Optical system having a diffractive optical element, and optical apparatus

• US 6,473,232 B2
• Filed: 03/06/2001
• Issued: 10/29/2002
• Est. Priority Date: 03/08/2000
• Status: Active Grant

• Current Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Original Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Inventors: Ogawa, Hideki
• Primary Examiner(s): Spyrou, Cassandra
• Assistant Examiner(s): Juba, Jr., John
• Application Number:
  US09/799,058
• Publication Number:
  US 20020015231A1
• Time in Patent Office: 602 Days
• Field of Search: 359/565, 359/576, 359/558, 359/566, 359/569, 359/570, 359/574
• US Class Current: 359/565
• CPC Class Codes: G02B 27/4211 correcting chromatic aberrations G02B27/0056, G02B27/4222, G02B27/4227 take precedence
• CPC Class Codes: G02B 5/1895 such optical elements having dioptric power

Abstract

An optical system includes a diffractive optical element having a diffraction grating provided, on a lens surface having a curvature, in a concentric-circles shape rotationally-symmetrical with respect to an optical axis. The sign of the curvature of the lens surface having the diffraction grating provided thereon is the same as the sign of a focal length, at a design wavelength, of a system composed of, in the optical system, a surface disposed nearest to an object side to a surface disposed immediately before the lens surface having the diffraction grating provided thereon, and is different from the sign of the distance from the optical axis to a position where the center ray of an off-axial light flux enters the lens surface having the diffraction grating provided thereon. Further, the apex of an imaginary cone formed by extending a non-effective surface of the diffraction grating is located adjacent to the center of curvature of the lens surface having the diffraction grating provided thereon.

Claims

1. An optical system, comprising:

a diffractive optical element having a diffraction grating provided, on a lens surface having curvature, in a concentric-circles shape rotationally-symmetrical with respect to an optical axis,

wherein the sign of the curvature of the lens surface having said diffraction grating provided thereon is the same as the sign of a focal length, at a design wavelength, of a system lying between and including the surface disposed nearest to a front side and a surface disposed immediately before the lens surface having said diffraction grating provided thereon, and is different from the sign of a distance from the optical axis to a position where a center ray of an off-axial light flux enters the lens surface having said diffraction grating provided thereon,

wherein diffraction grating is a laminated diffraction grating,

wherein said laminated diffraction grating is an adjacently-laminated diffraction grating in which two diffraction gratings are disposed adjacent to each other across an air layer,

wherein said adjacently-laminated diffraction grating is provided between two adjacent lens surfaces having substantially the same curvature, and is composed of three layers, including, in order from the front side, a first layer, a second layer and a third layer, said second layer being the thin air layer.

2. An optical system according to claim 1, wherein an apex of an imaginary cone formed by extending a non-effective surface of said diffraction grating is located adjacent to the center of curvature of the lens surface having said diffraction grating provided thereon.

3. An optical system according to claim 2, wherein said optical system satisfies the following condition:

4. An optical system according to claim 1, wherein said optical system satisfies the following condition:

5. An optical system according to claim 1, wherein said optical system satisfies the following condition:

6. An optical system according to claim 1, wherein each of the two diffraction gratings of said adjacently-laminated diffraction grating are formed with ultraviolet-curable plastic.

7. An optical system according to claim 1, wherein said diffraction grating is a blazed-type diffraction grating.

8. An optical apparatus, comprising:

an optical system according to claim 1.