Cross-Reference to Related Applications

This application is being filed on January 14, 2022 as a PCT International Patent Application and claims the benefit of U.S. Patent Application Serial No. 63/137,991, filed on January 15, 2021, the disclosure of which is incorporated herein by reference in its entirety.

Field of the Invention

The present invention is generally directed to optical communications, and more specifically to devices for tapping off a portion of an optical signal propagating from a central office to an end user, within an optical fiber network.

Background of the Invention

Passive optical networks are becoming prevalent in part because service providers want to deliver high bandwidth communication capabilities to customers. Passive optical networks are a desirable choice for delivering high-speed communication data because they can avoid the use of active electronic devices, such as amplifiers and repeaters, between a central office and a subscriber termination. The absence of active electronic devices can decrease network complexity and/or cost and may increase network reliability.

An example of an optical fiber network 100 used in providing optical communications to multiple end users is schematically illustrated in FIG. 1. The network 100 includes a central office 102 that may be connected to provide internet service to the end users 104 or to a public switched telephone network (PSTN). The network 100 may connect to the end users 104 via one or more fibers 106 that are located overhead or housed within underground conduits. The central office 102 typically includes an optical transmitter 102a for transmitting signals to the end users 104 and an optical receiver 102b for receiving signals from the end users 104. In this embodiment, the end users 104 are domestic users, and the optical network 100 may be a fiber to the home (FTTH) network.

The central office 102 is typically connected to a trunk fiber 106, which can also be referred to as a feeder fiber or feeder cable. A number of break-out locations 108 are located along the length of the feeder cable 106. At a break-out location 108 a portion of the optical signal is tapped from the feeder cable 106 and split into a number of user signals that are directed along local fibers 110 to a subset the end users 104.

The fraction of the optical signal that is tapped off the feeder cable 106 may have to be changed at various times. For example, a larger fraction may need to be tapped off the feeder cable if it is decided that a specific break-out location has to service an increased number of homes. Alternatively, it may be decided that a smaller fraction of the optical signal should be tapped off at a particular break-out location because service is no longer required in the locale served by that break-out location. Some examples of addressing this problem are discussed in WO 2020/028659A1.

The break-out location 108 typically includes both the optical tap and the optical splitter contained within a single housing, which may be ruggedized or weather-proofed, whether the feeder cable 106 is located above ground or underground. This arrangement can be inconvenient for the network manager, however, when the fraction of the signal to be tapped off at any particular break-out location 108 has to be changed. This operation requires the ruggedized housing to be opened up and the optical tap changed within it. Or, it can require that the ruggedized housing be replaced with a second housing that contains an optical tap of the correct fraction. Neither approach is satisfactory. Opening the ruggedized housing exposes delicate optical elements to the weather, and increases the chance that an optical component can be damaged. Replacing one ruggedized housing with another is expensive as the network manager has to maintain an inventory of ruggedized housings held in reserved as replacements.

A similar problem is found in a fiber network 200 that serves multiple wireless communication hubs 204, such as wi-fi hubs, as shown schematically in FIG. 2. In this case, the break-out locations 208 direct optical signals to the wireless hubs 204 from the central office 102, and from the wireless hubs 204 to the central office 102. In the illustrated case, the first, third and fourth wireless hubs 204 are not operating, so the break-out locations 208a, 208c and 208d tap off 0% of the optical signal from the central office 102. The second and fifth wireless hubs 204 are operable, and the respective breakout locations 208b, 208e tap off a desired percentage of the optical signal from the central office 102, in this case 3%. However, the configuration of the wireless network may change, and it may be desired to add or subtract operable wireless hubs 204, in which case the break-out locations 208 have to be changed to tap of the desired amount of the optical signal for the new configuration. There is a need, therefore, to simplify the process of changing the tap fraction at a break-out location while maintaining the integrity of the ruggedized housings and making the process less expensive. In addition, new approaches to providing a fiber tap can reduce the size of the tap used at the break-out location.

Summary of the Invention

An embodiment of the invention is directed to an optical device that has a first component having a ruggedized input, a first output and a second output. A fiber tap component is coupled between the input and the first and second outputs so that when an optical signal enters the first component via the input, a larger portion of the optical signal is directed via the tap component to the first output and a smaller portion fraction of the optical signal is directed to the second output. A second component has a ruggedized housing. The second component has a first input, and a first output. A splitter is coupled between the first input of the second component and the first output of the second component. The splitter is configured to split the smaller portion of the optical signal into a plurality of splitter output signals. The plurality of splitter output signals is coupled out of the second component via the second output. The fiber tap component includes one of a multi-core fiber tap or a bend-insensitive fiber tap.

Another embodiment of the invention is directed to an optical network method that includes passing an optical signal into a first ruggedized component from an upstream feed fiber. A portion of the optical signal is tapped from the optical signal in a fiber tap in the first ruggedized component to form a tapped signal. The fiber tap includes one of a multicore fiber tap or a bend-insensitive fiber tap. A remainder of the optical signal is propagated through a second ruggedized component to a downstream feed fiber. The tapped signal is propagated into the second ruggedized component. The tapped signal is split into a plurality of splitter output signals inside the second ruggedized component. The plurality of the splitter output signals is directed out of the second ruggedized component.

Another embodiment of the invention is directed to an optical tap having an input coupled to a first core of multi -core fiber (MCF) at a first end of the MCF. The MCF has at least a second core, the second core of the MCF disposed laterally proximate to the first core of the MCF so that a portion of an optical signal propagating within the first core of the multi-core MCF from the input is coupled into the second core of the MCF. An optical fan-out is coupled at a second end of the MCF to receive light from the first and second cores of the MCF. The optical fan-out has a first optical path to a first tap output for light propagating into the optical fan-out from the first core of the MCF and a second optical path to a second tap output for light propagating into the optical fan-out from the second core of the MCF.

Another embodiment of the invention is directed to an optical tap that has an input coupled to a first end of a first bend-insensitive fiber (BIF). The first BIF has a first core, and a first output at a second end of the first BIF. A second BIF has a second core and a second output at an end of the second BIF. A fiber biconical taper is formed between the first and second BIFs resulting in a coupling region. When an optical signal propagates along the first BIF between the input and the output, a portion of the optical signal propagating in the first core of the first BIF is coupled into the second core of the second BIF at the coupling region as a tap signal. The tap signal propagates towards the second output of the second BIF.

The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and the detailed description which follow more particularly exemplify these embodiments.

Brief Description of the Drawings

The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which:

FIG. 1 schematically illustrates a first prior art fiber communication network;

FIG. 2 schematically illustrates a second prior art fiber communication network;

FIG. 3 schematically illustrates an embodiment of a ruggedized terminal box;

FIG. 4 schematically illustrates an embodiment of an optical fiber network having taps located outside the ruggedized terminal boxes;

FIG. 5 schematically illustrates a ruggedized break-out unit in which the tap unit and splitter unit are housed separately, according to an embodiment of the present invention;

FIG. 6 schematically illustrates a tap unit implemented using a multi-core fiber, according to an embodiment of the present invention;

FIGs. 7A and 7B schematically show fiber cross sections at respective positions within the tap unit of FIG. 6, according to an embodiment of the present invention; FIG. 8 schematically illustrates a tap unit implemented using a multi-core fiber with a tapered and drawn coupling region, according to an embodiment of the present invention;

FIG. 9 schematically illustrates a tap unit implemented using a multi-core fiber with a thermally expanded core coupling region, according to an embodiment of the present invention;

FIG. 10 schematically illustrates a break-out location unit having separate housings for the multi -core fiber tap unit and the splitter unit, according to an embodiment of the present invention;

FIG. 11 schematically illustrates a break-out location unit having separate housings for the multi -core fiber tap unit and the splitter unit, according to another embodiment of the present invention;

FIG. 12 schematically illustrates a tap unit using a biconical fiber taper (BFT) tap implemented in bend-insensitive fiber (BIF) according to an embodiment of the present invention;

FIG. 13 schematically illustrate the BFT of the tap unit shown in FIG. 12, according to an embodiment of the present invention;

FIG. 14 schematically illustrates a break-out unit having separate housings for the BFT BIF tap unit and the splitter unit, according to an embodiment of the present invention;

FIG. 15 schematically illustrates a break-out unit having a wavelength division multiplexed (WDM) splitter unit according to an embodiment of the present invention;

FIG. 16 schematically illustrates a break-out unit having a wavelength division multiplexed (WDM) splitter unit and passive splitter network according to an embodiment of the present invention; and

FIG. 17 schematically illustrates a break-out unit in which the main optical signal from the tap unit bypasses the splitter unit, according to an embodiment of the present invention.

While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. Detailed Description

The present invention is directed to providing optical tap components that are simple to swap out while still maintaining the ruggedized protection for the tap and splitter elements associated with a break-out location.

The term “ruggedized” as used herein to describe an item, for example a housing or a fiber coupling or connector, means that the device has been designed to include environmental sealing that allows use outdoors. For example, the sealing can provide protection against intrusion, dust, accidental contact and/or water. One example of environmental protection is in accordance with the Ingress Protection Code (IP Code) IEC Standard 60529, published by the International Electrotechnical Commission. The equivalent European standard is EN 60529. Some devices, such as fiber couplings and connectors, and housings, are classified as IP67 or IP68 for environmental protection. Other levels of environmental protection can be greater or lesser in the kinds of protections offered.

FIG. 3 schematically illustrates an embodiment of a ruggedized housing 300, also referred to as an enclosure (lacking a lid so as to permit viewing inside the enclosure 300). The ruggedized enclosure 300 conventionally encloses a tap element 314 and a splitter element 318. The enclosure 300 includes an input port 302 that is coupled to the upstream feeder cable 304, that includes an upstream feeder fiber, which derives from the central office. The enclosure 300 has a first output port 306 coupled to the downstream feeder cable 308, that includes a downstream feeder fiber, that carries the main optical signal from the central office to subsequent enclosures along the network. A first main signal fiber 310 carries main optical signal from the input port 302 signal to a tap/splitter unit 312. The first main signal fiber 310 may be coupled to the fiber of the upstream feeder cable 304 via a ruggedized fiber connector. The ruggedized connector may use a ferrule, or may be ferrule-less . Examples of ruggedized connectors that may be used here and in other ruggedized connections described herein include, but are not limited to LC connectors, SC connectors, MPO connectors and the like.

The tap/splitter unit has a tap element 314 that taps off a portion of the optical signal. The remainder of the optical signal is directed to the first output port 306 via a second main signal fiber 316. The second main signal fiber 316 may be connected to the fiber of the downstream feeder cable 308 via a ruggedized single fiber connector, such as a ruggedized LC connector. The tapped signal is directed to a splitter 318 that splits the tapped signal into a plurality of individual signals that may be subsequently directed to individual end users. In the illustrated embodiment the splitter 318 is a 1x4 passive splitter network that splits the tapped signal into four individual signals, although the splitter may split the tapped signal into a greater or small number of individual signals. The individual signals are directed to the wall of the enclosure via individual signal fibers 320. In the illustrated embodiment, the individual signal fibers 320 are coupled at a multifiber output port 322 to fibers of a multifiber cable 324. The multifiber output port 322 may be, for example, a ruggedized MPO connector. The multifiber cable 324 carries the individual signals away from the enclosure 300 and the fibers of the multifiber cable 324 may carry the individual signals to their end destinations or to further processing. The tapping and splitting functions may take place in fiber or on an optical chip.

In the embodiment illustrated in FIG. 3, the functions of tapping and splitting both take place within the ruggedized enclosure 300, which reduces costs by reducing the number of ruggedized components. It is not convenient, however, for situations where it is desired that the fraction of the optical signal that is tapped off to the splitter has to be changed, as it involves opening the ruggedized enclosure, potentially subjecting the interior of the enclosure to dust, water and the like.

A different approach is schematically illustrated in FIG. 4, which shows an optical fiber network 400 that has a central office 402. The central office 402 may include an optical transmitter 402a for transmitting signals to the end users 404 and an optical receiver 402b for receiving signals from the end users 404. In this embodiment, the end users 404 are domestic users, and the optical network 400 may be a fiber to the home (FTTH) network.

The central office 402 is connected to a feeder fiber 406. The feeder fiber 402 may be a single mode fiber, or may be a multimode fiber. A number of break-out locations 408 are located along the length of the feeder fiber 406. It will be appreciated that the feeder fiber 406 need not be a single length of optical fiber, but may be formed of a plurality of fiber sections coupled together to carry the main optical signal. At each break-out location 408, a tap 408a is external to the ruggedized enclosure 408b that houses the splitter element. The tap 408a may be a fiber tap. Thus, two optical signals are fed into the ruggedized enclosure 408b from the tap 408a, namely the main optical signal and the tapped optical signal, which may also be referred to as the tap signal. The tap signal is passed to the splitter 409 within the ruggedized enclosure where it is split into a number of user signals that are directed along local fibers 410 to a subset of end users 404. In the illustrated embodiment the splitter 409 is a 1x4 passive splitter network. The splitter 409 may split the tapped optical signal equally among the user signals, or one or more of the user signals may have a larger share of the tapped signal than others.

In this approach, the percentage of the optical signal propagating along the feeder fiber 406 that is tapped from the main optical signal at any of the break-out locations 408 may be readily changed by swapping out tap 408a from one with a first tap percentage to another with a second tap percentage, without necessitating that the ruggedized enclosure be opened.

FIG. 5 schematically illustrates a fiber break-out unit 500 that includes a tap unit 502 coupled to a ruggedized enclosure 504 that houses a splitter unit. The tap unit 502 may be coupled to the enclosure 504 via at least one ruggedized connector 506. The ruggedized connector 506 may be a multi-fiber connector, such as a ruggedized MPO connector. In other embodiments, the ruggedized connector 506 may include two or more single fiber connectors within a ruggedized connector housing. The tap unit 502 includes an input connector 508 to receive the feeder fiber (not shown) from the upstream direction. The enclosure 504 has a first output connector 510 to connect to the feeder fiber (not shown) downstream from the enclosure 504. The enclosure also has a second output connector 512 for connecting to the user fibers (not shown). The connectors 508, 510 that connect to the feeder fiber may be ruggedized and may be single fiber connectors, for example ruggedized LC connectors. The second output connector 510 may also be ruggedized and may be a multi-fiber connector, for example a ruggedized MPO connector. In other embodiments, the enclosure 504 may be provided with multiple output connectors for connecting to user fibers or other fibers that are not the main feeder fiber. Such multiple output connectors may be single fiber connectors or multi-fiber connectors, and may be ruggedized.

FIG. 6 schematically illustrates part of an exemplary tap unit 600 that is based on a multi-core fiber, for example a dual core fiber. The tap unit 600 comprises a multi-core section 602 and a fan-out section 604. The tap unit 600 may also include a single core coupling section 606. Fiber connectors have been omitted from the figure, but it will be understood that the tap unit 600 may be terminated at each end with appropriate connectors, which may be ruggedized.

The multi -core section 602 includes a length of multi -core fiber (MCF) 610 that has at least a first core 612a and a second core 612b that is laterally separated from the first core 612a. In some embodiments, the first core 612a is centrally positioned within the cladding 614 of the MCF 610. This case is schematically illustrated in FIG. 7A, which shows a cross section of the MCF 610 taken at the line AA’. The first core 612a receives the main optical signal that has propagated along the feeder fiber from the central office. In embodiments where the tap 600 includes a single core coupling section 606, the single core coupling section 606 is coupled to the feeder fiber to receive the main optical signal, which then propagates to the multi -core section 602. In other embodiments, the multicore fiber 610 may be directly coupled to the feeder fiber. While propagating along the first core 612a, a portion of the main optical signal from the central office evanescently couples from the first core 612a to the second core 612b as the tap signal, so that there are optical signals propagating along both the first and second cores 612a, 612b at the right end of the multi-core section 602. In some embodiments the end face of the MCF 610 that couples to the fan-out section 604 may be polished for a ferrule-based connection to the fan-out section 604. In other embodiments, the MCF 610 may be fusion spliced to the fan-out section 604.

The fan-out section 604 includes a fan-out element 616 that has a multi -core end 618 coupled to the MCF 610 and a single core end 620 that includes at least a first single core fiber 620a and a second single core fiber 620b. The multi-core end 618 of the fanout element 616 includes a first core 622a and a second core 622b that are aligned respectively with the first and second cores 612a, 612b of the MCF 610. The main optical signal propagating along the first core 612a of the MCF 610 passes into the first core 622a of the fan-out element 616 and is directed into the first single core fiber 620a. The tap signal propagating along the second core 612b of the MCF 610 passes into the second core 622b of the fan-out element 616 and is directed into the second single core fiber 620b. A cross section of the fan-out element 616 through the single core fibers 620a, 620b, at the section BB’, is schematically shown in FIG. 7B. One embodiment of a fan-out element 616 may be formed via bi-tapering a fiber bundle of two parallel multi-mode fibers, each of which is tapered-spliced with respective single core fibers, as is described by Guo K et al., “All Fiber-Fan-Out Device for Varying Twin Core Fiber Types,” J. Lightwave Tech. (2017) 35 (23) 5121-5126, incorporated herein by reference. Additionally, fiber fan-out devices are available from Chiral Photonics, Pine Brook, New Jersey.

The separation distance between the first and second cores 612a, 612b, and the length over which the first and second cores 612a, 612b lie parallel may be selected to achieve the desired tap fraction for the tap unit 600. In some embodiments the separation distance between the first and second cores 612a, 612b maybe be constant along the length of the MCF 610. In other embodiments the separation between the cores 612a, 612b may not be constant along the length of the MCF 610. In the exemplary embodiment of tap unit 800 illustrated in FIG. 8, the separation distance between the first and second cores 612a, 612b is reduced at the coupling region 810, but not at the propagation region 811. A drawing/tapering process, for example via heating and stretching of the fiber 610, may be used to form the coupling region 810 in the MCF 610. The drawing/ tapering process results in the cores 612a, 612b being closer together and the diameter of the cores 612a, 612b being reduced in the coupling region 810, thus increasing the overlap of the optical mode in one core over the adjacent core. This increases the evanescent coupling between the first core 612a and the second core 612b. Additional protection may be added around the coupling region 810, which may be fragile following the drawing/tapering process, for example through the use of potting. In one approach to manufacturing the tap unit 800, the input face 804 of the MCF 610 is polished in a dual fiber connector. The output from the second core 612b is measured while the fiber 610 is drawn and tapered, with the drawing and tapering being stopped when the desired tap percentage is measured from the second core 612b.

Another approach to providing a dual -core fiber tap unit 900 shown schematically in FIG. 9. In this approach, the MCF 610 is includes a coupling region 910 where the first core 612a and the second core 612b have been thermally expanded. Thermally expandable cores (TECs) rely on the lateral diffusion of the core dopant under localized heating, resulting in expanded core sections 912a, 912b in the coupling region 910. The propagation region 911 has unexpanded cores 612a, 612b. This leads to expansion of the mode fields in the first and second cores 612a, 612b, in the coupling region 910, resulting in more mode overlap so that evanescent coupling increases between the cores 612a, 612b in the coupling region 910. Because the external shape of the MCF 610 is not changed during the heating process, the MCF 610 maintains high strength and stable responses to temperature and strain.

In one approach to manufacturing the tap unit 900, the input face 904 of the MCF 610 is polished in a dual fiber connector. The output from the second core 612b is measured while the fiber 610 is heated at the coupling region 910. The heating is removed when the desired tap percentage is measured from the second core 612b.

FIG. 10 schematically illustrates one approach to coupling a multi -core fiber tap unit 1000 in a fiber network. In this embodiment, the multi-core fiber tap unit 1000 is coupled to the feeder cable 1002 that is upstream to tap unit 1000 by a ruggedized connector 1004. This may be, for example, a ruggedized LC or SC connector. The tap unit 1000 is also coupled to a ruggedized enclosure 1006 via a multi-fiber ruggedized connector 1008, for example a ruggedized MPO connector. In this embodiment, the connector 1008 couples both the main optical signal and the tap signal to the enclosure 1006. In another approach, the ruggedized connector 1008 may include a plurality of single fiber connectors, such as LC or SC connectors, within a single ruggedized housing.

The ruggedized enclosure 1006 is provided with two outputs. A first output 1010 may be coupled to a downstream section of the feeder fiber. The first output 1010 may be part of a single fiber connector and may be ruggedized. For example, the first output 1010 may be part of a ruggedized LC or SC connector, with the other part of the ruggedized LC or SC connector on the downstream feeder fiber. A second output 1012 may be coupled to a multifiber cable to carry user signals from the splitter within the enclosure 1006. In this case the second output 1012 may be a multifiber output, and may also be ruggedized. For example the second output 1012 may include part of a ruggedized MPO connector, with the other part of the MPO connector attached to the multifiber cable that carries the user signals.

FIG. 11 schematically illustrates another approach to coupling a multi-core fiber tap unit 1100 in a fiber network. In this embodiment, the multi-core fiber tap unit 1100 is coupled to the feeder cable 1102 that is upstream to tap unit 1100 by a ruggedized connector 1104. This may be, for example, a ruggedized LC connector. The tap unit 1100 is also coupled to a ruggedized enclosure 1106 via a first ruggedized connector 1108, for example a ruggedized LC connector and a second ruggedized connector 1109, for example a ruggedized LC connector. In this embodiment, each connector 1108, 1109 may be a single fiber connector, with the first connector 1108 carrying the main optical signal into the enclosure 1106 and the second connector 1109 carrying the tap signal into the enclosure 1106.

The ruggedized enclosure 1106 is provided with two outputs. A first output 1110 may be coupled to a downstream section of the feeder fiber. The first output 1110 may be part of a single fiber connector and may be ruggedized. For example, the first output 1110 may be part of a ruggedized LC connector, with the other part of the ruggedized LC connector on the downstream feeder fiber. A second output 1112 may be coupled to a multifiber cable to carry user signals from the splitter within the enclosure 1106. In this case the second output 1112 may be a multifiber output, and may also be ruggedized. For example the second output 1112 may include part of a ruggedized MPO connector, with the other part of the MPO connector attached to the multifiber cable that carries the user signals.

Another embodiment of tap unit 1200, which uses a fused biconical taper (FBT) tap is schematically illustrated in FIG. 12. Since the tap unit 1200 is to be provided outside the ruggedized enclosure, it is advantageous that the tap unit 1200 be small. One approach to achieving small size is to implement the FBT using bend-insensitive fiber (BIF). The BIF is provided with a refractive index profile that is different from that of a conventional single mode fiber, or may be microstructured, so that the fiber is less sensitive to bending loss than conventional fiber. This permits the BIF FBT tap to be contained relatively tightly wound and contained within a housing 1202 having a smaller footprint than would be possible using a FBT tap based on a conventional single mode fiber.

The tap unit 1200 includes a first input 1204 that may be a ruggedized input, for example part of a ruggedized single fiber connector such as a ruggedized LC connector. A main BIF 1206 leads between the first input 1204 and a first output 1205 on the housing 1202 and is couplable, via the first input 1204, to an upstream part of the feeder fiber to receive the main optical signal. The main BIF may form a coil 1208 within the housing 1202. A tap BIF 1210 forms an FBT tap with the main BIF 1206 so that a portion of the main optical signal propagating along the main BIF 1206 is evanescently coupled from the main BIF 1206 to the tap BIF 1210. The FBT tap may be located along the coil 1208. The tap BIF 1210 may be connected to the first output 1205 where the first output 1205 is a multi -fiber output, for example an MPO output. The first output 1205 may be ruggedized. In other embodiments, the tap BIF 1210 may be connected to a second output, where the first and second output are each single fiber outputs. In another approach, the tap BIF 1210 and the main BIF 1206 may each be coupled to respective single-fiber connectors that are each contained within the same ruggedized connector housing.

The FBT tap 1300 is schematically illustrated in FIG. 13, which shows the tap BIF 1210 side-by-side with the main BIF 1206. The FBT tap 1300 includes an input taper section 1302 where the diameters of the main BIF 1206 and its core 1206a reduce towards a coupling section 1304. In the coupling section 1304 the diameters of the main BIF 1206 and its core 1206a are typically at a minimum. In the output taper section 1306 the diameters of the main BIF 1206 and its core 1206a taper back up to their original values. Likewise, at the input taper section 1302 the diameters of the tap BIF 1210 and its core 1210a reduce towards the coupling section 1304. In the coupling section 1304 the diameters of the tap BIF 1210 and its core 1210a are typically at a minimum. In the output taper section 1306 the diameters of the main BIF 1210 and its core 1210a taper back up to their original values. As a result of this structure, light can evanescently couple from the main BIF core 1206a to the tap BIF core 1210a in the coupling section 1304. One approach to making the FBT tap 1300 is to twist together exposed cladding regions of the fibers 1206, 1210. The application of heat at the exposed cladding region, while applying longitudinal tension results in stretching and formation of the taper sections 1302, 1306 and the coupling section 1304. The signal through the tap BIF 1210 may be monitored while the heating and stretching is proceeding and the process can be stopped when the signal on the tap BIF 1210 reaches level associated with a desired tap fraction. The tap 1300 may then be potted or otherwise protected and then mounted in the housing 1202.

FIG. 14 schematically illustrates an approach to coupling a BIF FBT tap into an optical fiber network in a break-out unit 1400. An upstream section of feeder fiber 1402 is connected to a tap housing 1404 that contains the BIF FBT tap via a connector 1406. The connector 1406 may be ruggedized and may be a single fiber connector such as an LC connector. A multifiber output 1408 from the tap housing 1404 is connected to the ruggedized enclosure 1410 that houses the splitter unit. The multifiber output 1408 is coupled to the ruggedized enclosure 1410 by a multifiber connector 1412, which may be a ruggedized connector, such as a ruggedized MPO connector. In another approach, the connector 412 may include two single fiber connectors, for example a duplex LC connector, contained within the same ruggedized connector housing.

The enclosure 1410 has a first output 1414 connected to a downstream section of the feeder fiber 1416 via a connector 1418 which may be ruggedized and a single fiber connector. The enclosure has a second output 1420 connected to a multifiber cable 1422, via a multifiber connector 1424, that carries multiple user fibers. The multifiber connector 1424 may be ruggedized, such as a ruggedized MPO connector.

Another approach to providing tapping and splitter functions at a break-out location of an optical fiber network is schematically illustrated in FIG. 15. The break-out unit 1500 includes a tap unit 1502 that is coupled to, but also external to, a splitter unit 1504 that is enclosed within a ruggedized housing. A feeder cable 1506, containing the feeder fiber, is coupled at an input connector 1508 to the tap unit 1502. The input connector 1508 may be a ruggedized connector. The tap unit 1502 may include a fiber optic tap 1510 as described above. The tap unit 1502 has a first output 1512 that carries the main optical signal and a second output 1514 that carries the tap signal. The first output 1512 may include a single fiber connected to the splitter unit 1504 using suitable connectors, while the second output may also be a single fiber connected to the splitter unit 1504 using suitable connectors. In other embodiments, the first and second outputs 1512, 1514 may include respective fibers in a multi-fiber cable that is connected to the tap unit 1502 and the splitter unit 1504 using suitable connectors, for example an MPO or other multi -fiber connector. Also, the first and second outputs 1512, 1514 may include single fibers with single fiber connectors that are housed in a ruggedized connector housing that accommodates both connect single fiber connectors, for example multiplexed LC or SC connectors. In another approach, the tap unit 1502 may plug into the splitter unit 1504 without any intermediate fiber between the tap unit 1502 and the splitter unit 1504.

The first output 1512 from the tap unit 1502 is passed into the splitter unit 1504. The main optical signal propagating along the first 1512 output may couple to a bypass 1516 within the splitter unit 1504 which simply transports the main optical signal to a first splitter output 1518. The first splitter output 1518 may be coupled to a subsequent length of feeder cable 1520 to carry the main optical signal to downstream locations of the optical network.

The second output 1514 from the tap unit 1502 is passed to a splitter subsystem 1522 in the splitter unit 1504. In this embodiment, the main optical signal is a wavelength division multiplexed (WDM) signal, having components at four different wavelengths, XI, X2, X3, and X4. The tap signal, which contains the same wavelength components as the main optical signal, propagates to a WDM splitter subunit 1522, which separates the tap signal into its separate wavelength components. The WDM splitter subunit 1522 may include any suitable optical component for separating the individual optical components, for example an arrayed waveguide grating (AWG) or a cyclic AWG. Individual wavelength outputs 1524 from the WDM splitter subunit 1522 contain signals at respective wavelengths corresponding to the component wavelengths of the main optical signal, XI, X2, X3, and X4. The individual wavelength outputs 1524, which may include separate fibers for each individual wavelength may be coupled to a multifiber output 1526, such as a ruggedized MPO output, which is connected to a multifiber cable 1528 that leads the individual wavelength signals to other downstream components of the network. While the WDM spliter subunit 1522 is shown to operate on four wavelengths, it will be appreciated that it may operate on a different number of wavelengths, for example, 2, 8, or 16.

A variation on the embodiment of break-out unit 1600 is schematically illustrated in FIG. 16. Similar elements as the previous figure have similar numbering. In this embodiment, the spliter subunit 1622 includes both a WDM spliter subunit 1622a and a passive spliter subunit 1622b. Individual wavelength outputs 1624 from the WDM spliter subunit 1622a are directed to the passive spliter subunit 1622b, so that the signal at each individual wavelength XI, X2, X3, and X4 is split into a plurality of individual wavelength split outputs 1625. These are fed to a multifiber output connector 1626, such as a ruggedized MPO connector, which is connected to a multifiber cable 1628 that leads the individual wavelength split signals to other downstream network components.

This embodiment illustrates a WDM spliter subunit 1622a that handles four different wavelengths, although it will be appreciated that the WDM spliter subunit 1622a may handle a greater or small number of individual wavelengths than this, for example 2, 8 or 16. Furthermore, the passive spliter subunit 1622b is shown to have four 1x4 passive spliter networks, one for each respective individual wavelength output 1624. It will also be appreciated that there is no requirement that the passive spliter networks be 1x4 networks, and they may have a different number of outputs, for example they may be 1x2, 1x8 or 1x16 passive spliter networks.

Another approach to providing tapping and spliter functions at a break-out location of an optical fiber network is schematically illustrated in FIG. 17. The break-out unit 1700 includes a tap unit 1702 that is coupled to, but also external to, a spliter unit 1704 that is enclosed within a ruggedized housing. A feeder cable 1706, containing the feeder fiber, is coupled at an input connector 1708 to the tap unit 1702. The input connector 1708 may be a ruggedized connector. The tap unit 1702 may include a fiber optic tap 1710 like those described above. The tap unit 1702 has a first output 1712 that carries the main optical signal and a second output 1714 that carries the tap signal. The first output 1712 is coupled to a downstream feeder cable 1720 so that the main optical signal bypasses the spliter unit 1704. This approach reduces insertion losses in the main optical signal because the number of connectors is reduced. The tap signal is directed into the spliter unit 1704 where a spliter subunit 1722 splits the tap signal into a number of split tap signal outputs 1724 that are coupled via a multifiber connector 1726 to a multifiber cable 1728. The spliter subunit 1722 may include a passive spliter network, a WDM spliter, or both.

In the present description of the invention it has generally been assumed that light signals propagate from left to right across a figure, in which case ports on the left side of a device have been referred to as inputs, and those on the right as outputs. It will be appreciated that in many optical devices optical signals may propagate through the device in opposing directions. For example, in one direction a tap may operate to split out a portion of the main optical signal propagating along the feeder fiber from the central office for directing to one or more users. In the reverse direction, however, the tap operates as a combiner, combining signals from the one or more users to the main optical signal propagating along the feeder fiber to the central office. Accordingly, although various waveguides, fibers, and ports may be labeled as “input” and “output” in this description, it should be understood that these labels are used only for ease of description. It should be understood that the waveguides, optical fibers and ports described herein may carry operate as inputs for optical signals propagating in one direction but as outputs for signals operating in the opposite direction.

Various modifications, equivalent processes, as well as numerous structures to which the present invention may be applicable will be readily apparent to those of skill in the art to which the present invention is directed upon review of the present specification. The claims are intended to cover such modifications and devices.

As noted above, the present invention is applicable to fiber optical communication and data transmission systems. Accordingly, the present invention should not be considered limited to the particular examples described above, but rather should be understood to cover all aspects of the invention as fairly set out in the atached claims.