Antireflection film, and optical element and optical system that include the same

Patent metadata

Field	Value
Publication number	US-9715044-B2
Application number	US-201514823375-A
Country	US
Kind code	B2
Filing date	Aug 11, 2015
Priority date	Aug 27, 2014
Publication date	Jul 25, 2017
Grant date	Jul 25, 2017

Abstract

An antireflection film formed on a substrate having a refractive index between 1.40 and 1.85 inclusive for light having a wavelength of 550 nm includes an intermediate layer formed on the substrate, and a concavo-convex layer formed on the intermediate layer, the concavo-convex layer includes a part has a refractive index that continuously increases from a side closer to a surface toward a side closer to the substrate, the intermediate layer includes a plurality of thin film layers having different refractive indices, and at least one of the thin film layers has a refractive index higher than the refractive index of the substrate, and the thin film layers include a first layer formed on the substrate and having a physical thickness d 1 , and a second layer formed on the first layer and having a physical thickness d 2 , and satisfy predetermined conditional expressions.

First claim

What is claimed is:

1. An optical element comprising:
a substrate having a refractive index between 1.40 and 1.85 inclusive for light having a wavelength of 550 nm, and
an antireflection film including an intermediate layer arranged on the substrate and a concavo-convex layer arranged on the intermediate layer, wherein:
the concavo-convex layer includes a part having a refractive index that continuously increases from a side closer to a surface toward a side closer to the substrate,
the intermediate layer includes a plurality of thin film layers having different refractive indices, and at least one of the thin film layers has a refractive index higher than the refractive index of the substrate,
the thin film layers include:
a first layer arranged on the substrate, and
a second layer arranged on the first layer and having a physical thickness d 2 (nm), and
the following conditional expressions are satisfied:
ns<n2,
1.72≦n2≦1.95, and

230≦n2d2≦290,

where ns is the refractive index of the substrate at a wavelength of 550 nm, and n 2 is a refractive index of the second layer at a wavelength of 550 nm.

2. The optical element according to claim 1 , wherein the following conditional expressions are satisfied:
1.55≦n1≦1.76, and

100≦n1d1≦300,

where n 1 is a refractive index of the first layer at a wavelength of 550 nm, and and d 1 (nm) is a physical thickness of the first layer.

3. The optical element according to claim 1 , wherein:
the concavo-convex layer includes a homogeneous layer having a refractive index that does not change in a thickness direction, and
the thin film layers further include a third layer formed on the second layer and having a physical thickness d 3 (nm), and
the following conditional expressions are satisfied:
1.35≦na≦1.58, and

70 ≦n 3 d 3 +nada≦ 100,

where na is a refractive index of the homogeneous layer at a wavelength of 550 nm, da (nm) is a physical thickness of the homogeneous layer, and n 3 is a refractive index of the third layer at a wavelength of 550 nm.

4. The optical element according to claim 1 , wherein the concavo-convex layer consists of plate crystal including aluminum oxide as a primary component.

5. The optical element according to claim 1 , wherein:
the concavo-convex layer is formed by performing a hot-water treatment on a layer including aluminum oxide as a primary component, and
the thin film layers are formed by an evaporation method or sputtering method.

6. The optical element according to claim 1 , wherein the concavo-convex layer has an average pitch smaller than a shortest wavelength in a use wavelength range.

7. The optical element according to claim 1 , wherein a use wavelength range is between 400 nm and 700 nm inclusive.

8. The optical element according to claim 1 , wherein the concavo-convex layer has an average pitch smaller than 400 nm.

9. The optical element according to claim 1 , wherein the concavo-convex layer has an optical thickness between 180 nm and 300 nm inclusive.

10. An optical system comprising a plurality of optical elements, wherein:
at least one of the optical elements includes a substrate having a refractive index between 1.40 and 1.85 inclusive for light having a wavelength of 550 nm, and an antireflection film including an intermediate layer arranged on the substrate and a concavo-convex layer arranged on the intermediate layer,
the concavo-convex layer includes a part having a refractive index that continuously increases from a side closer to a surface toward a side closer to the substrate,
the intermediate layer includes a plurality of thin film layers having different refractive indices, and at least one of the thin film layers has a refractive index higher than the refractive index of the substrate, and
the thin film layers include:
a first layer arranged on the substrate, and
a second layer arranged on the first layer and having a physical thickness d 2 (nm), and the following conditional expressions are satisfied:
ns<n2,
1.72≦n2≦1.95, and

230≦n2d2≦290,

where ns is the refractive index of the substrate at a wavelength of 550 nm, and n 2 is a refractive index of the second layer at a wavelength of 550 nm.

11. The optical element according to claim 1 , wherein the thin film layers further include a third layer arranged on the second layer and having a physical thickness d 3 (nm), and the following conditional expression are satisfied:
1.36≦n3≦1.55, and

n3d3≦100,

where n 3 is a refractive index of the third layer at a wavelength of 550 nm.

Assignees

• Canon Kk

Inventors

• Ishimatsu Rie

Classifications

• G02B1/115 Primary

  Multilayers · CPC title

• G02B1/118

  having sub-optical wavelength surface structures designed to provide an enhanced transmittance, e.g. moth-eye structures · CPC title

• G02B1/11

  Anti-reflection coatings · CPC title

• G02B1/113

  using inorganic layer materials only · CPC title