WO2020162463A1

WO2020162463A1 - Optical element and optical element manufacturing method

Info

Publication number: WO2020162463A1
Application number: PCT/JP2020/004180
Authority: WO
Inventors: 哲日下
Original assignee: 日本板硝子株式会社
Priority date: 2019-02-06
Filing date: 2020-02-04
Publication date: 2020-08-13
Also published as: TW202037930A

Abstract

An optical element (1a) is provided with a body (10) and a coating (20). The body (10) had a main surface (15). The main surface (15) includes a center section (11) and a peripheral section (12). The center section (11) forms a protruding surface. The peripheral section (12) is formed at the perimeter of the center section (11). The coating (20) is formed on the main surface (15). The optical element (1a) satisfies condition (i): d1<d0 and d1<d2.

Description

Optical element and method of manufacturing optical element

The present invention relates to an optical element and a method for manufacturing an optical element.

Conventionally, it is known to coat the surface of optical elements such as lenses with an antireflection film or the like. The antireflection film can reduce the occurrence of flare and ghost.

For example, Patent Document 1 describes an optical product in which an optical multilayer film for antireflection is formed on one side or both sides of a substrate. The optical multilayer film has a seven-layer structure in which low refractive index layers and high refractive index layers are alternately laminated.

Patent Document 2 describes a lens with an antireflection film having a convex or concave surface portion and an antireflection film formed on the surface portion. The film thickness of the antireflection film in the central part of the surface part is different from the film thickness of the antireflection film in the peripheral part. The film thickness of the antireflection film becomes thicker in a region where the incident angle is larger.

Patent Document 3 describes an optical lens provided in an optical information recording/reproducing apparatus. An antireflection film is provided on at least one lens surface of the optical lens. The film thickness of the antireflection film in the peripheral portion of the lens surface is equal to or larger than the film thickness of the antireflection film in the central portion of the lens surface.

Patent Document 4 describes an optical element for an optical pickup device. In this optical element, an antireflection film is formed on the surface of the lens. The antireflection film is formed to have an optical film thickness that has the lowest reflectance with respect to an incident/emitted light beam at an arbitrary position on the surface of the optical element. For example, the optical film thickness of the antireflection film is large in the peripheral portion of the lens where the lens curvature is large.

Patent Document 5 describes an optical member in which a plurality of fine concavo-convex structures having antireflection properties are provided on the surface of the lens surface. In the optical member, an intermediate layer is formed between the fine concavo-convex structure and the lens surface. The film thickness of the intermediate layer is continuously increased from the lens central portion to the lens peripheral portion.

[Patent Document 1] Japanese Unexamined Patent Publication No. JP, 10-160906, A JP, 2003-215310, A JP 2004-333908 A JP, 2009-139775, A

In Patent Document 1, the spatial variation of the thickness of the optical multilayer film in the optical product is not clear. According to Patent Documents 2 to 4, the thickness of the coating such as the antireflection film on the peripheral portion of the lens surface is larger than the thickness of the coating on the central portion of the lens surface. This cannot be said to be advantageous from the viewpoint of preventing the occurrence of cracks in the coating such as the antireflection film due to the temperature change.

In view of such circumstances, the present invention provides an optical element advantageous from the viewpoint of preventing the occurrence of cracks in the coating such as the antireflection film due to the temperature change. The present invention also provides a manufacturing method suitable for manufacturing such an optical element.

The present invention is
A main body having a main surface including a central portion forming a convex surface or a concave surface and a peripheral portion formed around the central portion;
A coating formed on the main surface,
Provided is an optical element satisfying the conditions of (i) d ₁ <d ₀ and d ₁ <d ₂ or (ii) d ₂ <d ₁ <d ₀ .
d ₀ is the thickness of the coating at the center of the center.
d ₁ is the thickness of the coating at a position where the distance from the center in the direction perpendicular to the optical axis is 90% of the distance between the center and the peripheral edge and the center.
d ₂ is the thickness of the coating at a position where the distance from the center in the direction perpendicular to the optical axis is 110% of the distance between the boundary and the center.

The present invention is
In the main surface of the main body having a main surface including a central portion forming a convex surface or a concave surface and a peripheral portion formed around the central portion, the distance from the center of the central portion in the direction perpendicular to the optical axis is The wettability with respect to the coating liquid of the first region including the position that is 90% of the distance between the boundary between the central portion and the peripheral portion and the center is defined as follows: Also increase,
Applying the coating liquid to the main surface to form a coating,
A method for manufacturing an optical element is provided.

The present invention is
A coating is formed by vapor deposition on the main surface of the main body having a main surface including a central portion forming a convex surface or a concave surface and a peripheral portion formed around the central portion,
In the vapor deposition, the coating is applied to a first region including a position in which a distance from a center of the central portion in a direction perpendicular to an optical axis is 90% of a distance between a boundary between the central portion and the peripheral portion and the center. The probability of the substance for depositing is lower than the probability of depositing the substance for the coating in the second region including the center,
A method for manufacturing an optical element is provided.

The above optical element is advantageous from the viewpoint of preventing cracks in the coating due to temperature changes. The above manufacturing method is suitable for manufacturing such an optical element.

FIG. 1A is a sectional view showing an example of an optical element according to the present invention. FIG. 1B is a sectional view showing another example of the optical element according to the present invention. FIG. 1C is a sectional view showing still another example of the optical element according to the present invention. FIG. 1D is a sectional view showing still another example of the optical element according to the present invention. FIG. 2 is a sectional view showing an optical element according to a comparative example. FIG. 3A is a diagram conceptually showing an example of the method for manufacturing an optical element according to the present invention. 3B is a plan view of the mask shown in FIG. 3A. FIG. 4A is a diagram conceptually showing another example of the method for manufacturing an optical element according to the present invention. FIG. 4B is a plan view of the mask shown in FIG. 4A. FIG. 5A is a photograph showing the appearance of the optical element according to the comparative example before the temperature cycle test. FIG. 5B is a photograph showing the appearance of the optical element according to the comparative example after the temperature cycle test.

The present inventor has devised the optical element according to the present invention based on the following new findings regarding the optical element.

For example, if an optical element such as a lens made of glass or resin has a coating such as an antireflection film on its surface, cracks may occur on the surface or inside of the coating during or after the temperature cycle test. is there. As used herein, the term “crack” means a crack or crack that occurs in a layer or film such as a coating. An example of the conditions of the temperature cycle test is that the cycle of changing the environmental temperature of the optical element in the temperature range of −40° C. to 85° C. over 15 minutes is repeated 500 times. It is considered that due to the difference between the coefficient of thermal expansion of the material forming the coating and the coefficient of thermal expansion of the material of the main body of the optical element, thermal stress is generated due to the temperature change and a crack is generated. When the main body of the optical element is made of resin and the coating is a layer of an inorganic material such as a metal oxide, it is considered that cracks are more likely to occur. When a crack is generated, the optical performance may be deteriorated at that portion, or moisture or the like may act on the material of the optical element body through the crack to deteriorate the property of the material.

The thermal stress σ _t generated when the environmental temperature of the optical element changes from the temperature Tb to the temperature Ta is represented by the following formula (1). E _f is the Young's modulus [N/m ² ] of the coating, α _s is the thermal expansion coefficient of the optical element body [1/° C.], α _f is the thermal expansion coefficient of the coating [1/° C.], ν _f is the Poisson's ratio of the coating.
σ _t =E _f ·(α _s −α _f )·(Ta−Tb)/(1-ν _f )(1)

The thermal stress σ _t causes compressive or tensile stress in the coating. As a result, the optical element is bent. The stress σ _f generated by the deflection is expressed by the equation (2) called the Stoney equation. E _s is the Young's modulus [N/m ² ] of the optical element body, D is the thickness [m] of the optical element body, ν _s is the Poisson's ratio of the optical element body, and R is deformed by thermal stress. It is the radius of curvature [m] of the optical element body, and d is the thickness [m] of the coating.
σ _f =E _s ·D ² /{6·(1-ν _s )·R·d} (2)

When S that satisfies S=E _s ·D ² /{6·(1-ν _s )·R} is used in the equation (2), the equation (2) is expressed as σ _f =S/d. S corresponds to the force per unit width of the coating. σ _t depends on the temperature change and the coefficient of thermal expansion of the material, and the force per unit width in the coating depends on the product of the stress σ _f and the coating thickness d. Since the larger the value of S, the larger the force applied to the coating, it is understood that when d is large, peeling and cracking of the coating are likely to occur.

Consider the case where the thickness of the coating in the peripheral portion of the optical element is made larger than the thickness of the coating in the central portion of the optical element for the purpose of reducing the amount of reflection of light rays and the like, as in the techniques described in Patent Documents 2 to 5. .. In this case, the thickness of the coating in the peripheral portion of the optical element is large, and it is considered that the coating is likely to crack due to temperature changes in the peripheral portion of the optical element. Therefore, the yield in manufacturing the optical element may be low, and thus the productivity in manufacturing the optical element may be low. In particular, the formation of the coating on the optical element can be performed at a temperature higher than room temperature from the viewpoint of improving the adhesion of the coating to the optical element body. Therefore, thereafter, due to the difference between the coefficient of thermal expansion of the material forming the coating and the coefficient of thermal expansion of the optical element body in the optical element returned to room temperature, thermal stress is likely to occur and cracks are likely to occur.

Therefore, as a result of repeated trial and error, the present inventor newly found a spatial variation in the thickness of the coating, which is advantageous from the viewpoint of preventing the coating from being cracked due to a change in temperature. An optical element according to the invention has been devised.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the following description relates to an example of the present invention, and the present invention is not limited to the following embodiments.

As shown in FIGS. 1A, 1B, 1C, and 1D, each of the

optical elements

1a, 1b, 1c, and 1d includes a body 10 and a coating 20. The main body 10 has a main surface 15. The main surface 15 includes a central portion 11 and a peripheral portion 12. The central portion 11 has a convex surface or a concave surface. In the optical element 1a and the optical element 1b, the central portion 11 has a convex surface. In the optical element 1c and the optical element 1d, the central portion 11 has a concave surface. The peripheral portion 12 is formed around the central portion 11. The coating 20 is formed on the main surface 15. The optical elements 1a to 1d satisfy the conditions (i) d ₁ <d ₀ and d ₁ <d ₂ or (ii) d ₂ <d ₁ <d ₀ . The

optical elements

1a and 1c satisfy the conditions of (i) d ₁ <d ₀ and d ₁ <d ₂ . The

optical elements

1b and 1d satisfy the condition (ii) d ₂ <d ₁ <d ₀ . d ₀ is the thickness of the coating 20 at the center P _C of the central portion 11. d ₁ is the thickness of the coating 20 at the position P ₉₀ where the distance from the center P _{C in the} direction perpendicular to the optical axis A is 90% of the distance between the boundary B and the center P _C. The boundary B is a boundary between the central portion 11 and the peripheral portion 12. d ₂ is the thickness of the coating 20 at the position P ₁₁₀ where the distance from the center P _{C in the} direction perpendicular to the optical axis A is 110% of the distance between the boundary B and the center P _C. The thicknesses d ₀ , d ₁ and d ₂ mean the thickness of the principal surface 15 in the normal direction.

FIG. 2 shows an optical element 2 according to a comparative example. The optical element 2 is configured in the same manner as the optical element 1a, except for the part particularly described. The constituent elements of the optical element 2 corresponding to the constituent elements of the optical element 1a are designated by the same reference numerals, and detailed description thereof will be omitted.

In the optical element 2, the condition of d ₂ >d ₁ >d ₀ is satisfied. In this case, d ₂ and d ₁ are larger than d ₀ , and the stress generated near the position P ₉₀ of the coating 20 and the stress generated near the position P ₁₁₀ of the coating 20 are likely to be large. Further, since the directions of these stresses are different, a force that tears the coating 20 near the boundary B easily works. Therefore, in the optical element 2, it is considered that cracks are likely to occur in the coating 20 due to the temperature change.

On the other hand, when the conditions (i) d ₁ <d ₀ and d ₁ <d ₂ are satisfied as in the

optical elements

1a and 1c, the stress generated near the position P ₉₀ of the coating 20 is small. Therefore, the force to tear the coating 20 near the boundary B becomes small. As a result, cracks are unlikely to occur in the coating 20 with changes in temperature.

If the condition (ii) d ₂ <d ₁ <d ₀ is satisfied as in the optical element 1b and the optical element 1d, the stress generated near the position P ₉₀ of the coating 20 and the position P _{110 of the} coating 20 are satisfied. The stress generated in the vicinity of is easily reduced. Therefore, the force to tear the coating 20 near the boundary B becomes small. As a result, cracks are unlikely to occur in the coating 20 with changes in temperature.

Each of the optical element 1a and the optical element 1c may further satisfy the condition of 1<d ₀ /d ₁ <2 and the condition of 1<d ₂ /d ₁ <2. As a result, cracks are less likely to occur in the coating 20 with changes in temperature. The value of d ₀ /d ₁ may be 1.05 to 1.5 or 1.1 to 1.3. The value of d ₂ /d ₁ may be 1.05 to 1.5, or 1.1 to 1.2.

Each of the optical element 1b and the optical element 1d may further satisfy the condition of 1<d ₀ /d ₁ <2 and the condition of 0<d ₂ /d ₁ <1. As a result, cracks are less likely to occur in the coating 20 with changes in temperature. The value of d ₀ /d ₁ may be 1.05 to 1.5 or 1.1 to 1.3. The value of d ₂ /d ₁ may be 0.01 to 0.9 or 0.1 to 0.7.

Each of the optical elements 1a to 1d is typically a lens. Each of the

optical elements

1a and 1b is, for example, a plano-convex lens. Each of the

optical elements

1c and 1d is, for example, a plano-concave lens. The central portion 11 may be, for example, a spherical surface or an aspherical surface.

The peripheral portion 12 has, for example, a flat surface. This flat surface is parallel to the plane perpendicular to the optical axis A. In this case, the direction of the stress generated near the position P ₉₀ of the coating 20 is different from the direction of the stress generated near the position P ₁₁₀ of the coating 20, and the force to tear the coating 20 near the boundary B is appear. However, in each of the optical elements 1a to 1d, since the above condition (i) or condition (ii) is satisfied, cracks are less likely to occur in the coating 20 due to temperature changes.

The main body 10 is formed of, for example, a translucent resin. In this case, the absolute value of the difference between the coefficient of thermal expansion of the material forming the coating 20 and the coefficient of thermal expansion of the main body 10 tends to be large. However, in each of the optical elements 1a to 1d, since the above condition (i) or condition (ii) is satisfied, cracks are less likely to occur in the coating 20 due to temperature changes. The translucent resin is not particularly limited. Examples of the translucent resin include acrylic resin, polycarbonate resin, and polyolefin resin. The main body 10 may be formed of translucent glass.

The coating 20 is not particularly limited as long as it is a film formed on the main surface. The coating 20 is, for example, an antireflection film. The antireflection film prevents reflection in a specific wavelength range. The antireflection film may be a single layer film or a multilayer film. The antireflection film may be, for example, a single-layer film formed of a material having a refractive index lower than that of the main body 10. Further, the coating 10 functioning as an antireflection film may be a laminated multilayer film in which a high refractive index layer and a low refractive index layer are alternately stacked. In this case, the material forming the high refractive index layer is, for example, cerium oxide, titanium oxide, tantalum oxide, zirconium oxide, or silicon nitride. The material forming the low refractive index layer is, for example, silicon oxide or magnesium fluoride.

An example of a method of manufacturing the optical elements 1a to 1d will be described. On the main surface 15 of the main body 10, the wettability of the first region R1 including the position P ₉₀ with the coating liquid is higher than the wettability of the second region R2 including the center P _C with the coating liquid. After that, the coating liquid is applied to the main surface 15 to form the coating 20. In the first region R1 having high wettability with the coating liquid, the thickness of the coating 20 is likely to be smaller than in the second region R2 having low wettability with the coating liquid. Therefore, this method is suitable for manufacturing the optical elements 1a to 1d. The coating liquid is applied by, for example, spin coating.

The position P ₁₁₀ may be included in the first region R1.

The method of increasing the wettability of the first region R1 with the coating liquid more than the wettability of the second region R2 with the coating liquid is not limited to a particular method. For example, as shown in FIG. 3A, by irradiating the main surface 15 with a predetermined plasma P in a state where the mask 50 is arranged on the main surface 15 of the main body 10, the wettability of the first region R1 with respect to the coating liquid is improved. The wettability of the second region R2 with respect to the coating liquid can be improved.

As shown in FIG. 3B, the mask 50 is a plate-shaped member having an annular through hole. The mask 50 has a central portion 51, an outer peripheral portion 52, and a support portion 53. The central portion 51 has a disc shape. The outer peripheral portion 52 is an annular member that surrounds the central portion 51 and has a circular through hole. The axis of the central portion 51 and the axis of the circular through hole coincide with each other. The radius of the central portion 51 is such that the distance from the center P _{C in the} direction perpendicular to the optical axis A is smaller than 90% of the distance between the boundary B and the center P _C. In addition, the radius of the circular through hole of the outer peripheral portion 52 is such that the distance from the center P _{C in the} direction perpendicular to the optical axis A is larger than 90% of the distance between the boundary B and the center P _C. Therefore, by disposing the mask 50 so that the center of the central portion 51 is located on the optical axis A, the plasma that has passed through the annular through hole is selectively applied to the first region R1. As a result, the wettability of the first region R1 with the coating liquid can be made higher than the wettability of the second region R2 with the coating liquid.

By selectively modifying a part of the main surface 15 of the main body 10 with ozone generated by irradiation of ultraviolet rays (UV), the wettability of the first region R1 with the coating liquid can be improved. It may be higher than sex.

Another example of the method of manufacturing the optical elements 1a to 1d will be described. In this manufacturing method, the coating 20 is formed on the main surface 15 of the main body 10 by vapor deposition. In this vapor deposition, the probability that the substance for the coating 20 adheres to the first region R1 including the position P ₉₀ on the main surface 15 is the probability that the substance for the coating 20 adheres to the second region R2 including the center P _C. Lower than. As a result, the thickness of the coating 20 in the first region R1 tends to be smaller than that in the second region R2. Therefore, this method is suitable for manufacturing the optical elements 1a to 1d.

The position P ₁₁₀ may be included in the first region R1.

The vapor deposition may be physical vapor deposition or chemical vapor deposition.

The method of reducing the probability that the substance for the coating 20 adheres to the first region R1 is lower than the probability that the substance for the coating 20 adheres to the second region R2 is not particularly limited. For example, the vapor deposition apparatus 70 shown in FIG. 4A can be used to manufacture the optical elements 1a to 1d.

The vapor deposition device 70 is a device for vacuum vapor deposition, and includes a vacuum chamber 72, a holder 74, a mask 75, and a vapor deposition source 76. The holder 74, the mask 75, and the vapor deposition source 76 are arranged inside the vacuum chamber 72. In the vapor deposition device 70, the main body 10 is arranged so that the main surface 15 of the main body 10 faces the vapor deposition source 76. The holder 74 is configured to be rotatable. The holder 74 rotates while the main body 10 is fixed to the holder 74. As a method for fixing the main body 10 to the holder 74, a known method can be used. For example, a method of gripping the edge surface of the main body 10 with a V groove or a U groove can be used. The mask 75 is arranged between the holder 74 and the vapor deposition source 76. As shown in FIG. 4B, the mask 75 has a notch narrowed from the center of the mask 75 toward the peripheral edge of the mask 75. Thereby, in the vapor deposition in the vapor deposition apparatus 70, the probability that the substance for the coating 20 adheres to the first region R1 is lower than the probability that the substance for the coating 20 adheres to the second region R2.

Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to the examples below.

<Example 1>
A plano-convex lens made of polymethylmethacrylate was prepared. The main surface having the convex surface of this plano-convex lens has a central portion forming a convex surface and a peripheral portion formed around the central portion. The convex surface at the center was a spherical surface having a radius of curvature of 4 mm. The peripheral portion had a flat surface parallel to the surface perpendicular to the optical axis. The diameter of the plano-convex lens was 7 mm, and the effective diameter of the convex surface was 5 mm.

A mask having the same mode as the mask 50 shown in FIG. 3 was prepared. This mask was manufactured such that the directional plasma was applied to a region corresponding to 80% to 120% of the effective diameter of the convex surface of the plano-convex lens. This mask was placed above the plano-convex lens, and the surface modification treatment of the main surface having the convex surface of the plano-convex lens was performed using an atmospheric pressure plasma device (Well, product name: WADP-200A). .. In this surface modification treatment, Ar (argon) gas is supplied at a flow rate of 15 slm (standard liter per minute), O ₂ (oxygen) is supplied at a flow rate of 15 sccm (standard cubic centimeter per minute), and RF discharge power is supplied. It was set to 200W. The plano-convex lens and the mask were arranged so that their central axes coincided with each other, and the distance between the plano-convex lens and the mask was adjusted to about 1 mm using a spacer. The plano-convex lens and the mask were conveyed in one direction by a belt conveyor made of wire, and plasma was irradiated from above. Further, since the shadow of the supporting portion of the mask is generated on the surface of the plano-convex lens, the plasma irradiation was performed twice by changing the phase about 5° around the central axis of the plano-convex lens and the mask.

0.6 g of tetraethoxysilane (TEOS, manufactured by Tokyo Chemical Industry Co., Ltd.), 1.18 g of methyltriethoxysilane (MTES, manufactured by Tokyo Chemical Industry Co., Ltd.), 0.82 g of 0.3% by weight formic acid (manufactured by Kishida Chemical Co., Ltd.), 3 g of hollow silica sol (manufactured by JGC Catalysts & Chemicals, product name: Thruria 4110, silica solid content: about 25 wt%) and 22.4 g of ethanol (manufactured by Kishida Chemical Co., Ltd.) were mixed at room temperature and reacted at 35° C. for 3 hours. A coating solution was prepared.

Next, using a spin coater (Mikasa, product name: MS-B100), the coating liquid was applied to the plano-convex lens to form a coating film. The flat surface opposite to the convex surface of the plano-convex lens was fixed on the spin axis of the spin coater by vacuum adsorption. Next, the rotation speed of the spin coater was gradually increased with the convex surface of the plano-convex lens facing upward, and the rotation speed was kept at 500 rpm (revolutions per minute). After that, an appropriate amount of the coating liquid was dropped toward the plano-convex lens with a syringe. Next, the rotation speed of the spin coater was raised to 4000 rpm and kept for 25 seconds, and the excess coating liquid was skipped. Then, the plano-convex lens was taken out, and the plano-convex lens was placed in a heating oven to gradually raise the temperature around the plano-convex lens. The temperature was kept at 200° C. for 10 minutes, and the coating film was dried to form a single-layer antireflection film. In this way, the optical element according to Example 1 was manufactured.

The thickness of the antireflection film in the optical element according to Example 1 was measured using a microspectrophotometer (manufactured by JASCO Corporation, product name: MSV-5000). In this measurement, the thickness d _{0 of the} antireflection film at the center of the convex surface of the plano-convex lens, the thickness d _{1 of the} antireflection film on the convex surface at the position corresponding to 90% of the diameter of the convex surface, and the thickness of the convex surface The thickness d _{2 of the} antireflection film on the flat peripheral portion outside the convex surface at the position corresponding to the diameter corresponding to 110% of the diameter was measured. As a result, in the optical element according to Example 1, d ₀ =115 nm, d ₁ =105 nm, and d ₂ =120 nm, and (i) the conditions of d ₁ <d ₀ and d ₁ <d ₂ are satisfied. It was The antireflection film near the end of the convex surface of the plano-convex lens is pulled by receiving stress in two directions due to the compressive stress in the antireflection film along the convex surface and the compressive stress in the antireflection film along the flat peripheral edge. it is conceivable that. Therefore, it is considered that the thickness of the antireflection film near the end of the convex surface of the plano-convex lens was reduced.

<Example 2>
An optical element according to Example 2 was made in the same manner as Example 1 except for the following points. A mask manufactured so that directional plasma was irradiated to a region corresponding to 80% to 140% of the effective diameter of the convex surface of the plano-convex lens was used. In forming the coating liquid, a spin coater (manufactured by Mikasa, product name: MS-B100) was used, and the rotation speed of the spin coater was gradually increased and kept at 1500 rpm while the plano-convex lens was fixed. Then, an appropriate amount of the coating liquid was dripped toward the plano-convex lens. Then, the spin coater was further rotated at 4000 rpm for 25 seconds. Then, the plano-convex lens was taken out, and the plano-convex lens was placed in a heating oven to gradually raise the temperature around the plano-convex lens. The temperature was kept at 200° C. for 10 minutes, and the coating film was dried to form a single-layer antireflection film. Thus, the optical element according to Example 2 was obtained.

The thicknesses d ₀ , d ₁ and d ₂ of the antireflection film of the optical element according to Example 2 were measured in the same manner as in Example 1. As a result, in the optical element according to Example 2, d ₀ =115 nm, d ₁ =105 nm, and d ₂ =95 nm, and (ii) the condition of d ₂ <d ₁ <d ₀ was satisfied. In the optical element according to Example 2, as compared with the optical element according to Example 1, the peripheral portion was surface-modified with a wider area, and the thickness of the antireflection film at the peripheral portion was smaller.

<Example 3>
For the same plano-convex lens as that used in Example 1, a vapor deposition apparatus configured in the same manner as the vapor deposition apparatus 70 shown in FIGS. 4A and 4B was used to perform vacuum vapor deposition on the main surface including the convex surface of the plano-convex lens. Then, an antireflection film was formed. In vacuum deposition, the pressure inside the vacuum chamber was reduced to about 10 ⁻³ Pa using a vacuum pump, and magnesium fluoride (MgF ₂ ) was heated and evaporated from the deposition source. The holder was rotated for a predetermined time in vacuum deposition. The vacuum deposition time was adjusted so that the antireflection film on the plano-convex lens had a predetermined thickness. Thus, the optical element according to Example 3 was obtained.

The thicknesses d ₀ , d ₁ and d ₂ of the antireflection film of the optical element according to Example 3 were measured in the same manner as in Example 1. As a result, in the optical element according to Example 3, d ₀ =115 nm, d ₁ =105 nm, and d ₂ =95 nm, and (ii) the condition of d ₂ <d ₁ <d ₀ was satisfied.

<Comparative Example 1>
An optical element according to Comparative Example 1 was produced in the same manner as in Example 1 except for the following points. In the production of the optical element according to Comparative Example 1, the above plano-convex lens was not irradiated with plasma. Using a spin coater (manufactured by Mikasa, product name: MS-B100), an appropriate amount of the coating liquid was dropped toward the plano-convex lens with the plano-convex lens fixed. Then, the rotation speed of the spin coater was gradually increased and kept at 4000 rpm for 25 seconds. Then, the plano-convex lens was taken out, and the plano-convex lens was placed in a heating oven to gradually raise the temperature around the plano-convex lens. The temperature was kept at 200° C. for 10 minutes, and the coating film was dried to form a single-layer antireflection film. In this way, the optical element according to Comparative Example 1 was obtained.

The thicknesses d ₀ , d ₁ and d ₂ of the antireflection film of the optical element according to Comparative Example 1 were measured in the same manner as in Example 1. As a result, in the optical element according to Comparative Example 1, d ₀ =115 nm, d ₁ =131 nm, and d ₂ =150 nm.

<Temperature cycle test>
A temperature cycle test was performed on the optical element according to each example and the optical element according to Comparative Example 1. In the temperature cycle test, a cycle in which the temperature around the optical element was changed in the temperature range of −40° C. to 85° C. over 15 minutes was repeated 500 times. In the optical element according to each example, no crack was generated on the surface of the antireflection film after the temperature cycle test.

On the other hand, as shown in FIGS. 5A and 5B, in the optical element according to Comparative Example 1, cracks occurred on the surface of the antireflection film after the temperature cycle test.

Claims

A main body having a main surface including a central portion forming a convex surface or a concave surface and a peripheral portion formed around the central portion;
A coating formed on the main surface,
An optical element satisfying the conditions of (i) d 1 <d 0 and d 1 <d 2 or (ii) d 2 <d 1 <d 0 .
d 0 is the thickness of the coating at the center of the center.
d 1 is the thickness of the coating at a position where the distance from the center in the direction perpendicular to the optical axis is 90% of the distance between the center and the peripheral edge and the center.
d 2 is the thickness of the coating at a position where the distance from the center in the direction perpendicular to the optical axis is 110% of the distance between the boundary and the center.
The optical element according to claim 1, wherein the peripheral portion forms a flat surface.
The optical element according to claim 1 or 2, wherein the coating is an antireflection film.
The optical element according to any one of claims 1 to 3, which satisfies the condition (i), the condition 1<d 0 /d 1 <2, and the condition 1<d 2 /d 1 <2.
The optical element according to any one of claims 1 to 3, which satisfies the condition (ii), the condition 1<d 0 /d 1 <2, and the condition 0<d 2 /d 1 <1.
In the main surface of the main body having a main surface including a central portion forming a convex surface or a concave surface and a peripheral portion formed around the central portion, the distance from the center of the central portion in the direction perpendicular to the optical axis is The wettability of the first region including the position that is 90% of the distance between the center and the boundary between the peripheral portion and the center from the wettability of the second region including the center to the coating liquid is Also increase,
Applying the coating liquid to the main surface to form a coating,
Optical element manufacturing method.
A coating is formed by vapor deposition on the main surface of the main body having a main surface including a central portion forming a convex surface or a concave surface and a peripheral portion formed around the central portion,
In the vapor deposition, the coating is applied to a first region including a position where a distance from a center of the central portion in a direction perpendicular to an optical axis is 90% of a distance between a boundary between the central portion and the peripheral portion and the center. The probability of the substance for depositing is lower than the probability of depositing the substance for the coating in the second region including the center,
Optical element manufacturing method.