Diffractive optical element, objective lens module, optical pickup, and optical information recording and reproducing apparatus

• US 20060146422A1
• Filed: 10/11/2005
• Published: 07/06/2006
• Est. Priority Date: 10/08/2004
• Status: Active Grant

• Current Assignee: Pioneer Corporation
• Original Assignee: Pioneer Corporation
• Inventors: Koike, Katsuhiro
• Granted Patent: US 7,227,704 B2
• Time in Patent Office: Days
• US Class Current: 359/742
• 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 27/4238 in optical recording or readout devices optical pick-up devices such as for CD, DVD or BD reader or recorder using diffraction optics G11B7/1353
• CPC Class Codes: G02B 5/188 Plurality of such optical elements formed in or on a supporting substrate
• CPC Class Codes: G11B 2007/0006 adapted for scanning different types of carrier, e.g. CD & DVD
• CPC Class Codes: G11B 2007/13727 Compound lenses, i.e. two or more lenses co-operating to perform a function, e.g. compound objective lens including a solid immersion lens, positive and negative lenses either bonded together or with adjustable spacing
• CPC Class Codes: G11B 7/1275 Two or more lasers having different wavelengths
• CPC Class Codes: G11B 7/1353 Diffractive elements, e.g. holograms or gratings diffraction gratings per se G02B5/18; holograms per se G02B5/32; grating systems G02B27/44
• CPC Class Codes: G11B 7/1374 Objective lenses optical objectives per se G02B9/00
• CPC Class Codes: G11B 7/13922 passive

Abstract

An objective lens module includes a light-converging lens that is coaxially disposed with respect to an optical axis of first laser light having a first wavelength, and a transmission-type diffractive optical element that is coaxially disposed to cause diffracted light of first laser light to be incident on the light-converging lens. The diffractive optical element has an incident surface and an emergent surface, and first, second, and third regions that are provided on at least of the incident surface and the emergent surface inthe vicinity of the optical axis, and are sequentially defined according to different radius distances from the optical axis to have different diffraction gratings of different diffraction angles, respectively. The first region diffracts odd-order diffracted light of first laser light to the light-converging lens, the second region diffracts even-order diffracted light of first laser light to the light-converging lens, and the third region diffracts even-order or zero-order diffracted light of first laser light to the light-converging lens, such that the light-converging lens converges diffracted light from the first, second, and third regions with a predetermined numerical aperture.

Claims

1. An objective lens module comprising:

a light-converging lens that is coaxially disposed with respect to an optical axis of first laser light having a first wavelength; and

a transmission-type diffractive optical element that is coaxially disposed to cause diffracted light of first laser light to be incident on the light-converging lens,

wherein the diffractive optical element has;

an incident surface and an emergent surface; and

first, second, and third regions that are provided on at least of the incident surface and the emergent surface in the vicinity of the optical axis, and are sequentially defined according to different radius distances from the optical axis to have different diffraction gratings of different diffraction angles, respectively, and

the first region diffracts odd-order diffracted light of first laser light to the light-converging lens, the second region diffracts even-order diffracted light of first laser light to the light-converging lens, and the third region diffracts even-order or zero-order diffracted light of first laser light to the light-converging lens, such that the light-converging lens converges diffracted light from the first, second, and third regions with a predetermined numerical aperture.

2. The objective lens module according to claim 1,

wherein, when second laser light having a second wavelength longer than the first wavelength and third laser light having a third wavelength longer than the second wavelength are incident on the first, second, and third regions along the optical path, the first region diffracts diffracted light of first and second laser light of a diffraction order lower than odd-order or even-order diffracted light of first laser light to the light-converging lens, such that the light-converging lens converges diffracted light from the first region with a second numerical aperture smaller than the predetermined numerical aperture.

3. The objective lens module according to claim 2,

wherein, even when second laser light and third laser light are incident on the first, second, and third regions along the optical path, the second region diffracts only specified diffracted light of second laser light of a diffraction order lower than odd-order or even-order of diffracted light of first laser light to the light-converging lens, such that the light-converging lens converges diffracted light from the second region with a third numerical aperture having a value between the predetermined numerical aperture and the second numerical aperture.

4. The objective lens module according to claim 1,

wherein the first, second, and third regions have a plurality of phase steps which cause diffracted light of a diffraction order to be generated so as to satisfy one of the following combinations:

a combination of the following equations of

F₁≧

F₂≦

F₃,
F₂=ROUND [λ

₁/(N₁−

1)×

(N₂−

1)/λ

₂×

F₁]=CEIL[λ

₁/(N₁−

1)×

(N₂−

1)/λ

₂×

F₁], and
F₃=CEIL[λ

₁/(N₁−

1)×

(N₃−

1)/λ

₃×

F₁],

a combination of the following equations of

F₁≧

F₂≧

F₃,
F₂=ROUND[λ

₁/(N₁−

1)×

(N₂−

1)/λ

₂×

F₁]=FLOOR[λ

₁/(N₁−

1)×

(N₂−

1)/λ

₂×

F₁], and
F₃=FLOOR[λ

₁/(N₁−

1)×

(N₃−

1)/λ

₃×

F₁], and

a combination of the following equations of

F₁≧

F₂≧

F₃,
F₂=ROUND[λ

₁/(N₁−

1)×

(N₂−

1)/λ

₂×

F₁], and
F₃=ROUND[λ

₁/(N₁−

1)×

(N₃−

1)/λ

₃×

F₁],

(where λ

₁ is the first wavelength, λ

₂ is the second wavelength, λ

₃ is the third wavelength, N₁ is a refractive index of a material used for the diffractive optical element with respect to the first wavelength, N₂ is a refractive index of amaterial used for the diffractive optical element with respect to the second wavelength, N₃ is a refractive index of a material used for the diffractive optical element with respect to the third wavelength, F₁ is a diffraction order of diffracted light of first laser light, F₂ is a diffraction order of diffracted light of second laser light, F₃ is a diffraction order of diffracted light of third laser light, ROUND [ ] is a function for rounding-off the value in [ ] with no digits after a decimal point so as to obtain an integer number, CEIL [ ] is a function for rounding-up the value in [ ] with no digits after a decimal point so as to obtain an integer number, and FLOOR [ ] is a function for rounding-down the value in [ ] with no digits after a decimal point so as to obtain an integer number), and

the first region is formed such that diffracted light to be generated when first laser light passes through the first region has an odd diffraction order.

5. The objective lens module according to claim 4,

wherein the first region is formed such that, from diffracted light to be generated when first laser light passes through the first region, diffracted light having the maximum diffraction efficiency has an odd diffraction order, excluding a multiple of five.

6. The objective lens module according to claim 5,

wherein the second region is formed such that, from diffracted light to be generated when first laser light passes through the second region, diffracted light having the maximum diffraction efficiency has an even diffraction order, excluding a multiple of ten.

7. The objective lens module according to claim 1,

wherein a radius distance of the diffractive optical element, in which a spherical aberration wavefront curved at an image surface position of third laser light passing through the first region and the second region is the maximum, is set to exist in the second region.

8. The objective lens module according to claim 1,

wherein the diffractive optical element is provided integrally with the light-converging lens.

9. The objective lens module according to claim 1, further comprising:

a diffractive lens structure for chromatic aberration correction that is provided on the incident or emergent surface of the diffractive optical element so as to correct a chromatic aberration due to a wavelength change of first laser light by a small amount.

57. An optical pickup comprising:

the objective lens module according to any one of claims 1 to 9.

58. An optical information recording and reproducing apparatus comprising:

the optical pickup according to claim 57.

10. A diffractive optical element which is provided on an optical path common to first laser light and plural laser light in order to cause an objective lens for converging first laser light on a first recording medium to be shared for plural laser light having wavelengths different from that of first laser light and a plurality of recording mediums corresponding to plural laser light, plural laser light having second laser light corresponding to a second recording medium and third laser light corresponding to a third recording medium, the diffractive optical element comprising:

a first diffractive lens structure that is provided in the vicinity of an optical axis so as to correct an aberration to be generated on the basis of the difference in wavelength between first laser light and second and third laser light; and

a second diffractive lens structure that is provided in the vicinity of the first diffractive lens structure so as to correct an aberration to be generated on the basis of the difference in wavelength between first laser light and second laser light.

11. The diffractive optical element according to claim 10,

wherein, when first, second, and third laser light are incident on the objective lens, diameters of diffraction surfaces in an incident or emergent surface of the diffractive optical element corresponding to effective diameters of first, second, and third laser light required for recording and reproducing the first, second, and third recording mediums, respectively, are a first diffraction effective diameter, a second diffraction effective diameter smaller than the first diffraction effective diameter, and a third diffraction effective diameter smaller than the second diffraction effective diameter, respectively.

12. The diffractive optical element according to claim 10,

wherein, when first, second, and third laser light are incident on the objective lens, diameters of diffraction surfaces in an incident or emergent surface of the diffractive optical element corresponding to effective diameters of first, second, and third laser light required for recording and reproducing the first, second, and third recording mediums, respectively, are a first diffraction effective diameter, a second diffraction effective diameter equal to or larger than the first diffraction effective diameter, and a third diffraction effective diameter smaller than the first diffraction effective diameter, respectively.

13. The diffractive optical element according to claim 10,

wherein the first diffractive lens structure is formed in a fourth diffraction effective diameter still smaller than the third diffraction effective diameter in an incident or emergent surface of the diffractive optical element, the second diffractive lens structure is formed in the second diffraction effective diameter in the incident or emergent surface of the diffractive optical element, and, in the fourth diffraction effective diameter, an image surface position is set such that a longitudinal spherical aberration by third laser light is zero.

14. The diffractive optical element according to claim 13,

wherein the second diffractive lens structure is formed in a fifth diffraction effective diameter still smaller than the second diffraction effective diameter and larger than the third diffraction effective diameter in the incident or emergent surface of the diffractive optical element, and, in the fifth diffraction effective diameter, an image surface position is set such that a longitudinal spherical aberration by second laser light is zero.

15. The diffractive optical element according to claim 10,

wherein the first recording medium has a recording layer for receiving light through a first transmissive protection layer having a first thickness, the second recording medium has a recording layer for receiving light through a second transmissive protection layer having a second thickness equal to or larger than the first thickness, and the third recording medium has a recording layer for receiving light through a third transmissive protection layer having a third thickness larger than the second thickness.

16. The diffractive optical element according to claim 15,

wherein the first diffractive lens structure corrects an aberration to be generated on the basis of the difference in thickness between the first transmissive protection layer and the second and third transmissive protection layers, in addition to the difference in wavelength between first laser light and second and third laser light, and the second diffractive lens structure corrects an aberration to be generated on the basis of the difference in thickness between the first transmissive protection layer and the second transmissive protection layer, in addition to the difference in wavelength between first laser light and second laser light.

17. The diffractive optical element according to claim 10,

wherein the first diffractive lens structure and the second diffractive lens structure are formed on one of an incident surface and an emergent surface together.

18. The diffractive optical element according to claim 17,

wherein the first diffractive lens structure and the second diffractive lens structure are built in different regions of the incident or emergent surface so as to have concentric circle shapes and orbicular zone shapes.

19. The diffractive optical element according to claim 13,

wherein a light-converging position at which third laser light passing through a region in the fourth diffraction effective diameter converges on the third recording medium in the incident or emergent surface of the diffractive optical element is disposed between a position at which corresponding laser light passing through a height from the optical axis closest to the optical axis outside the fourth diffraction effective diameter of the diffractive optical element intersects the optical axis and a position at which corresponding laser light passing through a height from the optical axis corresponding to the third diffraction effective diameter of the diffractive optical element required for the third recording medium intersects the optical axis.

20. The diffractive optical element according to claim 10,

wherein the first and second diffractive lens structures are diffractive lens structures, each having a plurality of concentric phase steps.

21. The diffractive optical element according to claim 13,

wherein the first diffractive lens structure is formed in a circle having the fourth diffraction effective diameter as an outer diameter, and the second diffractive lens structure is formed in a circle having the second diffraction effective diameter as an outer diameter in the incident surface or the emergent surface.

22. The diffractive optical element according to claim 21,

wherein the second diffractive lens structure is formed in an orbicular zone shape having the fourth diffraction effective diameter as an inner diameter.

23. The diffractive optical element according to claim 10,

wherein a difference in optical path length caused by each of phase steps constituting the first diffractive lens structure and a difference in optical path length caused by each of phase steps constituting the second diffractive lens structure are different from each other at the same wavelength.

24. The diffractive optical element according to claim 10,

wherein, from phase steps constituting the first diffractive lens structure, a difference in optical path length caused by an outermost phase step and a difference in optical path length caused by each of other phase steps are different from each other at the same wavelength.

25. The diffractive optical element according to claim 10,

wherein, from phase steps constituting the second diffractive lens structure, a difference in optical path length caused by an outermost phase step and a difference in optical path length caused by each of other phase steps are different from each other at the same wavelength.

26. The diffractive optical element according to claim 10,

wherein all phase steps constituting the first diffractive lens structure and some of phase steps constituting the second diffractive lens structure are mixed in a region within the third diffraction effective diameter in an incident or an emergent surface of the diffractive optical element.

27. The diffractive optical element according to claim 10,

wherein at least one phase step having a depth corresponding to the sum of a step amount of each of phase steps constituting the first diffractive lens structure and a step amount of each of phase steps constituting the second diffractive lens structure exists in a region within the third diffraction effective diameter in an incident or emergent surface of the diffractive optical element.

28. The diffractive optical element according to claim 10,

wherein a direction of each of phase steps constituting the first diffractive lens structure and a direction of each of phase steps of constituting the second diffractive lens structure are the same.

29. The diffractive optical element according to claim 10,

wherein the first diffractive lens structure is formed such that, from diffracted light to be generated when first laser light passes through the first diffractive lens structure, diffracted light having the maximum diffraction efficiency has an odd diffraction order.

30. The diffractive optical element according to claim 29,

wherein the first diffractive lens structure is formed such that, from diffracted light to be generated when first laser light passes through the first diffractive lens structure, diffracted light having the maximum diffraction efficiency has an odd diffraction order, excluding a multiple of five.

31. The diffractive optical element according to claim 10,

wherein the second diffractive lens structure is formed such that, from diffracted light to be generated when first laser light passes through the second diffractive lens structure, diffracted light having the maximum diffraction efficiency has an even diffraction order, excluding a multiple of ten.

32. The diffractive optical element according to claim 10,

wherein, when, from diffracted light to be generated when first laser light having a wavelength Xl passes through the diffractive lens structure, diffracted light having the maximum diffraction efficiency has a diffraction order of Fl, the diffractive lens structure causes diffracted light of a diffraction order which satisfies one of the following combinations:

a combination of the following equations of

F₁≧

F₂≦

F₃,
F₂=ROUND [λ

₁/(N₁−

1)×

(N₂−

1)/λ

₂×

F₁]=CEIL[λ

₁/(N₁−

1)×

(N₂−

1)/λ

₂×

F₁], and
F₃=CEIL[λ

₁/(N₁−

1)×

(N₃−

1)/λ

₃×

F₁],

a combination of the following equations of

F₁≧

F₂≧

F₃,
F₂=ROUND[λ

₁/(N₁−

1)×

(N₂−

1)/λ

₂×

F₁]=FLOOR[λ

₁/(N₁−

1)×

(N₂−

1)/λ

₂×

F₁], and
F₃=FLOOR[λ

₁/(N₁−

1)×

(N₃−

1)/λ

₃×

F₁], and

a combination of the following equations of

F₁≧

F₂≧

F₃,
F₂=ROUND[λ

₁/(N₁−

1)×

(N₂−

1)/λ

₂×

F₁], and
F₃=ROUND[λ

₁/(N₁−

1)×

(N₃−

1)/λ

₃×

F₁],

(where λ

₂ is the second wavelength, λ

₃ is the third wavelength, N₁ is a refractive index of a material used for the diffractive optical element with respect to the first wavelength, N₂ is a refractive index of a material used for the diffractive optical element with respect to the second wavelength, N₃ is a refractive index of a material used for the diffractive optical element with respect to the third wavelength, F₂ is a diffraction order of diffracted light of second laser light, F₃ is a diffraction order of diffracted light of third laser light, ROUND [ ] is a function for rounding-off the value in [ ] with no digits after a decimal point so as to obtain an integer number, CEIL [ ] is a function for rounding-up the value in [ ] with no digits after a decimal point so as to obtain an integer number, and FLOOR [ ] is a function for rounding-down the value in [ ] with no digits after a decimal point so as to obtain an integer number).

33. The diffractive optical element according to claim 10, further comprising:

a third diffractive lens structure that is providedwithin the first diffraction effective diameter on an incident surface or an emergent surface of the diffractive optical element so as to correct a chromatic aberration to be generated due to a wavelength change of first laser light by a very small amount.

34. The diffractive optical element according to claim 33,

wherein, in the incident surface or the emergent surface of the diffractive optical element, the third diffractive lens structure is formed on a different surface from the first diffractive lens structure and the second diffractive lens structure.

35. The diffractive optical element according to claim 33,

wherein, in the incident surface or the emergent surface of the diffractive optical element, the third diffractive lens structure is formed on the same surface as the first diffractive lens structure and the second diffractive lens structure.

36. The diffractive optical element according to claim 33,

wherein, in the incident surface or the emergent surface of the diffractive optical element, the second diffractive lens structure is formed on a different surface from the first diffractive lens structure.

37. The diffractive optical element according to claim 36,

wherein, in the incident surface or the emergent surface of the diffractive optical element, the third diffractive lens structure is formed on the same surface as the first diffractive lens structure.

38. The diffractive optical element according to claim 36,

wherein, in the incident surface or the emergent surface of the diffractive optical element, the third diffractive lens structure is formed on the same surface as the second diffractive lens structure.

39. The diffractive optical element according to claim 33,

wherein a difference in optical path length caused by each of phase steps constituting the first diffractive lens structure and a difference in optical path length caused by each of phase steps constituting the third diffractive lens structure are different from each other at the same wavelength.

40. The diffractive optical element according to claim 33,

wherein a difference in optical path length caused by each of phase steps constituting the second diffractive lens structure and a difference in optical path length caused by each of phase steps constituting the third diffractive lens structure are different from each other at the same wavelength.

41. The diffractive optical element according to claim 33,

wherein a difference in optical path length caused by each of phase steps constituting the first diffractive lens structure, a difference in optical path length caused by each of phase steps constituting the second diffractive lens structure, and a difference in optical path length caused by each of phase steps constituting the third diffractive lens structure are different from one another at the same wavelength.

42. The diffractive optical element according to claim 33,

wherein a difference in optical path length caused by each of phase steps in the vicinity of the fourth diffraction effective diameter from phase steps constituting the third diffractive lens structure and a difference in optical path length caused by each of other phase steps are different from each other at the same wavelength.

43. The diffractive optical element according to claim 33,

wherein a difference in optical path length caused by each of phase steps in the vicinity of the second diffraction effective diameter from phase steps constituting the third diffractive lens structure and a difference in optical path length caused by each of other phase steps are different from each other at the same wavelength.

44. The diffractive optical element according to claim 33,

wherein all phase steps constituting the first diffractive lens structure, some of phase steps constituting the second diffractive lens structure, and some of phase steps constituting the third diffractive lens structure are mixed in a region within the third diffraction effective diameter in the incident or emergent surface of the diffractive optical element.

45. The diffractive optical element according to claim 33,

wherein all phase steps constituting the first diffractive lens structure and some of phase steps constituting the third diffractive lens structure are mixed in a region within the fourth diffraction effective diameter in the incident or emergent surface of the diffractive optical element.

46. The diffractive optical element according to claim 33,

wherein at least one phase step having a depth corresponding to the sum of a step amount of each of phase steps constituting the first diffractive lens structure and a step amount of each of phase steps constituting the third diffractive lens structure exists within the fourth diffraction effective diameter of the diffractive optical element.

47. The diffractive optical element according to claim 28,

wherein at least one phase step having a depth corresponding to the sum of a step amount of each of phase steps constituting the first diffractive lens structure, a step amount of each of phase steps constituting the second diffractive lens structure, and a step amount of each of phase steps constituting the third diffractive lens structure exists within the third diffraction effective diameter of the diffractive optical element.

48. The diffractive optical element according to claim 33,

wherein a direction of each of phase steps constituting the first diffractive lens structure and a direction of each of phase steps constituting the third diffractive lens structure are different from each other.

49. The diffractive optical element according to claim 33,

wherein some of or all phase steps of the second diffractive lens structure and some of phase steps of the third diffractive lens structure are mixed in a region between the fourth diffraction effective diameter and the second diffraction effective diameter in the incident or emergent surface of the diffractive optical element.

50. The diffractive optical element according to claim 33,

wherein at least one phase step having a depth corresponding to the sum of a step amount of each of phase steps constituting the second diffractive lens structure and a step amount of each of phase steps constituting the third diffractive lens structure exists in a region between the fourth diffraction effective diameter and the second diffraction effective diameter of the diffractive optical element.

51. The diffractive optical element according to claim 33,

wherein, in a region between the fourth diffraction effective diameter and the second diffraction effective diameter, a direction of each of phase steps constituting the second diffractive lens structure and a direction of each of phase steps constituting the third diffractive lens structure are different from each other.

52. The diffractive optical element according to claim 33,

wherein the first diffractive lens structure, the second diffractive lens structure, and the third diffractive lens structure are formed on one of the incident surface and the emergent surface of the diffractive optical element together, and all directions of phase steps of the first, second, and third diffractive lens structures are the same.

53. The diffractive optical element according to claim 33,

wherein the third diffractive lens structure is formed such that, from diffracted light to be generated when first laser light passes through the third diffractive lens structure, diffracted light having the maximum diffraction efficiency has a diffractive order of a multiple of ten.

54. The diffractive optical element according to claim 10,

wherein first, second, and third laser light incident on the diffractive optical element are substantially parallel light.

55. The diffractive optical element according to claim 10,

wherein the diffractive optical element is provided integrally with the objective lens.

56. The diffractive optical element according to claim 10,

wherein first, second, and third laser light have first, second, and third wavelengths, respectively, the second wavelength is longer than the first wavelength, and the third wavelength is longer than the second wavelength.

59. An optical pickup comprising:

the diffractive optical element according to any one of claims 10 to 56.

60. An optical information recording and reproducing apparatus comprising:

the optical pickup according to claim 59.