JP2002022918A - Wavelength division filter and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a structure of a resonant mode grating filter used for WDM(wavelength division multiplexing) or the like which is low in cost and easy in mass production. SOLUTION: The filter has optical separators 8 in the number corresponding to the number of wavelengths of the light to be divided, each separator having an entrance face 9 on which a reflection grating as a resonant mode grating filter is formed by transferring resin from a microprocessed face of a die and having an exit face 11 where the light transmitting the entrance face exits in such a manner that the component of the light obliquely incident on the entrance face and corresponding to the resonant wavelength is extracted by reflection and other components are transmitted to exit from the exit face 11. The separators 8 are prepared as many as the number of wavelengths to be separated in series so that the light exiting from the exit face 11 of the preceding stage enters the entrance face 9 of the next stage. The resonant wavelengths of the entrance faces of optical separators 8 are controlled to coincide with the respective wavelengths to be divided which are different from one another.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an optical wavelength division multiplexing (WD) system.
M) and the like.

[0002]

2. Description of the Related Art When wideband multimedia services become widely used at the beginning of the 21st century, it is expected that a terabit (T bit / sec) class system whose trunk communication capacity will be two orders of magnitude larger than the current situation will be required. . According to the data of the Optical Industry and Technology Promotion Association, the communication capacity of optical communication is 20
According to the report, 100 GB / sec in 2005, 1 TB / sec in 2010, and an 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 increased communication capacity,
Optical wavelength multiplexing (WDM) is expected as a next-generation communication technology.

The optical wavelength division multiplexing (WDM) enables large-capacity transmission by multiplexing light of a plurality of different wavelengths on a wavelength axis and transmitting the multiplexed light through a single optical fiber. It is characterized in that branching / insertion is performed at an optical level without performing optical-electrical conversion by an optical passive device such as an optical filter, so that various signals can be transmitted simultaneously regardless of the net signal form and transmission speed.

In order to spread the WDM system, a wavelength separation filter for splitting signals having different wavelengths is required.
It becomes an indispensable optical element. Conventionally, this wavelength separation filter has a narrow band by polishing an optical crystal to form a birefringent polarizer and stacking a number of dielectric thin films (some of which exceed 70 to 80 layers). We have been producing a perfect wavelength filter. For example, a four-wavelength narrow-band bandpass filter requires more than 30 optical multilayer coatings and is made of glass.

[0006]

The above-mentioned conventional wavelength separation filter for WDM is made of an optical multilayer film and made of glass. Therefore, the productivity is low and the cost is high. For the main line of communication, it was still good, but at the subscriber level it was not a very affordable price-general consumers,
This will be a major obstacle in promoting its use to subscribers such as companies.

It is conceivable to manufacture this thin-film filter using plastics that can be easily molded instead of glass. However, micro-cracks due to differences in linear expansion coefficients occur in multiple thin-film layers, resulting in surface roughness or peeling. This adoption is inappropriate because it causes it.

On the other hand, it has been reported that a filter similar to the above-mentioned thin-film filter can be realized by forming a grating on the surface at the same level as the wavelength of light.

This is based on the fact that when a grating pitch is determined so as to satisfy a certain resonance condition, a resonance phenomenon occurs and a strong reflection occurs. This makes it possible to use a very narrow band called a resonance mode grating filter. A reflection type wavelength filter can be created.

When a wavelength separation filter for a WDM is to be manufactured with this grating structure, it is necessary to make the light to be branched to be obliquely incident on the grating surface in order to extract the light to be branched. In this case, polarized light is generated, and there arises a problem that required performance cannot be satisfied.

The problem of the polarization dependency is that a two-dimensionally arranged grating layer is provided so as to generate two equivalent wavenumber vectors of resonant light in the grating plane. The problem can be solved by making the wave number vector of light symmetrical with respect to the human projection surface of human radiation. This structure will be described next.

FIG. 6 is a perspective view showing the structure of the resonance mode grating filter, and FIG. 7 is an explanatory diagram for explaining the relationship between the resonance mode grating filter shown in FIG. 6 and incident light. FIG. 8 is an explanatory view for explaining the principle of eliminating the polarization dependence by the resonance mode grating filter shown in FIG. 6, and FIG. 9 is a diagram showing the wavelength and reflectance of the reflected light of the resonance mode grating filter shown in FIG. 6 is a graph showing the relationship of.

As shown in FIG. 6, the resonance mode grating filter includes a grating layer 1, a waveguide layer 2, and a substrate 3. The waveguide layer 2 is formed on the substrate 3, and on the waveguide layer 2,
A lattice layer 1 is formed. A plurality of rectangular concave portions 4 are formed in the lattice layer 1 at a predetermined pitch in a lattice shape, and the lattice layer 1 is composed of the concave portions 4, for example, air and a medium having a low refractive index other than the concave portions 4. The waveguide layer 2 having a refractive index becomes a waveguide.
The lattice layer 1 may use a lattice 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 concave portion or the peak portion formed in the lattice layer 1 has a mirror-symmetric and rotationally symmetric shape, and is preferably a square, 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 gourd may be used. In this specification, a rotationally symmetric shape refers to a shape that overlaps the original shape when the shape is rotated by 180 degrees.

As shown in FIG. 7, the incident surface I of the incident light I which is incident at an angle θ with respect to the direction orthogonal to the lattice layer 1 has a wave number of two resonance lights described below. Azimuth angle 45 so that the vector is symmetrical with respect to the incident surface of the incident light.
° (the angle between the human projection surface and one side of the square of the grid). At this time, the human light I resonates due to the lattice layer 1, and reflected light R of a specific wavelength is reflected. In the following description, a case will be described in which human radiation propagates in a TE mode (a mode in which an electric field travels while oscillating in parallel to a layer), but a TM mode (a mode in which a magnetic field travels while oscillating in a direction parallel to a layer). ) Can be similarly applied.

In the above case, as shown in FIG. 8, the light of the p-polarized light propagates in the TE mode to the upper right and lower right, respectively, and the light of the s-polarized light also propagates in the TE direction in the same direction. . In this embodiment, the propagation constant propagating by p-polarized human radiation is p-
β, the propagation constant propagating by s-polarized human radiation is s-β,
Assuming that the tangential component of the wave number vector of human radiation is k and the lattice vector, which is the wave number vector of the two resonance lights, is K, k
And K are set so that the sum of the vectors of K and K is equal to p-β and s-β.
Therefore, two equivalent resonance wave number vectors symmetrical with respect to the human projection surface of the human sunlight can be generated in the lattice plane, and p
The resonance wavelengths of the polarized human radiation and the s-polarized human radiation can be matched, and the half width of the resonance wavelength can be matched. As a result, the polarization dependency can be eliminated when the human rays illuminate the lattice plane obliquely. In addition, by adjusting the angle of human radiation, resonance can be obtained at a desired wavelength, and the center wavelength can be moved.

However, as a method of manufacturing this resonance mode grating filter, a conventionally known method is to form an SiO ₂ film as a waveguide layer 2 on a quartz substrate and further form an electron beam resist layer thereon. Is applied, and after a pattern is drawn by an electron beam drawing apparatus for about 5 hours, development is performed to form a grid pattern. Note that a TiO ₂ film may be formed as the waveguide layer 2 in some cases.

As described above, the conventional method of manufacturing a resonance mode grating filter is limited to an experimental level that does not take the manufacturing time into consideration, and research and development of a method of mass-producing the filter and efficiently manufacturing an element have progressed. Not in. For this reason, practical application was difficult.

Further, in the above-described conventional resonance mode grating filter, since light transmitted through the waveguide layer 2 cannot be used, only light of one type of wavelength can be separated and cannot be used as a WDM element.

Accordingly, it is an object of the present invention to provide a plastic wavelength separation filter using a resonance mode grating filter with a structure that is much lower in cost and easier to mass-produce than conventional ones.

[0020]

According to a first aspect of the present invention, there is provided a wavelength separation filter comprising a resin-molded light-transmitting substrate having an incident surface and an exit surface for emitting light transmitted through the incident surface. A reflection grating, which is a resonance mode grating filter, is formed by forming a grating pattern layer having a higher refractive index than the resin material of the base on the incidence surface, and light incident obliquely on the incidence surface. The component corresponding to the resonance wavelength is extracted by reflection, and the other component is transmitted and emitted from the emission surface.

According to a second aspect of the present invention, the wavelength separation filter according to the first aspect is used as one unit of light separator by the number of wavelengths of the light to be separated, and the output of the preceding stage light separator is used. The light emitted from the surface is continuously arranged so as to be incident on the next incident surface, and the resonance wavelength of each incident surface of each optical separator is matched to a different wavelength of the separating light. And

According to a third aspect of the present invention, in the wavelength separation filter according to the second aspect, the shape of each of the light separators is such that light transmitted through the incident surface is totally reflected by the reflection surface and is reflected from the emission surface. In order to emit light in the same direction as the incident direction, a DOVE prism shape in which the entrance surface and the exit surface are oblique to the reflection surface,
The distance between the light separators is such that the separated light reflected on the incident surface does not hit the adjacent light separator, and the light separator is connected and integrated at the reflection surface side and resin-molded.

The invention according to claim 4 of the present invention is arranged such that the shape of each light separator is such that light transmitted through the incident surface is totally reflected by the reflecting surface and emitted from the emitting surface in the same direction as the incident direction. The entrance surface and the exit surface are oblique to the reflection surface in the form of a DOVE prism, and the respective light separators are connected and integrated at the portion on the reflection surface side to form a resin, and the reflection of the reflection grating formed on the entrance surface The direction is orthogonal to the reflection surface of the transmitted light.

According to a fifth aspect of the present invention, there is provided a method of manufacturing a wavelength separation filter, wherein the pattern is formed by resin molding using a mold having a diffraction grating pattern formed at a pitch equal to or less than the wavelength of light. Forming a reflection grating, which is a resonance mode grating filter that reflects light having a resonance wavelength and transmits the remaining light by depositing a high-refractive layer on the surface on which the transfer pattern is formed by transferring the light to an object; It is characterized by.

According to a sixth aspect of the present invention, in the wavelength separation filter according to any one of the first to fourth aspects, the lattice pattern layer having a higher refractive index than the resin material of the base is formed of a resin molding metal. It is characterized in that it is formed by transferring a micro-machined surface formed in a mold and depositing a high refractive layer.

[0026]

FIG. 1 is a longitudinal sectional view of a four-wavelength narrow bandpass filter 7 according to an embodiment of the present invention. this is,
The four light separators 8 are integrally formed by resin molding in a connected shape. The width of the filter 7 in the direction perpendicular to the paper surface is large enough to allow the separated light beam to pass through. The light separator 8 has a DOVE prism structure that is inclined so that the distance between the incident surface 9 and the exit surface 11 disposed on both sides of the reflection surface 10 decreases as the distance from the reflection surface 10 increases. As shown in FIG. 2 which is an enlarged view of a portion A in FIG. 1, this DOVE prism structure refracts light incident parallel to the reflecting surface (obliquely to the incident surface) at the incident surface 9 and forms the light on the reflecting surface 10. The light is totally reflected by the reflection surface, refracted by the emission 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 that resonates at the diffraction grating is reflected, and the remaining light is transmitted and refracted.

The diffraction grating formed on the incident surface is formed by transferring a fine shape formed on a resin molding die. As a material used for resin molding, for example, a polycarbonate resin is used, and the reflection wavelength λ of the resonance mode
1, λ2, λ3, λ4 are, for example, 1280, 1300, 132
It is set to 0.1340 nm.

This lattice structure is formed by arranging a plurality of concave portions or mountain portions in a lattice shape. The concave portions or convex portions are mirror-symmetrical in order to generate two equivalent resonance wavenumber vectors in the lattice plane. It is preferable that the projection surface has a rotationally symmetric shape and the incident surface of the incident light is positioned on a bisector of a concave portion or a mountain portion. The shape of the concave portion or the mountain portion is preferably a square or a rhombus, but may be another shape such as a circle, an ellipse, or a gourd. The arrangement of the concave portions or the convex portions is, for example, a checkered pattern.

The incident light λ has, for example, a wavelength of 1280,1.
Light of 300, 1320, and 1340 nm is synthesized, and is incident parallel to the reflecting surface 10. Since the incident surface 9 has an angle (for example, 10 °) at which the reflection of the diffraction grating can be performed efficiently, the incident surface 9 is inclined with respect to the reflecting surface 10 by this angle θ.

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 reflecting surface 10 in the direction of the optical axis (one unit of the light separator) and the inclination of the exit surface 11 (the same direction and the same direction as the incident surface but different directions) are determined.

In the above embodiment, since the four light splitters 8 are connected linearly, it is necessary that the separated light reflected on the incident surface 9 is not obstructed by the adjacent light splitters 8. There is. Therefore, the arrangement interval of each light splitter 8 is determined according to this purpose. With this structure, it is possible to simultaneously mold a plurality of light separators simultaneously while forming a grating pattern on the incident surface by transfer, and independently mold the light separators to form a fixed arrangement relationship. This eliminates the need for the work of positioning and fixing, thereby reducing costs.

In the above embodiment, the reflection angle θ of the incident surface 9 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 convenience of disposing the light receiving portion (detector such as a photoelectric conversion element) of the separated light. Can be.

FIGS. 3 and 4 show the case where the light incident on the incident surface 9 is reflected in a direction perpendicular to the reflection surface 10 of the transmitted light. Thereby, the detector of the separated light is reflected by the reflecting surface 10.
, The assembling structure can be simplified, the arrangement interval between the light separators 8 can be minimized, and the size can be reduced.

A resonant mode grating filter is formed on the incident surface 9
As a method of forming a high refractive index layer for
(A) As shown in FIG.
TiO _TwoFilm and SiO_TwoA film is formed and an electron beam
Grating pattern is formed by exposure technology and etching technology
And a fine addition to the mold as shown in FIG.
The grid pattern formed by the
After transferring directly to the elephant, the concave and convex portions of the
O_TwoThere is a method of uniformly forming a film or the like by vapor deposition. FIG.
In the method shown in (b), molding is performed at a time by transfer.
Therefore, the processing cost is reduced as compared with the method shown in FIG.
Can be The mold used for this transfer is
For the corresponding part, for example, submicron on the metal surface of the mold
Laser drawing a lattice pattern designed in units
Used directly. The pattern of this mold
Can be repeatedly transferred and wavelength separated at low cost
A filter can be manufactured.

The embodiment shown in FIG. 1 and FIG.
Although shown as a wavelength separation filter for WDM that separates various wavelength components, this series number can be manufactured by connecting as many as necessary according to the number of wavelength components to be separated.

Further, the present invention can be used in place of another wavelength separation filter such as a dichroic mirror. For example, when using instead of a dichroic mirror that separates light into three primary colors of RGB,
One that is integrally molded in series can be used.

Although the light separator of the above embodiment has a DOVE prism shape in order to make the incident and exit optical axes coincide with each other in the light separator, a structure other than the DOVE prism shape, that is, the light axis is identical. It is also possible to use a structure that does not allow the light to be reflected or a structure that does not use a reflection surface.

[0038]

According to the wavelength separation filter of the first aspect of the present invention, a reflection grating, which is a resonance mode grating filter, is formed on an incident surface of a substrate formed by resin molding.
The manufacturing cost can be reduced to 1/100 or less as compared with the case where a reflective layer using an optical thin film is formed.

According to a second aspect of the present invention, a filter for simultaneously separating a plurality of wavelength components by using a plurality of wavelength separation filters according to the first aspect can be provided at low cost. When manufactured as a separation filter, it is possible to easily spread a high-speed and comfortable communication environment to general consumers.

According to a third aspect of the present invention, there is provided a structure capable of integrally molding the separation filter of a plurality of wavelengths according to the second aspect, and it is possible to reduce the size of parts and the cost of assembly.

According to a fourth aspect of the present invention, in a structure in which a separation filter of a plurality of wavelengths is integrally formed, light incident on the incident surface 9 is reflected in a direction orthogonal to the reflection surface 10 of transmitted light. In addition, the assembly structure can be simplified and downsized.

In the invention according to claim 5 of the present invention, a grating pattern is formed on a resin molded product by transfer from a mold, and a reflection grating is formed on the incident surface by simply performing vapor deposition on the entire surface. It can be greatly reduced.

According to a sixth aspect of the present invention, there is provided a method for transferring a grating pattern according to the fourth aspect, wherein the wavelength separation filter according to any one of the first to fourth aspects is manufactured, and the manufacturing cost can be greatly reduced. .

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a light separation filter according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view showing a portion A in FIG. 1;

FIG. 3 is a cross-sectional view illustrating a configuration of a light separation filter according to another embodiment of the present invention.

FIG. 4 is an enlarged sectional view showing a portion B in FIG. 3;

FIG. 5 is a cross-sectional view illustrating a method of manufacturing the wavelength separation filter of FIG.

FIG. 6 is a perspective view showing a configuration of a resonance mode grating filter which is a premise of the present invention.

FIG. 7 is an explanatory diagram for explaining a relationship between the resonance mode grating filter shown in FIG. 6 and incident light.

FIG. 8 is an explanatory diagram for explaining the principle of eliminating polarization dependence by the resonance 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 resonance mode grating filter shown in FIG.

[Explanation of symbols]

7 wavelength separation filter (4 wavelength narrow bandpass filter) 8 light separator 9 entrance surface 10 reflection surface 11 emission surface

Continued on front page F-term (reference) 2H042 CA01 CA06 CA17 2H048 FA01 FA05 FA09 FA12 FA22 2H049 AA07 AA13 AA33 AA37 AA40 AA44 AA59 AA64 AA65

Claims (6)

[Claims] 1. A light-transmissive substrate having an incident surface and an exit surface for emitting light transmitted through the incident surface is formed by resin molding, and has a higher refractive index on the incident surface than the resin material of the substrate. The reflection grating, which is a resonance mode grating filter, is formed by forming a grating pattern layer having a ratio of the refractive index, and a component corresponding to a resonance wavelength of light obliquely incident on the incident surface is extracted by reflection, and other components are extracted. A wavelength separation filter, which is transmitted and emitted from an emission surface. 2. The wavelength separation filter according to claim 1 is used as many as the number of wavelengths of light to be separated as one unit of a light separator, and light emitted from an output surface of a former-stage light separator is transmitted to a next-stage light separator. What is claimed is: 1. A wavelength separation filter which is continuously arranged so as to be incident on an incident surface, wherein a resonance wavelength of each incident surface of each optical separator is made to coincide with a different wavelength of light to be separated. 3. The shape of each of the light separators is such that the incident surface and the outgoing surface are formed on the reflecting surface such that the light transmitted through the incident surface is totally reflected by the reflecting surface and is emitted from the outgoing surface in the same direction as the incident direction. Obliquely crossed DOVE prism shape, the separation interval of each light separator was set to a length that the separated light reflected on the incident surface did not hit the adjacent light separator, and the resin was molded by connecting and integrating at the reflection surface side. The wavelength separation filter according to claim 2, wherein: 4. The shape of each of the light separators is such that the incident surface and the outgoing surface are formed on the reflecting surface such that the light transmitted through the incident surface is totally reflected by the reflecting surface and emitted from the outgoing surface in the same direction as the incident direction. Each of the light separators is connected and integrated at a portion on the reflection surface side to form a resin, and the reflection direction of the reflection grating formed on the incident surface is changed to the reflection surface of the transmitted light. 3. The wavelength separation filter according to claim 2, wherein the wavelength separation filter is orthogonal to the wavelength separation filter. 5. A resin mold using a mold having a diffraction grating pattern formed at a pitch equal to or less than the wavelength of light, the pattern is transferred to a molding target, and the surface on which the transfer pattern is formed is formed. Forming a reflection grating, which is a resonance mode grating filter that reflects light having a resonance wavelength and transmits the remaining light by vapor deposition of a high refractive layer. 6. The wavelength separation filter according to claim 1, wherein a reflection surface which is a resonance mode grating filter is formed on the incident surface by the method according to claim 5.