# US 7,612,941 B2 · Diffractive optical element and optical system including the same

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- Number: US 7,612,941 B2
- Document ID: US7612941B2
- Status: Granted
- Kind: B2
- Application number: 11/849,971
- Filed: 2007-09-04
- Published: 2007-12-27
- Granted: 2009-11-03
- Earliest claimed: 2004-04-01
- Assignees: Canon Kabuhsiki Kaisha
- Inventors: Takehiko Nakai
- Web page: https://patentgrep.com/patent/US7612941B2

## CPC

- G02B 5/1895: {such optical elements having dioptric power}
- 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)}
- 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)}
- G02B 27/0037: {with diffracting elements (G02B27/0056 takes precedence; holographic optical elements G02B5/32; zone systems G02B5/1876)}
- G02B 27/42: Diffraction optics {, i.e. systems including a diffractive element being designed for providing a diffractive effect}(G02B27/60 takes precedence)
- G02B 27/4211: {correcting chromatic aberrations (G02B27/0056, G02B27/4222, G02B27/4227 take precedence)}
- G02B 27/4277: {being separated by an air space}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## 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

### Claim 1

An optical system comprising:
a diffractive optical element including a plurality of diffraction gratings laminated and being composed of at least two materials having different dispersions; and
a refractive optical element,
wherein at least one of the diffraction gratings includes a plurality of grating parts having a curved grating surface and grating tips that 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,
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,
wherein 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 an optical axis of the optical system, and
wherein the plurality of diffraction gratings are bonded together at an area where the grating parts are not formed.