Optical element

Abstract

This optical element, when viewed in a light transmission direction, comprises a transmission region through which a portion of light passes, and a light blocking region that blocks another portion of the light. The optical element comprises: a transparent glass body; and a light blocking film that is made of glass and forms the light blocking region inside the transparent glass body. The greater the distance from the boundary line between the light blocking region and the transmission region as viewed from the light transmission direction, the greater the average extinction coefficient of the light blocking film in the light transmission direction.

Description

Optical elements

[0001] The present disclosure relates to optical elements.

[0002] The optical unit described in Patent Document 1 includes a transparent first substrate, a transparent second substrate, and a diaphragm formed of a black resin that fills the periphery of a convex portion between the first substrate and the second substrate. The first substrate and the second substrate are transparent glass substrates or transparent resin substrates.

[0003] International Publication No. 2021 / 176704

[0004] In Patent Document 1, an optical element is constructed using a transparent resin substrate and black resin, or a transparent glass substrate and black resin. If the substrate is a resin substrate, the optical properties change significantly with temperature changes. Therefore, it is preferable that the substrate is a glass substrate. However, when an optical element is constructed using a glass substrate and black resin, the absolute value of the difference in average linear expansion coefficient between the glass and the resin is large, and the durability of the optical element against temperature changes is low.

[0005] One aspect of the present disclosure provides a technique that improves the durability of an optical element against temperature changes, while simultaneously reducing the maximum thickness of a light-shielding film and suppressing the generation of stray light.

[0006] An optical element according to one aspect of the present disclosure includes, as viewed from a light transmission direction, a transmission region that transmits a portion of the light and a light-shielding region that blocks another portion of the light. The optical element includes a transparent glass body and a glass light-shielding film that forms the light-shielding region inside the transparent glass body. The greater the distance from the boundary between the light-shielding region and the transmission region as viewed from the light transmission direction, the greater the average extinction coefficient of the light-shielding film in the light transmission direction.

[0007] According to one aspect of the present disclosure, since a glass light-shielding film is used, the absolute value of the difference in the average linear expansion coefficient between the transparent glass body and the light-shielding film can be reduced, thereby improving the durability of the optical element against temperature changes. Furthermore, according to one aspect of the present disclosure, since the average extinction coefficient of the light-shielding film increases as the distance from the boundary line increases, it is possible to reduce the maximum thickness of the light-shielding film while suppressing the generation of stray light.

[0008] FIG. 1A is a plan view of an optical element according to an embodiment, and FIG. 1B is a cross-sectional view of the optical element according to an embodiment. FIG. 2A is a diagram showing an example of the relationship between the stress generated at the boundary between the transmissive region and the light-blocking region and the difference in average linear expansion coefficient, and FIG. 2B is a diagram showing another example. FIG. 3 is a flowchart showing a method for manufacturing an optical element according to an embodiment. FIG. 4A is a cross-sectional view showing an example of S101, FIG. 4B is a cross-sectional view showing an example of S102, FIG. 4C is a cross-sectional view showing an example of S103, FIG. 4D is a cross-sectional view showing an example of S104, and FIG. 4E is a cross-sectional view showing an example of S105. FIG. 5 is a flowchart showing a modified example of the method for manufacturing an optical element. FIG. 6A is a cross-sectional view showing an example of S201, FIG. 6B is a cross-sectional view showing an example of S202, FIG. 6C is a cross-sectional view showing an example of S203, and FIG. 6D is a cross-sectional view showing an example of S204. Fig. 7(A) is a plan view showing a first modified example of the shape of the light-shielding region, Fig. 7(B) is a plan view showing a second modified example of the shape of the light-shielding region, Fig. 7(C) is a plan view showing a third modified example of the shape of the light-shielding region, and Fig. 7(D) is a plan view showing a fourth modified example of the shape of the light-shielding region. Fig. 8(A) is a cross-sectional view showing a first modified example of the cross-sectional shape of the light-shielding film, Fig. 8(B) is a cross-sectional view showing a second modified example of the cross-sectional shape of the light-shielding film, and Fig. 8(C) is a cross-sectional view showing a third modified example of the cross-sectional shape of the light-shielding film. Fig. 9(A) is a cross-sectional view showing a fourth modified example of the cross-sectional shape of the light-shielding film, Fig. 9(B) is a cross-sectional view showing a fifth modified example of the cross-sectional shape of the light-shielding film, and Fig. 9(C) is a cross-sectional view showing a sixth modified example of the cross-sectional shape of the light-shielding film. 10(A) is a diagram showing a first example of arrangement of a plurality of layers constituting a light-shielding film, FIG. 10(B) is a diagram showing a second example of arrangement of a plurality of layers constituting a light-shielding film, FIG. 10(C) is a diagram showing a third example of arrangement of a plurality of layers constituting a light-shielding film, and FIG. 10(D) is a diagram showing a fourth example of arrangement of a plurality of layers constituting a light-shielding film. FIG. 11 is a diagram showing an example of a method for calculating the average extinction coefficient of a light-shielding film. FIG. 12 is a diagram showing an example of a method for calculating the average extinction coefficient of a light-shielding film. ３１ Instead of R １３ 13 is a diagram illustrating an example of a method for calculating R １２14 is a diagram showing an example of a method for calculating α1 shown in FIG. 11 . FIG. 15 is a diagram showing an example of a method for calculating the extinction coefficient of any one of a plurality of layers constituting a light-shielding film. FIG. 16 is a diagram showing a first distribution of the extinction coefficient of the light-shielding film and T １０ and ΔI Ｓ 17 is a diagram showing the relationship between the second distribution of the extinction coefficient of the light-shielding film and T １０ and ΔI Ｓ FIG. 18 is a graph showing the relationship between the third distribution of the extinction coefficient of the light-shielding film and T １０ and ΔI Ｓ 19 is a diagram showing the relationship between the fourth distribution of the extinction coefficient of the light-shielding film and T １０ and ΔI Ｓ FIG. 20 is a graph showing the relationship between ΔI Ｓ 21A is a diagram showing an example of a tapered portion in which Δt / ΔL increases as L increases, and FIG. 21B is a diagram showing an example of a tapered portion in which Δt / ΔL decreases as L increases. FIG. 22 is a flowchart showing an example of a manufacturing method for an optical element in which a light-shielding film is formed using a plurality of glass materials with different extinction coefficients. FIG. 23A is a cross-sectional view showing a first example of S301, FIG. 23B is a cross-sectional view showing a first example of S302 for the first time, FIG. 23C is a cross-sectional view showing a first example of S302 for the second time, FIG. 23D is a cross-sectional view showing a first example of S304, and FIG. 23E is a cross-sectional view showing a first example of S307. Fig. 24(A) is a cross-sectional view showing a second example of S301, Fig. 24(B) is a cross-sectional view showing a second example of S302 for the first time, Fig. 24(C) is a cross-sectional view showing a second example of S302 for the second time, Fig. 24(D) is a cross-sectional view showing a second example of S304, and Fig. 24(E) is a cross-sectional view showing a second example of S307. Fig. 25(A) is a cross-sectional view showing a third example of S301, Fig. 25(B) is a cross-sectional view showing a third example of S302 for the first time, Fig. 25(C) is a cross-sectional view showing a third example of S302 for the second time, Fig. 25(D) is a cross-sectional view showing a third example of S302 for the third time, Fig. 25(E) is a cross-sectional view showing a third example of S304, and Fig. 25(F) is a cross-sectional view showing a third example of S307.

[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 their description may be omitted. In the specification, the symbol "to" indicating a range of values ​​means that the values ​​before and after it are included as the lower and upper limits.

[0010] An optical element 10 according to one embodiment will be described with reference to FIG. 1. In FIG. 1B, the arrow direction indicates the transmission direction of light LB. Note that the transmission direction of light LB may be opposite to the direction of the arrow. In this embodiment, the transmission direction of light LB is perpendicular to the main surface of the glass substrate, but may also be oblique to the glass substrate. In this embodiment, light LB is visible light (light with a wavelength of 400 nm to 800 nm), but may also be ultraviolet light or infrared light. The optical element 10 is used, for example, in the optical system of an imaging device.

[0011] As shown in Fig. 1A, when viewed from the transmission direction of light LB, the optical element 10 includes a transmission region A1 that transmits a portion of the light LB and a light-shielding region A2 that blocks another portion of the light LB, thereby adjusting the shape of the light LB. In Fig. 1A, A3 is the boundary between the transmission region A1 and the light-shielding region A2 when viewed from the transmission direction of light LB. The transmission direction of light LB may be a direction (first axis direction) perpendicular to two parallel planes of a constant-thickness portion 17 (described later). Note that the transmission direction of light LB coincides with the first axis direction, but may also be oblique to the first axis direction.

[0012] 1B, optical element 10 includes transparent glass body 11 and light-shielding film 15. Light-shielding film 15 forms light-shielding region A2 inside transparent glass body 11. Light-shielding region A2 is an area where light-shielding film 15 is provided. Transparent glass body 11 is provided on both the upstream and downstream sides of light-shielding film 15 in the transmission direction of light LB.

[0013] In this embodiment, the light-shielding film 15 is made of glass. If the light-shielding film 15 is made of glass, the absolute value of the difference Δα between the average linear expansion coefficients of the transparent glass body 11 and the light-shielding film 15 can be reduced, thereby improving the durability of the optical element 10 against temperature changes. Δα is the value obtained by subtracting the average linear expansion coefficient of the transparent glass body 11 from the average linear expansion coefficient of the light-shielding film 15.

[0014] The difference Δα between the average linear expansion coefficients of the transparent glass body 11 and the light-shielding film 15 is measured, for example, in accordance with JIS R3102:1995. The measurement temperature range is, for example, -40°C to 85°C. FIG. 2A shows an example of the relationship between the stress generated at the boundary A3 between the transmission region A1 and the light-shielding region A2 and the difference Δα between the average linear expansion coefficients of the transparent glass body 11 and the light-shielding film 15 when the temperature of the optical element 10 is 85°C. FIG. 2B shows an example of the relationship between the stress generated at the boundary A3 between the transmission region A1 and the light-shielding region A2 and the difference Δα between the average linear expansion coefficients of the transparent glass body 11 and the light-shielding film 15 when the temperature of the optical element 10 is -40°C. Note that although the composition of the light-shielding film 15 is constant in FIGS. 2A and 2B, the composition of the light-shielding film 15 may vary, as described below. In both the former and latter cases, the average linear expansion coefficient of the light-shielding film 15 refers to the average linear expansion coefficient of the entire light-shielding film 15.

[0015] The analysis conditions for Fig. 2(A) and Fig. 2(B) were as follows: Thermal stress analysis software: Solidworks Simulation manufactured by Dassault Systemes SolidWorks Corporation, Average linear expansion coefficient of transparent glass B1: 7.2 × 10 －６ / °C, Young's modulus of transparent glass B1: 70 GPa, Average linear expansion coefficient of black glass B2: 0.5 × 10 －６ / ℃~100×10 －６ / ° C., Young's modulus of black glass B2: 70 GPa, Average linear expansion coefficient of black resin B3: 100 × 10 －６ / °C, Young's modulus of black resin B3: 3 GPa.

[0016] In FIGS. 2A and 2B, the black circles indicate the case where the transparent glass body 11 is made of the above-mentioned transparent glass B1 and the light-shielding film 15 is made of the above-mentioned black glass B2, that is, when Δα is −6.7×10 －６ / ℃~92.8×10 －６ / °C. In addition, in Figures 2(A) and 2(B), the white circles indicate the stress generated when the transparent glass body 11 is made of the transparent glass B1 and the light-shielding film 15 is made of the black resin B3, that is, when Δα is 92.8 × 10 －６ / °C.

[0017] When the transparent glass body 11 was made of the transparent glass B1 and the light-shielding film 15 was made of the black resin B3 (see the open circles in FIG. 2A), the transparent glass body 11 broke when the temperature of the optical element 10 was increased from 20° C. to 85° C. On the other hand, when the transparent glass body 11 was made of the transparent glass B1 and the light-shielding film 15 was made of the black glass B2 (average linear expansion coefficient: 8.6×10 －６ / °C), the transparent glass body 11 did not break even when the temperature of the optical element 10 was raised from 20°C to 85°C. Furthermore, when the transparent glass body 11 was made of the transparent glass B1 and the light-shielding film 15 was made of the black resin B3 (see the open circles in Figure 2(B)), a heat cycle test was conducted in which the temperature was repeatedly raised and lowered between -40°C and 85°C, and the transparent glass body 11 broke. On the other hand, when the transparent glass body 11 was made of the transparent glass B1 and the light-shielding film 15 was made of the black glass B2 (average linear expansion coefficient: 8.6 x 10 －６ / °C), the transparent glass body 11 did not break even when subjected to the heat cycle test.

[0018] 2(A) and 2(B), the dashed lines indicate a stress of 50 MPa. From FIGS. 2(A) and 2(B) and the results of the heat cycle test described above, it is believed that breakage of the transparent glass body 11 can be suppressed if the stress generated at the boundary A3 between the transmission region A1 and the light-shielding region A2 is 50 MPa or less. Therefore, the absolute value of the difference Δα between the average linear expansion coefficients of the transparent glass body 11 and the light-shielding film 15 is preferably 10×10 －６ / °C or less, more preferably 5 × 10 －６ / °C or less, and more preferably 1 × 10 －６ / °C or less. The smaller the absolute value of Δα, the better. －６ / °C or higher is sufficient.

[0019] 1(B), the transparent glass body 11 may have a first transparent glass layer 12 and a second transparent glass layer 13. The first transparent glass layer 12 and the second transparent glass layer 13 are disposed in the transmission direction of light LB with a light-shielding film 15 sandwiched therebetween, and are continuously adjacent to each other in the transmissive region A1. In the transmissive region A1, there may be nothing between the first transparent glass layer 12 and the second transparent glass layer 13. The first transparent glass layer 12 and the second transparent glass layer 13 are bonded together.

[0020] The first transparent glass layer 12 and the second transparent glass layer 13 are each a glass substrate. The glass of the glass substrate is not particularly limited, but may be, for example, soda-lime glass, alkali-free glass, chemically strengthened glass, borosilicate glass, or lanthanum borate glass. The first transparent glass layer 12 and the second transparent glass layer 13 may be made of different glasses, but from the viewpoint of durability of the optical element 10 against temperature changes, they are preferably made of the same glass.

[0021] The first transparent glass layer 12 and the second transparent glass layer 13 have bonding surfaces 12a and 13a facing each other, respectively. The bonding surfaces 12a and 13a are preferably flat. The flat bonding surfaces 12a and 13a are provided in the transmissive region A1. If the bonding surfaces 12a and 13a are flat, the first transparent glass layer 12 and the second transparent glass layer 13 can be uniformly pressed against each other and bonded together in the transmissive region A1.

[0022] The first transparent glass layer 12 and the second transparent glass layer 13 have opposite surfaces 12b and 13b facing opposite to the bonding surfaces 12a and 13a. In this embodiment, both of the opposite surfaces 12b and 13b have flat surfaces, but at least one of them may have a curved surface. The curved surface may constitute a lens surface, and the optical element 10 may function as a lens. The lens may be any of a plano-convex lens, a biconvex lens, a plano-concave lens, and a biconcave lens.

[0023] The first transparent glass layer 12 and the second transparent glass layer 13 may have a recess 14 on at least one of the bonding surfaces 12 a, 13 a. In this embodiment, the recess 14 is formed on the bonding surface 12 a of the first transparent glass layer 12, but it may also be formed on the bonding surface 13 a of the second transparent glass layer 13, or on both bonding surfaces 12 a, 13 a. A light-shielding film 15 is embedded in the recess 14.

[0024] The light-shielding film 15 contains an amorphous inorganic oxide, i.e., glass, as a main component. The glass content in the light-shielding film 15 is 50% by volume or more. The light-shielding film 15 may be partially crystallized. The light-shielding film 15 is made of so-called black glass. The black glass may be a common type. In this embodiment, the black glass is a block obtained by molding black molten glass. The black glass may also be a sintered body obtained by firing a paste containing transparent glass powder and a black pigment. The sintered body contains the black pigment dispersed in the transparent glass. In other words, although the black glass is black in this embodiment, the glass itself may be transparent.

[0025] The light-shielding film 15 is made of glass, such as SiO ２ In addition to the glass containing Bi as the main component, the glass may also contain Bismuth-based glass or vanadium-based glass. ２ O ３ The vanadium-based glass contains V ２ O ５ Compared with bismuth-based glass and vanadium-based glass, ２ Glass containing this as its main component tends to have a low refractive index. In order to suppress reflection at the interface between the transparent glass body 11 and the light-shielding film 15, which will be described later, it is advisable to select a material for the light-shielding film 15 that has a refractive index close to that of the transparent glass body 11. In this specification, the term "main component" refers to the component that is contained in the largest amount among the components, and is preferably present in an amount of 50 wt % or more.

[0026] Table 1 shows the relationship between the refractive index difference Δn (Δn = |n1 - n2|) between the transparent glass body 11 and the light-shielding film 15, the extinction coefficient k of the light-shielding film 15, and the reflectance R (%) of light LB at the interface between the transparent glass body 11 and the light-shielding film 15. Note that although the composition of the light-shielding film 15 is constant in Table 1, the composition of the light-shielding film 15 may vary, as will be described later. In the latter case, it is preferable that the reflectance R of light LB at at least a portion of the interface between the transparent glass body 11 and the light-shielding film 15 be within a desired range.

[0027]

[0028] The reflectance R was calculated using the following formula (1): (1) R = ((n1 - n2) ２ +k ２ ) / ((n1+n2) ２ +k ２ ) The reflectance R varies mainly depending on the refractive index difference Δn and the extinction coefficient k. Note that n1 is the refractive index of the transparent glass body 11, and n2 is the refractive index of the light-shielding film 15. In Table 1, n1 is 1.52 (constant). n1, n2, and k are measured at the same wavelength as the light LB. The refractive index n1 of the transparent glass body 11 is measured, for example, by the V-block method. The refractive index n2 and extinction coefficient k of the light-shielding film 15 are measured, for example, by an ellipsometer.

[0029] The extinction coefficient k of the light-shielding film 15 can also be calculated by exposing the light-shielding film 15 by polishing or the like, measuring the thickness t of the light-shielding film 15 and the transmittance of the light-shielding film 15, and using the following formula (2). The thickness t of the exposed light-shielding film 15 is measured with, for example, a micrometer. The transmittance of the light-shielding film 15 is measured with, for example, a spectrophotometer. (2) k = α × λ / 4π In formula (2), α is the absorption coefficient of the light-shielding film 15, and λ is the wavelength of light used to measure the transmittance. The absorption coefficient α is calculated by the following formula (3). (3) I = I ０ ×exp(-α×t) In equation (3), I ０ is the intensity of light immediately after it enters the light-shielding film 15 from the air, and I is the intensity of light immediately before it is emitted from the light-shielding film 15 into the air. (I / I ０ ) is the internal transmittance of the light-shielding film 15. (I / I ０ ) is calculated by the following formula (4): (4) I / I ０=exp(-α×t) Internal transmittance (I / I ０ ) is the transmittance excluding losses due to surface reflection.

[0030] The reflectance R of the light LB at the interface between the transparent glass body 11 and the light-shielding film 15 may be measured, for example, by a microspectrometer.

[0031] It is preferable that the refractive index difference Δn is 0.10 or less and the extinction coefficient k is 0.05 or less. If the refractive index difference Δn is 0.10 or less and the extinction coefficient k is 0.05 or less, the reflectance R is 0.15% or less. If the reflectance R is 0.15% or less, the generation of stray light can be suppressed. The reflectance R is preferably 0.15% or less, and more preferably 0.10% or less.

[0032] The smaller the refractive index difference Δn, the smaller the reflectance R. The refractive index difference Δn is preferably 0.10 or less, more preferably 0.08 or less, and even more preferably 0.05 or less. Furthermore, the smaller the extinction coefficient k, the smaller the reflectance R. The extinction coefficient k is preferably 0.05 or less, and more preferably 0.01 or less. However, if the extinction coefficient k is too small, sufficient light blocking properties cannot be obtained. The extinction coefficient k is preferably 0.0001 or more.

[0033] The reflectance R also depends on the surface roughness Ra of the interface between the transparent glass body 11 and the light-shielding film 15. The surface roughness Ra is the arithmetic mean roughness as defined in JIS B0601:2013. The larger the surface roughness Ra, the smaller the reflectance R. If the surface roughness Ra is 100 nm or more, the reflectance R can be reduced to half or less compared to when the surface roughness Ra is 0 nm.

[0034] In Table 1, the surface roughness Ra is 0 nm. From the viewpoint of reflectance R, the surface roughness Ra is preferably 100 nm or more, and more preferably 120 nm or more. The surface roughness Ra is preferably 6400 nm or less.

[0035] When the black glass is a block obtained by molding black molten glass, that is, when the glass itself is colored black, the black glass contains, as a coloring component, at least one element selected from, for example, Fe, Cr, Mn, Co, Ni, Ti, V, and Cu.

[0036] Black glass is glass that is colored black by, for example, SiO ２ 50% to 75% Al ２ O ３ 0% to 20%, Na ２ O: 0% to 20%, K: ２ O 0% to 20%, MgO 0% to 15%, CaO 0% to 20%, B ２ O ３ 10% to 20%, ΣRO (R is Mg, Ca, Sr, Ba, Zn) 0% to 20%, ZrO ２ 0% to 5%, Fe ２ O ３ 1.0% to 14%, CoO or Co ３ O ４ 0% to 2%, SO ３ ΣRO is the total content of MgO, CaO, SrO, BaO and ZnO.

[0037] When coloring the glass itself black, V is used within the range that does not impair the coloring. ２ O ５ , CrO, MnO, CuO, MoO ３ and CeO ２ It may contain at least one selected from the following. ２ O ５ , CrO, MnO, CuO, MoO ３ , CeO ２ The total content of is preferably 0% to 3%, more preferably 0% to 1%, expressed in mass % on the oxide basis.

[0038] When coloring the glass itself black, black glass can be made by using SO as a fining agent within the range that does not impair the coloring. ３ , Sb ２ O ３ , SnO, Cl, and F. ３ , Sb ２ O ３ The total content of SnO, Cl and F is preferably 0% to 1%, and more preferably 0% to 0.5%.

[0039] When the black glass is a sintered body obtained by firing a paste containing a transparent glass powder and a black pigment, the black pigment contains, for example, a metal or a metal compound containing at least one element selected from Fe, Cr, Mn, Co, Ni, Ti, and Cu. The metal compound is, for example, an oxide.

[0040] The paste may contain additives other than the transparent glass powder (glass frit) and the black pigment, such as ceramic powder.

[0041] The firing temperature of the paste is set to a temperature equal to or higher than the softening point of the glass that constitutes the paste. The glass that constitutes the paste is the same as the glass that constitutes the light-shielding film 15. Therefore, it is preferable that the softening point of the glass that constitutes the light-shielding film 15 is equal to or lower than the yield point of the glass that constitutes the transparent glass body 11. This can prevent unintended deformation of the transparent glass body 11 during firing of the paste. The softening point of the glass is measured, for example, with a differential thermal analyzer. Note that, when the composition of the light-shielding film 15 changes as described below, the softening point of the light-shielding film 15 means the average softening point of the entire light-shielding film 15.

[0042] The light-shielding film 15 has a thickness t in the transmission direction of the light LB of a maximum value t ｍａｘ and the ratio of the width w in the direction perpendicular to the transmission direction of the light LB (t ｍａｘ / w) is preferably 1 to 1 / 500, more preferably 1 / 2 to 1 / 500, and even more preferably 1 / 4 to 1 / 250.

[0043] The light-shielding film 15 may have a tapered portion 16 at a boundary line A3 between the light-shielding region A2 and the transmission region A1. When viewed from the transmission direction of the light LB, the thickness t of the tapered portion 16 in the transmission direction of the light LB increases as the distance from the boundary line A3 increases. The tapered portion 16 is in contact with the boundary line A3. The tapered portion 16 is provided on at least a part of the boundary line A3, and preferably on the entire boundary line A3.

[0044] By providing the tapered portion 16, the internal transmittance of the light-shielding film 15 continuously increases as the distance from the boundary line A3 increases. ０) is calculated by the following formula (4) as described above. ０ = exp(-α×t) By providing the tapered portion 16, t can be changed continuously, and I / I ０ As a result, the diffraction of the light LB can be suppressed, and the occurrence of stray light can be suppressed. This will be described in detail later.

[0045] The light-shielding film 15 has a constant-thickness portion 17, whose thickness t in the transmission direction of the light LB is constant, in an area farther from the boundary line A3 than the tapered portion 16. The constant-thickness portion 17 is formed continuously with the tapered portion 16. The thickness t of the constant-thickness portion 17 is the maximum value t of the thickness t of the tapered portion 16. ｍａｘ The light-shielding film 15 does not necessarily have to have the constant-thickness portion 17, and may have only the tapered portion 16.

[0046] A method for manufacturing an optical element 10 according to one embodiment will be described with reference to Figures 3 and 4. As shown in Figure 3, the manufacturing method includes, for example, steps S101 to S105. Note that the manufacturing method does not necessarily include all of steps S101 to S105. For example, if optical elements 10 are manufactured one by one, step S105 may be omitted. Furthermore, the manufacturing method may include steps other than steps S101 to S105.

[0047] Step S101 includes preparing a first transparent glass layer 12, as shown in FIG. 4A, for example. The first transparent glass layer 12 has recesses 14 on its joining surface 12a. The recesses 14 are formed, for example, in a square lattice pattern. The groove width of the recesses 14 is, for example, 1 mm to 5 mm. The maximum depth of the recesses 14 is set to a value equal to the maximum value t of the thickness t of the light-shielding film 15. ｍａｘ When the depth of the recess 14 changes in steps S103 and S104 described later, the maximum value of the thickness t of the light-shielding film 15 after the completion of step S104 is t ｍａｘ The depth of the recess 14 is determined so that t ｍａｘ is set according to the extinction coefficient of the light-shielding film 15. When the extinction coefficient of the light-shielding film 15 is about 0.01, the maximum value t of the thickness t of the light-shielding film 15 is ｍａｘis, for example, 20 μm to 50 μm, and when the extinction coefficient of the light-shielding film 15 is about 0.001, the maximum value t of the thickness t of the light-shielding film 15 is ｍａｘ is, for example, 200 μm to 500 μm, and when the extinction coefficient of the light-shielding film 15 is about 0.0003, the maximum value t of the thickness t of the light-shielding film 15 is ｍａｘ is, for example, 800 μm to 1300 μm. In this embodiment, the recess 14 is formed on the joining surface 12 a of the first transparent glass layer 12, but it may also be formed on the joining surface 13 a of the second transparent glass layer 13, or on both joining surfaces 12 a, 13 a. Glass processing includes, for example, wet etching, mechanical processing, and thermoforming.

[0048] Step S102 includes shaping the light-shielding film 15, as shown in FIG. 4B , for example. When the light-shielding film 15 is a block obtained by shaping black molten glass, the light-shielding film 15 is softened by heating and pressed against the joining surface 12a of the first transparent glass layer 12, and embedded in the recesses 14. The heating temperature is set to a temperature equal to or higher than the glass transition point of the glass that constitutes the light-shielding film 15. Therefore, it is preferable that the glass transition point of the glass that constitutes the light-shielding film 15 is equal to or lower than the glass transition point of the glass of the first transparent glass layer 12. In step S102, unintended deformation of the first transparent glass layer 12 can be suppressed.

[0049] Step S103 includes exposing the bonding surface 12 a of the first transparent glass layer 12, as shown in FIG. 4C . The exposing of the bonding surface 12 a includes at least one of lapping and polishing. The exposing of the bonding surface 12 a may further include wet etching. By exposing the bonding surface 12 a, the light-shielding film 15 is formed in, for example, a square lattice pattern.

[0050] 4(D), for example, step S104 includes bonding the first transparent glass layer 12 and the second transparent glass layer 13 together, and bonding the light-shielding film 15 and the second transparent glass layer 13. The first transparent glass layer 12 and the second transparent glass layer 13 are bonded together by hydrogen bonds between OH groups imparted to the glass surfaces, covalent bonds formed by dehydration condensation after the formation of hydrogen bonds, or van der Waals forces between the glass surfaces.

[0051] For example, step S104 includes, in this order, modifying the surfaces of the glass substrates by plasma treatment, adding OH groups to the modified surfaces, stacking the glass substrates together with the surfaces to which OH groups have been added facing each other, and heat-treating the stacked glass substrates. The addition of OH groups is performed by supplying pure water or water vapor.

[0052] Alternatively, step S104 may include, in this order, treating the surfaces of the glass substrates with an alkaline detergent, cleaning the surfaces treated with the alkaline detergent with pure water, stacking the glass substrates together with the surfaces cleaned with pure water facing each other, and heat-treating the stacked glass substrates. Here, treating the surfaces of the glass substrates with an alkaline detergent can be omitted.

[0053] Step S104 may include welding the glass substrates together. The welding temperature is set to a temperature equal to or higher than the glass transition point of the glass substrates. During welding, the glass substrates may be pressed together.

[0054] Step S105 includes cutting the bonded body obtained in step S104 into a plurality of optical elements 10, as shown in Fig. 4E, for example. Cutting includes, for example, blade processing or laser processing.

[0055] A modified example of the method for manufacturing the optical element 10 will be described with reference to Figures 5 and 6. As shown in Figure 5, the manufacturing method includes, for example, steps S201 to S204. Note that the manufacturing method does not necessarily include all of steps S201 to S204. For example, if the optical elements 10 are manufactured one by one, step S204 may be omitted. Furthermore, the manufacturing method may include steps other than steps S201 to S204.

[0056] 6A, the light-shielding film 15 is processed into, for example, a square lattice shape. The processing of the light-shielding film 15 includes, for example, wet etching, mechanical processing, and thermoforming.

[0057] 6B, step S202 includes laminating a first transparent glass layer 12, a light-shielding film 15, and a second transparent glass layer 13 in this order. The first transparent glass layer 12 and the second transparent glass layer 13 are disposed with the light-shielding film 15 sandwiched between them.

[0058] Step S203 includes thermoforming the laminate obtained in step S202, as shown in FIG. 6C , for example. The first transparent glass layer 12 and the second transparent glass layer 13 are thermally deformed and come into contact with each other. At this time, the light-shielding film 15 does not need to be thermally deformed. The glass transition point of the glass constituting the light-shielding film 15 is preferably higher than the glass transition points of the first transparent glass layer 12 and the second transparent glass layer 13. Note that the thermal deformation of the first transparent glass layer 12 and the second transparent glass layer 13 may result in unevenness being formed on the bonding surface between the first transparent glass layer 12 and the second transparent glass layer 13.

[0059] Step S204 includes cutting the bonded body obtained in step S203 into a plurality of optical elements 10, as shown in Fig. 6D, for example. Cutting includes, for example, blade processing or laser processing.

[0060] First to fourth modified examples of the shape of the light-shielding region A2 as viewed from the transmission direction of light LB will be described with reference to FIG. 7 . In the above embodiment, the shape of the light-shielding region A2 as viewed from the transmission direction of light LB is a rectangular frame as shown in FIG. 1A , but is not limited to a rectangular frame. The shape of the light-shielding region A2 may be a shape formed by two parallel rectangles spaced apart as shown in FIG. 7A , a U-shape as shown in FIG. 7B , a ring shape as shown in FIG. 7C , or a circle as shown in FIG. 7D . The light-shielding region A2 may be disposed outside the transmitting region A1 as shown in FIGS. 1A , 7A , 7B, and 7C , or may be disposed inside the transmitting region A1 as shown in FIG. 7D .

[0061] 8 and 9, first to sixth modified examples of the cross-sectional shape of the light-shielding film 15 taken perpendicular to the boundary line A3 as viewed from the transmission direction of the light LB will be described. In the above embodiment, the cross-sectional shape of the light-shielding film 15 is a rectangular shape with one corner cut out by a quadrant as shown in FIG. 1B, but is not limited to this shape. The cross-sectional shape of the light-shielding film 15 may be a rectangular shape with one corner deformed into an S-shape as shown in FIG. 8A, a rectangular shape with two corners each cut out by a quadrant as shown in FIG. 8B, or a rectangular shape with two corners each deformed into an S-shape as shown in FIG. 8C.

[0062] As shown in Figures 1(B), 8(A), 8(B), and 8(C), the light-shielding film 15 may have a portion with a constant thickness. Furthermore, as shown in Figures 9(A) and 9(B), the light-shielding film 15 may not have a portion with a constant thickness. Furthermore, as shown in Figure 9(C), a plurality of light-shielding films 15 may be provided at intervals in the transmission direction of light LB.

[0063] Incidentally, when the composition of the light-shielding film 15 is constant, the extinction coefficient of the light-shielding film 15 is constant. In this case, if the thickness t of the light-shielding film 15 is constant, the internal transmittance of the light-shielding film 15 changes discontinuously at the boundary line A3 between the transmitting region A1 and the light-shielding region A2, which makes it easy for diffraction of the light LB to occur. When the composition of the light-shielding film 15 is constant, the provision of the tapered portion 16 can suppress the diffraction of the light LB.

[0064] However, when the composition of the light-shielding film 15 is constant, if the extinction coefficient of the light-shielding film 15 is small, the maximum value t of the thickness t of the light-shielding film 15 ｍａｘ This is because the thickness t is the maximum value t ｍａｘ The internal transmittance (I / I ０ This is because it is preferable that (I / I) is 0.1% or less. ０ ) is calculated by the following formula (4) as described above. ０ = exp(-α×t) α (absorption coefficient) is proportional to k (extinction coefficient) (see equation (2)). Therefore, if the extinction coefficient of the light-shielding film 15 is small, the maximum value t of the thickness t of the light-shielding film 15 ｍａｘ becomes larger.

[0065] On the other hand, when the composition of the light-shielding film 15 is constant, if the extinction coefficient of the light-shielding film 15 is large, the maximum value t of the thickness t ｍａｘ However, if the extinction coefficient of the light-shielding film 15 is large, even a small change in the thickness t of the light-shielding film 15 will result in a large change in the internal transmittance of the light-shielding film 15. Therefore, in order to achieve a desired distribution of the internal transmittance of the light-shielding film 15, high dimensional accuracy is required for the thickness t of the tapered portion 16, which makes it difficult to manufacture the optical element 10.

[0066] Therefore, it is preferable to change the composition of the light-shielding film 15 to change the extinction coefficient of the light-shielding film 15. This allows the maximum value t of the thickness t of the light-shielding film 15 to be ｍａｘ This makes it possible to both reduce the thickness of the light-shielding film 15 and suppress the generation of stray light by setting the distribution of the internal transmittance of the light-shielding film 15 to a desired distribution. Hereinafter, with reference to FIGS. 10(A) to 10(D), a description will be given of a light-shielding film 15 including multiple layers 15A to 15C having different extinction coefficients.

[0067] The light-shielding film 15 may have multiple layers 15A to 15C. The multiple layers 15A to 15C have different extinction coefficients. The extinction coefficient k2a of the layer 15A is greater than the extinction coefficient k2b of the layer 15B (k2a > k2b). The extinction coefficient k2b of the layer 15B is greater than the extinction coefficient k2c of the layer 15C (k2b > k2c). These extinction coefficients k2a, k2b, and k2c can be adjusted by, for example, the content of the black pigment. The greater the content of the black pigment, the greater the extinction coefficient.

[0068] 10(A) to 10(D), the average extinction coefficient k2 of the light-shielding film 15 in the transmission direction of light LB increases as the distance L from the boundary line A3 between the light-shielding region A2 and the transmission region A1 increases, as viewed from the transmission direction of light LB. While the average extinction coefficient k2 increases stepwise in FIGS. 10(A) to 10(D), it may also increase continuously. When the average extinction coefficient k2 increases continuously, the generation of stray light can be more effectively suppressed than when the average extinction coefficient k2 increases stepwise.

[0069] As the distance L from the boundary line A3 increases, the average extinction coefficient k2 of the light-shielding film 15 increases, and the thickness t reaches the maximum value t ｍａｘTherefore, the average extinction coefficient k2 at the position where the maximum value t of the thickness t is ｍａｘ Even if the value is small, the internal transmittance of the light-shielding film 15 can be reduced to 0.1% or less.

[0070] Maximum value of thickness t ｍａｘ From the viewpoint of thinning the optical element 10, the maximum value t of the thickness t is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 20 μm or less. ｍａｘ From the viewpoint of making the internal transmittance of the light-shielding film 15 0.1% or less, the thickness is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more.

[0071] Furthermore, if the average extinction coefficient k2 of the light-shielding film 15 increases as the distance L from the boundary line A3 increases, the average extinction coefficient k2 can be made sufficiently small near the boundary line A3. The internal transmittance of the light-shielding film 15 can be gradually changed near the boundary line A3, and the generation of diffracted light can be suppressed.

[0072] As shown in Figure 10 (A), even if the thickness t of the light-shielding film 15 is constant, if the composition of the light-shielding film 15 is changed according to the distance L, the average extinction coefficient k2 of the light-shielding film 15 can be changed according to the distance L.

[0073] 10B , the composition of the light-shielding film 15 may be changed in the tapered portion 16 of the light-shielding film 15. In the tapered portion 16, the greater the distance L, the greater the average extinction coefficient k2 of the light-shielding film 15. This makes it possible to further suppress the occurrence of diffracted light.

[0074] 10(C) and 10(D), the composition of the light-shielding film 15 may change along the transmission direction of the light LB, or the extinction coefficient of the light-shielding film 15 may change. The change is stepwise in FIGS. 10(C) and 10(D), but may also be continuous.

[0075] The light-shielding film 15 shown in Figure 10(C) has a region where the extinction coefficient of the light-shielding film 15 increases along the transmission direction of light LB. While this region includes the entire constant-thickness portion 17 in Figure 10(C), it may also include only a portion of the constant-thickness portion 17. Alternatively, this region may include the entire constant-thickness portion 17 and a portion of the tapered portion 16. In either case, increasing the extinction coefficient of the light-shielding film 15 along the transmission direction of light LB reduces the change in the extinction coefficient at the interface between the transparent glass body 11 and the light-shielding film 15. This therefore reduces reflection of light LB at the interface between the transparent glass body 11 and the light-shielding film 15, thereby suppressing the generation of stray light.

[0076] Here, referring to FIG. 11 , an example will be described of the extent to which reflection can be suppressed when the extinction coefficient of the light-shielding film 15 increases along the transmission direction of light LB1. The light-shielding film 15 shown in FIG. 11 has layers 15B and 15A, in this order, along the transmission direction of light LB1. The reflectance of light LB1 without layer 15B is approximately 0.24%, while the reflectance of light LB1 with layer 15B is approximately 0.10%. The following physical quantities were used to calculate the reflectance: Layer 15B has a refractive index of 1.52, an extinction coefficient of 0.001, and a thickness of 20 μm. Layer 15A has a refractive index of 1.52 and an extinction coefficient of 0.150. The transparent glass body 11 has a refractive index of 1.52 and an extinction coefficient of 0.000. The wavelength of light LB1 is 550 nm.

[0077] The light-shielding film 15 shown in FIG. 10(D) has a region where the extinction coefficient of the light-shielding film 15 increases and then decreases along the light transmission direction. While the region includes the entire constant-thickness portion 17 in FIG. 10(D), it may also include only a portion of the constant-thickness portion 17. Alternatively, the region may include the entire constant-thickness portion 17 and a portion of the tapered portion 16. In either case, the extinction coefficient of the light-shielding film 15 increases and then decreases along the light transmission direction of the light LB, thereby minimizing the change in the extinction coefficient at the interface between the transparent glass body 11 and the light-shielding film 15. This suppresses reflection of the light LB at the interface between the transparent glass body 11 and the light-shielding film 15 and the generation of stray light. Additionally, reflection of light propagating in the opposite direction to the light LB (e.g., stray light) can also be suppressed.

[0078] Next, an example of a method for calculating the average extinction coefficient k2 of the light-shielding film 15 will be described with reference to FIG. 11 . The optical element 10 has a "01 surface," a "12 surface," a "31 surface," and a "10 surface," in this order, along the path of the light LB1. The "01 surface" is the boundary surface where the medium of the light LB1 changes from air to the transparent glass body 11. The "12 surface" is the boundary surface where the medium of the light LB1 changes from the transparent glass body 11 to the light-shielding film 15. The "31 surface" is the boundary surface where the medium of the light LB1 changes from the light-shielding film 15 to the transparent glass body 11. The "10 surface" is the boundary surface where the medium of the light LB1 changes from the transparent glass body 11 to air. The "01 surface," "12 surface," "31 surface," and "10 surface" are preferably perpendicular to the path of the light LB1. The perpendicular surfaces may be created by processing such as polishing. t1 is the distance from the "01 surface" to the "12 surface". t2 is the distance from the "12 surface" to the "31 surface". t3 is the distance from the "31 surface" to the "10 surface". α1 is the absorption coefficient of the transparent glass body 11. α2 is the average absorption coefficient of the light-shielding film 15. The light-shielding film 15 has a layer 15B and a layer 15A in this order along the transmission direction of the light LB1. T is the external transmittance of the optical element 10. λ is the wavelength of the light LB1.

[0079] As shown in Fig. 11, by modifying equation (5), equations (6) and (7) can be derived. k2 is calculated by substituting α2 and λ into equation (7). α2 is calculated based on the following equations: T, R ０１ , R １２ , R ３１ , α1, t1, t2, and t3 are substituted into equation (6). ０１ is measured, for example, by a microspectrophotometer. １２ , R ３１ and α1 are measured by the methods described below. t1, t2, and t3 are measured by measuring the cross section with a length measuring microscope, for example.

[0080] 11, the extinction coefficient of the light-shielding film 15 changes along the transmission direction of the light LB1, but it does not have to change. In the latter case, the average extinction coefficient k2 of the light-shielding film 15 in the transmission direction of the light LB1 can be calculated in the same way as in the former case. However, in the latter case, in equation (6), R ３１ R １２Read as follows.

[0081] Next, referring to FIG. 12, the R ３１ Instead of R １３ An example of a method for calculating R will be described. ３１ and R １３ have the same value. The optical element 10 has a "01 surface," a "13 surface," and a "10 surface," in this order, along the path of the light LB2. The "01 surface" is the boundary surface where the medium of the light LB2 changes from air to the transparent glass body 11. The "13 surface" is a reflecting surface of the light LB2 and is the boundary surface between the transparent glass body 11 and the light-shielding film 15. The "10 surface" is the boundary surface where the medium of the light LB2 changes from the transparent glass body 11 to air. The "01 surface" and the "10 surface" are the same surface. The "01 surface," the "13 surface," and the "10 surface" are preferably surfaces perpendicular to the path of the light LB2. A perpendicular surface may be created by processing such as polishing. t3 is the distance from the "01 surface" to the "13 surface." t3 is also the distance from the "13 surface" to the "10 surface." α1 is the absorption coefficient of the transparent glass body 11. The wavelength of the light LB2 is the same as the wavelength of the light LB1 shown in FIG.

[0082] As shown in FIG. 12, by modifying equation (8), equation (9) can be derived. R13 is a function of R, R ０１ , α1, and t3 into equation (9). R is measured, for example, with a microspectrometer. By adjusting the focus of the objective lens of the microspectrometer to the "13th surface," the influence of reflection at the "01 surface" can be reduced. When t3 is small, in order to reduce the influence of reflection at the "01 surface," a refractive index matching agent may be applied to the "01 surface" and then a glass plate made of the same material as the transparent glass body 11 may be attached to artificially increase t3. R ０１ is measured by the method described above. α1 is measured by the method described below. t3 is measured by the method described above.

[0083] Next, referring to FIG. 13, the R １２An example of a method for calculating α1 will be described. The optical element 10 has a "01 surface," a "12 surface," and a "10 surface," in this order, along the path of the light LB3. The "01 surface" is the boundary surface where the medium of the light LB3 changes from air to the transparent glass body 11. The "12 surface" is a reflecting surface of the light LB3 and is the boundary surface between the transparent glass body 11 and the light-shielding film 15. The "10 surface" is the boundary surface where the medium of the light LB3 changes from the transparent glass body 11 to air. The "01 surface" and the "10 surface" are the same surface. The "01 surface," the "12 surface," and the "10 surface" are preferably surfaces perpendicular to the path of the light LB3. A perpendicular surface may be created by processing such as polishing. t3 is the distance from the "01 surface" to the "12 surface." t3 is also the distance from the "12 surface" to the "10 surface." α1 is the absorption coefficient of the transparent glass body 11. The wavelength of the light LB3 is the same as the wavelength of the light LB1 shown in FIG.

[0084] As shown in FIG. 13, by modifying equation (10), equation (11) can be derived. R12 is a function of R, R ０１ , α1, and t3 into equation (11). R is measured, for example, with a microspectrometer. By adjusting the focus of the objective lens of the microspectrometer to the "12th surface," the influence of reflection at the "01 surface" can be reduced. When t3 is small, in order to reduce the influence of reflection at the "01 surface," a refractive index matching agent may be applied to the "01 surface" and then a glass plate made of the same material as the transparent glass body 11 may be attached to artificially increase t3. R ０１ is measured by the method described above. α1 is measured by the method described below. t3 is measured by the method described above.

[0085] Next, with reference to FIG. 14 , an example of a method for calculating α1 shown in FIG. 11 will be described. The optical element 10 has a "01 surface" and a "10 surface" in this order along the path of the light LB4. The "01 surface" is the boundary surface where the medium of the light LB4 changes from air to the transparent glass body 11. The "10 surface" is the boundary surface where the medium of the light LB4 changes from the transparent glass body 11 to air. The "01 surface" and the "10 surface" are preferably surfaces perpendicular to the path of the light LB4. The perpendicular surfaces may be created by processing such as polishing. t0 is the distance from the "01 surface" to the "10 surface." α1 is the absorption coefficient of the transparent glass body 11. T is the external transmittance of the optical element 10. The wavelength of the light LB4 is the same as the wavelength of the light LB1 shown in FIG. 11 .

[0086] As shown in FIG. 14, by modifying equation (12), equation (13) can be derived. α1 is a function of T, R ０１ and t0 are substituted into equation (13). ０１ is measured by the method described above. t0 is measured, for example, with a micrometer.

[0087] Next, referring to FIG. 15 , an example of a method for calculating the extinction coefficient of one of the multiple layers 15A and 15B (e.g., layer 15B) constituting the light-shielding film 15 is shown. The optical element 20 shown in FIG. 15 is fabricated by cutting the optical element 10 shown in FIG. 11 at the dashed line. The optical element 20 has a "02 surface" and a "20 surface," in this order, along the path of the light LB5. The "02 surface" is the boundary surface where the medium of the light LB5 changes from air to layer 15B. The "20 surface" is the boundary surface where the medium of the light LB5 changes from layer 15B to air. The "02 surface" and the "20 surface" are preferably perpendicular to the path of the light LB5. The perpendicular surfaces are created by processing such as cutting and polishing. t4 is the distance from the "02 surface" to the "20 surface." α2b is the absorption coefficient of layer 15B. T is the external transmittance of the optical element 20. λ is the wavelength of the light LB5, which is the same as the wavelength of the light LB1 shown in FIG.

[0088] As shown in Fig. 15, by modifying equation (14), equations (15) and (16) can be derived. k2b is calculated by substituting α2b and λ into equation (16). α2b is calculated based on the following equations: T, R ０２ and t4 into equation (15). T is measured by the method described above. R ０２ is R ０１ Similarly, the measurement is performed using, for example, a microspectrophotometer. By focusing the objective lens of the microspectrophotometer on the "02 surface," the influence of reflection at the "20 surface" can be reduced. If the distance t4 from the "02 surface" to the "20 surface" is short, the "20 surface" may be roughened or coated with a black pigment in order to reduce the influence of reflection at the "20 surface." t4 is measured using, for example, a micrometer.

[0089] Next, referring to FIGS. 16 to 19, the distribution of the extinction coefficient of the light-shielding film 15 and T １０ and ΔI Ｓ 16 to 19, the closer the color of the light-shielding film 15 is to black from white, the larger the extinction coefficient of the light-shielding film 15. Also, in FIGS. 16 to 19, L indicates the distance from the boundary line A3. A positive L indicates a position shifted from the boundary line A3 to the light-shielding region A2. A negative L indicates a position shifted from the boundary line A3 to the transmission region A1. Furthermore, in FIGS. 16 to 19, T １０ is the internal transmittance of the optical element 10.

[0090] In FIGS. 16 to 19, I Ｓ is the intensity (relative value) of light on the projection surface onto which the optical element 10 projects light. In the transmission area A1, the intensity I Ｓ is set as the reference value (1.0). The intensity I of the light transmitted through the transmission area A1 Ｓ The average value of ΔI Ｓ is the light intensity I Ｓ The fluctuation range of ΔI is the difference between the maximum value and the reference value. Ｓ 16 to 19, the distance from the light blocking film 15 to the projection surface is 5 mm.

[0091] The light-shielding film 15 of the optical element 10 shown in Fig. 16 has only a constant thickness portion 17. The constant thickness portion 17 has a constant thickness t regardless of the distance L. The constant thickness portion 17 also has a constant extinction coefficient regardless of the distance L. Therefore, at the position where the distance L is 0, the internal transmittance T １０ As a result, the diffraction of the light LB occurs easily, and ΔI Ｓ is large.

[0092] The light-shielding film 15 of the optical element 10 shown in Fig. 17 has only a constant thickness portion 17. The constant thickness portion 17 has a constant thickness t regardless of the distance L. However, the constant thickness portion 17 has an extinction coefficient that continuously increases as the distance L increases from 0. Therefore, as the distance L increases from 0, the internal transmittance T １０ As a result, the diffraction of the light LB is less likely to occur, and ΔI Ｓ is small.

[0093] The light-shielding film 15 of the optical element 10 shown in Fig. 18 has only a constant thickness portion 17. The constant thickness portion 17 has a constant thickness t regardless of the distance L. However, the constant thickness portion 17 has an extinction coefficient that increases stepwise as the distance L increases from 0. Therefore, as the distance L increases from 0, the internal transmittance T １０ As a result, the diffraction of the light LB is less likely to occur, and ΔI Ｓ is small.

[0094] The light-shielding film 15 of the optical element 10 shown in FIG. 19 has a tapered portion 16 and a constant-thickness portion 17. The thickness t of the tapered portion 16 increases continuously as the distance L increases. The extinction coefficient of the tapered portion 16 is constant, and the extinction coefficient of the constant-thickness portion 17 is also constant. However, the extinction coefficient of the constant-thickness portion 17 is greater than that of the tapered portion 16. In other words, the extinction coefficient of the tapered portion 16 is smaller than that of the constant-thickness portion 17. As a result, diffraction of the light LB is less likely to occur, and ΔI Ｓ is small.

[0095] Next, referring to FIG. 20, ΔI Ｓ As shown in FIG. 20, ΔI Ｓ 17 to 19. ＳThis shows that the diffraction of the light LB can be suppressed as the distance L increases and the average extinction coefficient of the light-shielding film 15 increases.

[0096] As shown in Fig. 21A, it is preferable that the larger L is, the larger (Δt / ΔL) is for the tapered portion 16. (Δt / ΔL) is the ratio of the increase in t, Δt, to the increase in L, ΔL. Note that, as shown in Fig. 21B, the larger L is, the smaller (Δt / ΔL) may be, or, as shown in Fig. 19, the constant (Δt / ΔL) may be independent of L.

[0097] As shown in FIG. 21A, when the value of (Δt / ΔL) is large as L is large, the increase in the distance from the light-shielding film 15 to the projection surface is smaller than in other cases. Ｓ Generally, the greater the distance from the light-shielding film 15 to the projection surface, the greater the increase in ΔI Ｓ The ΔI Ｓ This can suppress the increase in

[0098] Next, a first example of a method for manufacturing the optical element 10 will be described with reference to Figures 22 and 23, in which a light-shielding film 15 is formed using a plurality of materials G1 and G2 with different extinction coefficients. As shown in Figure 22, this manufacturing method includes, for example, steps S301 to S307. Note that steps S305 and S306 may be omitted. The extinction coefficient of material G1 is greater than the extinction coefficient of material G2.

[0099] Step S301 includes preparing a first transparent glass layer 12, as shown in Fig. 23(A), for example. The first transparent glass layer 12 has a recess 14 on its joining surface 12a. Note that while the recess 14 is formed on the joining surface 12a of the first transparent glass layer 12 in Fig. 23(A), it may also be formed on the joining surface 13a of the second transparent glass layer 13, or on both joining surfaces 12a, 13a.

[0100] Step S302 includes applying material G1 to the recess 14 and drying it, as shown in FIG. 23B . Next, step S303 includes checking whether step S302 has been performed a set number of times. The set number of times is multiple times. If step S302 has been performed less than the set number of times (NO in step S303), the processes from step S302 onward are performed again.

[0101] The second step S302 includes applying material G2 to the recess 14 and drying it, as shown in Fig. 23C, for example. Material G2 is applied to the recess 14 in the width direction, sandwiching material G1 therebetween. If the number of times step S302 has been performed reaches the set number of times (YES in step S303), processing from step S304 onwards is performed. Note that the set number of times may be any number of times, is not limited to two, and may be three or more.

[0102] Step S304 includes baking the materials G1 and G2 to form the light-shielding film 15, as shown in Fig. 23D, for example. The light-shielding film 15 has a layer 15A formed by baking the material G1 and a layer 15B formed by baking the material G2.

[0103] In step S305, although not shown, the light-shielding film 15 is heated to cause thermal diffusion between the layers 15A and 15B. This allows the change in the extinction coefficient of the light-shielding film 15 to change continuously from a stepwise change. The heating temperature in step S305 is preferably higher than the heating temperature in step S304.

[0104] Although not shown, step S306 includes polishing the surface of first transparent glass layer 12 and the surface of light-shielding film 15. This makes it possible to make the surface of first transparent glass layer 12 and the surface of light-shielding film 15 flush with each other. This makes it possible to apply pressure uniformly to the bonding interface in step S307.

[0105] 23(E), for example, step S307 includes bonding the first transparent glass layer 12 and the second transparent glass layer 13 together, and bonding the light-shielding film 15 and the second transparent glass layer 13 together. By cutting the bonded body obtained in step S307, a plurality of optical elements 10 can be obtained.

[0106] Next, a second example of the method for manufacturing the optical element 10 will be described with reference to Fig. 24, in which the light-shielding film 15 is formed using a plurality of materials G1 to G2 with different extinction coefficients. The differences from the first example shown in Fig. 23 will be described below. In the first example, as shown in Fig. 23, the plurality of materials G1 to G2 are arranged in the width direction of the recess 14. On the other hand, in the second example, as shown in Fig. 24, the plurality of materials G1 to G2 are arranged in the depth direction of the recess 14.

[0107] Step S302 includes applying material G2 to the recesses 14 and drying the material, as shown in FIG. 24B, for example. Material G2 may shrink as it dries, forming recesses on the surface. Note that the recesses may also be formed using a tool or the like. The second step S302 includes applying material G1 to the recesses on the surface of material G2 and drying the material, as shown in FIG. 24C, for example. The processes from step S303 onward are omitted because they are the same as those in the first example.

[0108] Next, with reference to FIG. 25 , a third example of a method for manufacturing an optical element 10 will be described, in which a light-shielding film 15 is formed using a plurality of materials G1 to G2 with different extinction coefficients. Differences from the first example shown in FIG. 23 will be described below. In the first example, as shown in FIG. 23 , the surface of the first transparent glass layer 12 has a recess 14, and a plurality of materials G1 to G2 are applied to the recess 14. On the other hand, in the third example, as shown in FIG. 25 , the surface of the first transparent glass layer 12 does not have a recess 14. The surface of the first transparent glass layer 12 is flat, and a plurality of materials G1 to G2 are applied to the flat surface. In addition to the materials G1 to G2 of the light-shielding film 15, the material G3 of the transparent bonding layer 18 is also applied.

[0109] Step S302 includes applying and drying material G1 to the flat surface of first transparent glass layer 12, as shown in Fig. 25(B), for example. A second step S302 includes applying and drying material G2 to the flat surface of first transparent glass layer 12, as shown in Fig. 25(C), for example. Material G2 is applied while sandwiching material G1.

[0110] 25D, the third step S302 includes applying and drying material G3 to the flat surface of first transparent glass layer 12. Material G3 has a smaller extinction coefficient than materials G1 and G2 and has an extinction coefficient similar to that of first transparent glass layer 12.

[0111] 25E, for example, step S304 includes firing materials G1, G2, and G3 to form light-shielding film 15 and transparent bonding layer 18. Light-shielding film 15 has layer 15A formed by firing material G1 and layer 15B formed by firing material G2. Transparent bonding layer 18 is a layer formed by firing material G3.

[0112] In step S305, although not shown, the light-shielding film 15 and the transparent bonding layer 18 are heated to cause thermal diffusion between the light-shielding film 15 and the transparent bonding layer 18. This allows the change in the extinction coefficient of the light-shielding film 15 to change continuously from a stepwise change. The heating temperature in step S305 is preferably higher than the heating temperature in step S304.

[0113] Although not shown, step S306 includes polishing the surface of the light-shielding film 15 and the surface of the transparent bonding layer 18. This makes it possible to make the surface of the light-shielding film 15 and the surface of the transparent bonding layer 18 flush with each other. This makes it possible to apply pressure uniformly to the bonding interface in step S307.

[0114] 25(F), for example, step S307 includes bonding the transparent bonding layer 18 to the second transparent glass layer 13 and bonding the light-shielding film 15 to the second transparent glass layer 13. By cutting the bonded body obtained in step S307, a plurality of optical elements 10 can be obtained.

[0115] The optical element according to the present disclosure has been described above, but the present disclosure is not limited to the above-described 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.

[0116] This application claims priority based on Japanese Patent Application No. 2023-134555, filed with the Japan Patent Office on August 22, 2023, the entire contents of which are incorporated herein by reference.

[0117] 10 Optical element 11 Transparent glass body 15 Light-shielding film A1 Transmitting area A2 Light-shielding area A3 Boundary line LB Light

Claims

1. An optical element comprising a transmissive region that transmits a portion of the light when viewed from the light transmission direction, and a shading region that blocks another portion of the light, comprising: a transparent glass body; and a glass shading film that forms the shading region inside the transparent glass body, wherein the shading film has an average extinction coefficient in the light transmission direction that increases with the distance from the boundary between the shading region and the transmissive region when viewed from the light transmission direction.

2. The optical element according to claim 1, wherein the light-shielding film has a region in which the extinction coefficient of the light-shielding film is large along the light transmission direction.

3. The optical element according to claim 1, wherein the light-shielding film has a region in which the extinction coefficient of the light-shielding film increases and then decreases along the light transmission direction.

4. An optical element according to any one of claims 1 to 3, wherein the light-shielding film has a tapered portion whose thickness in the light transmission direction increases with increasing distance from the boundary line between the light-shielding region and the light-transmitting region when the light-shielding film is viewed in the light transmission direction, and the tapered portion is in contact with the boundary line.

5. The optical element according to claim 4, wherein in the tapered portion, the greater the distance from the boundary line between the light-shielding region and the light-transmitting region as viewed in the light transmission direction, the greater the average extinction coefficient in the light transmission direction.

6. The optical element according to any one of claims 1 to 3, wherein the maximum thickness of the light-shielding film in the light transmission direction is 100 μm or less.

7. The optical element according to any one of claims 1 to 3, wherein the internal transmittance of the light-shielding film is 0.1% or less at a position where the thickness of the light-shielding film in the light transmission direction is at a maximum value.

8. The absolute value of the difference between the average linear expansion coefficients of the transparent glass body and the light-shielding film is 10 x 10 －６ 4. The optical element according to claim 1, wherein the temperature is 0.15 to 1.5° C. or less.

9. An optical element described in any one of claims 1 to 3, wherein the transparent glass body has a first transparent glass layer and a second transparent glass layer, the first transparent glass layer and the second transparent glass layer are disposed in the light transmission direction with the light-shielding film therebetween, and are continuously in contact with each other in the transmission region.

10. An optical element described in any one of claims 1 to 3, wherein the transparent glass body has a first transparent glass layer and a second transparent glass layer, the first transparent glass layer and the second transparent glass layer are arranged in the light transmission direction with the light-shielding film sandwiched between them, and the transparent glass body has a transparent bonding layer that bonds the first transparent glass layer and the second transparent glass layer in the transmission region.

Images