Diffractive optical element and optical system having the same

• US 6,330,110 B2
• Filed: 04/24/2001
• Issued: 12/11/2001
• Est. Priority Date: 07/28/1997
• Status: Expired due to Term

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Nakai, Takehiko
• Primary Examiner(s): Schuberg, Darren
• Assistant Examiner(s): ASSAF, FAYEZ G
• Application Number:
  US09/840,232
• Publication Number:
  US 20010013975A1
• Time in Patent Office: 231 Days
• Field of Search: 359/576, 359/566, 359/571, 359/569, 359/575
• US Class Current: 359/576
• CPC Class Codes: G02B 5/1852 using mechanical means, e.g. ruling with diamond tool, moulding
• CPC Class Codes: G02B 5/1895 such optical elements having dioptric power

Abstract

In a diffractive optical element composed of three or more laminated layers and having a diffraction grating at each interface between adjacent layers, each even-number-th layer has a uniform thickness.

Claims

1. A diffractive optical element comprises three or more layers made of at least three kinds of materials wherein a plurality of diffraction grating surfaces are formed at interfaces between adjacent layers, wherein each even-number-th layer has a uniform thickness, and

wherein the materials of first and third layers are different from each other in the dispersion, and for each of a plurality of different wavelengths, the optical-path-length difference generated between light beams having the wavelength passing said plurality of diffraction grating surfaces is an integral multiple of the wavelength.

2. A diffractive optical element according to claim 1, wherein the wavelength is λ

0, the refractive index of the second layer is no2, and the thickness of said second layer is d2, and the following is satisfied;

$\mathrm{no2}\times <br><br>\mathrm{d2}=\left(\frac{\mathrm{\lambda <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>o}{4}\right).$

9. An optical system using a diffractive optical element according to one of claims 1 and 2 to 8.

10. An optical system according to claim 9, wherein said optical system is an image forming optical system.

11. An optical system according to claim 9, wherein said optical system is an observation optical system.

12. An optical apparatus or an electronic apparatus having an optical system according to claim 9.

3. A diffractive optical element comprises three or more layers made of at least three kinds of materials,

wherein, where said three or more layers are counted in order as an I-th layer, a plurality of diffraction grating surfaces are formed such that a first diffraction grating surface which is formed at a boundary between the first layer and the second layer, a second diffraction grating surface which is formed at a boundary between the second layer and the third layer, up through an L-th diffraction grating surface which is formed at a boundary between the L-th layer and the (L+1)-th layer, and each even-number-th layer is a layer having a uniform thickness over an entire area thereof, and

wherein the materials of first and third layers are different from each other in dispersion, and for each of a plurality of different wavelengths, the optical-path-length difference generated between light beams having the wavelength passing said plurality of diffraction grating surfaces is an integral multiple of the wavelength.

4. A diffractive optical element according to claim 3, wherein the thickness of the uniform-thickness layer is greater than the depth of a grating groove of a diffraction grating surface formed at a boundary between the uniform-thickness layer and an adjacent layer.

5. A diffractive optical element according to claim 3, wherein the uniform-thickness layer has such a thickness as to provide a reflection-preventing characteristic.

6. A diffractive optical element according to claim 3, wherein the uniform-thickness layer is made of a plastic optical material or an ultraviolet curable resin.

7. A diffractive optical element according to claim 3, wherein the useful wavelength region is a visible spectrum.

8. A diffractive optical element according to claim 3, wherein the first layer is formed on a base plate, and the first layer and the base plate are made of the same material.