JP2010020120A - Optical filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical filter compatible with a multi wavelength band (e.g. 3 to 5 um band and 8 to 14 um band of IR), the optical filter having excellent long time reliability even in a special environment such as space, and to provide an optical device using the same. <P>SOLUTION: Three-dimensional solid structure to be a multi-structure of a wavelength size sufficiently smaller than the wavelength band to be aimed is formed on the surface or both surfaces of the optical filter. Thereby an effective refractive index is changed in a step shape to improve transmission characteristics of the targeted multi wavelength band. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical component that transmits light or prevents reflection of light, such as a band limiting filter used in a photographing camera, a window (optical window) that transmits incident light, and a lens.

  In a light emitting device, a light receiving device, a photographing device, or the like, an optical component (for example, an optical filter) is required to exhibit a high transmittance with respect to light transmitted through the optical component. Therefore, a material having a low absorptance with respect to light in a target wavelength region is generally selected as a material constituting the optical component. Further, the loss of transmittance generated on the surface (incident surface and transmission surface) of the optical component based on the difference between the refractive index of the material constituting the optical component and the refractive index of the medium (usually air) in contact with the optical component. In order to reduce this, an antireflection film may be provided on the surface of the optical component.

  For example, in the conventional infrared optical filter, Ge, ZnS, ZnSe, Si, or the like is often used as a window material of the optical filter, and a metal fluoride or the like is employed as an antireflection film (for example, patents). Reference 3).

  Also, instead of forming an antireflection film on the surface of the optical component, the surface of the optical component is antireflective by microfabricating a regular three-dimensional structure with a space smaller than the wavelength of light on the surface. There have been attempts to provide functions (see, for example, Patent Documents 1 and 2 and Non-Patent Document 1).

JP 2002-287370 A JP-T-2004-521329 JP 2003-177210 A OPTICS LETTERS, Vol. 24, No. 20, October 15, p1422 (Optical Society of America)

  In recent years, there has been an increasing demand for higher functionality and higher efficiency of imaging devices, and in order to answer this, it has become necessary to make the optical wavelength band handled by imaging devices multiband. However, when the multilayer antireflection film as described above is applied to an optical component, the refractive index of the film or the linear expansion of the film is taken into consideration in the environment (for example, high temperature, heat cycle) in which the optical component is used. It was necessary to select the material of the film in consideration of material characteristics such as coefficient. That is, when used in an environment that exceeds the design specifications, phenomena such as peeling of the antireflection film, residual distortion, and release of residual gas from the antireflection film may hinder long-term reliability. In addition, when the band pass filter has a steep wavelength selectivity, the number of layers further increases, and there is a problem that the use environment is restricted due to the problem of the material selection.

  On the other hand, in a structure in which fine irregularities are formed on the surface of an optical component as shown in Patent Document 1 and an antireflection effect is aimed, it is required to select a desired wavelength band with a steep wavelength selectivity. It was particularly difficult to obtain a multiband optical filter.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an optical filter having excellent wavelength selectivity and excellent reliability.

  The optical filter according to the present invention transmits light targeted by the optical filter and has a wavelength of light in an upper layer defined by a substrate, a main surface of the substrate, and a surface separated from the main surface by a predetermined distance. A middle layer within a middle layer defined by a block group consisting of blocks having a thickness smaller than that of the block, a surface adjacent to the upper layer and a predetermined second distance away from the main surface, and the surface of the upper layer A block group consisting of blocks having the thickness of the block, and the ratio of the occupied area of the block group and the other area when the main surface is viewed in plan is a predetermined ratio in each layer. The blocks are arranged in each layer.

  Moreover, the optical filter according to the present invention is a hole having an opening smaller than the wavelength λ of light targeted by the optical filter, and is dug into the substrate of the optical filter at a predetermined depth from the main surface of the substrate. A plurality of holes are provided for each predetermined depth, and the area occupied by the plurality of holes at the depth and the remaining area of the substrate other than the holes are provided for each predetermined depth in plan view of the main surface. In this case, holes are provided in the substrate so that the ratios of the two are predetermined ratios.

  According to the present invention, a three-dimensional structure having a multilayer structure on the surface of the substrate can obtain desired transmittance characteristics by setting the filling rate of the structure in each layer and the thickness of each layer to predetermined values. it can. Moreover, there is no problem such as peeling due to the multilayer laminated film, and an optical filter having excellent reliability and excellent wavelength selectivity can be obtained.

Embodiment 1 FIG.
FIG. 1 is a perspective view showing a schematic configuration of the optical filter according to the first embodiment. FIG. 2 is a schematic view of FIG. 1 shown in a perspective view in plan view. FIG. 3 is a schematic view of a cross section of the optical filter taken along the line III-III shown in FIG.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings, taking an optical filter for an infrared detector as an example. In the following description, the present invention will be described by taking a multiband optical filter corresponding to the 3-5 μm band and the 8-12 μm band as an example, but other forms are naturally included in the technical scope of the present invention. . It is also effective for light in other wavelength bands without being limited to the infrared wavelength band.

First, the overall configuration of the optical filter 1 will be described.
In FIG. 1, the optical filter 1 includes a lower small cylinder 31 and a large cylinder 4 disposed on a substrate 2, and an upper small cylinder 11 disposed on the large cylinder 4. Further, the combination of these large and small cylinders will be referred to as the surface three-dimensional structure 3 for convenience. The material of the substrate 2 and the large cylinder 4 is Si that transmits infrared rays. In place of Si, Ge, ZnSe or a composite material thereof can be used as the substrate.

  With reference to FIG. 3, the surface three-dimensional structure 3 described above has a three-layer structure of a lower layer structure 30, a middle layer structure 20, and an upper layer structure 10 in order from the side closer to the substrate 2. Further, the surface three-dimensional structure 3 can be equivalently considered as a three-layer optical multilayer film in terms of optical characteristics. Hereinafter, the reason will be described.

First, considering the case where the surface three-dimensional structure 3 is a single layer, that is, a state in which only the lower small cylinder 31 is simply disposed on the substrate 2 (the state in which there is no large cylinder 4), refraction that determines the characteristics of the optical filter. It will be explained that the rate is determined by the shape of the surface three-dimensional structure.
When an optical component (here, an optical filter) is disposed in contact with a certain medium (usually air), all three-dimensional structures (here, lower layers) are used in order to prevent scattering of incident light on the light transmission surface. The distance L between the small cylinders 31) is designed to be equal to or smaller than the wavelength of the incident light. In such a three-dimensional structure, the area ratio between the concave portion and the convex portion (here, the area of the upper bottom surface of the lower small cylinder 31 is the area of the convex portion, and the portion not occupied by the lower small cylinder 31 on the substrate 2) Is considered as the area of the recess), the effective refractive index (n _x ) of the layer can be controlled. When the area ratio of the concave portion filled with air of the substrate 2 is set to f (when all concave portions are set to f = 1), the effective refractive index (n _x ) of this single layer is expressed by the formula ( It can be obtained from 1).

As described above, since the refractive index of a single layer can be calculated according to the equation (1), in the case of a three-layer surface three-dimensional structure 3, the refractive index is calculated for each layer of the upper layer to the lower layer structure. Can do. When applied to the three-dimensional structure as shown in FIG. 3, a three-layer structure in which the area ratio f is f ₁ , f ₂ , f ₃ from the upper layer can be obtained. The effective refractive index (n _x ) in this case is n ₁ , n ₂ , and n ₃ depending on each layer. As described above, by changing the area ratio f, it is possible to obtain the same effect as in the case of stacking multilayer films whose refractive indexes change stepwise. In addition, since the effective refractive index (n _x ) is determined by the area ratio f, for example, the lower small cylinders 31 may be arranged at random, and it is not particularly necessary that the uneven portion has a periodic structure.

Next, the wavelength peak of the single layer described above is determined from the formula (2) by the height of the convex portion of the effective refractive index portion (that is, the depth of the concave portion: d).

Therefore, in order to calculate the target wavelength band in which infrared rays are desired to be transmitted, the refractive index (n _x ) is calculated for each layer structure using the above equation (1), and the wavelength band desired to be transmitted is adjusted to (2). The thickness (d _x ) of each layer structure of the upper layer to the lower layer structure can be obtained using the formula.

When designing an optical filter of a multi-band corresponding to the 3~5μm band and 8~14μm band, (1), (2) appropriate equation based on the refractive index _(n x), the thickness _{(d x)} Calculate and combine them, and verify whether the desired transmittance characteristics can be obtained by a normal optical multilayer film calculation method. For example, in the case of a three-layer structure as shown in FIG. 3, the area ratio between the concave portion and the convex portion is appropriately selected, and the effective refractive index n ₁ = 1.5, n ₂ = 2.0, n ₃ = 2. .5 and when the depth of the recess is d ₁ = 0.5 μm, d ₂ = 0.9 μm, and d ₃ = 0.25 μm, it is good in the two wavelength bands targeted for design as shown in FIG. It is possible to obtain transmission characteristics.

  Further, in the present embodiment, the shape of the convex portion is a columnar shape, but it is not particularly necessary to be a columnar shape, and there is no problem even if it is a shape such as a prism. Further, it has been found that the wavelength selectivity is improved by making the effective refractive index stepwise, and it is desirable that the variation in the area ratio of each step is small.

  Next, an example of a method for manufacturing the optical filter of the present invention will be described with reference to the drawings. The manufacturing method described here is merely an example, and the above-described structure can be realized by other manufacturing methods.

  A method for manufacturing the above-described three-dimensional structure in which the effective refractive index is controlled on the substrate 2 will be described. 5 to 9 are schematic cross-sectional views illustrating the manufacturing method according to the present embodiment in the order of steps. The cross-sectional position corresponds to the position along the line III-III shown in FIG. Hereinafter, it demonstrates in order of a process.

  In the first step shown in FIG. 5, a pattern of a photoresist 41 is formed on the substrate 2 and used as a mask.

  In the second step shown in FIG. 6, a predetermined depth is dug by dry etching or the like.

  In the third step shown in FIG. 7, the photoresist 41 is temporarily removed and masked by the photoresist 42 so as to protect the deepest portion and dig the uppermost portion. Next, the surface layer portion is dug to a predetermined depth by dry etching or the like.

  In the fourth step shown in FIG. 8, the photoresist 42 is removed again and masked with the photoresist 43 so as to protect the outermost surface. In this state, the deepest convex portion is etched by dry etching or the like to be cut to a predetermined depth.

  Finally, the photoresist 43 is removed in a fifth step shown in FIG. The etching and exposure processes are repeated to realize an expected surface three-dimensional structure on the substrate surface.

Embodiment 2. FIG.
In the above-described first embodiment, the control example using the cylindrical projection is shown to realize the optical filter for infrared rays. However, the example has been described, but the surface three-dimensional structure is not necessarily a cylindrical projection. The area ratio f may be controlled by providing a large number of holes in the substrate for controlling the effective refractive index. FIG. 10 shows such a configuration, and is a perspective view showing a schematic configuration of the optical filter as in FIG. In the present embodiment, a cylindrical projection and a substrate are combined with a cylindrical hole. The same effect can be obtained by this configuration.

Embodiment 3 FIG.
In the second embodiment described above, the control example using the cylindrical protrusion is shown for realizing the optical filter. However, in the present embodiment, as shown in FIG. 11, the depth of the hole is different in three stages. The area ratio f is controlled by machining a hole in the substrate. The same effect can be obtained by this configuration.

Embodiment 4 FIG.
In the first embodiment described above, an example in which the effective refractive index (n _x ) is n ₁ <n ₂ <n ₃ from the outermost surface in order to realize the optical filter has been described. An optical filter can also be realized by producing a three-dimensional structure so that the distribution of n ₁ <n ₃ <n ₂ is satisfied. Hereinafter, the structure of this embodiment will be described. FIG. 13 is an exploded perspective view of the optical filter of the present embodiment for easy understanding of the structure, and is shown separated at the boundary between the third layer structure and the middle layer structure. Moreover, the schematic diagram of the cross section of an optical filter is shown in FIG.

  The structure of this embodiment will be described. The lower layer structure 30 is obtained by processing the surface of the substrate 2 and providing an intermediate cylinder. A thin Si substrate is used as the middle layer structure 20, and the upper layer structure 10 is formed by processing the surface of the Si substrate to form the upper layer small cylinder 11. The structure of this embodiment is a three-layer structure in which the bottom surface of the Si substrate (intermediate layer structure 20) is joined to the upper surface of the middle cylinder.

With this structure, the effective refractive index distribution described above can be realized. For example, as shown in FIG. 14, the effective refractive index n ₁ = 1.5, n ₂ = 2.5, n ₃ = 2.0 (= controlled from the area ratio) and the depth of the recess (d ₁ = 2. In the case of 0 μm, d ₂ = 0.6 μm, d ₃ = 0.7 μm), good transmission characteristics can be obtained in the two target wavelength bands.

  In the above-described embodiment 4, the lower layer structure is formed of a cylinder, but there is no problem even if the area ratio is controlled by another shape, and the same effect can be obtained with a prism, hexagonal hole, or groove.

Embodiment 5 FIG.
In the first embodiment described above, the example of the three-layer structure has been described so as to be equivalently a three-layer optical multilayer film. In the fifth embodiment, a two-layer structure in which blocks are periodically arranged as an optical filter will be described. That is, an example will be described in which the two-layer structure of the lower layer structure and the upper layer structure is equivalently a two-layer optical multilayer film.

  In the structure described in the present embodiment, the transmittance in the 8 to 12 μm band is increased in the lower layer structure in the first layer, and the transmittance in the 3 to 5 μm band is increased in the upper layer structure in the second layer. This is an example of design. A large block 45 corresponding to the first lower layer structure formed on the substrate 44 and a smaller block 46 corresponding to the second upper structure are formed. Hereinafter, the configuration of the optical filter for the infrared detector will be described.

  FIG. 15 is a schematic view of only the lower layer structure of the optical filter according to the optical design of the present embodiment. FIG. 16 is a graph of the calculation result of the transmittance characteristics of the optical filter of only the lower layer structure using the block size shown in FIG. 15 as a parameter. FIG. 17 is a graph showing the deviation between the structural parameter L, the peak wavelength of the transmittance, and the wavelength of 10 μm in order to examine the optimum block size range from the calculation result. FIG. 18 is a perspective view showing a schematic configuration of an optical filter having a two-layer structure according to the present embodiment. FIG. 19 is a graph showing a result of calculating transmittance characteristics with the size of the lower layer structure fixed and the size of the second layer block as the upper layer structure as a parameter. FIG. 20 is a graph showing the relationship between the transmittance at 4 μm and the block size in order to examine the optimum block size range from the calculation result.

  First, the optical design of the lower layer structure will be described. Consider the structure of only the block 45 in which the first layer is as shown in FIG. Here, the vertical, horizontal, and height sizes of the blocks 45 are Lx, Ly, and d, and the intervals between adjacent blocks 45 are vertical and horizontal, respectively, sy and sx. Further, for example, if only Lx is lengthened, optical anisotropy in this direction occurs. Therefore, the optical design is made so that the optical anisotropy is as small as possible, as sx = sy = Lx = Ly = d. Further, the structure parameter L is defined as L = sx = sy = Lx = Ly = d. Here, the block 45 is a cube.

  The transmittance was calculated by changing the structural parameter L around 1 μm. The analysis uses exact coupled wave analysis. The material was silicon having a refractive index of 3.4. Representative results of the analysis results are shown in FIG. Referring to FIG. 16, it can be seen that a transmittance window (that is, a region with high transmittance) is formed in the vicinity of 8 to 12 μm, and the transmittance peak is shifted to the longer wavelength side as L is increased. .

  The purpose of the optical design of the lower layer structure is to design the absorptance in the 8-12 μm band to be maximum. Therefore, paying attention to the deviation between the peak wavelength appearing in this band and the wavelength of 10 μm, which is the central wavelength of the 8 to 12 μm band, the range where this deviation is minimized is considered the optimum range for optical design, and the structural parameter L is set to 0. The transmittance when changing from 9 μm to 1.7 μm was calculated. FIG. 17 is a graph showing a change in deviation between the peak wavelength of transmittance and the wavelength of 10 μm when the structural parameter L is changed. Further, the smaller the deviation, the more the transmission band of the structure is in the 8 to 12 μm band, and the infrared light in the target wavelength region can be transmitted well.

  Referring to FIG. 17, if the amount of deviation between the peak value of the transmittance in the 8 to 12 μm band of the lower layer structure and the wavelength of 10 μm is 2 μm or more (shaded area in the figure), It can be seen that it is appropriate to set the displacement in the L range of 1.05 μm to 1.6 μm where the deviation is 2 μm or less. It can also be seen that Lx = Ly = d = 1.3 μm transmits the desired wavelength region most efficiently.

Next, the optical design of the upper layer structure will be described.
As described above, since the case of sx = sy = Lx = Ly = d = 1.3 μm was optimal as the lower layer structure, the upper layer structure was formed on the block 45 of the lower layer structure shown in FIG. Two smaller blocks 46 were arranged. Such a form is shown in FIG.

  Similar to the optical design of the lower layer structure described above, the size of the block 46 in the vertical, horizontal, and height directions is set to Lx2, Ly2, and d2, and L2 = Lx2 = Ly2 = d2, and the structural parameter L2 of the upper layer structure is changed. Let me calculate. FIG. 19 shows the transmittance characteristics of typical values of L2. In such a two-layer structure, a transmittance peak appears anew in the vicinity of the 3-5 μm band in addition to the vicinity of 8-12 μm. FIG. 20 shows the transmittance at a wavelength of 4 μm, which is the center wavelength of the 3 to 5 μm band, with respect to L2.

  Referring to FIG. 20, when L2 = 0.4 μm or more, the transmittance rapidly increases and becomes 90% or more. Therefore, it can be seen that L2 = 0.4 μm or more is desirable in the above-described two-layer structure. In particular, when Lx2 = Ly2 = d2 = 0.65 μm, the transmittance is highest in the vicinity of the 3 to 5 μm band. That is, a two-layer structure of sx = sy = Lx = Ly = d = 1.3 μm and Lx2 = Ly2 = d2 = 0.65 μm is an optimum structure as an optical filter of a multiband (3-5 μm band and 8-12 μm band). It becomes.

  As described above, if the optical design is performed appropriately under the condition that the three sides are equal and the distance between the blocks is equal to the length of one side of the block, the transmittance peak in the target wavelength band. And optical anisotropy hardly occurs.

  Furthermore, on the block group in the first layer under the condition that the blocks having the same three sides and the interval between the blocks have the same length as one side of the block, the second layer composed of the block groups having the same three sides is provided. By adopting the mounted configuration, it is possible to obtain an optical filter having transmittance peaks in two wavelength bands.

  In the above-described embodiment, the example in which two small blocks 46 are arranged on the block 45 constituting the lower layer structure as the block group constituting the upper layer structure is shown. If it is a size that can be arranged on the block 45, two or more may be arranged. Even in this case, if the optical design is appropriately performed, a peak of transmittance can be produced in the target wavelength band.

  In this way, by forming a two-layer structure of micron and submicron scale blocks, it is possible to form a multiband optical filter that selectively transmits different wavelength ranges corresponding to each scale.

Embodiment 6 FIG.
In the above-described fifth embodiment, the example of the two-layer structure in which the blocks having the same three sides are periodically arranged as the optical filter has been described. In the sixth embodiment, by appropriately selecting the number of blocks arranged or the planar shape, the ratio of the block group existing in the layer (that is, the area ratio defined in the first embodiment described above) is manipulated. Explain that the transmittance can be controlled.

  FIG. 21 is a perspective view showing a schematic configuration of an optical filter having a two-layer structure according to the present embodiment. FIG. 22 shows a plan view of the portion surrounded by the dotted line A in the figure as viewed from above. In FIG. 22, the dimensions of the blocks (block 45, block 46) are sx = sy = Lx = Ly = d = 1.3 μm, which is the optimum structure described in the fifth embodiment, and Lx2 = Ly2 = d2 =. 0.65 μm. This size will be described as an example. Referring to FIG. 22, a block 46 constituting the second layer upper layer structure is placed on a block 45 constituting the first layer lower layer structure. Here, the number of the second layer blocks 46 placed on each block 45 of the first layer is two. Now, if the occupied area of the second layer block 46 with respect to the first layer block 45 is defined as the filling rate, the second layer block 46 is compared to the first layer block 45 in this state. Since the occupied area is 50%, the filling rate is 50% in the above case.

  Next, as shown in FIG. 23, it is assumed that the size of the block 46 in the second layer is half that of the block 46 in FIG. The filling rate at this time is 25%. However, the depth direction (perpendicular to the paper surface) is kept at 0.65 μm (the height is not changed even in the following example). Similarly, as shown in FIG. 24, when the number of the second layer blocks 46 in the state of FIG. 22 is increased and doubled, the filling rate becomes 50%. Next, as shown in FIG. 25, the block 46 of the second layer is deformed from the state of FIG. 23 to increase the occupied area to a filling rate of 65%. FIG. 26 is a graph showing the transmittance characteristics shown in FIG. 26 when the transmittance is obtained when the filling rate of the block 46 of the second layer is changed as in the cases of FIGS. Referring to FIG. 26, it can be seen that the transmittance particularly in the 3 to 5 μm band varies greatly according to the filling rate.

  FIG. 27 shows the relationship between the minimum value in the 3 to 5 μm band for each case described above (for example, the arrow portion shown in the vicinity of the wavelength of 4 μm for the transmittance curve of 50% filling rate in FIG. 26) and the filling rate. It can be seen from FIG. 27 that the filling rate is between 55% and 78% when entering the high transmission region where the transmittance is about 95% or more.

  As described above, when the main surface of the substrate of the optical filter is viewed in plan and the ratio of the area of the block in the second layer to the area of the block in the first layer is a predetermined value, the first layer A second transmission band can be formed on a shorter wavelength side than a predetermined transmission band by the block group. Therefore, it is possible to obtain a multiband optical filter by setting the above-described filling rate to a predetermined value.

  The above-described embodiment is an exemplification, and the present invention is not limited to the scope of the illustrated embodiment. For example, in the above-described embodiment, the example in which the concavo-convex shape is added to one main surface of the filter substrate has been described, but the filter substrate may be formed on the other main surface of the filter substrate. The present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a perspective view of the optical filter of Embodiment 1 of the present invention. It is a top view of the optical filter of Embodiment 1 of the present invention. It is sectional drawing of the optical filter of Embodiment 1 of this invention. It is an example of the transmission characteristic of the optical filter of Embodiment 1 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 1 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 1 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 1 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 1 of this invention. It is sectional drawing in the manufacturing process of the optical filter of Embodiment 1 of this invention. It is a perspective view of the optical filter of Embodiment 2 of the present invention. It is a perspective view of the optical filter of Embodiment 3 of the present invention. It is sectional drawing of the optical filter of Embodiment 4 of this invention. It is a perspective view of the optical filter of Embodiment 4 of this invention. It is an example of the transmission characteristic of the optical filter of Embodiment 4 of this invention. It is a perspective view explaining the optical filter of Embodiment 5 of this invention. It is the transmittance | permeability characteristic in Embodiment 5 of this invention. It is a figure explaining the change of the transmittance | permeability in Embodiment 5 of this invention. It is a perspective view of the optical filter of Embodiment 5 of the present invention. It is the transmittance | permeability characteristic in Embodiment 5 of this invention. It is a figure explaining the change of the transmittance | permeability in Embodiment 5 of this invention. It is a perspective view of the optical filter of Embodiment 6 of this invention. It is a top view of the optical filter of Embodiment 6 of the present invention. It is a top view of the structure of the filling rate 25% in Embodiment 6 of this invention. It is a top view of the structure of 50% of filling rate in Embodiment 6 of this invention. It is a top view of the structure of the filling rate 65% in Embodiment 6 of this invention. It is the transmittance | permeability characteristic in Embodiment 6 of this invention. It is a figure explaining the change of the transmittance | permeability in Embodiment 6 of this invention.

Explanation of symbols

1 optical filter,
2 substrates,
3 surface three-dimensional structure,
4 Large cylinder 10 Upper layer structure,
11 Upper small cylinder,
12 Etching hole 13 Upper layer substrate 20 Middle layer structure,
30 Underlayer structure,
31 Lower cylinder,
32 Etching hole 33 Etching groove 40 Photoresist 41 Photoresist 42 Photoresist 43 Photoresist 44 Substrate 45 First layer block 46 Second layer block

Claims (9)

An optical filter substrate;
In the first layer defined by the main surface of the substrate and a surface separated by a predetermined distance from the main surface, the optical filter is a block that transmits light of interest and is smaller than the wavelength of the light, A block group consisting of blocks whose distance is the thickness;
The thickness of the second layer is defined as the thickness of the second layer adjacent to the first layer and defined by the surface separated from the main surface by a predetermined second distance and the surface of the first layer. A block group consisting of blocks,
The blocks are arranged in each layer so that the ratio of the area occupied by the block group when the main surface is viewed in plan and the other area is a predetermined ratio in each layer. An optical filter. In a third layer that is adjacent to the second layer and defined by a surface separated from the main surface of the substrate by a third distance and the surface of the second layer, from a block having the thickness of the third layer as its thickness With a block group
2. The optical filter according to claim 1, wherein the main surface is viewed in plan, and blocks are arranged in each layer at a predetermined area ratio in each layer.   The optical filter according to claim 2, wherein the thicknesses of the first layer, the second layer, and the third layer are 1/4 of the wavelength λ of the light targeted by the optical filter.   3. The optical filter according to claim 1, wherein the block group is a plurality of blocks each having a concavo-convex shape on a main surface of the substrate and made of a cylinder, a prism, an irregular column, or a combination thereof. .   The block is provided with a plurality of holes having an opening smaller than the wavelength λ of light targeted by the optical filter at a predetermined depth, and the occupied area of the plurality of holes and the area of the remaining portion of the block other than the holes The optical filter according to claim 1, wherein the ratio is defined as a predetermined value. On the substrate of the optical filter,
The optical filter is a hole having an opening smaller than the wavelength λ of the target light, and includes a plurality of holes each having a predetermined depth dug from the main surface of the substrate.
The ratio of the area occupied by the plurality of holes at the depth and the area of the remaining area of the substrate other than the holes becomes a predetermined ratio at each predetermined depth when the main surface is viewed in plan. An optical filter, wherein a hole is provided in the substrate.   The difference between the digging depth of one predetermined hole and the digging depth of another predetermined hole is ¼ of the wavelength λ of light targeted by the optical filter. Optical filter. A group of blocks that are cubic blocks in the first layer and in which the spacing between adjacent blocks is equal to one side of the cube;
2. The optical filter according to claim 1, wherein the second layer includes a block group that is arranged adjacent to the block in the first layer and includes cubic blocks smaller than the block in the first layer. A group of blocks that are cubic blocks in the first layer and in which the distance between adjacent blocks is equal to one side of the cube;
The second layer has a block group that is arranged adjacent to the block in the first layer, and is composed of blocks smaller than the block in the first layer,
The optical filter according to claim 1, wherein the ratio of the area of the block in the second layer to the area of the block in the first layer is set to a predetermined value in plan view of the main surface of the substrate of the optical filter.

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