Diffraction grating

Abstract

This diffraction grating comprises a glass plate (11) and a resin layer (12), and is used by allowing light to pass through in the direction from the glass toward the resin layer. An anti-reflection film (13) is provided between one surface of the glass plate and the surface on the opposite side from the grating surface of the resin layer. The diffraction grating, for example, causes light incident on the resin layer from the glass plate to be diffracted by the grating surface of the resin layer and to be emitted from the grating surface to the outside of the diffraction grating.

Description

diffraction grating

[0001] The present invention relates to a diffraction grating.

[0002] Conventionally, a widely used technique for mass-producing diffraction gratings is to replicate replica diffraction gratings from a master diffraction grating. Replica diffraction gratings are fabricated by bonding the grating surface of a master diffraction grating to a glass substrate with an adhesive, curing the adhesive, and then peeling the glass substrate and the cured adhesive from the master diffraction grating. A replica diffraction grating fabricated in this manner has a resin layer made of the cured adhesive on the glass substrate, and the surface of the resin layer has a grating surface with a shape that is the inverse of the concave and convex shapes of the grating surface of the master diffraction grating. A replica diffraction grating with this configuration can be used as a transmission diffraction grating by irradiating light from the glass substrate toward the resin layer.

[0003] Alternatively, a reflective diffraction grating can be produced by covering the grating surface of the replica diffraction grating with a reflective film made of metal. Such a reflective diffraction grating is usually used by irradiating light onto the front surface of the reflective film (the surface opposite to the surface facing the resin layer), but depending on the application, it may also be used by irradiating light onto the back surface of the reflective film through the glass substrate and the resin layer.

[0004] Furthermore, Patent Document 1 describes a reflective diffraction grating in which a protective glass plate is attached to the front surface of the reflective film via a resin layer other than the above. This diffraction grating is used by irradiating light onto the front surface of the reflective film through the protective glass plate and the resin layer.

[0005] Japanese Patent Application Laid-Open No. 10-307203 (Fig. 1(A))

[0006] However, when a diffraction grating is used that allows light to pass from the glass (i.e., the glass substrate or the protective glass plate) toward the resin (i.e., the resin layer) as described above, it has been found that spectral lines are observed at wavelengths where no spectrum actually exists (i.e., stray light is generated). In many cases, the stray light observed here can be ignored, but when the device using the diffraction grating is an analytical device, a high-speed communication device, or the like, its influence may not be negligible.

[0007] The present invention has been made in consideration of the above points, and its object is to prevent the generation of stray light in a diffraction grating that is used by allowing light to pass in a direction from glass toward resin.

[0008] The diffraction grating of the present invention, which has been made to solve the above-mentioned problems, comprises a glass plate, a first resin layer having a grating surface, and an anti-reflection film, in which one surface of the glass plate and a surface of the first resin layer opposite the grating surface are bonded to each other with the anti-reflection film sandwiched therebetween.

[0009] According to the diffraction grating of the present invention having the above-described configuration, it is possible to prevent the occurrence of stray light in a diffraction grating that is used by passing light in a direction from the glass toward the resin.

[0010] 1 is a schematic diagram of a diffraction grating according to a first embodiment of the present invention; 2 is a schematic diagram showing a manufacturing process of a diffraction grating according to the same embodiment; 3 is a schematic diagram of a diffraction grating according to a second embodiment of the present invention; 4 is a schematic diagram of a diffraction grating according to a third embodiment of the present invention; 5 is a graph showing the reflectance characteristics at the interface between the glass plate and the resin layer of diffraction gratings according to Example 1 of the present invention and a comparative example; 6 is a graph showing the reflectance characteristics at the interface between the glass plate and the resin layer of diffraction gratings according to Example 2 of the present invention and a comparative example; 7 is a graph showing the reflectance characteristics at the interface between the glass plate and the resin layer of diffraction gratings according to Example 3 of the present invention and a comparative example;

[0011] As a result of extensive research into how to solve the above problem, the inventors identified that the problem was caused by light reflection at the interface between the glass plate and resin layer included in the diffraction grating, and came up with the idea of ​​providing an anti-reflection film at the interface in order to suppress this reflection.

[0012] [Embodiment 1] A diffraction grating according to a first embodiment of the present invention will be described with reference to Fig. 1. The diffraction grating according to this embodiment is a transmission type diffraction grating that is used to allow light to pass through, as shown in Fig. 1.

[0013] The diffraction grating according to this embodiment includes a flat glass substrate 11 (corresponding to the glass plate in this invention), a resin layer 12 (corresponding to the first resin layer in this invention) provided on the substrate 11, and an anti-reflection film 13 made of a dielectric film interposed therebetween. The surface of the resin layer 12 opposite the surface facing the substrate 11 (i.e., the upper surface in FIG. 1 ) is formed with grating grooves, which are a striped uneven pattern. Hereinafter, the surface of the resin layer 12 on which the grating grooves are formed will be referred to as the grating surface, and the opposite surface (the lower surface in FIG. 1 ) will be referred to as the back surface. Furthermore, the surface of the substrate 11 facing the resin layer 12 (the upper surface in FIG. 1 ) will be referred to as the front surface, and the opposite surface will be referred to as the back surface. While the application of the diffraction grating according to this embodiment is not particularly limited, for applications requiring precise spectral performance, it is desirable that the groove width of the grating grooves be 10 μm or less and that the number of grooves per unit length (mm) be 100 or more.

[0014] The type of glass constituting the substrate 11 is not particularly limited as long as it is transparent at the wavelength used by the diffraction grating, and examples of such glass include soda-lime glass, borosilicate glass, and quartz glass. The type of resin constituting the resin layer 12 is also not particularly limited as long as it is transparent at the wavelength used by the diffraction grating, and examples of such resin include thermosetting resin, ultraviolet-curing resin, and visible-light-curing resin, and more specifically, epoxy resin, urea resin, melamine resin, and phenol resin.

[0015] The material for the anti-reflection film 13 is not particularly limited as long as it is transparent to the wavelength used for the diffraction grating. For example, tantalum pentoxide (Ta ２ O ５ ), aluminum oxide (Al ２ O ３ ), or silicon dioxide (SiO ２) or the like can be used. The anti-reflection film 13 is preferably a multi-layer film formed by laminating a plurality of types of layers. When the wavelength band targeted by the diffraction grating is wide, it is preferable to design the number of layers to be greater than when the wavelength band is narrow. The material constituting the anti-reflection film 13 is preferably a high refractive index material having a refractive index of 2 or more (for example, Ta ２ O ５ ), a medium refractive index material with a refractive index of 1.6 to 1.8 (e.g., Al ２ O ３ ), or a low refractive index material having a refractive index of less than 1.6 (e.g., SiO ２ It is desirable to use an appropriate combination of these materials, but the present invention is not limited to this. Furthermore, if the total thickness (physical film thickness) of the antireflection film 13 is thinner than 10 nm, it will not be able to exhibit a sufficient antireflection effect, and if it is thicker than 200 nm, the absorption rate of transmitted light will increase, so it is desirable to set the total thickness (physical film thickness) of the antireflection film 13 to 10 nm to 200 nm (more desirably 40 nm to 200 nm), but the present invention is not limited to this.

[0016] The diffraction grating according to this embodiment is manufactured as a replica diffraction grating by replicating a previously prepared master diffraction grating 18, for example. A method for manufacturing the diffraction grating according to this embodiment in this case will be described with reference to FIG. 2 . When manufacturing the diffraction grating according to this embodiment, a master diffraction grating 18 is first prepared as a matrix ( FIG. 2( a)). The master diffraction grating 18 is manufactured by forming striped grating grooves on a master substrate made of a glass plate or the like by mechanical ruling, lithography, holographic exposure, or the like. Next, an antireflection film 13 is formed on one surface (the front surface) of the replica substrate (i.e., substrate 11) ( FIG. 2( c)). The antireflection film 13 may be formed by any method, including, for example, a dry method such as vacuum deposition, sputtering, or chemical vapor deposition, or a wet method such as coating or a sol-gel method. Next, a release agent 19 is applied to the grating surface of the master diffraction grating 18 (FIG. 2B), and an adhesive 17 made of a thermosetting resin, an ultraviolet-curable resin, a visible-light-curable resin, or the like is applied to the front surface of the substrate 11 (the surface on which the anti-reflection film 13 is formed) (FIG. 2D). The grating surface of the master diffraction grating 18 and the front surface of the substrate 11 are then bonded together via the adhesive 17 (FIG. 2E). The adhesive 17 is then cured by heating or by irradiation with ultraviolet or visible light, and the substrate 11 is peeled off from the master diffraction grating 18 together with the resin layer 12 formed by the cured adhesive 17 (FIG. 2F). This results in the diffraction grating according to this embodiment having the configuration shown in FIG. 1.

[0017] As shown in FIG. 1 , the diffraction grating according to this embodiment is used by irradiating light from the back surface of the substrate 11. The light incident from the back surface of the substrate 11 (the incident light in FIG. 1 ) travels from the substrate 11 toward the resin layer 12. At the lattice surface of the resin layer 12, the light components of the incident light are reinforced at different angles for each wavelength, resulting in diffracted light (the transmitted diffracted light in FIG. 1 ). In conventional diffraction gratings, a portion of the incident light is reflected at the interface between the substrate 11 and the resin layer 12, resulting in the generation of stray light. That is, the light reflected at the interface is reflected again by the back surface of the substrate 11 and reaches the lattice surface of the resin layer 12. The angle of incidence of this reflected light on the lattice surface differs from the original angle of incidence of the incident light, adversely affecting spectral performance. In contrast, the diffraction grating according to this embodiment includes an anti-reflection film 13 between the substrate 11 and the resin layer 12, thereby reducing the reflection of light at the interface and preventing the generation of stray light.

[0018] [Embodiment 2] A diffraction grating according to a second embodiment of the present invention will be described with reference to Fig. 3. As shown in Fig. 3, the diffraction grating according to this embodiment is a reflective diffraction grating that is used by reflecting light. Note that in Fig. 3, components that are the same as or correspond to those shown in Fig. 1 are assigned reference numerals with the same last digit, and descriptions thereof will be omitted below as appropriate.

[0019] The diffraction grating according to this embodiment includes a flat substrate 21 (corresponding to the glass plate in this invention) made of glass, a resin layer 22 (corresponding to the first resin layer in this invention) provided on the substrate 21, an anti-reflection film 23 provided between the substrate 21 and the resin layer 22, and a reflective film 24 covering the grating surface of the resin layer 22. The diffraction grating according to this embodiment can be manufactured, for example, by forming a reflective film 24 made of a thin metal film on the grating surface of a replica diffraction grating manufactured by a method similar to that of embodiment 1. Examples of metals that can be used to form the reflective film 24 include, but are not limited to, aluminum and gold. The reflective film 24 can be formed by any method, such as vacuum deposition or sputtering.

[0020] As shown in FIG. 3 , the diffraction grating according to this embodiment is used by irradiating light from the rear surface of the substrate 21. The light incident from the rear surface of the substrate 21 (the incident light in FIG. 1 ) travels from the substrate 21 toward the resin layer 22, reaches the grating surface, and is reflected by a reflective film 24 provided on the grating surface. At this time, the light of each wavelength contained in the incident light constructively interacts with each other at angles corresponding to the wavelengths, and this constructive light (the reflected diffracted light in FIG. 1 ) passes through the resin layer 22 and the substrate 21 and exits from the rear surface of the substrate 21. In conventional diffraction gratings, when the incident light enters the resin layer 22 from the substrate 21, and when the reflected diffracted light enters the substrate 21 from the resin layer 22, a portion of the incident light and a portion of the reflected diffracted light are reflected at the interface between the substrate 21 and the resin layer 22, causing stray light. That is, the light reflected at the interface is reflected again by the rear surface of the substrate 21 and reaches the grating surface of the resin layer 22. The angle of incidence of this reflected light on the grating surface is different from the original angle of incidence of the incident light, which has an adverse effect on the spectral performance. In contrast, in the diffraction grating according to this embodiment, the anti-reflection film 23 is provided between the substrate 21 and the resin layer 22, which reduces the reflection of light at the interface between the substrate 21 and the resin layer 22, thereby preventing the generation of stray light as described above.

[0021] [Embodiment 3] A diffraction grating according to a third embodiment of the present invention will be described with reference to Fig. 4. In Fig. 4, components that are the same as or correspond to those shown in Fig. 1 and Fig. 3 are denoted by reference numerals with the same last digit, and descriptions thereof will be omitted below as appropriate.

[0022] As shown in FIG. 4 , the diffraction grating according to this embodiment is a reflective diffraction grating that uses a reflective film 34 to reflect light, and has a protective cover 36 made of a glass plate attached to its grating surface. That is, the diffraction grating according to this embodiment includes a substrate 31 made of a glass plate, a resin layer (hereinafter referred to as the substrate-side resin layer 32) provided on the substrate 31 and having grating grooves, which are groove-like irregularities, on its surface, a reflective film 34 that covers the surface of the substrate-side resin layer 32 that has the grating grooves, another resin layer (hereinafter referred to as the protective cover-side resin layer 35) provided on the reflective film 34, a protective cover 36 made of a glass plate provided on the protective cover-side resin layer 35, and an anti-reflection film 33 provided between the protective cover 36 and the protective cover-side resin layer 35. In this embodiment, the protective cover 36 corresponds to the glass plate in the present invention, and the substrate 31 corresponds to the plate material in the present invention. The protective cover-side resin layer 35 corresponds to the first resin layer in the present invention, and the substrate-side resin layer 32 corresponds to the second resin layer in the present invention. Furthermore, the surface of the protective cover side resin layer 35 opposite to the surface facing the anti-reflection film 33 (corresponding to the grating surface in the present invention) has a shape that is an inversion of the concave and convex shapes of the grating grooves of the substrate side resin layer 32 (i.e., the concave and convex parts are reversed).

[0023] When manufacturing the diffraction grating according to this embodiment, first, a reflective diffraction grating including a substrate 31, a substrate-side resin layer 32, and a reflective film 34 is produced by the same method as in Embodiment 3 (however, in this embodiment, it is not necessary to form an anti-reflection film on the substrate 31). Next, a glass plate that will become the protective cover 36 is prepared, and an anti-reflection film 33 is formed on one surface of the glass plate (hereinafter, this surface will be referred to as the back surface, and the opposite surface will be referred to as the front surface). Then, an adhesive made of a thermosetting resin, an ultraviolet-curing resin, a visible-light-curing resin, or the like is applied to the surface of the reflective film 34 of the reflective diffraction grating (or the surface of the glass plate on which the anti-reflection film 33 is formed), and the surface of the reflective diffraction grating having grating grooves and the surface of the glass plate that will become the protective cover 36 having the anti-reflection film 33 are bonded together via the adhesive. Thereafter, the adhesive is cured by heating or irradiation with ultraviolet or visible light, etc., to form a protective-cover-side resin layer 35. This results in a diffraction grating according to this embodiment having the configuration shown in FIG. 4.

[0024] As shown in FIG. 4 , the diffraction grating according to this embodiment is used by irradiating light from the front surface side of the protective cover 36. The light incident on the protective cover 36 (the incident light in FIG. 4 ) travels from the protective cover 36 toward the protective cover-side resin layer 35 and is reflected by the reflective film 34. At this time, the light of each wavelength contained in the incident light constructively interacts with each other at angles corresponding to the wavelengths, and this constructive light (the reflected diffracted light in FIG. 4 ) passes through the protective cover-side resin layer 35 and the protective cover 36 and exits from the front surface of the protective cover 36. In conventional diffraction gratings, when the incident light enters the protective cover-side resin layer 35 from the protective cover 36, and when the reflected diffracted light enters the protective cover 36 from the protective cover-side resin layer 35, a portion of the incident light and a portion of the reflected diffracted light are reflected at the interface between the protective cover 36 and the protective cover-side resin layer 35, causing stray light. That is, the light reflected at the interface reaches the grating surface directly or by being reflected again at the front surface of the protective cover 36. The incident angle of this reflected light on the grating surface is different from the original incident angle of the incident light, which has an adverse effect on the spectral performance. In contrast, in the diffraction grating according to this embodiment, the anti-reflection film 33 is provided between the protective cover 36 and the protective cover-side resin layer 35. Therefore, when the incident light enters the protective cover-side resin layer 35 from the protective cover 36, and when the reflected diffracted light enters the protective cover 36 from the protective cover-side resin layer 35, reflection of light at the interface between the protective cover 36 and the protective cover-side resin layer 35 can be prevented, and the generation of stray light as described above can be prevented.

[0025] Although specific examples of embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and various modifications are permitted within the spirit and scope of the present invention. For example, although the diffraction gratings according to the above embodiments are planar diffraction gratings, the diffraction gratings according to the present invention may be concave diffraction gratings. Furthermore, the diffraction gratings according to the present invention are not limited to so-called blazed diffraction gratings having grating grooves with sawtooth cross sections as shown in FIGS. 1 to 4 , but may also be, for example, laminar diffraction gratings having grating grooves with rectangular cross sections. Furthermore, the diffraction gratings according to the present invention do not necessarily have to be manufactured by replicating a master diffraction grating.

[0026] Table 1 shows a first design example of a diffraction grating according to the present invention. The diffraction grating in this design example is a transmission type diffraction grating having the same configuration as that shown in FIG. 1. As shown in Table 1, synthetic quartz (quartz glass) is used as the constituent material of the substrate 11 (glass substrate), and epoxy resin is used as the constituent material of the resin layer 12. The anti-reflection film 13 has a multilayer structure consisting of a first layer, a second layer, a third layer, and a fourth layer in order from the side closest to the substrate 11, and the first and third layers are made of Al. ２ O ３ The second and fourth layers are made of SiO ２ The refractive index at a wavelength of 550 nm of the materials constituting the substrate 11, each layer of the anti-reflection coating 13, and each resin layer 12, as well as the physical thickness of each layer of the anti-reflection coating 13, are all as shown in Table 1.

[0027]

[0028] FIG. 5 shows the results of simulating the reflectance characteristics at the interface between the substrate 11 and the resin layer 12 when light in the visible light range is incident at an incident angle of 0° on a diffraction grating according to this design example (hereinafter referred to as the diffraction grating of Example 1) and a diffraction grating without the antireflection coating 13 (hereinafter referred to as the diffraction grating of the comparative example). The diffraction grating of the comparative example has the same configuration as the diffraction grating of Example 1, except that it does not have the antireflection coating 13. As shown in FIG. 5, the reflectance of the diffraction grating of the comparative example is a maximum of 0.13% in the wavelength range of 400 nm to 700 nm, whereas the reflectance of the diffraction grating of Example 1 is 0.01% or less in the same wavelength range.

[0029] A second design example of the diffraction grating according to the present invention is shown in Table 2. The configuration of the diffraction grating in this design example is the same as that of the diffraction grating in Example 1, except for the physical film thickness of each layer of the antireflection coating 13.

[0030]

[0031] The results of simulating the reflectance characteristics at the interface between the substrate 11 and the resin layer 12 when light in the visible light range was incident at an incident angle of 0° on the diffraction grating according to this design example (hereinafter referred to as the diffraction grating of Example 2) and the diffraction grating of the comparative example are shown in Figure 6. As shown in the figure, the reflectance of the diffraction grating of the comparative example was a maximum of 0.09% in the wavelength range of 750 nm to 1550 nm, whereas the reflectance of the diffraction grating of Example 2 in the same wavelength range was 0.01% or less.

[0032] A third design example of the diffraction grating according to the present invention is shown in Table 3. The configuration of the diffraction grating in this design example is the same as that of the diffraction gratings in Examples 1 and 2, except for the physical film thickness of each layer of the antireflection coating 13.

[0033]

[0034] 7 shows the results of simulating the reflectance characteristics at the interface between the substrate 11 and the resin layer 12 when light in the visible light range is incident at an incident angle of 30° on the diffraction grating according to this design example (hereinafter referred to as the diffraction grating of Example 3) and the diffraction grating of the comparative example. As shown in the figure, the reflectance of the diffraction grating of the comparative example is a maximum of 0.15% in the wavelength range of 350 nm to 750 nm, whereas the reflectance of the diffraction grating of Example 3 in the same wavelength range is 0.01% or less.

[0035] Aspects It will be apparent to those skilled in the art that the exemplary embodiments described above are examples of the following aspects.

[0036] (Item 1) A diffraction grating according to one aspect of the present invention comprises a glass plate, a first resin layer having a grating surface, and an anti-reflection film, in which one surface of the glass plate and a surface of the first resin layer opposite the grating surface are bonded to each other with the anti-reflection film sandwiched therebetween.

[0037] (Item 2) The diffraction grating according to item 2 is the diffraction grating according to item 1, wherein light incident in a direction from the glass plate toward the first resin layer is diffracted by the grating surface of the first resin layer and emitted from the grating surface to the outside of the diffraction grating.

[0038] (Item 3) The diffraction grating according to item 3 is the diffraction grating according to item 1, further comprising a reflective film covering the grating surface of the first resin layer, and light incident in a direction from the glass plate toward the first resin layer is diffracted by the grating surface and reflected by the reflective film, and is emitted to the outside of the diffraction grating from the surface of the glass plate opposite to the surface facing the anti-reflection film.

[0039] (Item 4) The diffraction grating according to item 4 is the diffraction grating according to item 3, further comprising: a plate member facing the reflective film; and a second resin layer interposed between the plate member and the reflective film.

[0040] (Item 5) The method for manufacturing a diffraction grating according to Item 5 is a method for manufacturing a replica diffraction grating by copying the shape of the grating surface of a master diffraction grating, which includes forming an anti-reflection film on one surface of a glass plate, bonding the grating surface of the master diffraction grating to the surface of the glass plate on which the anti-reflection film is formed via an adhesive, and after hardening the adhesive, removing the glass plate together with the adhesive from the master diffraction grating, thereby manufacturing a replica diffraction grating that includes the glass plate, a resin layer made of the hardened adhesive, and the anti-reflection film interposed between the glass plate and the resin layer.

[0041] REFERENCE SIGNS LIST 11, 21, 31... Substrate 12, 22... Resin layer 32... Substrate-side resin layer 13, 23, 33... Anti-reflection film 24, 34... Reflection film 35... Protective cover-side resin layer 36... Protective cover

Claims

1. A diffraction grating comprising: a glass plate; a first resin layer having a grating surface; and an anti-reflection film, wherein one surface of the glass plate and a surface of the first resin layer opposite the grating surface are bonded to each other with the anti-reflection film sandwiched between them.

2. A diffraction grating according to claim 1, wherein light incident in a direction from the glass plate toward the first resin layer is diffracted by the grating surface of the first resin layer and emitted from the grating surface to the outside of the diffraction grating.

3. A diffraction grating according to claim 1, further comprising a reflective film covering the grating surface of the first resin layer, wherein light incident in a direction from the glass plate toward the first resin layer is diffracted by the grating surface and reflected by the reflective film, and emitted to the outside of the diffraction grating from the surface of the glass plate opposite to the surface facing the anti-reflection film.

4. A diffraction grating according to claim 3, further comprising: a plate member facing said reflective film; and a second resin layer interposed between said plate member and said reflective film.

5. A method for manufacturing a replica diffraction grating by copying the shape of the grating surface of a master diffraction grating, comprising: forming an anti-reflection film on one surface of a glass plate; bonding the grating surface of the master diffraction grating to the surface of the glass plate on which the anti-reflection film is formed via an adhesive; hardening the adhesive, and then removing the glass plate together with the adhesive from the master diffraction grating, thereby manufacturing a replica diffraction grating comprising the glass plate, a resin layer made of the hardened adhesive, and the anti-reflection film interposed between the glass plate and the resin layer.

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