DIFFRACTIVE OPTICAL ELEMENT AND OPTICAL SYSTEM HAVING THE SAME

• US 20080055727A1
• Filed: 08/29/2007
• Published: 03/06/2008
• Est. Priority Date: 09/04/2006
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Inoguchi, Kazutaka
• Granted Patent: US 7,710,650 B2
• Time in Patent Office: Days
• US Class Current: 359/574
• CPC Class Codes: G02B 27/0037 with diffracting elements G02B27/0056 takes precedence; holographic optical elements G02B5/32; zone systems G02B5/1876
• CPC Class Codes: G02B 27/4211 correcting chromatic aberrations G02B27/0056, G02B27/4222, G02B27/4227 take precedence
• CPC Class Codes: G02B 27/4277 being separated by an air space
• CPC Class Codes: G02B 27/4288 having uniform diffraction efficiency over a large spectral bandwidth
• CPC Class Codes: G02B 5/1895 such optical elements having dioptric power

Abstract

A diffractive optical element includes a plurality of layered diffraction gratings which includes two diffraction gratings made of materials having different dispersive powers. The plurality of diffraction gratings includes a first diffraction grating having a plurality of grating portions provided on a first base surface, and a second diffraction grating having a plurality of grating portions which are provided on a second base surface. In the second diffraction grating, a height of the grating portion of the central circular zone from the second base surface is greater than a height of the grating portion of the peripheral circular zone from the second base surface.

Claims

1. A diffractive optical element comprising:

a plurality of diffraction gratings which includes two diffraction gratings made of materials having different dispersive powers, the plurality of diffraction gratings including,

a first diffraction grating having a plurality of circular-zone-like grating portions which are provided on a first base surface, and

a second diffraction grating having a plurality of circular-zone-like grating portions which are provided on a second base surface, the plurality of grating portions of the second diffraction grating including a grating portion of a central circular zone and a grating portion of a peripheral circular zone,

wherein in the second diffraction grating, a height of the grating portion of the central circular zone from the second base surface is greater than a height of the grating portion of the peripheral circular zone from the second base surface.

2. The diffractive optical element according to claim 1,

wherein the plurality of grating portions of the first diffraction grating includes a grating portion of a central circular zone and a grating portion of a peripheral circular zone, and

wherein the grating portion of the peripheral circular zone of the first diffraction grating, and the grating portion of the peripheral circular zone of the second diffraction grating are disposed with an air layer interposed therebetween.

3. The diffractive optical element according to claim 1, wherein a grating surface of the grating portion of the central circular zone of the second diffraction grating, and a grating surface of the grating portion of the central circular zone of the first diffraction grating are in a contact state.

4. The diffractive optical element according to claim 3, wherein in each of the first and second diffraction gratings, a profile of the grating portion of the central circular zone and a profile of the grating portion of the peripheral circular zone are determined in accordance with different phase functions.

5. The diffractive optical element according to claim 3, wherein a grating height d of each of the grating portions of the central circular zones of the first and second diffraction gratings is determined as follows:

d=mλ

0/(n01−

n02)

where n01 is a refractive index of the material of the first diffraction grating with a wavelength λ

e, n02 is a refractive index of the material of the second diffraction grating with the wavelength λ

0, and m is an integer.

6. The diffractive optical element according to claim 3, wherein an optical path difference function φ

(r) of the diffractive optical element is determined as follows;

φ

(r)=C1·

r²+C2·

r⁴+C3·

r⁶+ . . .

where r is a distance from the center of the diffractive optical element, and C1, C2, C3, . . . are constants, and

wherein a curvature radius R of each of the grating surfaces of the grating portions of the central circular zones of the first and second diffraction gratings in the contact state satisfies the following condition;

R=−

0.5×

(n02−

n01)/C1

where n01 is a refractive index of the material of the first diffraction grating with a wavelength λ

0, and n02 is a refractive index of the material of the second diffraction grating with the wavelength λ

0.

7. A diffractive optical element comprising:

a plurality of diffraction gratings which includes two diffraction gratings made of materials having different dispersive powers, the plurality of diffraction gratings including,

a first diffraction grating having a plurality of circular-zone-like grating portions which are provided on a first base surface, the plurality of grating portions of the first diffraction grating including a grating portion of a central circular zone and a grating portion of a peripheral circular zone, and

a second diffraction grating having a plurality of circular-zone-like grating portions which are provided on a second base surface, the plurality of grating portions of the second diffraction grating including a grating portion of a central circular zone and a grating portion of a peripheral circular zone,

wherein a distance between a grating surface of the grating portion of the central circular zone of the first diffraction grating and a grating surface of the grating portion of the central circular zone of the second diffraction grating is smaller than a distance between a grating surface of the grating portion of the peripheral circular zone of the first diffraction grating and a grating surface of the grating portion of the peripheral circular zone of the second diffraction grating.

8. The diffractive optical element according to claim 7,

wherein the grating portion of the peripheral circular zone of the first diffraction grating, and the grating portion of the peripheral circular zone of the second diffraction grating are disposed with an air layer interposed therebetween.

9. The diffractive optical element according to claim 7, wherein a grating surface of the grating portion of the central circular zone of the second diffraction grating, and a grating surface of the grating portion of the central circular zone of the first diffraction grating are in a contact state.

10. An optical system comprising:

a diffractive optical element which includes,

a plurality of diffraction gratings which includes two diffraction gratings made of materials having different dispersive powers, the plurality of diffraction gratings including,

a first diffraction grating having a plurality of circular-zone-like grating portions which are provided on a first base surface, and

a second diffraction grating having a plurality of circular-zone-like grating portions which are provided on a second base surface, the plurality of grating portions of the second diffraction grating including a grating portion of a central circular zone and a grating portion of a peripheral circular zone,

wherein in the second diffraction grating, a height of the grating portion of the central circular zone from the second base surface is greater than a height of the grating portion of the peripheral circular zone from the second base surface; and

a refractive optical element.

11. An optical system comprising:

a diffractive optical element including,

a plurality of diffraction gratings which includes two diffraction gratings made of materials having different dispersive powers, the plurality of diffraction gratings including,

a first diffraction grating having a plurality of circular-zone-like grating portions which are provided on a first base surface, the plurality of grating portions of the first diffraction grating including a grating portion of a central circular zone and a grating portion of a peripheral circular zone, and

a second diffraction grating having a plurality of circular-zone-like grating portions which are provided on a second base surface, the plurality of grating portions of the second diffraction grating including a grating portion of a central circular zone and a grating portion of a peripheral circular zone,

wherein a distance between a grating surface of the grating portion of the central circular zone of the first diffraction grating and a grating surface of the grating portion of the central circular zone of the second diffraction grating is smaller than a distance between a grating surface of the grating portion of the peripheral circular zone of the first diffraction grating and a grating surface of the grating portion of the peripheral circular zone of the second diffraction grating; and

a refractive optical element.