Diffractive optical element, and optical system and optical apparatus provided with the same

• US 20030231396A1
• Filed: 06/02/2003
• Published: 12/18/2003
• Est. Priority Date: 06/17/2002
• Status: Active Grant

• Current Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Original Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Inventors: Nakai, Takehiko
• Granted Patent: US 6,930,833 B2
• Time in Patent Office: Days
• US Class Current: 359/569
• CPC Class Codes: G02B 27/0056 by using a diffractive optical element
• CPC Class Codes: G02B 5/1895 such optical elements having dioptric power

Abstract

A layered diffractive optical element is disclosed, with which a high diffraction efficiency is attained over a broad region of used wavelengths, and with which diffraction light of unnecessary diffraction orders can be suppressed. A diffractive optical element of the present invention includes a plurality of diffraction gratings made of materials with different Abbe numbers, the plurality of diffraction gratings being layered with each other. Moreover, the partial dispersion ratio with respect to a g-line and a F-line of the material constituting at least one of the plurality of diffraction gratings satisfies the condition represented by a specified expression.

Claims

1. A diffractive optical element comprising:

a plurality of diffraction gratings made of materials with different Abbe numbers ν

_d, wherein the plurality of diffraction gratings are layered with each other, leaving a certain interval therebetween;

wherein a partial dispersion ratio θ

_{g, F} with respect to a g-line and a F-line of the material constituting at least one of the plurality of diffraction gratings satisfies the following condition;

θ

_{g, F}<

(−

{fraction (1/600)})ν

_d+0.55

where

θ

_{g, F}=(n_g−

n_F)/(n_F−

n_c) ν

_d=(n_d−

1)/(n_F−

n_c)

and n_g, n_F, n_d and n_c are the refractive indices at the g-line, the F-line, a d-line and a C-line, respectively.

2. The diffractive optical element according to claim 1,

wherein the grating thickness of each of the plurality of diffraction gratings is 10 μ

m or less.

3. The diffractive optical element according to claim 1,

wherein the Abbe number of the material satisfying the condition is 30 or less.

4. The diffractive optical element according to claim 1,

wherein the Abbe number of at least one material which does not satisfy the condition, of the plurality of diffraction gratings is 40 or more.

5. The diffractive optical element according to claim 1,

wherein the material satisfying the condition is a material obtained by mixing particles whose Abbe number is 15 or less into a resin.

6. The diffractive optical element according to claim 5,

wherein a particle diameter of the particles is {fraction (1/20)} of the wavelength of incident light or less.

7. The diffractive optical element according to claim 5,

wherein the particle material is TiO₂ or ITO.

8. The diffractive optical element according to claim 5,

wherein the resin material is a UV curing resin.

9. The diffractive optical element according to claim 1,

wherein a change direction of the grating thickness in grating period direction of at least one of the plurality of diffraction gratings is different from a change direction of the grating thickness of another diffraction grating.

10. The diffractive optical element according to claim 1,

wherein each of the plurality of diffraction gratings satisfies the following condition:

d/P<

⅙

where P is grating pitch and d is grating thickness.

11. The diffractive optical element according to claim 1,

wherein light of a visible wavelength region is incident on the diffractive optical element.

12. An optical system comprising:

a refractive optical element; and

a diffractive optical element according to claim 1.