JP4435406B2 - Wavelength separation filter and manufacturing method thereof - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a wavelength separation filter used for an optical wavelength division multiplexing (WDM) or the like.
[0002]
[Prior art]
As broadband multimedia services become widespread at the beginning of the 21st century, it is expected that a terabit (T bit / second) class system having a trunk line communication capacity that is two orders of magnitude larger than the current level will be required. According to the materials of the Japan Optical Industry Technology Promotion Association, the communication capacity of optical communication will be 100 GB / second in 2005, 1 TB / second in 2010, and the all-optical network will be completed around 2013. At that time, a communication capacity of 100 MB / sec for all homes and 1 GB / sec for large users is realized.
[0003]
In response to such a demand for increasing communication capacity, optical wavelength division multiplexing (WDM) is expected as a next-generation communication technology.
[0004]
This optical wavelength division multiplexing (WDM) enables large-capacity transmission by multiplexing multiple wavelengths of light on the wavelength axis and transmitting them over a single optical fiber. Is performed at an optical level without optical-electrical conversion by an optical passive device such as an optical filter, and various signals can be transmitted simultaneously regardless of the net signal form and transmission speed.
[0005]
In order to spread the WDM system, a wavelength separation filter for branching signals having different wavelengths becomes a necessary and indispensable optical element. Conventionally, this wavelength separation filter is made by creating a birefringent polarizer by polishing an optical crystal, and by stacking multiple layers of dielectric thin films (some have more than 70 to 80 layers). A simple wavelength filter was manufactured. For example, a 4-wavelength Nagi bandpass filter requires an optical multilayer coating of more than 30 layers and is made of glass.
[0006]
[Problems to be solved by the invention]
The conventional wavelength separation filter for WDM is made of an optical multilayer film and made of glass. Therefore, productivity is low and cost is high. That's okay for the main line of communications, but it's not a very affordable price at the subscriber level-it's a major obstacle to disseminating to consumers, businesses and other subscribers.
[0007]
Although it is conceivable to make this thin film filter with plastic that can be easily molded instead of glass, micro cracks due to the difference in linear expansion coefficient occur in the multilayer thin film layer, which causes surface roughness or peeling. Therefore, this adoption is inappropriate.
[0008]
On the other hand, it has been reported that a filter similar to the thin film filter can be realized by forming a grating having the same size as the light wavelength on the surface.
[0009]
This is based on the fact that a resonance phenomenon occurs when the grating pitch is determined so as to satisfy a certain resonance condition, and that strong reflection occurs. Wavelength filters can be created.
[0010]
If an attempt is made to create a WDM wavelength separation filter with this grating structure, it is necessary to enter the grating surface obliquely in order to extract the light to be branched. In this case, polarized light is generated, causing a problem that the required performance cannot be satisfied.
[0011]
The problem of this polarization dependence is that a lattice layer having a lattice structure arranged two-dimensionally so as to generate two equivalent wave number vectors of resonant light in the lattice plane, the wave number of the two resonant lights is provided. the base vector, can be solved by symmetrical with respect to input reflecting surface of the incoming Shako. This structure will be described next.
[0012]
FIG. 6 is a perspective view showing the configuration of this resonance mode grating filter, FIG. 7 is an explanatory diagram for explaining the relationship between the resonance mode grating filter shown in FIG. 6 and incident light, and FIG. FIG. 9 is an explanatory diagram for explaining the principle of eliminating the polarization dependency by the resonance mode grating filter shown in FIG. 6, and FIG. 9 shows the relationship between the wavelength of reflected light and the reflectance of the resonance mode grating filter shown in FIG. It is a graph to show.
[0013]
As shown in FIG. 6, the resonance mode grating filter includes a grating layer 1, a waveguide layer 2, and a substrate 3. A waveguide layer 2 is formed on the substrate 3, and a lattice layer 1 is formed on the waveguide layer 2. A plurality of rectangular recesses 4 are formed in a lattice pattern at a predetermined pitch in the lattice layer 1, and the lattice layer 1 is configured by the recesses 4, for example, air and a medium having a low refractive index other than the recesses 4. The refractive index waveguide layer 2 becomes a waveguide. Note that the grating layer 1 may use a grating layer composed of a plurality of convex portions instead of the concave portions 4, and the concave portions may be filled with another medium having a different refractive index. The shape of the recesses or peaks formed in the lattice layer 1 is preferably a square shape having a mirror symmetry and a rotational symmetry in order to generate two equivalent resonance wave number vectors in the lattice plane. However, other shapes such as a circle, an ellipse, and a bowl may be used. In this specification, a rotationally symmetric shape refers to a shape that overlaps the original shape when the shape is rotated 180 degrees.
[0014]
As shown in FIG. 7, the input reflecting surface P of the incident light I, Isa input inclined by an angle θ with respect to a direction perpendicular to the grating layer 1, two wavenumber base vector of the resonant optical described below incident to be symmetrical with respect to light incident reflecting surface, azimuth 45 ° (incident morphism plane angle between one side of the square grid) is set to be. At this time, input Shako I is resonated by lattice layer 1, the reflected light R at a specific wavelength is reflected. In the following description, incoming Shako but is describes the case of propagating in the TE mode (electric field to the layer progresses while oscillating in parallel), TM mode (field to the layer progresses while oscillating in parallel The same can be applied to the case of propagating in).
[0015]
In the above case, as shown in FIG. 8, the light of p-polarized light incident morphism propagates in the TE mode, respectively in the upper right and lower right, s-polarized light incident morphism light also propagates in the TE mode in the same direction. In this embodiment, the propagation constants of propagating morphism p-polarized human and p-beta, the propagation constants of propagating morphism s-polarized light incident as the s-beta, and the tangential component of the wave base vector of the incoming Shako and k, two resonance Assuming that the lattice vector which is the wave number vector of light is K, the lattice pitch A (= 2π / K) is set so that the sum of the vectors of k and K is equal to p-β and s-β. Yes. Thus, a symmetrical two equivalent resonant wavenumber base vector can be generated in the lattice plane, causes one Itasa the resonance wavelength of the p-polarized light incident elevation and s-polarized light incident elevation relative to input reflecting surface of the incoming Shako, The half width of the resonance wavelength can be matched. As a result, it is possible to eliminate the polarization dependence when the incident light is morphism input from obliquely with respect to the grating surface. Further, by adjusting the incident angle of incident light, resonance can be obtained at a desired wavelength, and the center wavelength can be moved.
[0016]
However, as a manufacturing method of this resonance mode lattice filter, a conventionally known method is to form a SiO ₂ film as a waveguide layer 2 on a quartz substrate and further apply an electron beam resist layer thereon. Then, after a pattern is drawn by an electron beam drawing apparatus over about 5 hours, development is performed to create a lattice pattern. A TiO ₂ film may be formed as the waveguide layer 2 in some cases.
[0017]
As described above, the conventional method for manufacturing a resonant mode grating filter is limited to an experimental level that does not take the manufacturing time into consideration, and little research and development has been made on a method for mass-producing this to efficiently manufacture an element. For this reason, practical use was difficult.
[0018]
In addition, since the light transmitted through the waveguide layer 2 cannot be used in the above conventional resonance mode grating filter, only light of one type of wavelength can be separated and cannot be used as an element for WDM.
[0019]
Accordingly, an object of the present invention is to provide a plastic wavelength separation filter using a resonance mode grating filter with a structure that is much cheaper and easier to mass-produce than conventional ones.
[0020]
The wavelength separation filter according to claim 1 of the present invention is formed by resin molding, and includes an incident surface, a reflective surface that reflects light transmitted through the incident surface, and an output surface that emits light reflected by the reflective surface. having provided a light transparent substrate, by forming a reflection grating is a resonant mode lattice filter form a lattice pattern layer with a high refractive index than the resin material of the substrate on the incident surface of the substrate, incident surface The component corresponding to the resonance wavelength of the light incident obliquely to the light is extracted by reflection, and the other components are transmitted and reflected by the reflection surface, and separated from the light exit surface. As many as the number of wavelengths of light are continuously arranged so that the light emitted from the exit surface of the preceding optical separator enters the incident surface of the next stage, and the resonance wavelength of each incident surface of each optical separator is separated. Wavelength separation filter matched to different wavelengths of the light In other,
Each light separator has a DOVE prism shape in which the entrance surface and the exit surface are obliquely intersected with the reflection surface so that the light transmitted through the entrance surface is totally reflected by the reflection surface and is emitted from the exit surface in the same direction as the incidence direction. In addition, it is characterized in that it is resin-molded by connecting and integrating at the reflecting surface side portion .
[0022]
The invention according to claim 2 of the present invention, in the wavelength separation filter according to claim 1, the arrangement interval of each light separator separating light reflected at the incident surface is Satoshi length does not strike the optical separator adjacent It is characterized by that.
[0023]
The invention according to claim 3 of the present invention is the wavelength separation filter according to claim 1 , wherein the reflection direction of the reflection grating formed on the incident surface is orthogonal to the reflection surface of the transmitted light. And
[0024]
The manufacturing method of the wavelength separation filter according to claim 4 of the present invention is formed by resin molding, and emits light incident on the incident surface, a reflecting surface that reflects light transmitted through the incident surface, and light reflected on the reflecting surface. By providing a light-transmitting substrate having an exit surface and forming a grating pattern layer having a higher refractive index than the resin material of the substrate on the incident surface of the substrate to form a reflection grating that is a resonance mode lattice filter A light separator that is configured such that a component corresponding to the resonance wavelength of light incident obliquely on the incident surface is extracted by reflection, and other components are transmitted and reflected by the reflective surface and emitted from the output surface. The number of wavelengths of light to be separated is continuously arranged so that the light emitted from the exit surface of the preceding optical separator enters the incident surface of the next stage, and the resonance of each incident surface of each optical separator Waves matched to different wavelengths of the light that separates the wavelengths In the manufacturing method of the separation filter, each light separator is connected and integrated at the portion on the reflecting surface side and molded with resin, and light transmitted through the incident surface is totally reflected by the reflecting surface and is in the same direction as the incident direction from the emitting surface. The DOVE prism shape in which the entrance surface and the exit surface are obliquely intersected with the reflection surface is formed by connecting and integrating the resin on the reflection surface side, and the reflection grating of the light separator The step of transferring the pattern to the incident surface by resin molding with a mold in which a diffraction grating pattern is formed at a pitch equal to or less than the wavelength of light at the same time as connecting and integrating the separator, and the transfer pattern a high refractive layer and a process of vapor deposited on the formed incident surface, the remaining light reflects light resonance wavelength and forming to transmit.
[0026]
Embodiment
FIG. 1 shows a longitudinal sectional view of a four-wavelength narrow bandpass filter 7 which is an embodiment of the present invention. This is formed integrally by resin molding in a shape in which four light separators 8 are connected. The width of the filter 7 in the direction perpendicular to the paper surface is such that the separated light beam can pass through. The light separator 8 has a DOVE prism structure that is inclined so that the distance between the entrance surface 9 and the exit surface 11 disposed opposite to each other on both sides of the reflection surface 10 becomes narrower as the distance from the reflection surface 10 increases. As shown in FIG. 2 which shows an enlarged view of part A in FIG. 1, this DOVE prism structure refracts light incident parallel to the reflecting surface (obliquely intersecting with the incident surface) at the incident surface 9 to form the reflecting surface 10. The light is totally reflected by the reflecting surface, refracted by the emitting surface 11 and emitted in the same direction as the incident direction. When a resonance mode grating filter (color separation filter) is formed on the incident surface, light having a wavelength resonating with the diffraction grating is reflected, and the remaining light is transmitted and refracted.
[0027]
The diffraction grating formed on the incident surface is made by transferring a fine shape formed on a resin molding die. The material used for resin molding is, for example, a polycarbonate resin, and the reflection wavelengths λ1, λ2, λ3, λ4 of the resonance mode grating filters on the respective incident surfaces are set to, for example, 1280, 1300, 1320, 1340 nm.
[0028]
In this lattice structure, a plurality of concave portions or mountain portions are arranged in a lattice shape, and the concave portions or convex portions are mirror-symmetric and rotationally symmetric in order to generate two equivalent resonance wave number vectors in the lattice plane. shaped, it is preferred to position the input reflecting surface of the light incident on the bisector of the recess or crests. The shape of the recess or peak is preferably a square or rhombus, but may be other shapes such as a circle, an ellipse, and a bowl. The arrangement of the recesses or projections is, for example, a checkered pattern.
[0029]
The incident light λ is, for example, a combination of light having wavelengths of 1280, 1300, 1320, and 1340 nm, and is incident parallel to the reflecting surface 10. Since the incident surface 9 has an angle (for example, 10 °) at which the diffraction grating can be efficiently reflected, the incident surface 9 is inclined with respect to the reflective surface 10 by this angle θ.
[0030]
In order to make the optical axis of the incident light λ coincide with the optical axis of the light emitted from the emission surface 11, the length of the reflection surface 10 in the optical axis direction (one unit of the optical separator) according to the inclination of the incidence surface 9. The inclination of the exit surface 11 (the direction and the direction of the incident surface are the same and the direction is different) is determined.
[0031]
In the above embodiment, since the connecting straight four light separator 8, it is necessary to separate light obtained by reflecting the incident surface 9 is not impeded by the optical separator 8 adjacent. Therefore, the arrangement interval of each light separator 8 is determined in accordance with this purpose. With this structure, it becomes possible to simultaneously mold a plurality of light separators while creating a grating pattern on the entrance surface by transfer, and the light separators are independently molded with resin, and these are in a fixed arrangement relationship. Thus, the work for positioning and fixing is unnecessary, and the cost can be reduced.
[0032]
The reflection angle θ of the incident surface 9 in the above embodiment reflects the separated light in a direction inclined with respect to the reflection surface 10 of the transmitted light. The reflection angle θ can be arbitrarily determined within a certain range depending on the structure of the reflection grating, and is appropriately determined in consideration of the arrangement of the separated light receiving unit (detector such as a photoelectric conversion element). Can do.
[0033]
3 and 4 reflect light incident on the incident surface 9 in a direction orthogonal to the reflecting surface 10 of the transmitted light. Thereby, the detector of the separated light is arranged in parallel with the reflecting surface 10 to simplify the assembly structure, the arrangement interval of each light separator 8 can be minimized, and the size can be reduced.
[0034]
As a method for forming a high refractive index layer for constituting a resonant mode grating filter on the incident surface 9, as shown in FIG. 5A, a TiO ₂ film or SiO ₂ film is deposited on the resin-formed incident surface 9 by vapor deposition. Etc., and a lattice pattern formed by fine processing on a mold as shown in FIG. 5 (b) is incident upon resin molding. There is a method in which, after transferring directly to the surface 9 , a TiO ₂ film or the like is uniformly formed on the concave and convex portions of the transfer surface by vapor deposition. Since the method shown in FIG. 5B performs molding at a time by transfer, the processing cost can be reduced as compared with the method shown in FIG. As the mold used for this transfer, for example, a part directly formed by laser drawing a lattice pattern designed in submicron units on the metal surface of the mold is used at a portion corresponding to the incident surface 9. This mold pattern can be repeatedly transferred, and a wavelength separation filter can be manufactured at low cost.
[0035]
The embodiment shown in FIG. 1 and FIG. 3 shows what is configured as a wavelength separation filter for WDM that separates four types of wavelength components, but this number in series is matched to the number of wavelength components to be separated. It can be produced by connecting as many as necessary.
[0036]
The present invention can also be used in place of other wavelength separation filters such as a dichroic mirror. For example, when the light is used in place of a dichroic mirror that separates the three primary colors of RGB, it is possible to use three light separators integrally formed in series.
[0038]
【The invention's effect】
The wavelength separation filter according to claim 1 of the present invention forms a reflection grating, which is a resonance mode grating filter, on the incident surface of a substrate molded by resin molding. Therefore, when a reflection layer using an optical thin film is formed. In comparison, the manufacturing cost can be reduced to 1/100 or less. Also, a filter that simultaneously separates a plurality of wavelength components by using a plurality of optical separators can be provided at a low cost. For example, when manufactured as a wavelength separation filter for WDM, a high-speed and comfortable communication environment for general consumers. Can be easily spread. Furthermore, since the optical separator has a DOVE prism shape and is integrally formed with a resin on the reflection surface side, a plurality of wavelength separation filters can be integrally formed, thereby reducing the assembly cost of components. be able to.
[0040]
The invention according to claim 2 of the present invention can reduce the size of parts.
[0041]
The invention according to claim 3 of the present invention is an assembly structure in which the light incident on the incident surface 9 is reflected in a direction orthogonal to the reflecting surface 10 of the transmitted light in a structure in which a separation filter having a plurality of wavelengths is integrally formed. Can be simplified and downsized.
[0042]
In the invention according to claim 4 of the present invention, a grating pattern is formed on the incident surface by transferring from the mold at the same time as connecting and integrating the optical separator, and the reflective grating is incident only by depositing a high refractive layer on the entire surface. Since it is formed on the surface, the manufacturing cost of the wavelength separation filter can be greatly reduced.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a configuration of a light separation filter according to an embodiment of the present invention.
2 is an enlarged cross-sectional view of a portion A in FIG.
FIG. 3 is a cross-sectional view showing a configuration of a light separation filter according to another embodiment of the present invention.
4 is an enlarged cross-sectional view of a portion B in FIG.
5 is a cross-sectional view illustrating a method for manufacturing the wavelength separation filter of FIG. 1. FIG.
FIG. 6 is a perspective view showing a configuration of a resonance mode grating filter which is a premise of the present invention.
7 is an explanatory diagram for explaining the relationship between the resonance mode grating filter shown in FIG. 6 and incident light;
8 is an explanatory diagram for explaining the principle of eliminating polarization dependence by the resonant mode grating filter shown in FIG. 6;
9 is a graph showing the relationship between the wavelength of reflected light and the reflectance of the resonant mode grating filter shown in FIG. 6;
[Explanation of symbols]
7 Wavelength separation filter (4-wavelength narrow bandpass filter)
8 Light separator 9 Entrance surface 10 Reflection surface 11 Output surface

Claims (4)

It is formed by resin molding , and includes a light transmissive substrate having an incident surface, a reflective surface that reflects light transmitted through the incident surface, and an output surface that emits light reflected by the reflective surface. Corresponding to the resonant wavelength of light incident obliquely to the incident surface by forming a reflective grating that is a resonant mode grating filter by forming a grating pattern layer with a higher refractive index than the resin material of the base on the surface The optical separator is extracted by reflection, the other components are transmitted and reflected by the reflection surface, and emitted from the output surface . A wavelength separation filter that allows light emitted from the exit surface of the light separator to enter the incident surface of the next stage and matches the resonance wavelength of each incident surface of each light separator to a different wavelength of the light to be separated. In
Each light separator has a DOVE prism shape in which the entrance surface and the exit surface are obliquely intersected with the reflection surface so that the light transmitted through the entrance surface is totally reflected by the reflection surface and is emitted from the exit surface in the same direction as the incidence direction. In addition, the wavelength separation filter is characterized in that it is connected and integrated at the portion on the reflective surface side and resin-molded . Wavelength separation filter according to claim 1, separating light reflected at the incident surface of the arrangement interval of each light separator was et no length was equivalent to the optical separator adjacent. The reflection direction of the reflection grating formed on the incident surface, the wavelength separation filter according to claim 1 which has been perpendicular to the reflecting surface of the transmitted light. It is formed by resin molding, and includes a light transmissive substrate having an incident surface, a reflective surface that reflects light transmitted through the incident surface, and an output surface that emits light reflected by the reflective surface. Corresponding to the resonant wavelength of light incident obliquely on the incident surface by forming a reflective grating that is a resonant mode lattice filter by forming a grating pattern layer with a higher refractive index than the resin material of the base on the surface The optical separator is extracted by reflection, the other components are transmitted and reflected by the reflection surface, and emitted from the output surface. A wavelength separation filter that allows light emitted from the exit surface of the light separator to enter the incident surface of the next stage and matches the resonance wavelength of each incident surface of each light separator to a different wavelength of the light to be separated. In the manufacturing method of
Each light separator has a DOVE prism shape in which the entrance surface and the exit surface are obliquely intersected with the reflection surface so that the light transmitted through the entrance surface is totally reflected by the reflection surface and is emitted from the exit surface in the same direction as the incidence direction. In addition, it is connected and integrated at the part on the reflective surface side and resin molded,
Reflecting grating of the light separator, by resin molding in a mold in which the diffraction grating pattern is formed at a wavelength equal to or less than the pitch of integrally connected at the same time light of the light separator incident surface this pattern and transferring to, and a process of depositing form a high refractive layer on the incident surface of the transfer pattern is formed, the remaining light reflects light resonance wavelength and forming to transmit A method for manufacturing a wavelength separation filter.

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