Optical element, and optical system and optical apparatus using same
The optical element of the present invention has an anti-reflection film formed on a substrate. Here, the anti-reflection film comprises a first layer formed on the substrate; a second layer formed on the first layer and consisting of a material different from that of the first layer; and a third layer formed on the second layer and consisting of a concave-convex structure. Also, the third layer has three regions of which a refractive index for each thickness changes at a constant rate by continuously changing the space filling factor of the concave-convex structure.
1. An optical element having an anti-reflection film formed on a substrate, wherein the anti-reflection film comprises:
a first layer formed on the substrate;
a second layer formed on the first layer and consisting of a material different from that of the first layer; and
a third layer formed on the second layer and consisting of a concave-convex structure,
wherein, when a wavelength defining a refractive index is 550 nm, the substrate has a refractive index in the range of from 1.65 to 2.20, the first layer has a thickness in the range of from 30 to 70 nm and a refractive index in the range of from 1.52 to 1.82, the second layer has a thickness in the range of from 10 to 50 nm and a refractive index in the range of from 1.40 to 1.58, and the third layer has a thickness in the range of from 200 to 300 nm and the refractive index of the third layer changes from a value in the range of from 1.40 to 1.58 toward 1.0, and
wherein the third layer comprises, in order from the second layer:
a first region that has a thickness in the range of from 15 to 45 nm and a refractive index changing at a rate in the range of from 4.4 to 12×10 −3 nm −1 ;
a second region that has a thickness in the range of from 25 to 75 nm and a refractive index changing at a rate in the range of from 1.9 to 4.3×10 −3 nm −1 ; and
a third region that has a thickness in the range of from 120 to 200 nm and a refractive index changing at a rate in the range of from 0.9 to 1.8×10 −3 nm −1 .
2. The optical element according to claim 1 , wherein the first layer, the second layer, and the third layer are formed by a wet process.
3. The optical element according to claim 1 , wherein the first layer is an organic resin layer.
4. The optical element according to claim 1 , wherein the second layer is a porous layer whose principal component is aluminum oxide.
5. The optical element according to claim 1 , wherein the third layer is formed of a plate-like crystal whose principal component is aluminum oxide.
6. An optical system having at least two or more optical elements, wherein at least one of the optical elements is the optical element according to claim 1 .
7. An optical apparatus having an optical system, wherein the optical system is the optical system according to claim 6 .