Optical element

Abstract

To provide a technique for rapidly changing light transmittance at a boundary between an antireflection film and a light-shielding film.SOLUTION: An optical element includes a transparent base material that transmits light, an antireflection film that prevents light reflection, and a light-shielding film that shields light transmission. The transparent base material has, on a surface on which the light is incident, an optical effective surface that is a region in which the antireflection film is formed, and a groove provided over the entire outer periphery of the optical effective surface. The light-shielding film is filled inside the groove, is in contact with the transparent base material inside the groove, and surrounds the outer periphery of the antireflection film.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to optical elements. [Background technology]

[0002] The optical element described in Patent Document 1 includes a lens substrate, an anti-reflection film, and a light-shielding film. The lens substrate has a smooth surface and a rough surface surrounding the outer periphery of the smooth surface. The anti-reflection film is formed continuously with the smooth surface and part of the rough surface. The anti-reflection film has a fine uneven structure on the surface opposite the lens substrate. The light-shielding film covers the outer periphery of the anti-reflection film. The outer periphery of the anti-reflection film and the inner periphery of the light-shielding film overlap on the smooth surface. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-141822 A Summary of the Invention [Problem to be solved by the invention]

[0004] A light-shielding film is generally formed by applying a coating liquid and drying it. The closer to the edge of the liquid film, the thinner the coating liquid is likely to become due to surface tension. Therefore, the thickness of the inner circumference of the light-shielding film tends to be thin. As a result, it has been difficult to suddenly change the light transmittance at the boundary between the anti-reflection film and the light-shielding film.

[0005] One aspect of the present disclosure provides a technique for suddenly changing the light transmittance at the boundary between an anti-reflection film and a light-shielding film. [Means for solving the problem]

[0006] An optical element according to one aspect of the present disclosure includes a transparent substrate that transmits light, an anti-reflection film that prevents reflection of the light, and a light-shielding film that blocks transmission of the light. The transparent substrate has an optically effective surface on a surface onto which the light is incident, which is an area on which the anti-reflection film is formed, and a groove provided along an outer periphery of the optically effective surface. The light-shielding film is filled inside the groove, contacts the transparent substrate inside the groove, and surrounds the outer periphery of the anti-reflection film. Effect of the Invention

[0007] According to one aspect of the present disclosure, a groove is provided along the outer periphery of the optically effective surface. The groove is filled with a light-shielding film, thereby increasing the thickness of the light-shielding film. As a result, the light transmittance can be abruptly changed at the boundary between the anti-reflection film and the light-shielding film, and light leakage to the outside of the optically effective surface can be suppressed. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1(A) is a plan view of an optical element according to one embodiment, FIG. 1(B) is a cross-sectional view of the optical element according to one embodiment, and FIG. 1(C) is a cross-sectional view showing an enlarged portion of FIG. 1(B). [Diagram 2] FIG. 2A is a plan view showing an example of Δr1 and Δr2, and FIG. 2B is a plan view showing an example of d1 and d2. [Diagram 3] FIG. 3(A) is a plan view of an optical element according to a first modified example, FIG. 3(B) is a plan view of an optical element according to a second modified example, and FIG. 3(C) is a plan view of an optical element according to a third modified example. [Figure 4] FIG. 4A is a cross-sectional view of an optical element according to a fourth modified example, and FIG. 4B is an enlarged cross-sectional view showing a part of FIG. 4A. [Diagram 5] FIG. 5(A) is a cross-sectional view of an optical element according to a fifth modified example, and FIG. 5(B) is an enlarged cross-sectional view showing a part of FIG. 5(A). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each drawing, the same or corresponding components are denoted by the same reference numerals, and the description may be omitted. In the specification, the symbol "~" indicating a range of values ​​means that the values ​​before and after the symbol are included as the lower and upper limits.

[0010] An optical element according to one embodiment will be described with reference to Fig. 1(A), Fig. 1(B) and Fig. 1(C). The optical element 2 includes a transparent substrate 10, an anti-reflection film 20 and a light-shielding film 30. The transparent substrate 10 transmits light LB. The anti-reflection film 20 prevents reflection of the light LB. The light-shielding film 30 blocks transmission of the light LB. The light LB is, for example, visible light.

[0011] The transparent substrate 10 has, on its surface 11 onto which light LB is incident, an optically effective surface 12 which is an area on which an antireflection film 20 is formed, and a groove 13 provided along an outer periphery 12a of the optically effective surface 12. The light-shielding film 30 is filled inside the groove 13, contacts the transparent substrate 10 inside the groove 13, and surrounds the outer periphery 20a of the antireflection film 20. Each component will be described below.

[0012] In this embodiment, the transparent substrate 10 is a glass substrate. The glass constituting the glass substrate is, for example, borosilicate glass. Borosilicate glass is easy to process and can suppress the occurrence of scratches or foreign matter. Instead of borosilicate glass, glass that does not contain an alkali component can also be used. Glass that does not contain an alkali component has good adhesion and weather resistance. Examples of glass constituting the glass substrate include borosilicate glass, alkali-containing glass, alkali-free glass, alumina silicate glass, barium-based glass, lanthanum-based glass, titanium-based glass, and fluorine-based glass.

[0013] Glass that absorbs infrared rays can also be used as the glass constituting the glass substrate. Examples of such glass include fluorophosphate glass or phosphate glass with CuO or the like added. This glass has high transmittance for visible light and can sufficiently absorb near infrared rays.

[0014] As long as the transparent substrate 10 is transparent in the wavelength band to be used, the material of the transparent substrate 10 may be any of inorganic materials, organic materials, and mixed materials of inorganic and organic materials. Examples of organic materials include polyester resin, polyolefin resin, norbornene resin, acrylic resin, urethane resin, vinyl chloride resin, fluororesin, polycarbonate resin, polyvinyl butyral resin, and polyvinyl alcohol resin. The material of the transparent substrate 10 may be quartz glass, crystal, lithium niobate, sapphire, or the like.

[0015] Transparent substrate 10 has surface 11, and surface 11 has optically effective surface 12 and groove 13. As shown in Fig. 1(B), groove 13 is provided, for example, spaced apart from the outer periphery of surface 11. In this case, surface 11 further has a non-optically effective surface 14 on the opposite side of groove 13 to optically effective surface 12. Note that, as shown in Fig. 4(A), groove 13 may be provided on the outer periphery of surface 11, and non-optically effective surface 14 may not be present.

[0016] The transparent substrate 10 is, for example, a lens substrate. The optically effective surface 12 has a refractive surface that refracts the light LB. The refractive surface may be a convex curved surface as shown in FIG. 1(B) and FIG. 4(A), or a concave curved surface as shown in FIG. 5(A). The lens may be a spherical lens or an aspheric lens. The lens may be a cylindrical lens, an axially asymmetric (anamorphic) lens, a free-form lens, or the like. The non-optically effective surface 14 may be a convex curved surface as shown in FIG. 1(B), or a flat surface as shown in FIG. 5(A).

[0017] The transparent substrate 10 has a rear surface 15 from which the light LB is emitted. In this embodiment, the transparent substrate 10 has a front surface 11 which is a refractive surface and a rear surface 15 which is a flat surface, but the front surface 11 may have a flat surface and the rear surface 15 may have a refractive surface. Also, both the front surface 11 and the rear surface 15 may have refractive surfaces. The lens may be any of a plano-convex lens, a biconvex lens, a plano-concave lens, a biconcave lens, and a convex-concave lens.

[0018] The transparent substrate 10 has an end surface 16 called an edge. A light-shielding film 30, which will be described later, may be provided on the end surface 16. The light-shielding film 30 suppresses internal reflection of light at the end surface 16 of the transparent substrate 10 and suppresses the generation of stray light. In order to suppress internal reflection of light at the interface between the transparent substrate 10 and the light-shielding film 30, the transparent substrate 10 and the light-shielding film 30 have approximately the same refractive index. The absolute value of the refractive index difference between the transparent substrate and the light-shielding film is, for example, preferably 0.3 or less, more preferably 0.2 or less, and even more preferably 0.1 or less. The respective refractive indices of the transparent substrate and the light-shielding film are measured by reflectance spectroscopy (wavelength 550 nm). For measurement by reflectance spectroscopy, for example, an Olympus microspectrophotometer USPM can be used.

[0019] When viewed from the transmission direction of light LB (the direction of the arrow in FIG. 1(B)), the outer periphery 10a of the transparent substrate 10 is, for example, circular as shown in FIG. 1(A). When viewed from the transmission direction of light LB, the outer periphery 10a of the transparent substrate 10 may have a shape obtained by cutting out a part of a circle as shown in FIG. 3(A), FIG. 3(B), and FIG. 3(C). When viewed from the transmission direction of light LB, the center 10C of the transparent substrate 10 may be determined based on the outer periphery 10a of the transparent substrate 10, and may be, for example, the center of a circle.

[0020] The antireflection film 20 improves the transmittance of the light LB by preventing reflection of the light LB. The antireflection film 20 is, for example, a dielectric multilayer film in which low-refractive index dielectric layers and high-refractive index dielectric layers are alternately laminated. The refractive index of the low-refractive index dielectric layers is preferably 1.6 or less, and more preferably 1.2 to 1.6. The refractive index of the high-refractive index dielectric layers is preferably 1.7 or more, and more preferably 1.7 to 2.5. Here, the refractive index is the refractive index for light with a wavelength of 550 nm.

[0021] The material of the low refractive index dielectric layer is, for example, silica (SiO2), alumina, lanthanum fluoride, magnesium fluoride, or sodium aluminum hexafluoride. The material of the high refractive index dielectric layer is, for example, titania (TiO2), zirconia (ZrO2), tantalum pentoxide (Ta2O5), niobium pentoxide (Nb2O5), silicon nitride (SiN), lanthanum oxide, yttria, zinc oxide, or zinc sulfide. The silicon nitride (SiN) layer can provide high scratch resistance. The SiN layer only needs to contain silicon (Si) and nitrogen (N), and the ratio of elements constituting the SiN layer is not limited to the stoichiometric ratio.

[0022] The dielectric multilayer film is formed by a sputtering method, a vacuum deposition method, an ion beam method, an ion plating method, or a CVD method. Among these, the sputtering method and the ion plating method are superior in that they can improve the adhesion of the dielectric multilayer film to the transparent substrate 10.

[0023] The anti-reflection film 20 is a multi-layer film in this embodiment, but may be a single-layer film. The material of the anti-reflection film 20 is an inorganic material in this embodiment, but may be an organic material. For example, a silicone-based material or a fluoromethacrylate-based material can be used as the organic material. The anti-reflection film 20 can also be formed by a sol-gel method.

[0024] The antireflection film 20 has a thickness of, for example, 100 nm to 1000 nm.

[0025] The light-shielding film 30 is, for example, a light-shielding resin film. The light-shielding resin film contains an inorganic colorant or an organic colorant. The inorganic adhesive is, for example, carbon black or titanium black. The type of resin is not particularly limited, and any of photocurable resin, thermoplastic resin, and thermosetting resin can be used. Here, "light-shielding property" refers to the property of blocking the transmission of light LB mainly by absorbing the light LB.

[0026] The light-shielding film 30 is formed, for example, by applying a coating liquid and drying it. The application and drying may be performed in multiple steps. In addition, before applying the coating liquid, a treatment may be performed using a silane coupling agent or the like to increase the adhesion between the transparent substrate 10 and the light-shielding film 30. The photocurable resin is cured by irradiating it with ultraviolet light. It is possible to form the light-shielding film 30 in a specific area by using a mask to narrow down the area irradiated with ultraviolet light.

[0027] The coating liquid can be applied by a method such as spin coating, bar coating, dip coating, casting, spray coating, bead coating, wire bar coating, blade coating, roller coating, curtain coating, slit die coating, gravure coating, slit reverse coating, microgravure, or comma coating. In addition, brush coating or spraying can be used. For the spraying method, an inkjet or jet dispenser can be used. The drying and curing method is preferably a thermal process, but is not particularly limited as long as the desired light-shielding film 30 can be obtained.

[0028] The coating liquid becomes thinner due to surface tension as it approaches the periphery of the liquid film. Therefore, the thickness of the inner circumference 30a of the light-shielding film 30 is likely to be thin. According to this embodiment, the light-shielding film 30 can be increased in thickness by filling the inside of the groove 13 with the light-shielding film 30. As a result, the transmittance of the light LB can be abruptly changed at the boundary between the anti-reflection film 20 and the light-shielding film 30, and leakage of the light LB to the outside of the optically effective surface 12 can be suppressed. The groove 13 can also mitigate the variation in thickness of the light-shielding film 30 caused by the variation in the amount of coating liquid applied.

[0029] By forming the grooves 13 after forming the anti-reflection film 20, the inner periphery 13a of the grooves 13 can be made to coincide with the outer periphery 20a of the anti-reflection film 20, and the inner periphery 13a of the grooves 13 can be made to coincide with the outer periphery 12a of the optically effective surface 12. Then, the light-shielding film 30 is formed. Inside the grooves 13, the anti-reflection film 20 is not present, and the light-shielding film 30 comes into contact with the transparent substrate 10. Compared to a case in which the anti-reflection film 20 is present between the transparent substrate 10 and the light-shielding film 30, the difference in refractive index can be reduced, and internal reflection can be reduced.

[0030] The light-shielding film 30 is formed so as not to protrude from the inner circumference 13a of the groove 13 onto the optically effective surface 12. The edge of the coating liquid can be stopped at the corner of the inner circumference 13a of the groove 13. That is, a so-called pinning effect is obtained. Due to the pinning effect, the inner circumference 30a of the light-shielding film 30 coincides with the inner circumference 13a of the groove 13 over at least a part (preferably the entirety) of the outer circumference 12a of the optically effective surface 12. Note that a part of the inner circumference 30a of the light-shielding film 30 may protrude from the inner circumference 13a of the groove 13 onto the optically effective surface 12. The protruding amount is preferably 100 μm or less.

[0031] By making the inner periphery 30a of the light-shielding film 30 coincident with the inner periphery 13a of the groove 13, the following effects (A) and (B) can be obtained. (A) As described below, by imparting irregular unevenness to the inner periphery 13a of the groove 13, it is possible to impart irregular unevenness to the inner periphery 30a of the light-shielding film 30. Note that irregular unevenness may or may not be imparted to the outer periphery 13b of the groove 13. (B) Since the light-shielding film 30 does not ride up onto the anti-reflection film 20, it is possible to improve the resistance of the light-shielding film 30 to peeling off. This is because the light-shielding film 30 adheres more easily to the transparent substrate 10 than the anti-reflection film 20.

[0032] The groove 13 may be formed in the middle of the convex curved surface as shown in Fig. 1(B), may be formed at the corner between the convex curved surface and the end face as shown in Fig. 4(A), or may be formed at the corner between the concave curved surface and a flat surface as shown in Fig. 5(A). In the cross sections below, the groove 13 may be recessed with respect to a straight line connecting the inner circumference 13a and the outer circumference 13b as shown in Fig. 1(C), Fig. 4(B), and Fig. 5(B). Here, the cross section is a plane including a straight line L0 that passes through the center 10C of the transparent substrate 10 and extends in the transmission direction of the light LB.

[0033] The depth D of the groove 13 is measured in the above cross section. For example, the measurement sample is embedded in resin and cut, the cut surface is precisely polished, and then the depth D of the groove 13 is measured with an optical microscope. As the optical microscope, for example, a digital microscope VHX manufactured by KEYENCE is used. The depth D of the groove 13 is the maximum depth from the reference line Lref. The reference line Lref is created, for example, by extrapolating the optically effective surface 12. As an extrapolation method, for example, polynomial approximation is used. Note that, if it is difficult to extrapolate the optically effective surface 12, a tangent to the outer periphery 12a of the optically effective surface 12 may be adopted as the reference line Lref. The depth D of the groove 13 is measured in a range of 300 μm from the outer periphery 12a of the optically effective surface 12 along the reference line Lref in a direction perpendicular to the reference line Lref.

[0034] It is preferable that the depth D of the grooves 13 is 0.5 μm or more in at least a part (preferably the entirety) of the outer periphery 12a of the optically effective surface 12. If the depth D of the grooves 13 is 0.5 μm or more, the transmittance of the light LB can be changed suddenly at the boundary between the anti-reflection film 20 and the light-shielding film 30, and leakage of the light LB to the outside of the optically effective surface 12 can be suppressed. The depth D of the grooves 13 is more preferably 1 μm or more. The depth D of the grooves 13 may be 20 μm or less.

[0035] The thickness of the light-shielding film 30 is preferably 0.1 μm to 400 μm at the end face 16 of the transparent substrate 10. If the thickness of the light-shielding film 30 is 0.1 μm or more, sufficient light-shielding properties can be obtained. If the thickness of the light-shielding film 30 is 400 μm or less, shrinkage of the resin during curing can be suppressed. The thickness of the light-shielding film 30 is more preferably 0.2 μm to 100 μm, and further preferably 0.5 μm to 20 μm at the end face 16 of the transparent substrate 10.

[0036] The grooves 13 are provided along the outer periphery 12a of the optically effective surface 12. For example, grinding is used to form the grooves 13. The grinding includes grinding with a grindstone. For the formation of the grooves 13, at least one selected from grinding, cutting, pressing, laser processing, etching, and blasting may be used. The area where the grooves 13 are not formed may be protected by a mask. The mask is, for example, a photomask, which is processed into a desired pattern by exposure and development. As other masking agents, water-soluble PVA (polyvinyl alcohol) polyvinyl acetate resin, water-soluble acrylic resin, etc. may also be used. As masking methods, brush coating, roller coating, spin coating, ribbon coating, spray coating, curtain coating, etc. may be used.

[0037] The grooves 13 are preferably provided over the entire outer periphery 12a of the optically effective surface 12. That is, the grooves 13 are preferably provided over the entire outer periphery 20a of the antireflection coating 20, as shown in Figures 1(A), 3(A) and 3(C). However, the grooves 13 may be provided in a part of the outer periphery 12a of the optically effective surface 12. That is, the grooves 13 may be provided in a part of the outer periphery 20a of the antireflection coating 20, as shown in Figure 3(B).

[0038] Incidentally, according to the present embodiment, as described above, it is possible to suddenly change the transmittance of the light LB at the boundary between the anti-reflection film 20 and the light-shielding film 30, thereby making it possible to prevent the light LB from leaking outside the effective optical surface 12. However, if the transmittance of the light LB is suddenly changed at the boundary between the anti-reflection film 20 and the light-shielding film 30, diffraction of the light LB becomes more likely to occur at the boundary, making it more likely that stray light will occur.

[0039] Therefore, in the optical element 2 of this embodiment, the inner circumference 13a of the groove 13 may have irregular unevenness as shown in FIG. 1(A) etc. when viewed from the transmission direction of the light LB. The irregular unevenness can suppress the diffraction of the light LB. The irregular unevenness is preferably unevenness that satisfies at least one of the following conditions (1) and (2). The irregular unevenness will be described below with reference to FIG. 2(A) and FIG. 2(B).

[0040] (1) As shown in FIG. 2(A), it is preferable that the irregular concaves and convexes have different height differences Δr1 and Δr2 between two adjacent pairs of concaves and convexes of 80% or more when viewed from the transmission direction of light LB shown in FIG. 1(B). Δr1 is the difference (r1a-r1b) between the distance r1a from the center 10C of the transparent substrate 10 to the apex of the concave and the distance r1b from the center 10C of the transparent substrate 10 to the apex of the convex. Δr2 is the difference (r2a-r2b) between the distance r2a from the center 10C of the transparent substrate 10 to the apex of the concave and the distance r2b from the center 10C of the transparent substrate 10 to the apex of the convex. The apex of the convex is the point where the distance from the center 10C of the transparent substrate 10 to the inner circumference 13a of the groove 13 is minimal. The apex of the concave is the point where the distance from the center 10C of the transparent substrate 10 to the inner circumference 13a of the groove 13 is maximal. The following method may be used to measure r1a, r1b, r2a, and r2b: A length measuring microscope (e.g., STM-7 manufactured by OLYMPUS) is used to determine the coordinates of the center 10C of the transparent substrate 10. The optical element 2 is placed on a stage that can rotate around the coordinates of the center 10C, and the change in the distance from the center 10C to the inner circumference 13a of the groove 13 is read while rotating the stage, and the maximum and minimum values ​​are repeatedly measured.

[0041] More preferably, Δr1 and Δr2 are different between 90% or more of two adjacent pairs of concaves and convexes when viewed from the transmission direction of light LB. Even more preferably, Δr1 and Δr2 are different between all (100%) of two adjacent pairs of concaves and convexes when viewed from the transmission direction of light LB. |Δr1-Δr2| is preferably 0.5 μm or more, more preferably 1 μm or more. The height difference of the concaves and convexes is the height difference between the apex of the adjacent concaves and the apex of the convexities. Note that the pair of adjacent concaves and convexities may be a pair of a concave and a convexity in a clockwise direction based on the concave when the transparent substrate 10 is viewed from the transmission direction of light LB. |Δr1-Δr2| is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 20 μm or less.

[0042] (2) As shown in FIG. 2(B), in the irregular asperities, when viewed from the transmission direction of the light LB shown in FIG. 1(B), the distance d1 between the vertices of two adjacent convexities is different from the distance d2 between the other two adjacent convexities in 80% or more of three adjacent convexities. More preferably, when viewed from the transmission direction of the light LB, d1 and d2 are different in 90% or more of three adjacent convexities. Even more preferably, when viewed from the transmission direction of the light LB, d1 and d2 are different in all (100%) of three adjacent convexities. |d1-d2| is preferably 1 μm or more, more preferably 2 μm or more. |d1-d2| is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less.

[0043] Although the optical element according to the present disclosure has been described above, the present disclosure is not limited to the above-mentioned embodiments. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope of the claims. These naturally fall within the technical scope of the present disclosure. [Explanation of symbols]

[0044] 2. Optical elements 10 Transparent base material 11 Surface 12 Optically effective surface 13 Groove 14 Non-optically effective surface 20 Anti-reflection coating 30 shading film LB Light

Claims

1. A transparent substrate that transmits light; an anti-reflection film that prevents reflection of the light; a light-shielding film that blocks the transmission of the light; Equipped with the transparent base material has, on a surface onto which the light is incident, an optically effective surface which is a region on which the antireflection film is formed, and a groove provided along an outer periphery of the optically effective surface; The optical element, wherein the light-shielding film is filled inside the groove, contacts the transparent base material inside the groove, and surrounds an outer periphery of the anti-reflection film.

2. The optical element according to claim 1 , wherein the groove is provided over the entire outer periphery of the optically effective surface.

3. The optical element according to claim 1 , wherein an inner periphery of the groove coincides with an inner periphery of the light-shielding film in at least a part of an outer periphery of the optically effective surface.

4. The optical element according to claim 3 , wherein, when viewed from the light transmission direction, the inner circumference of the groove has irregular concaves and convexes, and the irregular concaves and convexes have different height differences in 80% or more of two adjacent pairs of concaves and convexes.

5. The optical element described in claim 3, wherein, when viewed from the direction of light transmission, the inner circumference of the groove has irregular concaves and convexes, and in 80% or more of three adjacent convexes of the irregular concaves and convexes, the distance between the vertices of two adjacent convexes is different from the distance between another two adjacent vertices.

6. 3. The optical element according to claim 1, wherein the groove has a depth of 0.5 μm or more in at least a part of the outer periphery of the optically effective surface.

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