filter are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 16 so that the pass port of the first edge filter in Fig. 16 is changed to a reflection port in Fig. 16b, while the reflection port of the first edge filter in Fig. 16 is changed to a pass port in Fig. 16b. In this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its reflection port, while having a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its pass port.

[197] Fig. 16c illustrates a third alternative embodiment of an apparatus for combining and splitting wavelength bands according to the thirteenth embodiment of the present invention illustrated in Fig. 16.

[198] More specifically, an apparatus for combining and splitting wavelength bands according to the third alternative embodiment of the thirteenth embodiment as illustrated in Fig. 16c illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first edge filter and the first to the third CWDM filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 16 so that each pass port of the first edge filter and the first to the third CWDM filters in Fig. 16 is changed to a reflection port in Fig. 16c, while each reflection port of the first edge filter and the first to the third CWDM filters in Fig. 16 is changed to a pass port in Fig. 16c. In this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its reflection port, while having a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its pass port. The first CWDM filter outputs a signal having a wavelength band (Zl -band) with the range of 1480 ~ 1500 nm through each pass port, while outputting a signal having a remaining wavelength band except Zl -band through each reflection port. The second CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1550 ~ 1560 nm through each pass port, while outputting a signal having a remaining

wavelength band except Z2-band through each reflection port. In addition, the third CWDM filter outputs a signal having a wavelength band (Z3-band) with the range of 1300 ~ 1320 nm through its pass port, while outputting a signal having a remaining wavelength band except Z3-band through its reflection port.

[199] Fig. 17 illustrates a fourteenth embodiment of an apparatus for combining and splitting wavelength bands for bi-directional transmission according to the present invention illustrated in Fig. 3.

[200] More specifically, an apparatus for combining and splitting wavelength bands according to a fourteenth embodiment of the present invention illustrated in Fig. 17 comprises a first edge filter for splitting X-band having 1360 nm or less and Y-band having 1415 nm or more from a wavelength band of light being transmitted; a first CWDM filter for splitting Zl -band having a range of 1480 ~ 1500 nm within Y-band having 1415 nm or more; a second CWDM filter for splitting Z2-band having a range of 1550 ~ 1560 nm within Y-band having 1415 nm or more; and a third CWDM filter for splitting Z3-band having a range of 1300 ~ 1320 nm within X-band having 1360 nm or less. In this fourteenth embodiment of the present invention, a reflection port of the first edge filter is connected to a reflection port of the first CWDM filter, while a pass port of the first edge filter is connected to a pass port of the third CWDM filter. A reflection port of the third CWDM filter is connected to a common port of the second CWDM filter. A common port of the first CWDM filter is connected to a pass port of the second CWDM filter. In this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its pass port, and has a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its reflection port. The first CWDM filter outputs a signal having a wavelength band (Zl -band) with the range of 1480 ~ 1500 nm through each reflection port, while outputting a signal having a remaining wavelength band except Zl-band through each pass port. The second CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1550 ~ 1560 nm through each reflection port, while outputting a signal having a remaining wavelength band except Z2-band through each pass port. The third CWDM filter outputs a signal having a wavelength band (Z3-band) with the range of 1300 ~ 1320 nm through its reflection port, while outputting a signal having a remaining wavelength band except Z3-band through its pass port. Referring to Fig. 17, an apparatus for combining and splitting wavelength bands according to a fourteenth embodiment of the present invention illustrated in Fig. 17 performs substantially the same function as that performed by an apparatus for combining and splitting wavelength bands according to a thirteenth embodiment of the present invention il-

lustrated in Fig. 16.

[201] Fig. 17a illustrates a first alternative embodiment of an apparatus for combining and splitting wavelength bands according to the fourteenth embodiment of the present invention illustrated in Fig. 17.

[202] More specifically, an apparatus for combining and splitting wavelength bands according to the first alternative embodiment of the fourteenth embodiment as illustrated in Fig. 17a illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first to the third CWDM filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 17 so that each pass port of the first to the third CWDM filters in Fig. 17 is changed to a reflection port in Fig. 17a, while each reflection port of the first to the third CWDM filters in Fig. 17 is changed to a pass port in Fig. 17a. In this case, the first CWDM filter outputs a signal having a wavelength band (Zl -band) with the range of 1480 ~ 1500 nm through its pass port, while outputting a signal having a remaining wavelength band except Zl -band through its reflection port. The second CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1550 ~ 1560 nm through its pass port, while outputting a signal having a remaining wavelength band except Z2-band through its reflection port. Further, the third CWDM filter outputs a signal having a wavelength band (Z3-band) with the range of 1300 ~ 1320 nm through its pass port, while outputting a signal having a remaining wavelength band except Z3-band through its reflection port.

[203] Fig. 17b illustrates a second alternative embodiment of an apparatus for combining and splitting wavelength bands according to the fourteenth embodiment of the present invention illustrated in Fig. 17.

[204] More specifically, an apparatus for combining and splitting wavelength bands according to the second alternative embodiment of the fourteenth embodiment as illustrated in Fig. 17b illustrates a case that the functions of the pass port and the reflection port of the first edge filter are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 17 so that the pass port of the first edge filter in Fig. 17 is changed to a reflection port in Fig. 17b, while the reflection port of the first edge filter in Fig. 17 is changed to a pass port in Fig. 17b. In this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its reflection port, while having a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its pass port.

[205] Fig. 17c illustrates a third alternative embodiment of an apparatus for combining and splitting wavelength bands according to the fourteenth embodiment of the present

invention illustrated in Fig. 17.

[206] More specifically, an apparatus for combining and splitting wavelength bands according to the third alternative embodiment of the fourteenth embodiment as illustrated in Fig. 17c illustrates a case that the functions of the respective pass ports and the respective reflection ports of the first edge filter and the first to the third CWDM filters are switched each other in an apparatus for combining and splitting wavelength bands illustrated in Fig. 17 so that each pass port of the first edge filter and the first to the third CWDM filters in Fig. 17 is changed to a reflection port in Fig. 17c, while each reflection port of the first edge filter and the first to the third CWDM filters in Fig. 17 is changed to a pass port in Fig. 17c. In this case, the first edge filter has a function of splitting a signal having a wavelength band (X-band) with 1360 nm or less among signals, being inputted into its common port, through its reflection port, while having a function of splitting a signal having a wavelength band (Y-band) with 1415 nm or more among the signals, being inputted into its common port, through its pass port. The first CWDM filter outputs a signal having a wavelength band (Zl -band) with the range of 1480 ~ 1500 nm through its pass port, while outputting a signal having a remaining wavelength band except Zl -band through its reflection port. The second CWDM filter outputs a signal having a wavelength band (Z2-band) with the range of 1550 ~ 1560 nm through its pass port, while outputting a signal having a remaining wavelength band except Z2-band through its reflection port. In addition, the third CWDM filter outputs a signal having a wavelength band (Z3-band) with the range of 1300 ~ 1320 nm through its pass port, while outputting a signal having a remaining wavelength band except Z3-band through its reflection port.

[207] Although it is illustrated and described, in the first to the fourteenth embodiments and their respective alternative embodiments as illustrated in Figs. 4 to 17, that an apparatus for combining and splitting wavelength bands having four ports according to the present invention comprises a combination of four WDM filters (either two edge filters and two CWDM filter, or one edge filter and three CWDM filters), any skilled person in the art may fully understand that an apparatus for combining and splitting wavelength bands having four ports according to the present invention can be embodied by any one integrated device having the same function as the combination of four WDM filters described above. Such a one integrated device has an advantage that it is capable of minimizing an insertion loss through the four input and output ports, when compared with the combination of four WDM filters. Further, the ranges of X- band, Y-band, and Z-band used in an apparatus for combining and splitting wavelength bands according to the present invention described above are illustrative, and thus the scope of the present invention is not intended to be limited to the specific ranges of X- band, Y-band, and Z-band. For example, in case that an apparatus for combining and

splitting wavelength bands according to the present invention is embodied by using wavelength-tunable WDM filters, the ranges of X-band, Y-band, and Z-band may be varied depending on necessity. An apparatus for combining and splitting wavelength bands according to the present invention described above has a function of combining and splitting wavelength bands for new bi-directional transmission, while accommodating an existing wavelength band as it is, where the existing wavelength band is transmitted bi-directionally through a transmission path in a one-line. Accordingly, when applying apparatus for combining and splitting wavelength bands according to the present invention to an existing metro network or access network, it is possible to expand the existing metro network or access network for the purpose of upgrading. For example, when applying an apparatus for combining and splitting wavelength bands according to a first embodiment of the present invention illustrated in Figs. 4 to 4c to an existing access network, it is possible to add Yl -band and Y2-band as bi-directional signal bands for a WDM-PON in bi-directional transmission signals of a TDM-PON where a wavelength band (X-band) with a range of 1260 ~ 1280 nm is used as an upstream signal, while a wavelength band (Zl -band) with a range of 1480 ~ 1500 nm is used as a downstream signal. Further, it is possible to add a wavelength band (Z2-band) with a range of 1550 ~ 1560 nm as a wavelength band for a video overlay signal. More specifically, when connecting the common port of the first edge filter of an apparatus for combining and splitting wavelength bands according to a first embodiment of the present invention illustrated in Figs. 4 to 4c to an optical line termination (OLT) at a central office (CO) of a TDM-PON, connecting the common port of the second edge filter thereof to a remote node (RN), connecting the pass port of the second CWDM filter to the OLT at CO of a WDM-PON, and positioning the reflection port of the second CWDM filter within CO of the WDM-PON, an added apparatus for combining and splitting wavelength bands according to the present invention can perform a function of combining and splitting new signals for bi-directional transmission, while simultaneously performing a function of upgrading an existing access network (i.e., a function of providing a service with a higher bandwidth by adding a WDM-PON and a video signal). Further, an apparatus for combining and splitting wavelength bands according to the present invention is possible to increase flexibility and expansibility of an existing access network, because an OLT at CO of a new access network may be added either at CO or at any positions of the existing access network, depending on the positions of an apparatus for combining and splitting wavelength bands according to the present invention to be added. Industrial Applicability

[209] An apparatus for combining and splitting wavelength bands having four input and output ports according to the present invention has the following advantages:

[210] 1. The present invention can be embodied at low costs and with a simple configuration so that it may function as the prior art add/drop multiplexers.

[211] 2. Unlike the prior art add/drop multiplexers which can combine and split only a signal with a specific wavelength, the present invention may combine a wavelength band having a certain range with or splitting it from an existing signal band so that high usability thereof can be accomplished in the present invention.

[212] 3. The present invention may be utilized as a device for upgrading and expanding an existing metro network or an existing access network so that performance of an optical communications system can be enhanced at low costs.

[213] 4. The present invention may increase flexibility and expansibility of an existing metro network or an existing access network.

[214] As various modifications could be made in the constructions and method herein described and illustrated without departing from the scope of the present invention, it is intended that all matters contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the above- described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.