Diffractive optical element and optical system including the same

• US 20050219702A1
• Filed: 03/29/2005
• Published: 10/06/2005
• Est. Priority Date: 04/01/2004
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Nakai, Takehiko
• Granted Patent: US 7,301,702 B2
• Time in Patent Office: Days
• US Class Current: 359/573
• 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 27/42 Diffraction optics , i.e. systems including a diffractive element being designed for providing a diffractive effectG02B27/60 takes precedence
• 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 5/1814 structurally combined with one or more further optical elements, e.g. lenses, mirrors, prisms or other diffraction gratings G02B5/189 takes precedence
• CPC Class Codes: G02B 5/1866 Transmission gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials G02B5/1809, G02B5/1828, G02B5/1833, G02B5/1838 and G02B5/1847 take precedence
• CPC Class Codes: G02B 5/1895 such optical elements having dioptric power

Abstract

A diffractive optical element includes a plurality of diffraction gratings. A diffraction grating within the plurality of diffraction gratings includes a plurality of grating parts having a curved grating surface and grating tips which connect to define a curved envelope face. The grating surface has a radius of curvature larger than a radius of curvature of the envelope face. In addition, two diffraction gratings within the plurality of diffraction gratings are composed of different materials having different dispersions. Therefore, even when the radius of curvature of the envelope face is small, the degradation of the diffraction efficiency is suppressed.

Claims

1. A diffractive optical element having

a plurality of diffraction gratings laminated and being composed of at least two materials having different dispersions, said diffractive optical element comprising:

a diffraction grating including a plurality of grating parts having a curved grating surface and grating tips which connect to define a curved envelope face,

wherein the grating surface has a radius of curvature larger than a radius of curvature of the envelope face.

2. The diffractive optical element according to claim 1, wherein the grating part has a grating side, and wherein the grating surface and the grating side define a first angle larger than a second angle defined between the grating surface and a normal to the envelope face, the normal to the envelope face being defined at a position where one of the grating tips lies on the envelope face.

3. The diffractive optical element according to claim 1, the grating parts of the diffraction grating are arranged concentrically with respect to each other, and the grating side of the grating part is substantially parallel to the optical axis.

4. The diffractive optical element according to claim 1, wherein the plurality of diffraction gratings are bonded together at an area where the grating parts are not formed.

5. The diffractive optical element according to claim 1, wherein the plurality of diffraction gratings including first and second diffraction gratings, and the first diffraction grating has a first grating thickness varying along a first direction and the second diffraction grating has a second grating thickness varying along a second direction different from the first direction.

6. The diffractive optical element according to claim 1, wherein, at a plurality of wavelengths in a wavelength range, a maximum difference in an optical path length of light passing through the plurality of diffraction gratings is an integral multiple of a corresponding wavelength.

7. The diffractive optical element according to claim 6, wherein the wavelength range is a visible range.

8. The diffractive optical element according to claim 1, further comprising an air gap defined between two diffraction gratings within the plurality of diffraction gratings.

9. An optical system comprising:

the diffractive optical element according to claim 1;

and

a refractive optical element.

10. The optical system according to claim 9, wherein an absolute value of the radius of curvature of the envelope face is between one-fifteenth of a focal length of the optical system to one-half of the focal length of the optical system, inclusive.