US-12625300-B2 - Optical element and optical device including the same

Abstract

An optical element includes a substrate made of a resin material and an antireflection film. The antireflection film consists of a dielectric layer formed on the substrate and a porous layer formed on the dielectric layer. The dielectric layer includes a first layer including silicon oxide and a second layer including tantalum oxide. The porous layer includes silicon oxide or magnesium fluoride.

Inventors

• Kazue Uchida

Assignees

• CANON KABUSHIKI KAISHA

Dates

Publication Date

20260512

Application Date

20211203

Priority Date

20201211

Claims (14)

1. 1 . An optical element comprising: a substrate made of a resin material; and an antireflection film, wherein the antireflection film consists of a dielectric layer formed on the substrate and a porous layer formed on the dielectric layer, the dielectric layer includes a first layer, and a second layer adjacent to the first layer and the porous layer, the porous layer comprises silicon oxide or magnesium fluoride, the first layer comprises silicon oxide at a weight ratio of 90% or more and aluminum oxide at a weight ratio of 10% or less, the second layer comprises tantalum oxide, and wherein the following inequality is satisfied: 1.15≤ n≤ 1.35 where n is a refractive index of the porous layer for the d-line.
2. 2 . The optical element according to claim 1 , wherein the second layer further comprises at least one of titanium oxide, lanthanum oxide, and zirconium oxide.
3. 3 . The optical element according to claim 1 , wherein the porous layer comprises a plurality of particles consisting of silicon oxide and a binder that binds the plurality of particles to each other.
4. 4 . The optical element according to claim 3 , wherein the plurality of particles are spherical hollow particles.
5. 5 . The optical element according to claim 3 , wherein the plurality of particles are solid particles and are bound to each other in a chain-like manner.
6. 6 . The optical element according to claim 1 , wherein the porous layer further comprises an alcohol with a density of 1.0 mg/cm 3 to 2.8 mg/cm 3 , the alcohol including at least one of an ether bond and an ester bond, including 4 to 7 carbon atoms, and having a branched structure.
7. 7 . The optical element according to claim 1 , wherein the dielectric layer consists of alternately stacked first and second layers.
8. 8 . The optical element according to claim 1 , wherein, among the layers forming the dielectric layer, the first layer is located at a position closest to the substrate.
9. 9 . The optical element according to claim 1 , wherein the following inequality is satisfied: 1.48≤ nd≤ 1.80 where nd is an average refractive index of the resin material for the d-line.
10. 10 . The optical element according to claim 1 , wherein the following inequality is satisfied: 1.5≤α≤30.0 where α is a coefficient of linear expansion (10 −5 /° C.) of the resin material.
11. 11 . The optical element according to claim 1 , wherein the optical element consists of the substrate and the antireflection film.
12. 12 . The optical element according to claim 1 , wherein the optical element consists of the substrate, the antireflection film, and a protective layer disposed on the antireflection film.
13. 13 . An optical device comprising: the optical element according to claim 1 ; and a holder holding the optical element.
14. 14 . An optical device comprising: the optical element according to claim 1 ; and an image-capturing element configured to receive light coming from the optical element.

Description

BACKGROUND OF THE INVENTION Field of the Invention The present disclosure relates to optical elements, for example, optical elements suitable for use in optical devices such as digital still cameras, digital video cameras, silver-halide film cameras, and telescopes. Description of the Related Art Japanese Patent Laid-Open No. 2017-134404 discloses an optical element including an antireflection film disposed on a substrate made of a resin material. The antireflection film consists of, in sequence, a multiple layer including a silicon oxide layer and a tantalum oxide layer, a homogeneous layer consisting of magnesium fluoride, and a homogeneous layer consisting of silicon oxide. In Japanese Patent Laid-Open No. 2017-134404, materials that can be formed without heating are used for the multiple layer disposed on the substrate to reduce thermal deformation of the substrate. However, a strong tensile stress occurs in the homogeneous layer consisting of magnesium fluoride according to Japanese Patent Laid-Open No. 2017-134404; therefore, film cracking (crack) or film peeling can occur due to changes in environmental conditions such as temperature. In addition, it is difficult to improve the antireflection performance of the antireflection film according to Japanese Patent Laid-Open No. 2017-134404 because the homogeneous layer consisting of silicon oxide is further disposed on the homogeneous layer consisting of magnesium fluoride. SUMMARY OF THE INVENTION An optical element according to an aspect of the present disclosure includes a substrate made of a resin material and an antireflection film. The antireflection film consists of a dielectric layer formed on the substrate and a porous layer formed on the dielectric layer. The dielectric layer includes a first layer including silicon oxide and a second layer including tantalum oxide. The porous layer includes silicon oxide or magnesium fluoride. Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A and 1B are schematic views of an optical element according to an embodiment of the present disclosure. FIG. 2 is a graph showing the reflectance characteristics of an optical element according to Example 1 of the present disclosure. FIG. 3 is a graph showing the reflectance characteristics of an optical element according to Example 2 of the present disclosure. FIG. 4 is a graph showing the reflectance characteristics of an optical element according to Example 3 of the present disclosure. FIG. 5 is a graph showing the reflectance characteristics of an optical element according to Example 4 of the present disclosure. FIG. 6 is a graph showing the reflectance characteristics of an optical element according to Example 5 of the present disclosure. FIG. 7 is a graph showing the reflectance characteristics of an optical element according to Example 6 of the present disclosure. FIG. 8 is a graph showing the reflectance characteristics of an optical element according to Example 7 of the present disclosure. FIG. 9 is a graph showing the reflectance characteristics of an optical element according to Example 8 of the present disclosure. FIG. 10 is a graph showing the reflectance characteristics of an optical element according to Example 9 of the present disclosure. FIG. 11 is a graph showing the reflectance characteristics of an optical element according to Example 10 of the present disclosure. FIG. 12 is a graph showing the reflectance characteristics of an optical element according to Example 11 of the present disclosure. FIG. 13 is a graph showing the reflectance characteristics of an optical element according to Example 12 of the present disclosure. FIG. 14 is a graph showing the reflectance characteristics of an optical element according to Comparative Example 1. FIG. 15 is a graph showing the reflectance characteristics of an optical element according to Comparative Example 2. FIG. 16 is a schematic view of an optical system according to an embodiment of the present disclosure. FIG. 17 is a schematic view of an optical device according to an embodiment of the present disclosure. DESCRIPTION OF THE EMBODIMENTS Embodiments of the present disclosure will now be described with reference to the drawings. The drawings may not be drawn to scale for purposes of illustration. In addition, the same members in the drawings are denoted by the same reference numerals, and a redundant description thereof is omitted. FIGS. 1A and 1B are schematic views (sectional views) of an optical element 300 according to an embodiment of the present disclosure. The optical element 300 includes a substrate (resin substrate) 200 made of a resin material and an antireflection film 100 formed on the substrate 200. “Resin material” according to the present embodiment refers to a material containing a resin (organic material) as a principal component, that is,