Optical element, optical system, and optical apparatus
An optical element has an area in which a transmittance varies, includes first and second antireflection layers, and an absorption layer disposed between the first and second antireflection layers, and satisfies certain conditions.
1. An optical element having an area in which a transmittance varies, the optical element comprising:
first and second antireflection layers;
an absorption layer disposed between the first and second antireflection layers; and
first and second light transmitting members,
wherein the first and second antireflection layers are disposed between the first and second light transmitting members,
wherein the absorption layer includes a first film adjacent to the first antireflection layer and a second film adjacent to the second antireflection layer,
wherein the first antireflection layer includes a third film adjacent to the first film,
wherein the second antireflection layer includes a fourth film adjacent to the second film, and
wherein the following conditional expressions are satisfied,
| n A −n 1 |≤0.35, and
| n B −n 2 |≤0.35,
where n A is a refractive index of the first film, n B is a refractive index of the second film, n 1 is a refractive index of the third film, and n 2 is a refractive index of the fourth film.
2. The optical element according to claim 1 , wherein the following conditional expression is satisfied,
| N s −N g |≤0.45,
where N s is a refractive index of the first light transmitting member and N g is a refractive index of the second light transmitting member.
3. The optical element according to claim 1 , wherein the number of films of the first antireflection layer is equal to the number of films of the second antireflection layer.
4. The optical element according to claim 1 , wherein the first antireflection layer includes a plurality of films including the third film, and the second antireflection layer includes a plurality of films including the fourth film.
5. The optical element according to claim 1 , wherein the first and second films are the same material.
6. The optical element according to claim 1 , wherein the absorption layer includes a plurality of films including the first and second films.
7. The optical element according to claim 1 , wherein the absorption layer has a concentric film thickness distribution.
8. The optical element according to claim 1 , wherein a film thickness of the absorption layer increases from a center to a peripheral portion.
9. The optical element according to claim 1 , wherein the absorption layer is not provided at a center in a radial direction.
10. The optical element according to claim 1 , wherein the following conditional expression is satisfied
0.05≤ k≤ 0.35,
where k is an extinction coefficient of the absorption layer.
11. An optical system comprising a plurality of optical elements, one of which has an area in which a transmittance varies and includes:
first and second antireflection layers;
an absorption layer disposed between the first and second antireflection layers; and
first and second light transmitting members,
wherein the first and second antireflection layers are disposed between the first and second light transmitting members,
wherein the absorption layer includes a first film adjacent to the first antireflection layer and a second film adjacent to the second antireflection layer,
wherein the first antireflection layer includes a third film adjacent to the first film,
wherein the second antireflection layer includes a fourth film adjacent to the second film, and
wherein the following conditional expressions are satisfied,
| n A −n 1 |≤0.35, and
| n B −n 2 |≤0.35,
where n A is a refractive index of the first film, n B is a refractive index of the second film, n 1 is a refractive index of the third film, and n 2 is a refractive index of the fourth film.
12. An optical apparatus comprising:
an image sensor;
an optical element having an area in which a transmittance varies; and
first and second light transmitting members,
wherein the first and second antireflection layers are disposed between the first and second light transmitting members,
wherein the optical element includes:
first and second antireflection layers; and
an absorption layer disposed between the first and second antireflection layers,
wherein the absorption layer includes a first film adjacent to the first antireflection layer and a second film adjacent to the second antireflection layer,
wherein the first antireflection layer includes a third film adjacent to the first film,
wherein the second antireflection layer includes a fourth film adjacent to the second film, and
wherein the following conditional expressions are satisfied,
| n A −n 1 |≤0.35, and
| n B −n 2 |≤0.35,
where n A is a refractive index of the first film, n B is a refractive index of the second film, n 1 is a refractive index of the third film, and n 2 is a refractive index of the fourth film.
13. The optical element according to claim 1 , wherein the following conditional expressions are satisfied,
N s >1.40, and
N g >1.40,
where N s is a refractive index of the first light transmitting member and N g is a refractive index of the second light transmitting member.