Picture taking apparatus having diffractive optical element

• US 6,757,104 B2
• Filed: 04/19/2001
• Issued: 06/29/2004
• Est. Priority Date: 04/20/2000
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Nakai, Takehiko
• Primary Examiner(s): Robinson, Mark A.
• Assistant Examiner(s): AMARI, ALESSANDRO V
• Application Number:
  US09/838,422
• Publication Number:
  US 20020034011A1
• Time in Patent Office: 1,167 Days
• Field of Search: 359/576, 359/569
• US Class Current: 359/569
• CPC Class Codes: G02B 27/4211 correcting chromatic aberrations G02B27/0056, G02B27/4222, G02B27/4227 take precedence
• CPC Class Codes: G02B 27/4216 correcting geometrical aberrations
• CPC Class Codes: G02B 27/4272 having plural diffractive elements positioned sequentially along the optical path
• CPC Class Codes: G02B 27/4277 being separated by an air space
• CPC Class Codes: G02B 5/1823 in an overlapping or superposed manner

Abstract

In order to obtain a diffractive optical element with which a high diffraction efficiency can be obtained in a wide wavelength range and color flare is not noticeable and a picture taking apparatus using this diffractive optical element, an image is formed on a picture taking unit by using a diffractive optical element in an optical system. The diffractive optical element has a grating structure obtained by stacking a plurality of diffraction gratings made of at least two types of materials with different dispersion properties to enhance diffraction efficiency for a particular design order throughout a predetermined wavelength region and a plurality of design wavelengths which exist in a predetermined design order and at which a maximum optical path length difference in the grating structure becomes an integer multiple of a wavelength, the diffractive optical element having a design wavelength λ0 satisfying predetermined conditions.

Claims

1. A picture taking apparatus having a diffractive optical element, which forms an image on photosensitive surface by using said diffractive optical element in an optical system, said diffractive optical element having a grating structure obtained by stacking a plurality of diffraction gratings made of at least two types of materials with different dispersion properties to enhance diffraction efficiency for a particular design order throughout a predetermined wavelength region and the grating structure is designed in such a way that a maximum optical path length difference becomes an integer multiple of a predetermined wavelength, wherein said diffractive optical element having a design wavelength λ

0, as the predetermined wave length, satisfying conditions given below;

2. An apparatus according to claim 1, wherein said plurality of diffraction gratings stacked on each other include at least one diffraction grating whose direction of an increasing or decreasing of a grating thickness differs from that of remaining diffraction gratings.

3. An apparatus according to claim 1, wherein the predetermined wavelength region is a visible region.

4. An apparatus according to claim 1, wherein said diffraction gratings are stacked on a substrate, and when said stacked diffraction gratings are named as a first diffraction grating, a second diffraction grating, and an ith diffraction grating, starting from said diffraction grating close to the substrate, said first diffraction grating and the substrate are made of the same material.

5. An apparatus according to claim 1, wherein said optical system comprises an imaging optical system.

6. A diffractive optical element used in an optical system to form an image on photosensitive surface, said diffractive optical element having a grating structure obtained by stacking a plurality of diffraction gratings made of at least two types of materials with different dispersion properties to enhance diffraction efficiency for a particular design order throughout a predetermined wavelength region and the grating structure is designed in such a way that a maximum optical path length difference becomes an integer multiple of a predetermined wavelength, wherein said diffractive optical element having a design wavelength λ

0, as the predetermined wavelength, satisfying conditions given below;

7. An element according to claim 6, wherein said plurality of diffraction gratings stacked on each other include at least one diffraction grating whose direction of an increasing or decreasing of a grating thickness differs from that of remaining diffraction gratings.

8. An element according to claim 6, wherein the predetermined wavelength region is a visible region.

9. An element according to claim 6, wherein said diffraction gratings are stacked on a substrate, and when said stacked diffraction gratings are named as a first diffraction grating, a second diffraction grating, and an ith diffraction grating, starting from said diffraction grating close to the substrate, said first diffraction grating and the substrate are made of the same material.

10. A diffractive optical element in which a maximized diffraction efficiency is obtained at a design order and design wavelength, said element comprising:

a plurality of diffraction gratings including a first diffraction grating and a second diffraction grating, each of the first diffraction grating and the second diffraction grating is formed from respective corresponding material with different dispersion properties,

wherein the designed wavelength is set such that, when the designed order is assumed to mth-order, a flare intensity of red component per unit area at a predetermined surface among sum of (m+1)th-order and (m−

1)th-order diffracted lights is substantially equal to a flare intensity of blue component per unit area at the predetermined surface among sum of (m+2)th-order and (m−

2)th-order diffracted lights.

11. An optical system forming an image on a predetermined surface, comprising:

a diffractive optical element in which a maximized diffraction efficiency is obtained at a design order and design wavelength, said diffractive optical element including a plurality of diffraction gratings including a first diffraction grating and a second diffraction grating, each of the first diffraction grating and the second diffraction grating is formed from respective corresponding material with different dispersion properties,

wherein the designed wavelength is set such that, when the designed order is assumed to mth-order, a flare intensity of red component per unit area at a predetermined surface among sum of (m+1)th-order and (m−

1)th-order diffracted lights is substantially equal to a flare intensity of blue component per unit area at the predetermined surface among sum of (m+2)th-order and (m−

2)th-order diffracted lights.