Technical Field

[0001] Embodiments relate to a method of manufacturing an optical structure.

Background

[0002] Change of refractive index may be required for fabrication of optical devices. One such utilization may be for fabrication of Bragg gratings that may be present in optical communication systems. Bragg grating may be utilized as filters in such systems and one purpose may be to reflect particular wavelengths of light and transmit all others. This may be achieved by adding a periodic variation to the refractive index of the waveguide, which may generate a wavelength specific dielectric mirror.

[0003] Waveguide that have a steep refractive index change at an interface between core section and cladding section may be referred to as a "step-type" and having a gradual change may be referred to as a "graded-type". Step-type waveguide may be fabricated by using two materials with contrasting refractive index through the process of photolithography and etching.

[0004] Another usage of change in refractive index may be for fabrication of an optical waveguide, mainly used for transmitting rays in an optical device. The optical waveguide may include a core section having a relatively higher refractive index and a cladding section having a relatively lower refractive index. With the difference, the region of higher refractive index may restrict the light, forming a wave guiding structure that may cause rays to be transmitted through the region of higher refractive index. Optical devices developed using this setup may include optical fibers, optical diffraction gratings and optical integrated circuits.

[0005] Refractive index changes have generally been done by using Femtosecond lasers on glass material. The process may cause the refractive index to increase in the glass material and may be used to fabricate the core section. However, any writing regime focused on the core section may subject the core section to changes that may significantly reduce the ability of the core section to transmit light efficiently.

[0006] Therefore, there is a need for an alternative method to achieve the refractive index changes which may not significantly reduce the ability of the waveguide to transmit light efficiently.

Summary

[0007] In various embodiments, a method of manufacturing an optical structure may be provided. The method may include forming a polymer layer on a substrate; forming a blocking structure over the polymer layer, the blocking structure including at least one radiation blocking portion configured to inhibit passage of radiation; and exposing the polymer layer to a radiation source to form the optical structure; the polymer layer including at least one exposed portion and at least one unexposed portion; wherein the at least one radiation blocking portion may be positioned over the at least one unexposed portion such that the at least one exposed portion experiences a reduction in refractive index when exposed to the radiation source. Brief Description of the Drawings

[0008] In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of various embodiments. In the following description, various embodiments of the invention are described with reference to the following drawings, in which:

FIG. 1 shows a flowchart illustrating a method of manufacturing an optical structure according to an embodiment;

FIGS. 2A to 2D show respective cross-sectional views of a method of manufacturing a waveguide according to an embodiment;

FIG. 3 shows a perspective view of exposing the polymer layer to a radiation source after a blocking structure may be formed over the polymer layer during a method of manufacturing a waveguide according to an embodiment;

FIG. 4A shows a top view of a waveguide according to an embodiment; FIG. 4B shows a perspective view of a waveguide according to an embodiment;

FIG. 5 shows a perspective view of exposing the polymer layer to a radiation source during a method of manufacturing a beam splitter according to an embodiment;

FIG. 6 shows a top view of a beam splitter according to an embodiment;

FIGS. 7A to 7D show respective cross-sectional views of a method of manufacturing a grating according to an embodiment;

FIG. 8 shows a perspective view of exposing the polymer layer to a radiation source during a method of manufacturing a grating according to an embodiment; FIG. 9 shows a cross-sectional view of forming a photomask over the polymer layer during a method of manufacturing a grating according to an embodiment;

FIG. 10 shows a cross-sectional view of forming a blocking structure from an interference of signals from two radiation sources over the polymer layer during a method of manufacturing a grating according to an embodiment; and

FIG. 11 shows a perspective view of forming a blocking structure from an interference of signals from two radiation sources over the polymer layer during a method of manufacturing a grating according to an embodiment.

Description

[0009] The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the invention. The various embodiments are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments.

[0010] The word "exemplary" is used herein to mean "serving as an example, instance, or illustration". Any embodiment or design described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments or designs. [0011] An embodiment may provide a method of manufacturing an optical structure. The method may include forming a polymer layer on a substrate, forming a blocking structure over the polymer layer, the blocking structure including at least one radiation blocking portion configured to inhibit passage of radiation and exposing the polymer layer to a radiation source to form the optical structure; the optical structure including at least one exposed portion and at least one unexposed portion, wherein the at least one radiation blocking portion may be positioned over the at least one unexposed portion such that the at least one exposed portion may experience a reduction in refractive index when exposed to the radiation source. The polymer layer may include a characteristic such that at least a portion of the polymer layer may experience a reduction in refractive index when exposed to a radiation source.

[0012] In an embodiment, forming the polymer layer on the substrate may include spin- coating the polymer layer on the substrate and soft-baking the polymer layer for a predetermined period of time and a predetermined temperature. The predetermined period of time may be between about 1 minute to 10 minutes, for example about 5 minutes. The predetermined temperature may be between about 50 degree Celsius to about 200 degree Celsius, for example about 100 degree Celsius.

[0013] In an embodiment, forming the blocking structure over the polymer layer may include forming the blocking structure directly on the polymer layer. For example, the blocking structure may be in direct contact with a portion of the polymer layer.

[0014] In an embodiment, forming the blocking structure over the polymer layer may include forming the blocking structure at a predetermined distance away from the polymer layer. The predetermined distance may be such as the blocking structure may still be able to block off a portion of the polymer layer from the radiation. The predetermined distance may be between a range of between about 1 um to about 10000 um.

[0015] In an embodiment, the method may further include providing heat treatment after exposing the polymer layer to the radiation source.

[0016] In an embodiment, the blocking structure may further include at least one radiation non-blocking portion configured to allow passage of radiation. The at least one radiation non-blocking portion may be a part of a photomask, or the bright fringes of an interference fringes formed by an interference of signals from two radiation sources. The at least one radiation non-blocking portion may be integrated with the radiation blocking portion as a single layer or may be separate from each other depending on user and design requirements. The at least one radiation non-blocking portion and the at least one radiation blocking portion may form a pattern corresponding to the resultant optical structure on the substrate.

[0017] In an embodiment, the at least one radiation non-blocking portion may be positioned over the at least one exposed portion. The at least one radiation non-blocking portion and the at least one radiation blocking portion may be positioned at the same distance away from the substrate or may be positioned at respective different distances from the substrate depending on user and design requirements. Alternatively, each or both of the at least one radiation non-blocking portion and the at least one radiation blocking portion may be positioned substantially directly on the substrate.

[0018] Bi an embodiment, each, of the at least one radiation blocking portion and the at least one radiation non-blocking portion may be arranged in an alternating pattern in a single layer. The dimensions of each of the at least one radiation blocking portion and the at least one radiation non-blocking portion may vary depending on user and design requirements.

[0019] In an embodiment, forming the blocking structure may include forming the blocking structure from an interference of signals from two radiation sources. The interferences of two signals from two different or same radiation sources may result in a layer of interference fringes. The layer of interference fringes may include at least one or a plurality of respective bright fringes and dark fringes positioned in any pattern relative to each other. For example each of the plurality of bright fringes and dark fringes may be positioned relative to each other in an alternating pattern. Each white fringe may be positioned over each exposed portion and each dark fringe may be positioned over each unexposed portion.

[0020] In an embodiment, the substrate may include silicon, glass, or any other suitable materials with a lower refractive index than the polymer layer.

[0021] In an embodiment, the blocking structure may include a metal wire, a masking layer, a photomask, a metal mask. For example if the blocking structure may include the metal wire, then the blocking structure may be the same as the at least one radiation blocking portion. If the blocking structure may include the photomask, then the blocking structure may include only the at least one radiation blocking portion or may include both the at least one radiation blocking portion and the at least one radiation non-blocking portion. The blocking structure or the at least one radiation blocking portion may include any material which is non-transparent to radiation. [0022] In an embodiment, the radiation source may include an electromagnetic radiation with a wavelength shorter than visible light (wavelength of between about 10 nm to about 400 nm). Examples of such a radiation source may include UV laser and UV lamps.

[0023] In an embodiment, the radiation source may be configured to provide radiation with a wavelength in a range from about 10 nm to about 400 nm.

[0024] In an embodiment, the optical structure may be for example a waveguide, a beam splitter, a grating, a filter, a mirror, a lens or a light coupler.

[0025] In an embodiment, the at least one unexposed portion may form a core portion. The dimension of the core portion may be relative to the dimension of the at least one radiation blocking portion. The dimension of the core portion may vary according to the dimension of the at least one radiation blocking portion.

[0026] In an embodiment, the at least one exposed portion may form a cladding portion. The cladding portion may be positioned such that the cladding portion substantially surround the core portion or may be positioned such that the cladding portion may be positioned on one or both sides of the core portion.

[0027] In an embodiment, the at least one unexposed portion may be configured to channel light. For example, the core portion may be configured to channel light.

[0028] In an embodiment, the reduction in refractive index may include a range from about 0.001 to about 0.004.

[0029] In an embodiment, the at least one radiation blocking portion may be configured to inhibit passage of ultra-violet (UV) radiation.

[0030] In an embodiment, the blocking structure may be of any suitable design depending on the resultant optical structure. The blocking structure may also be of any suitable thickness and size depending on user and design requirements. The blocking structure may be of any suitable material, which may not be transparent to the radiation, depending on design and user requirements.

[0031] In an embodiment, the at least one radiation blocking portion may be positioned over the at least one unexposed portion such that the at least one unexposed portion experiences no substantial change in refractive index.

[0032] In an embodiment, the radiation from the radiation source may be incident in a direction substantially perpendicular to the substrate such that the at least one unexposed portion may be positioned directly below the at least one radiation blocking portion. The radiation from the radiation source may also be incident at an angle to the substrate.

[0033] In an embodiment, the radiation from the radiation source may be an unfocused light beam. For example, the radiation source may not be focused on a particular spot within the polymer layer.

[0034] In an embodiment, a method of manufacturing the optical structure may include decreasing an index of refraction of the polymer by about 0.001 using laser radiation.

[0035] In an embodiment, the method of manufacturing the optical structure may include at least one step of an electromagnectic radiation with a wavelength shorter than visible light (a wavelength of between about lOnm to about 400nm). The electromagnetic radiation may be UV laser or UV exposure. UV laser may be a pulse or continuous laser that may emit a high intensity and coherent UV light. UV exposure may be any source that may emit UV radiation, including lamps that emit UV light.

[0036] In an embodiment, a method of decreasing the index of refraction of a polymeric material by exposing the polymeric material to laser radiation at a particular energy. The energy from the laser radiation may induce a decrease in index of refraction of the polymeric material. The refractive index changes may induce a contrast with an unaltered portion of the polymeric material. This may be useful in the fabrication of optical devices such as optical waveguides and gratings, interference filter.

[0037] In an embodiment, a method to decrease the refractive index of polymer may be used to define the cladding sections. The method may not utilize focusing of laser radiation and may be able to adjust the region of the refractive index change of the cladding and therefore enabling a user to easily vary the required diameter of the core region. In addition, with a refractive index of about 10 ^"3 , a shorter distance may be needed to fabricate optical structure which may include gratings and interference filters, for example.

[0038] Producing waveguides by writing a surrounding cladding portion of the waveguides may have several advantages over writing a core portion of the waveguide.

Unlike writing regimes focused, on the core portion, corresponding writing regimes focused on the cladding portion may not subject the core portion to changes that may significantly reduce the ability of the core portion to transmit light efficiently.

[0039] In an embodiment, areas or portions of the polymer that may be exposed to certain energy level of laser radiation may show a decrease in refractive index.

[0040] In an embodiment, the width or diameter of the core portion may be adjusted by adjusting the designated area of cladding portion that may be exposed to laser radiation.

[0041] In an embodiment, the core portion may not be subjected to changes that may significantly reduce the ability of the core portion to transmit light efficiently. [0042] In an embodiment, optical structures on the support substrate may be fabricated using mask of a certain thickness. Respective areas blocked by the mask may be the optical structures that may need to be fabricated.

[0043] In an embodiment, patterns on the mask may depend on the optical structure to be fabricated.

[0044] In an embodiment, at least one step of UV exposure may be needed after the laser radiation. The UV exposure may be for a period of between about 10 seconds to about 150 seconds.

[0045] In an embodiment, at least one step of hotplate heating may be needed after the laser radiation.

[0046] In an embodiment, at least one step of oven heating may be needed after the laser radiation. The oven heating step may be to facilitate the refractive index (RI) changes in the polymer layer. If there may not be the oven heating step, RI changes may still occur but may be at a relatively slower rate or smaller. The temperature for the oven heating may be from about 100 degree Celsius to about 180 degree Celsius. The duration of the oven heating may be from about 15 seconds to about 300 seconds.

[0047] FIG. 1 shows a flowchart 1000 illustrating a method of manufacturing an optical structure 100 according to an embodiment.

[0048] At 1002, a polymer layer 104 may be formed on a substrate 106.

[0049] At 1004, a blocking structure 110 may be formed over the polymer layer 104, the blocking structure 110 including at least one radiation blocking portion 112 configured to inhibit passage of radiation. [0050] At 1006, the polymer layer 104 may be exposed to a radiation source 108 to form the optical structure. The optical structure may include at least one exposed portion 116 and at least one unexposed portion 118.

[0051] At 1008, the at least one radiation blocking portion 112 may be positioned over the at least one unexposed portion 118 such that the at least one exposed portion 116 may experience a reduction in refractive index when exposed to the radiation source 108.

[0052] FIGS. 2A to 2D show respective cross-sectional views of a method of manufacturing a waveguide 102 according to an embodiment.

[0053] FIG. 2A shows a polymer layer 104 formed on a substrate 106. The substrate 106 may include silicon, glass, or any other suitable materials with a lower refractive index than the polymer layer. The polymer layer 104 may include a material such that at least a portion of the polymer layer 104 may experience a reduction in refractive index when exposed to a radiation source (not shown). The polymer materials may be epoxy materials, methacryl compounds with calboxylic acid, acrylate compounds with calboxylic acid, PMMA, polyimide, for example.

[0054] The polymer layer 104 may be formed on the substrate 106 by spin-coating the polymer layer 104 on the substrate 106 and soft-baking the polymer layer 104 for a predetermined period of time and temperature.

[0055] FIG. 2B shows a blocking structure 110 formed over the polymer layer 104. The blocking structure 110 may include at least one radiation blocking portion 112 configured to inhibit passage of radiation. In FIG. 2B, the blocking structure 110 may be the same as the at least one radiation blocking portion 112 and may include a metal wire 114 which may be configured to inhibit radiation. The dimensions of the metal wire 114 may vary according to design and user requirements. The dimensions of the metal wire 114 may also vary relative to the required dimensions of the resultant core portion 140 of the waveguide 102 (as shown in FIG. 2D). The metal wire 114 may be formed at a predetermined distance away from the polymer layer 104. The dimension of the metal wire 114 may be modulated from about 1 micron to about 300 mm.

[0056] FIG. 2C shows the polymer layer 104 being exposed to a radiation source 108 to form the waveguide 102. The radiation source 108 may include an electromagnetic radiation with a shorter wavelength than visible light. The radiation source 108 may be configured to provide radiation with a wavelength in a range from about 10 nm to about 400 nm.

[0057] After exposing to the radiation source 108, the polymer layer 104 may include at least one exposed portion 116 (which may subsequently form the cladding portion 138 of the waveguide 102 as shown in FIG. 2D) and at least one unexposed portion 118 (which may subsequently form the core portion 140 of the waveguide 102 as shown in FIG. 2D).

[0058] The blocking structure 110, the at least one radiation blocking portion 112 or the metal wire 114 may be positioned over the unexposed portion 118 such that the unexposed portion 118 may experience no substantial change in refractive index and the exposed portion 116 may experience a reduction in refractive index when exposed to the radiation source 108.

[0059] Heat treatment at a temperature of between about 100 degree Celsius to about 180 degree Celsius and duration of between about 15 seconds to about 300 seconds may be provided after exposing the polymer layer 104 to the radiation source 108. [0060] FIG. 2D shows the resultant waveguide 102 disposed on the substrate 106. The waveguide 102 may include the core portion 140 and the cladding portion 138. The core portion 140 may correspond to the at least one unexposed portion 118 in FIG. 2C and the cladding portion 138 may correspond to the at least one exposed portion 116 in FIG. 2C.

[0061] FIG. 3 shows a perspective view of exposing the polymer layer 104 to a radiation source 108 after a blocking structure 110 may be formed over the polymer layer 104 during a method of manufacturing a waveguide (not shown) according to an embodiment.

[0062] FIG. 3 may be similar to FIG. 2C and the blocking structure 110 may include a metal wire 114 which may be configured to inhibit radiation. The dimensions of the metal wire 114 may vary according to design and user requirements. The dimensions of the metal wire 114 may also vary relative to the resultant core portion 140 of the waveguide 102. Alternatively, the metal wire 114 may be larger than the resultant core portion 140 of the waveguide 102.

[0063] After exposing to the radiation source 108, the polymer layer 104 may include at least one exposed portion 116 (which may subsequently form the cladding portion 138 of the waveguide 102) and at least one unexposed portion 118 (covered by the metal wire 114) (which may subsequently form the core portion 140 of the waveguide 102) disposed on the substrate 106.

[0064] FIG. 4A shows a top view of a waveguide 102 according to an embodiment and FIG. 4B shows a perspective view of the waveguide 102 according to an embodiment. [0065] The waveguide 102 may be formed on the substrate 106 (only shown in FIG. 4B). The waveguide 102 may include at least one cladding portion 138 and at least one core portion 140. The dimensions of the at least one cladding portion 138 and the at least one core portion 140 may vary relative to each other. The at least one core portion 140 may be configured to channel light.

[0066] FIG. 5 shows a perspective view of exposing the polymer layer 104 to a radiation source 108 during a method of manufacturing a beam splitter (not shown) according to an embodiment.

[0067] FIG. 5 may be similar to FIG. 3 with the difference in the shape of the metal wire 114 used. FIG. 3 shows an elongated metal wire 114 and FIG. 5 shows a "Y" shape metal wire 114. After exposing to the radiation source 108, the polymer layer 104 may include at least one exposed portion 116 and at least one unexposed portion (covered by the metal wire 114) (which may subsequently form the beam splitter) disposed on the substrate 106. The at least one unexposed portion may be similar in shape to the "Y" shape metal wire 114.

[0068] The design of the beam splitter on the substrate 106 may be varied by varying the design of the metal wire 114.

[0069] FIG. 6 shows a top view of a beam splitter 120 according to an embodiment. The beam splitter 120 may include a Y shape. The beam splitter 120 may include any suitable shape such that light may be split accordingly. The dimensions of the beam splitter 120 may also vary according to user and design requirements. [0070] FIGS. 7A to 7D show respective cross-sectional views of a method of manufacturing a grating 122 (a type of an interference filter) according to an embodiment.

[0071] The method shown in FIGS. 7A to 7D may be similar to the method shown in FIG. 2 A to 2D with the difference in the blocking structure 110. The blocking structure 110 in FIG. 2 A to 2D may include a metal wire 114 while the blocking structure 110 in FIGS. 7A to 7D may include a plurality of metal wires 114, each of the plurality of metal wires 114 may be arranged spaced apart from each other in a same plane or row. Each of the plurality of metal wires 114 may also be arranged in different planes from each other depending on design and user requirements. Each of the plurality of metal wires 114 may be configured to inhibit passage of radiation and may be the radiation blocking portion 112. The blocking structure 110 may also include other suitable structures configured to inhibit passage of radiation.

[0072] FIG. 7A shows a polymer, layer 104 formed on a substrate 106. The substrate 106 may include silicon, glass, or any other suitable materials with a lower ref active index than the polymer layer. The polymer layer 104 may include a material such that at least a portion of the polymer layer 104 may experience a reduction in refractive index when exposed to a radiation source (not shown).

[0073] The polymer layer 104 may be formed on the substrate 106 by spin-coating the polymer layer 104 on the substrate 106 and soft-baking the polymer layer 104 for a predetermined period of time and temperature.

[0074] FIG. 7B shows the blocking structure 110 formed over the polymer layer 104. The blocking structure 110 may include a plurality of radiation blocking portions 112 and each radiation blocking portion 112 may include a metal wire 114. Each of the plurality of metal wires 114 may be configured to inhibit passage of radiation. Each of the plurality of metal wires 114 may be arranged spaced apart from each other in the same plane.

[0075] The dimension of each of the plurality of metal wires 114 may be the same or different according to design and user requirements. The dimension of each of the plurality of metal wires 114 may also vary according to the required dimensions (grating pitch) of the resultant grating 122. Each of the plurality of metal wires 114 may be formed or positioned above the polymer layer 104 at a predetermined distance away from the polymer layer 104.

[0076] FIG. 7C shows the polymer layer 104 being exposed to a radiation source 108 to form the grating (not shown). The radiation source 108 may include a laser source or an UV source. The radiation source 108 may be configured to provide radiation with a wavelength in a range from about 10 nm to about 400 nm.

[0077] After exposing to the radiation source 108, the polymer layer 104 may include a plurality of exposed portions 116 (which may subsequently form the cladding portions 138 of the grating 122 as shown in FIG. 7D) and a plurality of unexposed portions 118 (which may subsequently form the core portions 140 of the grating 122 as shown in FIG. 7D).

[0078] Each of the plurality of metal wires 114 may be positioned over each of the plurality of unexposed portions 118 such that each of the plurality of unexposed portions 118 may experience no substantial change in refractive index and the plurality of exposed portions 116 not covered or blocked by the plurality of metal wires 114 may experience a reduction in refractive index when exposed to the radiation source 108.

[0079] Heat treatment may be provided after exposing the polymer layer 104 to the radiation source 108.

[0080] FIG. 7D shows the resultant grating 122 disposed on the substrate 106. The grating 122 may include a plurality of core portions 140 and a plurality of cladding portions 138. Each of the plurality of core portions 140 may correspond to each of the plurality of unexposed portions 118 as shown in FIG. 7C and each of the plurality of the cladding portions 138 may correspond to each of the plurality of exposed portions 116 as shown in FIG. 7C.

[0081] FIG. 8 shows a perspective view of exposing the polymer layer 104 to a radiation source 108 during a method of manufacturing a grating (not shown) according to an embodiment.

[0082] FIG. 8 may be similar, to FIG. 7C except that the blocking structure 110 may include a metal mask 124 rather than a plurality of separate metal wires 114 as shown in FIG. 7C. The metal mask 124 may include a plurality of radiation blocking portions 112 configured to inhibit passage of radiation and a plurality of radiation non-blocking portions 126 configured to allow passage of radiation, each of the plurality of radiation blocking portions 112 and the plurality of radiation non-blocking portions 126 arranged in an alternating pattern in a single mask layer.

[0083] The polymer layer 104 may be formed on the substrate 106 and the metal mask 124 may be positioned over the polymer layer 104. Upon exposing the polymer layer 104 to the radiation source 108, the resultant grating (not shown) may be formed on the substrate 106.

[0084] FIG. 9 shows a cross-sectional view of forming a photomask 128 over the polymer layer 104 during a method of manufacturing a grating (not shown) according to an embodiment.

[0085] FIG. 9 may be similar to FIG. 8 except that the blocking structure 110 may include a photomask 128 instead of a metal mask 124.

[0086] Like the metal mask 124, the photomask 128 may include a plurality of radiation blocking portions 112 configured to inhibit passage of radiation and a plurality of radiation non-blocking portions 126 configured to allow passage of radiation, each of the plurality of radiation blocking portions 112 and the plurality of radiation non- blocking portions 126 arranged in an alternating pattern in a single mask layer. The photomask 128 may include any other desired pattern.

[0087] The polymer layer 104 may be formed on the substrate 106 and the photomask 128 may be positioned over the polymer layer 104. Upon exposing the polymer layer 104 to the radiation source 108, the desired grating (not shown) may be formed on the substrate 106.

[0088] The polymer 104 may include a plurality of exposed portions 116 and a plurality of unexposed portions 118. Each of the plurality of exposed portions 116 may correspond to each of the plurality of radiation non-blocking portions 126 and each of the plurality of unexposed portions 118 may correspond to each of the plurality of radiation blocking portions 112. [0089] FIG. 10 shows a cross-sectional view of forming a blocking structure 110 from an interference of signals from two radiation sources 108 over the polymer layer 104 during a method of manufacturing a grating (not shown) according to an embodiment.

[0090] Interference occurs when two signals or light beams from the two radiation sources 108 may be superimposed. Interference may arise from the addition of oscillations of the two signals or light beams from two radiation sources 108 that may have similar wavelengths.

[0091] After the occurrence of the interference, the resultant signal may be an interference signal or an interference pattern 130 including both bright fringes or white fringes 132 and dark fringes 134. Only the bright fringe or white fringe 132 may cause a reduction of refractive index in the polymer layer 104.

[0092] The blocking structure 110 may include the interference pattern 130 including a plurality of interference fringes, namely a plurality of bright fringes 132 and a plurality of dark fringes 134.

[0093] After exposing to the two radiation sources 108, the polymer layer 104 may include a plurality of exposed portions 116 and a plurality of unexposed portions 118. Each of the plurality of exposed portions 116 may correspond to each of the plurality of bright fringes 132 and each of the plurality of unexposed portions 118 may correspond to each of the plurality of dark fringes 134.

[0094] Each of the plurality of unexposed portions 118 may experience no substantial change in refractive index and each of the plurality of exposed portions 116 may experience a reduction in refractive index when exposed to the two radiation sources 108. [0095] FIG. 11 shows a perspective view of forming a blocking structure 110 from an interference of signals from two radiation sources 108 over the polymer layer 104 during a method of manufacturing a grating according to an embodiment.

[0096] FIG. 11 may be similar to that as shown in FIG. 10 except that FIG. 10 shows a cross-sectional view while FIG. 11 shows a perspective view.

[0097] While the invention has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The scope of the invention is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.