DIFFRACTIVE OPTICAL ELEMENT AND OPTICAL SYSTEM INCLUDING THE SAME

• US 20090141354A1
• Filed: 12/03/2008
• Published: 06/04/2009
• Est. Priority Date: 12/03/2007
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Kobayashi, Mikio
• Granted Patent: US 8,159,747 B2
• Time in Patent Office: Days
• US Class Current: 359/571
• CPC Class Codes: B29D 11/0073 Optical laminates
• CPC Class Codes: G02B 5/1852 using mechanical means, e.g. ruling with diamond tool, moulding
• CPC Class Codes: G02B 5/188 Plurality of such optical elements formed in or on a supporting substrate

Abstract

A diffractive optical element includes at least one element portion including a base, a diffraction grating, a substrate, and an intermediate layer. The base and the diffraction grating are disposed above the substrate through the intermediate layer, and are formed of a same material. An extinction coefficient for the d-line of the material of the diffraction grating and an extinction coefficient for the d-line of a material of the intermediate layer are properly set to satisfied conditional expressions.

Claims

1. A diffractive optical element comprising:

at least one element portion including a base, a diffraction grating, a substrate, and an intermediate layer, the base and the diffraction grating disposed above the substrate through the intermediate layer,

wherein the base and the diffraction grating are formed of a same material, and

wherein the following conditional expressions are satisfied;

3.0×

10<sup>−

4</sup><

Ka<

1.0×

10<sup>−

3</sup>, and

Kb<

3.0×

10<sup>−

4</sup>

where Ka and Kb are an extinction coefficient for the d-line of the material of the diffraction grating and an extinction coefficient for the d-line of a material of the intermediate layer respectively.

2. The diffractive optical element according to claim 1, wherein the diffraction grating includes a sawtooth grating portion,

wherein a sawtooth periodic structure is provided at an interface between the intermediate layer and the base, has a period that is the same as a grating period of the diffraction grating, and is formed of a material that is the same as that of the intermediate layer, and

wherein the following conditional expression is satisfied:

|dx×

Δ

N_d|/λ

_d<

0.2

where dx is a grating height of a grating section of the periodic structure within any period, and Δ

N_d is a difference between refractive indices at a wavelength λ

_d of the d-line of the material of the diffraction grating and the d-line of the material of the intermediate layer.

3. The diffractive optical element according to claim 2, wherein the following conditional expressions are satisfied:

0.4<

|Δ

N_g/Δ

N_d|<

1.5, and

0.6<

|Δ

N_C/Δ

N_d|<

2.2

where Δ

N_g is a difference between refractive indices for the g-line of the material of the diffraction grating and the g-line of the material of the intermediate layer, Δ

N_d is a difference between the refractive indices for the d-line of the material of the diffraction grating and the d-line of the material of the intermediate layer, and Δ

N_C is a difference between refractive indices for the C-line of the material of the diffraction grating and the C-line of the material of the intermediate layer.

4. The diffractive optical element according to claim 1, wherein the diffraction grating includes a sawtooth grating portion,

wherein a sawtooth periodic structure is provided at an interface between the intermediate layer and the base, has a period that is the same as a grating period of the diffraction grating, and is formed of a material that is the same as that of the intermediate layer, and

wherein the following conditional expression is satisfied:

|dx×

Δ

N_d×

Δ

P|/(λ

_d×

P)<

0.013

where dx is a grating height of a grating section of the sawtooth periodic structure within any period, Δ

N_d is a difference between refractive indices at a wavelength λ

_d of the d-line of the material of the diffraction grating and the d-line of the material of the intermediate layer, P is a grating pitch of the diffraction grating, and Δ

P is a distance in a grating pitch direction between a position of a maximum height of the grating section of the sawtooth periodic structure and a grating apex of the sawtooth grating portion of the diffraction grating within the same period.

5. The diffractive optical element according to claim 1, wherein the diffraction grating includes a sawtooth grating portion,

wherein a sawtooth periodic structure is provided at an interface between the intermediate layer and the base, has a period that is the same as a grating period of the diffraction grating, and is formed of a material that is the same as that of the intermediate layer, and

wherein a grating section of the sawtooth periodic structure is oriented so that directions in which heights of the grating section and the sawtooth grating portion of the diffraction grating are increased and decreased are the same.

6. The diffractive optical element according to claim 1, wherein the following conditional expression is satisfied:

(Da−

D)<

8 (μ

m)

where D (μ

m) is a maximum grating thickness of the grating portion of the diffraction grating, and Da (μ

m) is a sum of the maximum grating thickness of the grating portion and a maximum grating thickness of the base.

7. The diffractive optical element according to claim 1, wherein the following conditional expression is satisfied:

10 (μ

m)<

Db

where Db (μ

m) is a thickness of the intermediate layer.

8. The diffractive optical element according to claim 1, wherein the material of the diffraction grating is one in which a fine-particle material is mixed with a resin material.

9. The diffractive optical element according to claim 8, wherein an average particle diameter of the fine-particle material is less than or equal to 1/20 of 590 nm.

10. The diffractive optical element according to claim 8, wherein the fine-particle material is indium tin oxide.

11. The diffractive optical element according to claim 8, wherein the resin material is ultraviolet curable resin.

12. An optical system comprising:

a refractive optical element; and

the diffractive optical element of claim 1.

13. An optical apparatus comprising:

the optical system according to claim 12; and

a photoelectric conversion element that receives an image that is formed by the optical system.

14. A method of producing a diffractive optical element comprising:

a first step in which a first material, including first light energy curable resin, is squeezed in a mold, where a diffraction surface of a periodic structure is formed, or the first material is molded with a flat mold to flatten an interface, after which a change in shape is concentrated at a free-surface side of the first material that is not in contact with the mold, for hardening the first material; and

a second step in which a second material, including second light energy curable resin having an extinction coefficient that is smaller than that of the first material, is molded at the free-surface side of the hardened first material by replica molding.