Optical system having a diffractive optical element, and optical apparatus

• US 20020015231A1
• Filed: 03/06/2001
• Published: 02/07/2002
• 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
• Granted Patent: US 6,473,232 B2
• Time in Patent Office: Days
• US Class Current: 359/566
• 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 curvature, in a concentric-circles shape rotationally-symmetrical with respect to an optical axis. A sign of the curvature of the lens surface having the diffraction grating provided thereon is the same as a sign of a focal length, in 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 a 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 the diffraction grating provided thereon. Further, an 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 a sign of the curvature of the lens surface having said diffraction grating provided thereon is the same as a sign of a focal length, in a design wavelength, of a system composed of, in said optical system, a surface disposed nearest to an object side to a surface disposed immediately before the lens surface having said diffraction grating provided thereon, and is different from a 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.

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:

|DL/R|<

0.3

where DL is a distance from the apex of the imaginary cone to the center of curvature of the lens surface having said diffraction grating provided thereon, and R is a radius of curvature of the lens surface having said diffraction grating provided thereon.

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

|D/R|<

5

where D is a distance from the center of curvature of the lens surface having said diffraction grating provided thereon to a focus, in the design wavelength, of the system composed of, in said optical system, the surface disposed nearest to the object side to the surface disposed immediately before the lens surface having said diffraction grating provided thereon, and R is a radius of curvature of the lens surface having said diffraction grating provided thereon.

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

C₁·

P<

0

where P is a refractive power of the lens surface having said diffraction grating provided thereon, and C₁ is a phase coefficient for a second-degree term when a phase shape of said diffraction grating is expressed by the following equation;

φ

(Y)=(2π

/λ

₀) (C₁Y²+C₂Y⁴+C₃ Y⁶+ . . . )

where Y is the height in a vertical direction from the optical axis, λ

₀ is the design wavelength, and C₁ is a phase coefficient (i=1, 2, 3 . . . ).

6. An optical system according to claim 1, wherein said diffraction grating is a laminated diffraction grating.

7. An optical system according to claim 6, 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.

8. An optical system according to claim 7, 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 object side, a first layer, a second layer and a third layer, said second layer being the thin air layer.

9. An optical system according to claim 7, wherein each of the two diffraction gratings of said adjacently-laminated diffraction grating are formed with ultraviolet-curable plastic.

10. An optical system according to claim 1, wherein said optical system comprises a plurality of diffractive optical elements each of which is equivalent to said diffractive optical element.

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

13. An optical system according to claim 12, wherein said optical system satisfies the following condition:

|DL/R|<

0.3

where DL is a distance from the apex of the imaginary cone to the center of curvature of the lens surface having said diffraction grating provided thereon, and R is a radius of curvature of the lens surface having said diffraction grating provided thereon.

14. An optical system according to claim 12, wherein said optical system satisfies the following condition:

|D/R|<

5

where D is a distance from the center of curvature of the lens surface having said diffraction grating provided thereon to a focus, in a design wavelength, of a system composed of, in said optical system, a surface disposed nearest to an object side to a surface disposed immediately before the lens surface having said diffraction grating provided thereon, and R is a radius of curvature of the lens surface having said diffraction grating provided thereon.

15. An optical system according to claim 12, wherein said optical system satisfies the following condition:

C₁·

P<

0

where P is a refractive power of the lens surface having said diffraction grating provided thereon, and C₁ is a phase coefficient for a second-degree term when a phase shape of said diffraction grating is expressed by the following equation;

φ

(Y)=(2π

/λ

₀)(C₁Y²+C₂Y⁴+C₃Y⁶+ . . . )

where Y is the height in a vertical direction from the optical axis, λ

₀ is a design wavelength, and C_i is a phase coefficient (i=1, 2, 3 . . . ).

16. An optical system according to claim 12, wherein said diffraction grating is a laminated diffraction grating.

17. An optical system according to claim 16, 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.

18. An optical system according to claim 17, 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 an object side, a first layer, a second layer and a third layer, said second layer being the thin air layer.

19. An optical system according to claim 17, wherein each of the two diffraction gratings of said adjacently-laminated diffraction grating are formed with ultraviolet-curable plastic.

20. An optical system according to claim 12, wherein said optical system comprises a plurality of diffractive optical elements each of which is equivalent to said diffractive optical element.

21. An optical system according to claim 12, wherein said diffraction grating is a blazed-type diffraction grating.

22. An optical apparatus, comprising:

an optical system according to claim 1 or 12.

12. 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 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.