Optical element and optical apparatus
The optical element includes in order from a light-entering side, a first layer ( 012 ), a second layer ( 013 ), and a base member ( 011 ). The first layer includes a concavo-convex structure with convex portions ( 012 a ) and concave portions ( 012 b ) alternately formed at a pitch smaller than a wavelength λ of entering light, and the second layer satisfies the following conditions: nb · n s - 0.15 ≤ n A ≤ nb · n s + 0.10 λ 8 · n A ≤ dA ≤ λ n A where ns represents an effective refractive index of the first layer, nb represents a refractive index of the base member, and nA and dA respectively represent a refractive index and a thickness of the second layer.
1. An optical element comprising in order from a light-entering side:
a first layer;
a second layer; and
a base member,
wherein the first layer includes a concavo-convex structure with convex portions and concave portions alternately formed at a pitch smaller than a wavelength λ of entering light, and
wherein the second layer satisfies the following conditions:
nb
·
n
s
-
0.15
≤
n
A
≤
nb
·
n
s
+
0.10
λ
8
·
n
A
≤
dA
≤
λ
n
A
where ns represents an effective refractive index of the first layer, nb represents a refractive index of the base member, and nA and dA respectively represent a refractive index and a thickness of the second layer.
2. An optical element according to claim 1 , wherein the convex portion and the concave portion change in width in a thickness direction of the first layer, wherein ns represents an effective refractive index of part of the concavo-convex structure, the part being closest to the base member.
3. An optical element according to claim 1 or 2 , further comprising a third layer disposed between the first layer and the second layer, the third layer satisfying the following condition:
0
<
d
B
≤
λ
5
·
nB
where nB and dB respectively represent a refractive index and a thickness of the third layer.
4. An optical element according claim 1 or 2 , wherein the first layer and a layer adjacent to the first layer include mutually different materials.
5. An optical apparatus, comprising:
an optical element according to claim 1 or 2 .
6. An optical element according to claim 3 , wherein the first layer and a layer adjacent to the first layer include mutually different materials.
7. An optical apparatus, comprising:
an optical element according to claim 3 .
8. An optical apparatus, comprising:
an optical element according to claim 4 .
9. An optical apparatus, comprising:
an optical element according to claim 6 .