Diffractive optical element and optical system having the same

• US 6,873,463 B2
• Filed: 09/24/2001
• Issued: 03/29/2005
• Est. Priority Date: 09/27/2000
• Status: Expired due to Fees

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Nakai, Takehiko
• Primary Examiner(s): BOUTSIKARIS, LEONIDAS
• Application Number:
  US09/960,283
• Publication Number:
  US 20020036827A1
• Time in Patent Office: 1,282 Days
• Field of Search: 359/565, 359/566, 359/569, 359/571, 359573-575, 359/570, 36911203-11209
• US Class Current: 359/574
• CPC Class Codes: G02B 27/0037 with diffracting elements G02B27/0056 takes precedence; holographic optical elements G02B5/32; zone systems G02B5/1876
• CPC Class Codes: G02B 27/4211 correcting chromatic aberrations G02B27/0056, G02B27/4222, G02B27/4227 take precedence
• 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 5/1814 structurally combined with one or more further optical elements, e.g. lenses, mirrors, prisms or other diffraction gratings G02B5/189 takes precedence
• CPC Class Codes: G02B 5/1876 Diffractive Fresnel lenses; Zone plates; Kinoforms G02B5/1842, G02B5/1847 take precedence; optical systems having diffractive correction means G02B27/0037; Fresnel lenses operating by refraction G02B3/08
• CPC Class Codes: G02B 5/1895 such optical elements having dioptric power

Abstract

Disclosed is a diffractive optical element which is made of at least two materials of different dispersions and which includes at least two diffraction gratings being accumulated one upon another, wherein each diffraction grating is formed on a curved surface of a substrate, and wherein a diffraction grating, of the at least two diffraction gratings, in which a curvature radius of the curved surface and a curvature radius of a grating surface in a portion where a grating pitch is largest, have different signs, is one of the at least two diffraction gratings which has a smallest grating thickness.

Claims

1. A diffractive optical element made of at least two materials of different dispersions, and including at least two diffraction gratings accumulated one upon another, wherein:

each diffraction grating is formed on a curved surface of a substrate; and

a diffraction grating, from among said at least two diffraction gratings, in which a curvature radius of the curved surface and a curvature radius of a grating surface in a portion where a grating pitch is largest, have different signs, is one of said at least two diffraction gratings which has a smallest grating thickness.

2. A diffractive optical element according to claim 1, wherein said diffraction grating having a smallest grating thickness is structured so that an angle which is defined between the grating surface and a grating edge of that diffraction grating is obtuse and is greater than an angle which is defined between the grating surface and a normal to the surface at a position where a plane connecting grating free ends of the smallest-thickness diffraction grating and the grating surface intersect with each other.

3. A diffractive optical element according to claim 1 or 2, wherein the grating edge of the diffraction grating is made parallel to an optical axis.

4. A diffractive optical element according to claim 1 or 2, wherein the curvature of the plane connecting the grating free ends is approximately even, in each diffraction grating of said at least two accumulated diffraction gratings.

5. A diffractive optical element acceding to claim 1 or 2, wherein at least one of said at least two diffraction gratings is formed at an interface of two different materials having different dispersions.

6. A diffractive optical element according to claim 1 or 2, wherein said at least two accumulated diffraction gratings are bonded with each other in a non-grating region.

7. A diffractive optical element according to claim 1 or 2, wherein said at least two diffraction gratings include at least one grating of a shape in which a direction of the grating thickness is different.

8. A diffractive optical element according to claim 1 or 2, wherein said diffractive optical element is effective to improve a diffraction efficiency of a predetermined order, over a whole visible light region of a used wavelength.

9. A diffractive optical element according to claim 1 or 2, wherein there is a wavelength included in the used wavelength range which wavelength satisfies the following relation:

±

(n01−

1)d1±

(n03−

1)d2±

(n02−

1)d2=mλ

0

where n01 is a refractive index of the material of a first diffraction grating with respect to a wavelength λ

0, n02 is a refractive index of the material of a second diffraction grating with respect to the wavelength λ

0, n03 is a refractive index of the material of a third diffraction grating with respect to the wavelength λ

0, d1 and d2 are thicknesses of the first and second diffraction gratings, and m is a diffraction order.

10. A diffractive optical element according to claim 1 or 2, wherein the substrate has a lens function.

11. A diffraction optical system including a diffractive optical element as recited in claim 1 or 2.

12. A diffraction optical system according to claim 11, wherein said optical system is an imaging optical system.

13. A diffraction optical system according to claim 12, wherein said diffractive optical element is provided at one of a lens cemented surface and a lens surface, or inside a lens.

14. A diffraction optical system according to claim 11, wherein said optical system is an observation optical system.

15. A diffraction optical system according to claim 14, wherein said diffractive optical element is provided at a side of a lens, constituting the observation optical system, which faces an objective lens side thereof.

16. A diffractive optical element having a plurality of laminated diffraction gratings made of at least two materials having different dispersions, said element comprising:

two diffraction gratings provided on two curved surfaces,

wherein, in one of the two diffraction gratings, an optical power attributable to diffraction and an optical power attributable to refraction of that curved surface having the one diffraction grating formed thereon have mutually different signs,

wherein, in the other diffraction grating, an optical power attributable to diffraction and an optical power attributable to refraction of that curved surface having the other diffraction grating formed thereon have the same sign, and

wherein the one diffraction grating has a grating thickness smaller than the other diffraction grating.

17. The diffractive optical element to claim 16, wherein optical powers of the two curved surfaces attributable to refraction have mutually different signs.

18. The diffractive optical element according to claim 16, wherein the one diffraction grating is a diffraction grating formed on a concave surface and has a positive optical power, and

wherein the other diffraction grating is a diffracting grating formed on a convex surface and has a positive optical power.

19. The diffractive optical element according to claim 16, further comprising another diffraction grating in close contact with the other diffraction grating and being made of a material different in dispersion from the other diffraction grating.

20. A diffractive optical element having a plurality of laminated diffraction gratings, and including at least two materials having different dispersions, said element comprising:

a first diffraction grating provided on a first curved surface, wherein an optical power of said first diffraction grating has a sign different from that of an optical power due to refraction of the first curved surface; and

a second diffraction grating provided on a second curved surface, wherein an optical power of the second diffraction grating has the same sign as that of an optical power due to refraction of the second curved surface,

wherein said first diffraction grating has a grating thickness smaller than the second diffraction grating.

21. The diffractive optical element according to claim 20, wherein the optical powers of the first and second curved surfaces attributable to refraction have mutually different signs.

22. The diffractive optical element according to claim 20, further comprising a third diffraction grating in close contact with said second diffraction grating and being made of a material different in dispersion from said second diffraction grating.

23. A diffractive optical element having a plurality of laminated diffraction gratings laminated, and including at least two materials having different dispersions, said element comprising:

a first diffraction grating provided on a curved surface having a concave shape and a positive optical power; and

a second diffraction grating provided on a curved surface having a convex shape and a positive optical power,

wherein said first diffraction grating has a grating thickness smaller than said second diffraction grating.

24. The diffraction optical element according to claim 23, further comprising a third diffraction grating in close contact with said second diffraction grating and having a negative optical power, said third diffraction grating being made of a material different in dispersion from said second diffraction grating.

25. A diffractive optical element having a plurality of diffraction gratings laminated and including at least two materials having different dispersions, said element comprising:

a diffraction grating provided on a curved surface, wherein, in said diffraction grating, an optical power attributable to diffraction has a sign different from that of an optical power attributable to refraction at that curved surface having said diffraction grating formed thereon, and wherein said diffraction grating formed on said curved surface has a smallest grating thickness among said plurality of diffraction gratings.