Optical element, aberration correcting element, light converging element, objective optical system, optical pickup device, and optical information recording reproducing device

• US 20040257958A1
• Filed: 06/15/2004
• Published: 12/23/2004
• Est. Priority Date: 06/18/2003
• Status: Active Grant

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.), Konica Minolta OPTO Incorporated (Konica Minolta Inc.)
• Original Assignee: Konica Minolta OPTO Incorporated (Konica Minolta Inc.)
• Inventors: Kimura, Tohru, Atarashi, Yuichi, Yamashita, Kiyoshi, Mori, Nobuyoshi
• Granted Patent: US 7,369,481 B2
• Time in Patent Office: Days
• US Class Current: 369/112.03
• 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 7/1369 Active plates, e.g. liquid crystal panels or electrostrictive elements
• CPC Class Codes: G11B 7/1374 Objective lenses optical objectives per se G02B9/00
• CPC Class Codes: G11B 7/1376 Collimator lenses collimators per se G02B27/30
• CPC Class Codes: G11B 7/1378 Separate aberration correction lenses; Cylindrical lenses to generate astigmatism; Beam expanders
• CPC Class Codes: G11B 7/13922 passive
• CPC Class Codes: G11B 7/13925 active, e.g. controlled by electrical or mechanical means

Abstract

An optical system for use in an optical pickup apparatus comprises a first optical surface having a superposition type diffractive structure including a plurality of ring-shape zones which are formed concentrically around an optical axis, wherein each ring-shaped zone is composed of a plurality of stepped sections stepwise, and a second optical surface having a diffractive structure including a plurality of ring-shaped zones which are formed concentrically around an optical axis, wherein each of the plurality of ring-shaped zones are divided by a stepped section to generate a diffractive light ray of diffractive order whose absolute value is not small than 1 for the light flux.

Claims

1. An optical system for use in an optical pickup apparatus in which reproducing and/or recording information is conducted for a first optical information recording medium equipped with a protective layer having a thickness t1 by using a light flux having a first wavelength λ

1 emitted from a first light source and reproducing and/or recording information is conducted for a second optical information recording medium equipped with a protective layer having a thickness t2 (t2≦

t1) by using a light flux having a second wavelength λ

2 (λ

2>

λ

1) emitted from a second light source, comprising;

a first optical surface having a superposition type diffractive structure including a plurality of ring-shaped zones which are formed concentrically around an optical axis, wherein each ring-shaped zone is composed of a plurality of stepped sections stepwise, and

a second optical surface having a diffractive structure including a plurality of ring-shaped zones which are formed concentrically around an optical axis, wherein each of the plurality of ring-shaped zones are divided by a stepped section to generate a diffractive light ray of diffractive order whose absolute value is not small than 1 for the light flux.

2. The optical system of claim 1, wherein the depth of the stepped section of the diffractive structure satisfies the following formula (1):

n1>

n2

where n1 is a diffraction order of a diffracted ray having the maximum diffraction efficiency among diffracted rays generated when a light flux having the first light wavelength λ

1 enters into the diffractive structure, and n2 is a diffraction order of a diffracted ray having the maximum diffraction efficiency among diffracted rays generated when a light flux having the second light wavelength λ

2 enters into the diffractive structure.

3. The optical system of claim 2, wherein when the first wavelength λ

1 (μ

m) and the second wavelength λ

2 (μ

m) satisfy the formulas (2) and (3) respectively,

0.39<

λ

1<

0.42  

 

(2) 0.63<

λ

2<

0.68  

 

(3),

a combination of the diffraction orders n1 and n2 is any of (n1, n2)=(2,

     1), (3,

     2), (5,

     3), (8,

     5) and (10,

     6).

4. The optical system of claim 3, wherein an optical element having the second optical surface has a refractive index of 1.5 to 1.6 and is made of a material having Abbe constant of 50 to 60 for d-line, and the depth d1 of the stepped section of a ring-shaped zone located closest to the optical axis among the plurality of ring-shaped zones of the diffractive structure satisfies any one of formulas (4) to (8):

1.2 μ

m<

d1<

1.7 μ

m  

 

(4) 2.0 μ

m<

d1<

2.6 μ

m  

 

(5) 3.4 μ

m<

d1<

4.1 μ

m  

 

(6) 5.6 μ

m<

d1<

6.5 μ

m  

 

(7) 6.9 μ

m<

d1<

8.1 μ

m  

 

(8)

5. The optical system of claim 4, wherein a cross sectional form of the diffractive structure including the optical axis is shaped stepwise.

6. The optical system of claim 5, wherein the optical system of the optical pickup apparatus consists of a single optical element and one optical surface of the optical element includes the superposition type diffractive structure and the other optical surface includes the diffractive structure.

7. The optical system of claim 6, wherein the superposition type diffractive structure does not substantially provide an optical path difference between neighboring stepped sections for the first wavelength λ

1 and provide an optical path difference between neighboring stepped sections for the first wavelength λ

2.

8. The optical system of claim 7, wherein the first wavelength λ

1 (μ

m) and the second wavelength λ

2 (μ

m) satisfy the formulas (2) and (3) respectively,

0.39<

λ

1<

0.42  

 

(2) 0.63<

λ

2<

0.68  

 

(3).

9. The optical system of claim 4, wherein a cross sectional form of the diffractive structure including the optical axis is shaped in saw-tooth.

10. The optical system of claim 9, wherein the optical system of the optical pickup apparatus consists of a single optical element and one optical surface of the optical element includes the superposition type diffractive structure and the other optical surface includes the diffractive structure.

11. The optical system of claim 10, wherein the superposition type diffractive structure does not substantially provide an optical path difference between neighboring stepped sections for the first wavelength λ

1 and provide an optical path difference between neighboring stepped sections for the first wavelength λ

2.

12. The optical system of claim 11, wherein the first wavelength λ

1 (μ

m) and the second wavelength λ

2 (μ

m) satisfy the formulas (2) and (3) respectively,

0.39<

λ

1<

0.42  

 

(2) 0.63<

λ

2<

0.68  

 

(3).

13. An objective optical system for use in an optical pickup apparatus including the optical system described in claim 12, to converge the first wavelength λ

1 onto an information recording plane of the first optical information recording medium and to converge the second wavelength λ

2 onto an information recording plane of the second optical information recording medium, wherein the diffractive structure has a function to refrain a chromatic aberration caused by the objective optical system due to wavelength fluctuation when the first wavelength λ

1 fluctuates within a range of ±

10 nm.

14. The objective optical system of claim 13, wherein when the first wavelength λ

1 fluctuates within a range of ±

10 nm, the diffractive structure refrains a longitudinal chromatic aberration caused by the objective optical system.

15. The objective optical system of claim 14, wherein when the first wavelength λ

1 fluctuates within a range of ±

10 nm, the diffractive structure refrains a change of a spherical aberration caused by the objective optical system due to the wavelength fluctuation.

16. The objective optical system of claim 12, wherein the objective optical system includes a plastic lens having a positive power on paraxial and the diffractive structure has a function to refrain a change of a spherical aberration caused due to a change of a refractive index of the plastic lens when environmental temperature changes.

17. The objective optical system of claim 16, wherein the objective optical system has a wavelength dependency in a spherical aberration such that when the first wavelength λ

1 changes toward to a longer wavelength side, a spherical aberration changes toward to be under-corrected and when the first wavelength λ

1 changes toward to a shorter wavelength side, a spherical aberration changes toward to be over-corrected.

18. The objective optical system of claim 17, wherein objective optical system comprises a correcting optical system and a light converging element to converge a light flux having a wavelength λ

1 emitted from the correcting optical system on an information recording plane of the first optical information recording medium and to converge a light flux having a wavelength λ

2 emitted from the correcting optical system on an information recording plane of the second optical information recording medium.

19. The objective optical system of claim 18, wherein the superposition type diffractive structure has a function to correct a spherical aberration caused due to a difference in thickness between a protective substrate of the first optical information recording medium and a protective substrate of the second optical information recording medium.

20. The optical system of claim 1, wherein the superposition type diffractive structure does not substantially provide an optical path difference between neighboring stepped sections for the first wavelength λ

1 and provide an optical path difference between neighboring stepped sections for the first wavelength λ

2.

21. An objective optical system for use in an optical pickup apparatus including the optical system described in claim 1, to converge the first wavelength λ

1 onto an information recording plane of the first optical information recording medium and to converge the second wavelength λ

2 onto an information recording plane of the second optical information recording medium, wherein the diffractive structure has a function to refrain a chromatic aberration caused by the objective optical system due to wavelength fluctuation when the first wavelength λ

1 fluctuates within a range of ±

10 nm.

22. The objective optical system of claim 21, wherein when the first wavelength λ

1 fluctuates within a range of ±

10 nm, the diffractive structure refrains a longitudinal chromatic aberration caused by the objective optical system.

23. The objective optical system of claim 22, wherein when the first wavelength λ

1 fluctuates within a range of ±

10 nm, the diffractive structure refrains a change of a spherical aberration caused by the objective optical system due to the wavelength fluctuation.

24. An objective optical system for use in an optical pickup apparatus including the optical system described in claim 1, to converge the first wavelength λ

1 onto an information recording plane of the first optical information recording medium and to converge the second wavelength λ

2 onto an information recording plane of the second optical information recording medium, wherein the objective optical system includes a plastic lens having a positive power on paraxial and the diffractive structure has a function to refrain a change of a spherical aberration caused due to a change of a refractive index of the plastic lens when environmental temperature changes.

25. The objective optical system of claim 24, wherein the objective optical system has a wavelength dependency in a spherical aberration such that when the first wavelength λ

1 changes toward to a longer wavelength side, a spherical aberration changes toward to be under-corrected and when the first wavelength λ

1 changes toward to a shorter wavelength side, a spherical aberration changes toward to be over-corrected.

26. The objective optical system of claim 25, wherein objective optical system comprises a correcting optical system and a light converging element to converge a light flux having a wavelength λ

1 emitted from the correcting optical system on an information recording plane of the first optical information recording medium and to converge a light flux having a wavelength λ

2 emitted from the correcting optical system on an information recording plane of the second optical information recording medium.

27. The objective optical system of claim 26, wherein the superposition type diffractive structure has a function to correct a spherical aberration caused due to a difference in thickness between a protective substrate of the first optical information recording medium and a protective substrate of the second optical information recording medium.

28. An optical system for use in an optical pickup apparatus in which reproducing and/or recording information is conducted for a first optical information recording medium equipped with a protective layer having a thickness t1 by using a light flux having a first wavelength λ

1 emitted from a first light source and reproducing and/or recording information is conducted for a second optical information recording medium equipped with a protective layer having a thickness t2 (t2≧

t1) by using a light flux having a second wavelength λ

2 (λ

2>

λ

1) emitted from a second light source, comprising;

a first optical surface having a superposition type diffractive structure including a plurality of ring-shaped zones which are formed concentrically around an optical axis, wherein each ring-shaped zone is composed of a plurality of stepped sections stepwise, and

a second optical surface having an optical path difference providing structure including a plurality of ring-shaped zones which are formed concentrically around an optical axis, wherein each of the plurality of ring-shaped zones is divided by a stepped section so as to provide a predetermined optical path difference, and wherein an optical path length of each of the plurality of ring-shaped zones changes in response to a height from the optical axis.

29. The optical system of claim 28, wherein among the plurality of ring-shaped zones to construct the optical path difference providing structure, a ring-shaped zone located inside from a ring-shaped zone positioned at a predetermined height within the maximum effective radius is displaced along the optical axis so as to make an optical path length shorter as the ring-shaped zone is located apart more from the optical axis and a ring-shaped zone located outside from the ring-shaped zone positioned at a predetermined height within the maximum effective radius is displaced along the optical axis so as to make an optical path length longer as the ring-shaped zone is located apart more from the optical axis.

30. The optical system of claim 29, wherein a central portion of the ring-shaped zone positioned at the predetermined height has a height from the optical axis that is 60% to 85% of the maximum effective radius.

31. The optical system of claim 30, wherein φ

1 and φ

2 represented with formulas (9) and (10) satisfy formulas (11) to (13);

φ

1=d2(Nλ

1−

1)/λ

1  

 

(9) φ

2=d2(Nλ

2−

1)/λ

2  

 

(10) INT(φ

1)≦

20  

 

(11) 0≦

|INT(φ

1)−

φ

1|≦

0.4  

 

(12) 0≦

|INT(φ

2)−

φ

2|≦

0.4  

 

(13)

where INT(φ

i) (i=1,

     2) is an integer obtained by rounding the value of φ

I,

λ

1 is the first wavelength (μ

m),

λ

2 is the second wavelength (μ

m),

d2 is a depth (μ

m), along the optical axis, of a stepped section located closest to the optical axis among the stepped sections in the optical path difference providing structure,

Nλ

1 is a refractive index, for the first wavelength λ

1, of an optical element having the second optical surface among the optical system, and

Nλ

2 is a refractive index, for the second wavelength λ

2, of an optical element having the second optical surface among the optical system.

32. The optical system of claim 31, wherein an optical element having the second optical surface has a refractive index of 1.5 to 1.6 and is made of a material having Abbe constant of 50 to 60 for d-line, and the following formulas (14) and (15) are satisfied:

INT(φ

1)=5 p  

 

(14) INT(φ

2)=3 p  

 

(15)

33. The optical system of claim 32, wherein the optical system consists of a single optical element.

34. The optical system of claim 33, wherein the superposition type diffractive structure does not substantially provide an optical path difference between neighboring stepped sections for the first wavelength λ

1 and provide an optical path difference between neighboring stepped sections for the first wavelength λ

2.

35. The optical system of claim 34, wherein the first wavelength λ

1 (μ

m) and the second wavelength λ

2 (μ

m) satisfy the formulas (2) and (3) respectively,

0.39<

λ

1<

0.42  

 

(2) 0.63<

λ

2<

0.68  

 

(3).

36. The optical system of claim 28, wherein the optical system consists of a single optical element.

37. The optical system of claim 28, wherein the superposition type diffractive structure does not substantially provide an optical path difference between neighboring stepped sections for the first wavelength kl and provide an optical path difference between neighboring stepped sections for the first wavelength λ

2.

38. The optical system of claim 37, wherein the first wavelength λ

1 (μ

m) and the second wavelength λ

2 (μ

m) satisfy the formulas (2) and (3) respectively,

0.39<

λ

1<

0.42  

 

(2) 0.63<

λ

2<

0.68  

 

(3).

39. An objective optical system for use in an optical pickup apparatus including the optical system described in claim 28, to converge the first wavelength λ

1 onto an information recording plane of the first optical information recording medium and to converge the second wavelength λ

2 onto an information recording plane of the second optical information recording medium, wherein when the first wavelength λ

1 fluctuates within a range of ±

10 nm, the optical path difference providing structure has a function to refrain a change of a spherical aberration caused by the objective optical system due to the wavelength fluctuation.

40. The objective optical system of claim 39, wherein objective optical system comprises a correcting optical system and a light converging element to converge a light flux having a wavelength λ

1 emitted from the correcting optical system on an information recording plane of the first optical information recording medium and to converge a light flux having a wavelength λ

2 emitted from the correcting optical system on an information recording plane of the second optical information recording medium.

41. The objective optical system of claim 39, wherein the superposition type diffractive structure has a function to correct a spherical aberration caused due to a difference in thickness between a protective substrate of the first optical information recording medium and a protective substrate of the second optical information recording medium.

42. The objective optical system of claim 39, wherein a optical path difference added to a transmitted wave-front by the superposition type diffractive structure is defined by the following arithmetic expression, signs of B₂ and B₄ are different from each other,

43. The objective optical system of claim 40, wherein the light converging element is constructed with a plastic lens structured with one group one lens and a paraxial power P1 (mm⁻

1) of the aberration correcting optical system for the first wavelength λ

1 satisfies the following formula (20).

P1>

0  

 

(20)

44. The objective optical system of claim 40, wherein the light converging element is constructed with a plastic lens structured with one group one lens and a ratio of a paraxial power P1 (mm⁻

1) of the aberration correcting optical system for the first wavelength λ

1 to a paraxial power P2 (mm<sup>−

1</sup>) of the light converging element for the first wavelength λ

1 satisfies the following formula (21).

|P1/P2|≦

0.2  

 

(21)

45. The objective optical system of claim 44, wherein the light converging element is a cyclic poly-olefin series plastic lens and the plastic lens satisfies the following formulas (22) to (24):

1.54<

N405<

1.58  

 

(22) 50<

ν

d<

60  

 

(23) −

10×

10<sup>−

5</sup>(°

C.<sup>−

1</sup>)<

dN405/dT<

−

8×

10<sup>−

5</sup>(°

C.<sup>−

1</sup>)  

 

(24)

where N405 is a refractive index for a wavelength 405 nm at a temperature of 25°

C., ν

d is Abbe'"'"'s constant for d-line, and dN405/dT is a changing ratio of a refractive index for a wavelength of 405 nm when a temperature is changed within a temperature range of −

5°

C. to 70°

C.

46. The objective optical system of claim 44, wherein the light converging element is made of a material in which particles having a diameter not larger than 30 μ

m are dispersed in a plastic material.

47. The objective optical system of claim 44, wherein the light converging element is a glass lens.

48. An objective optical system for use in an optical pickup apparatus including the optical system described in claim 28, to converge the first wavelength λ

1 onto an information recording plane of the first optical information recording medium and to converge the second wavelength λ

2 onto an information recording plane of the second optical information recording medium, wherein the objective optical system includes a plastic lens having a positive power on paraxial and the diffractive structure has a function to refrain a change of a spherical aberration caused due to a change of a refractive index of the plastic lens when environmental temperature changes.

49. The objective optical system of claim 48, wherein the objective optical system has a wavelength dependency in a spherical aberration such that when the first wavelength λ

1 changes toward to a longer wavelength side, a spherical aberration changes toward to be under-corrected and when the first wavelength λ

1 changes toward to a shorter wavelength side, a spherical aberration changes toward to be over-corrected.

50. The objective optical system of claim 48, wherein among the plurality of ring-shaped zones to construct the optical path difference providing structure, a ring-shaped zone located inside from a ring-shaped zone positioned at a predetermined height within the maximum effective radius is displaced along the optical axis so as to make an optical path length shorter as the ring-shaped zone is located apart more from the optical axis and a ring-shaped zone located outside from the ring-shaped zone positioned at a predetermined height within the maximum effective radius is displaced along the optical axis so as to make an optical path length longer as the ring-shaped zone is located apart more from the optical axis.

51. The objective optical system of claim 50, wherein a central portion of the ring-shaped zone positioned at the predetermined height has a height from the optical axis that is 60% to 85% of the maximum effective radius.

52. An optical system for use in an optical pickup apparatus in which reproducing and/or recording information is conducted for a first optical information recording medium equipped with a protective layer having a thickness t1 by using a light flux having a first wavelength λ

1 emitted from a first light source and reproducing and/or recording information is conducted for a second optical information recording medium equipped with a protective layer having a thickness t2 (t2≧

t1) by using a light flux having a second wavelength λ

2 (λ

2>

λ

1) emitted from a second light source, comprising;

a correcting optical system;

a light converging element to converge a light flux having a wavelength λ

1 emitted from the correcting optical system on an information recording plane of the first optical information recording medium and to converge a light flux having a wavelength λ

2 emitted from the correcting optical system on an information recording plane of the second optical information recording medium;

wherein an optical surface of the correcting optical system has a plurality of optical functional zones, and a superposition type diffractive structure is formed within one of the plurality of optical functional zones such that a plurality of ring-shaped zones are formed concentrically around the optical axis and plural stepped sections shaped stepwise are formed within each ring-shaped zone.

53. The optical system of claim 52, wherein a first magnification ml in the case that reproducing and/or recording information is conducted for a first optical information recording medium almost coincides with a second magnification m2 in the case that reproducing and/or recording information is conducted for a second optical information recording medium.

54. The optical system of claim 53, wherein the optical system is used to conduct reproducing and/or recording information for a third optical information recording medium equipped with a protective layer having a thickness t3 (t3≧

t2>

t1) by using a light flux having a third wavelength λ

3 (λ

3>

λ

2>

λ

1) emitted from a third light source different from the first and second light sources.

55. The optical system of claim 53, wherein the optical system converges a light flux having the first wavelength λ

1 emitted from a light source module, in which the first and second light sources are packaged, on an information recording plane of the first optical information recording medium and converges a light flux having the second wavelength λ

2 emitted from the light source module on an information recording plane of the second optical information recording medium.

56. The optical system of claim 54, wherein the optical system converges a light flux having the second wavelength λ

2 emitted from a light source module, in which the second and third light sources are packaged, on an information recording plane of the second optical information recording medium and converges a light flux having the third wavelength λ

3 emitted from the light source module on an information recording plane of the third optical information recording medium.

57. The optical system of claim 52, wherein the optical system is used to conduct reproducing and/or recording information for a third optical information recording medium equipped with a protective layer having a thickness t3 (t3≧

t2>

t1) by using a light flux having a third wavelength λ

3 (λ

3>

λ

2>

λ

1) emitted from a third light source different from the first and second light sources.

58. The optical system of claim 57, wherein a second magnification ml in the case that reproducing and/or recording information is conducted for a second optical information recording medium almost coincides with a third magnification m3 in the case that reproducing and/or recording information is conducted for a third optical information recording medium.

59. The optical system of claim 58, wherein a first magnification ml in the case that reproducing and/or recording information is conducted for a first optical information recording medium satisfies the following formula:

m1=0

60. The optical system of claim 57, wherein the optical system converges a light flux having the second wavelength λ

2 emitted from a light source module, in which the second and third light sources are packaged, on an information recording plane of the second optical information recording medium and converges a light flux having the third wavelength λ

3 emitted from the light source module on an information recording plane of the third optical information recording medium.

61. The optical system of claim 52, wherein the optical functional zone including an optical axis of the plurality of optical functional zones has a superposition type diffractive structure including a plurality of ring-shaped zones which are formed concentrically around an optical axis, wherein each ring-shaped zone is composed of a plurality of stepped sections stepwise, and the first wavelength λ

1 and the minimum value P of a distance in a direction perpendicular to the optical axis between neighboring stepped sections in each ring-shaped zone satisfy the following formulas (30) and (31);

0.39 μ

m<

λ

1<

0.42 μ

m  

 

(30) P>

3 μ

m  

 

(31)

62. The optical system of claim 61, wherein the optical system is used to conduct reproducing and/or recording information for a third optical information recording medium equipped with a protective layer having a thickness t3 (t3≧

t2>

t1) by using a light flux having a third wavelength λ

3 (λ

3>

λ

2>

λ

1) emitted from a third light source different from the first and second light sources.

63. The optical system of claim 52, wherein an optical path difference added to a transmitted wave-front by the superposition type diffractive structure is defined by the following arithmetic expression, signs of B2 and B₄ are different from each other,

64. The optical system of claim 63, wherein the optical system is used to conduct reproducing and/or recording information for a third optical information recording medium equipped with a protective layer having a thickness t3 (t3≧

t2>

t1) by using a light flux having a third wavelength λ

3 (λ

3>

λ

2>

λ

1) emitted from a third light source different from the first and second light sources.

65. The optical system of claim 52, wherein the superposition type diffractive structure is formed within two optical functional zones of the plurality of optical functional zones, and wherein the number N of the stepped sections in each ring-shaped zone or a depth Δ

(μ

m), in the optical axis direction, of the stepped sections is different from each optical functional zone.

66. The optical system of claim 65, wherein the optical system is used to conduct reproducing and/or recording information for a third optical information recording medium equipped with a protective layer having a thickness t3 (t3≧

t2>

t1) by using a light flux having a third wavelength λ

3 (λ

3>

λ

2>

λ

1) emitted from a third light source different from the first and second light sources.

67. The optical system of claim 52, wherein on an optical surface of the correcting optical system is formed a diffractive structure including a plurality of ring-shaped zones which are formed concentrically around an optical axis, wherein each of the plurality of ring-shaped zones is divided by the stepped section to generate a diffractive light ray of diffractive order whose absolute value is not small than 1 for the light flux.

68. The optical system of claim 67, wherein the optical system is used to conduct reproducing and/or recording information for a third optical information recording medium equipped with a protective layer having a thickness t3 (t3≧

t2>

t1) by using a light flux having a third wavelength λ

3 (λ

3>

λ

2>

λ

1) emitted from a third light source different from the first and second light sources.

69. The optical system of claim 52, wherein on an optical surface of the correcting optical system is formed an optical path difference providing structure having a central region including the optical axis and a plurality of ring-shaped zones divided with a stepped section at the outside of the central region.

70. The optical system of claim 69, wherein the optical system is used to conduct reproducing and/or recording information for a third optical information recording medium equipped with a protective layer having a thickness t3 (t3≧

t2>

t1) by using a light flux having a third wavelength λ

3 (λ

3>

λ

2>

λ

1) emitted from a third light source different from the first and second light sources.

71. A correcting optical system for use in an optical pickup apparatus in which reproducing and/or recording information is conducted for a first optical information recording medium equipped with a protective layer having a thickness t1 by using a light flux having a first wavelength λ

1 emitted from a first light source and reproducing and/or recording information is conducted for a second optical information recording medium equipped with a protective layer having a thickness t2 (t2≧

t1) by using a light flux having a second wavelength λ

2 (λ

2>

λ

1) emitted from a second light source, wherein the correcting optical system is provided on an optical path between both of the first and second light sources and a light converging element to converge a light flux having the first wavelength λ

1 emitted from the first light source and a light flux having the second wavelength λ

2 emitted from the second light source respectively onto an information recording plane of the first and second optical information recording mediums; and

the correcting optical system comprising;

an optical surface having a plurality of ring-shaped optical functional zones, and a superposition type diffractive structure is formed on one of the plurality of optical functional zones such that a plurality of ring-shaped zones are formed concentrically around the optical axis and plural stepped sections shaped stepwise are formed within each ring-shaped zone.

72. The correcting optical system of claim 71, wherein the correcting optical system is used to conduct reproducing and/or recording information for a third optical information recording medium equipped with a protective layer having a thickness t3 (t3≧

t2>

t1) by using a light flux having a third wavelength λ

3 (λ

3>

λ

2>

λ

1) emitted from a third light source different from the first and second light sources, and is provided between all of the first, second and third light sources and the light converging element.

73. The correcting optical system of claim 71, wherein the optical functional zone including an optical axis of the plurality of optical functional zones has a superposition type diffractive structure including a plurality of ring-shaped zones which are formed concentrically around an optical axis, wherein each ring-shaped zone is composed of a plurality of stepped sections stepwise, and the first wavelength λ

1 and the minimum value P of a distance in a direction perpendicular to the optical axis between neighboring stepped sections in each ring-shaped zone satisfy the following formulas (30) and (31);

0.39 μ

m<

λ

1<

0.42 μ

m  

 

(30) P>

3 μ

m  

 

(31)

74. The correcting optical system of claim 73, wherein the correcting optical system is used to conduct reproducing and/or recording information for a third optical information recording medium equipped with a protective layer having a thickness t3 (t3>

t2>

t1) by using a light flux having a third wavelength λ

3 (λ

3>

λ

2>

λ

1) emitted from a third light source different from the first and second light sources, and is provided between all of the first, second and third light sources and the light converging element.

75. The correcting optical system of claim 71, wherein an optical path difference added to a transmitted wave-front by the superposition type diffractive structure is defined by the following arithmetic expression, signs of B₂ and B₄ are different from each other,

76. The correcting optical system of claim 75, wherein the correcting optical system is used to conduct reproducing and/or recording information for a third optical information recording medium equipped with a protective layer having a thickness t3 (t3≧

t2>

t1) by using a light flux having a third wavelength λ

3 (λ

3>

λ

2>

λ

1) emitted from a third light source different from the first and second light sources, and is provided between all of the first, second and third light sources and the light converging element.

77. The correcting optical system of claim 71, wherein the superposition type diffractive structure is formed within two optical functional zones of the plurality of optical functional zones, and wherein the number N of the stepped sections in each ring-shaped zone or a depth Δ

(μ

m), in the optical axis direction, of the stepped sections is different from each optical functional zone.

78. The correcting optical system of claim 77, wherein the correcting optical system is used to conduct reproducing and/or recording information for a third optical information recording medium equipped with a protective layer having a thickness t3 (t3≧

t2>

t1) by using a light flux having a third wavelength λ

3 (λ

3>

λ

2>

λ

1) emitted from a third light source different from the first and second light sources, and is provided between all of the first, second and third light sources and the light converging element.

79. The correcting optical system of claim 71, wherein a superposition type diffractive structure is formed within one of the plurality of optical functional zones and the correcting optical system further comprises an optical surface having a diffractive structure which includes a plurality of ring-shaped zones formed concentrically around an optical axis, wherein each of the plurality of ring-shaped zones is divided by a stepped section to generate a diffractive light ray of diffractive order whose absolute value is not small than 1 for the light flux.

80. The correcting optical system of claim 79, wherein the correcting optical system is used to conduct reproducing and/or recording information for a third optical information recording medium equipped with a protective layer having a thickness t3 (t3≧

t2>

t1) by using a light flux having a third wavelength λ

3 (λ

3>

λ

2>

λ

1) emitted from a third light source different from the first and second light sources, and is provided between all of the first, second and third light sources and the light converging element.

81. The correcting optical system of claim 71, wherein the correcting optical system comprises a optical path difference providing structure to provide a predetermined optical path difference, and wherein a plurality of ring-shaped zones are formed continuously around an optical axis on the optical path difference providing structure and each ring-shaped zone is divided with a stepped section.

82. The correcting optical system of claim 81, wherein the correcting optical system is used to conduct reproducing and/or recording information for a third optical information recording medium equipped with a protective layer having a thickness t3 (t3≧

t2>

t1) by using a light flux having a third wavelength λ

3 (λ

3>

λ

2>

λ

1) emitted from a third light source different from the first and second light sources, and is provided between all of the first, second and third light sources and the light converging element.

83. A light converging element for use in an optical pickup apparatus in which reproducing and/or recording information is conducted for a first optical information recording medium equipped with a protective layer having a thickness t1 by using a light flux having a first wavelength λ

1 emitted from a first light source and reproducing and/or recording information is conducted for a second optical information recording medium equipped with a protective layer having a thickness t2 (t2≧

t1) by using a light flux having a second wavelength λ

2 (λ

2>

λ

1) emitted from a second light source, comprising;

an optical surface of the light converging element having a plurality of optical functional zones, and a superposition type diffractive structure is formed within one of the plurality of optical functional zones such that a plurality of ring-shaped zones are formed around the optical axis and plural stepped sections shaped stepwise are formed within each ring-shaped zone.

84. The light converging element of claim 83, wherein the light converging element is used to conduct reproducing and/or recording information for a third optical information recording medium equipped with a protective layer having a thickness t3 (t3≧

t2>

t1) by using a light flux having a third wavelength λ

3 (λ

3>

λ

2>

λ

1) emitted from a third light source different from the first and second light sources.

85. The light converging element of claim 83, wherein a first magnification ml in the case that reproducing and/or recording information is conducted for a first optical information recording medium almost coincides with a second magnification m2 in the case that reproducing and/or recording information is conducted for a second optical information recording medium.

86. The light converging element of claim 85, wherein the light converging element is used to conduct reproducing and/or recording information for a third optical information recording medium equipped with a protective layer having a thickness t3 (t3≧

t2>

t1) by using a light flux having a third wavelength λ

3 (λ

3>

λ

2>

λ

1) emitted from a third light source different from the first and second light sources.

87. The light converging element of claim 83, wherein the light converging element is used to conduct reproducing and/or recording information for a third optical information recording medium equipped with a protective layer having a thickness t3 (t3≧

t2>

t1) by using a light flux having a third wavelength λ

3 (λ

3>

λ

2>

λ

1) emitted from a third light source different from the first and second light sources, the light converging element is located at a position to face the first optical information recording medium, the second optical information recording medium and the third optical information recording medium, and a second magnification ml in the case that reproducing and/or recording information is conducted for a second optical information recording medium almost coincides with a third magnification m3 in the case that reproducing and/or recording information is conducted for a third optical information recording medium.

88. The light converging element of claim 87, wherein the light converging element is used to conduct reproducing and/or recording information for a third optical information recording medium equipped with a protective layer having a thickness t3 (t3≧

t2>

t1) by using a light flux having a third wavelength λ

3 (λ

3>

λ

2>

λ

1) emitted from a third light source different from the first and second light sources.

89. The light converging element of claim 83, wherein an optical functional zone including an optical axis of the plurality of optical functional zones has a superposition type diffractive structure including a plurality of ring-shaped zones which are formed concentrically around an optical axis, wherein each ring-shaped zone is composed of a plurality of stepped sections stepwise, and the first wavelength λ

1 and the minimum value P of a distance in a direction perpendicular to the optical axis between neighboring stepped sections in each ring-shaped zone satisfy the following formulas (30) and (31);

0.39 μ

m<

λ

1<

0.42 μ

m  

 

(30) P>

3 μ

m  

 

(31)

90. The light converging element of claim 89, wherein the light converging element is used to conduct reproducing and/or recording information for a third optical information recording medium equipped with a protective layer having a thickness t3 (t3≧

t2>

t1) by using a light flux having a third wavelength λ

3 (λ

3>

λ

2>

λ

1) emitted from a third light source different from the first and second light sources.

91. The light converging element of claim 83, wherein the superposition type diffractive structure is formed within the optical functional zone including the optical axis of the plurality of optical functional zones and an optical path difference added to a transmitted wave-front by the superposition type diffractive structure is defined by the following arithmetic expression, signs of B₂ and B₄ are different from each other,

92. The light converging element of claim 91, wherein the light converging element is used to conduct reproducing and/or recording information for a third optical information recording medium equipped with a protective layer having a thickness t3 (t3≧

t2>

t1) by using a light flux having a third wavelength λ

3 (λ

3>

λ

2>

λ

1) emitted from a third light source different from the first and second light sources.

93. The light converging element of claim 83, wherein the superposition type diffractive structure is formed within two optical functional zones of the plurality of optical functional zones, and wherein the number N of the stepped sections in each ring-shaped zone or a depth Δ

(μ

m), in the optical axis direction, of the stepped sections is different from each optical functional zone.

94. The light converging element of claim 93, wherein the light converging element is used to conduct reproducing and/or recording information for a third optical information recording medium equipped with a protective layer having a thickness t3 (t3≧

t2>

t1) by using a light flux having a third wavelength λ

3 (λ

3>

λ

2>

λ

1) emitted from a third light source different from the first and second light sources.

95. The light converging element of claim 83, wherein the superposition type diffractive structure is formed within one of the plurality of optical functional zones and the correcting optical system further comprises an optical surface having a diffractive structure which includes a plurality of ring-shaped zones formed concentrically around an optical axis, wherein each of the plurality of ring-shaped zones are divided by a stepped section to generate a diffractive light ray of diffractive order whose absolute value is not small than 1 for the light flux.

96. The light converging element of claim 95, wherein the light converging element is used to conduct reproducing and/or recording information for a third optical information recording medium equipped with a protective layer having a thickness t3 (t3≧

t2>

t1) by using a light flux having a third wavelength λ

3 (λ

3>

λ

2>

λ

1) emitted from a third light source different from the first and second light sources.

97. The light converging element of claim 83, wherein the light converging element comprises a optical path difference providing structure to provide a predetermined optical path difference, and wherein a plurality of ring-shaped zones are formed continuously around an optical axis on the optical path difference providing structure and each ring-shaped zone is divided with a stepped section.

98. The light converging element of claim 97, wherein the light converging element is used to conduct reproducing and/or recording information for a third optical information recording medium equipped with a protective layer having a thickness t3 (t3≧

t2>

t1) by using a light flux having a third wavelength λ

3 (λ

3>

λ

2>

λ

1) emitted from a third light source different from the first and second light sources.

99. An optical pickup apparatus for conducting recording and/or reproducing information for plural different recording mediums with plural wavelength light fluxes, comprising:

a first light source to emit a light flux having a first wavelength λ

1 for conducting recording and/or reproducing information for a first information recording medium equipped with a protective substrate having a thickness t1;

a second light source to emit a light flux having a second wavelength λ

2 (λ

2>

λ

1) for conducting recording and/or reproducing information for a second information recording medium equipped with a protective substrate having a thickness t2 (t2≧

t1);

a third light source to emit a light flux having a third wavelength λ

3 (λ

3>

λ

2>

λ

1) for conducting recording and/or reproducing information for a third information recording medium equipped with a protective substrate having a thickness t3 (t3≧

t2);

an objective optical system to converge a light flux having the wavelength λ

1, λ

2 or λ

3 onto the first, second or third information recording medium respectively;

a diaphragm;

a driving device to drive the objective system and the diaphragm as one unit in a direction perpendicular to the optical axis;

an entering devise to make at least one light flux among light fluxes having the first, second and third wavelengths λ

1, λ

2 and λ

3 enter in not parallel to the optical axis into the objective optical system; and

a coma aberration correcting element provided between the objective lens and a light source to emit a light flux which enters in not parallel to the optical axis into the objective optical system and to reduce a coma aberration generated when the objective optical system is driven in the direction perpendicular to the optical axis by the driving device;

wherein an optical surface of the objective optical system has a plurality of optical functional zones, and a superposition type diffractive structure is formed within the optical functional zone including an optical axis of the plurality of optical functional zones such that a plurality of ring-shaped zones are formed around the optical axis and plural stepped sections shaped stepwise are formed within each ring-shaped zone.

100. The optical pickup apparatus of claim 99, wherein the second light source and the third light source are packaged in a light source module.

101. An optical pickup apparatus for conducting recording and/or reproducing information for plural different recording mediums with plural wavelength light fluxes, comprising:

a first light source to emit a light flux having a first wavelength λ

1 for conducting recording and/or reproducing information for a first information recording medium equipped with a protective substrate having a thickness t1;

a second light source to emit a light flux having a second wavelength λ

2 (λ

2>

λ

1) for conducting recording and/or reproducing information for a second information recording medium equipped with a protective substrate having a thickness t2 (t2≧

t1);

a third light source to emit a light flux having a third wavelength λ

3 (λ

3>

λ

2>

λ

1) for conducting recording and/or reproducing information for a third information recording medium equipped with a protective substrate having a thickness t3 (t3≧

t2);

an objective optical system to converge a light flux having the wavelength λ

1, λ

2 or λ

3 onto the fist, second or third information recording medium respectively, wherein an optical surface of the objective optical system has a plurality of optical functional zones, and a superposition type diffractive structure is formed within an optical functional zone including an optical axis of the plurality of optical functional zones such that a plurality of ring-shaped zones are formed around the optical axis and plural stepped sections shaped stepwise are formed within each ring-shaped zone;

an entering device to enter at least two light fluxes with respective different magnifications into the objective optical system among light fluxes having the first, second and third wavelengths λ

1, λ

2 and λ

3;

an divergent angle converting element having an optical surface including a superposition type diffractive structure, wherein the superposition type diffractive structure includes a plurality of ring-shaped zones which are formed concentrically around an optical axis, wherein each ring-shaped zone is composed of a plurality of stepped section stepwise, the divergent angle converting element to convert a divergent angle of at least a light flux having one of the first, second and third wavelengths λ

1, λ

2 and λ

3;

wherein light sources to emit at least two light fluxes entering with respective different magnifications into the objective optical system among the first, second and third light sources are packaged in a light source module and the divergent angle converting element is located on a optical path between the light source module and the objective optical system.

102. An optical pickup apparatus for conducting recording and/or reproducing information for plural different recording mediums with plural wavelength light fluxes, comprising:

a first light source to emit a light flux having a first wavelength λ

1 for conducting recording and/or reproducing information for a first information recording medium equipped with a protective substrate having a thickness t1;

a second light source to emit a light flux having a second wavelength λ

2 (λ

2>

λ

1) for conducting recording and/or reproducing information for a second information recording medium equipped with a protective substrate having a thickness t2 (t2≧

t1);

a third light source to emit a light flux having a third wavelength λ

3 (λ

3>

λ

2>

λ

1) for conducting recording and/or reproducing information for a third information recording medium equipped with a protective substrate having a thickness t3 (t3≧

t2);

a diffractive lens having an optical surface including a superposition type diffractive structure,

wherein the superposition type diffractive structure includes a plurality of ring-shaped zones which are formed concentrically around an optical axis, wherein each ring-shaped zone is composed of a plurality of stepped section stepwise, wherein the superposition type diffractive structure has a function to provide substantially no optical path difference to the first and third light fluxes and to provide an optical path difference only to the second light flux; and

a light converging element to converge a light flux having the wavelength λ

1, λ

2 or λ

3 having passed through the diffractive lens onto the first, second or third information recording medium respectively;

wherein the following formula (173) is satisfied;

m1≧

m2>

m3  

 

(173)

where m1 is a magnification of an optical system structured by the diffractive lens and the light converging element for a light flux having the first wavelength λ

1, m2 is a magnification of an optical system structured by the optical member and the light converging element for a light flux having the second wavelength λ

2 and m3 is a magnification for a light flux having the third wavelength λ

3.

103. An optical pickup apparatus for conducting recording and/or reproducing information for plural different recording mediums with plural wavelength light fluxes, comprising:

a first light source to emit a light flux having a first wavelength λ

1 for conducting recording and/or reproducing information for a first information recording medium equipped with a protective substrate having a thickness t1;

a second light source to emit a light flux having a second wavelength λ

2 (λ

2>

λ

1) for conducting recording and/or reproducing information for a second information recording medium equipped with a protective substrate having a thickness t2 (t2≧

t1);

a third light source to emit a light flux having a third wavelength λ

3 (λ

3>

λ

2>

λ

1) for conducting recording and/or reproducing information for a third information recording medium equipped with a protective substrate having a thickness t3 (t3≧

t2);

a light converging element to converge a light flux having the wavelength λ

1, λ

2 or λ

3 onto the first, second or third information recording medium respectively;

a correcting optical system having an optical surface including a predetermined stepped structure; and

a spherical aberration correcting member;

wherein the correcting optical system has a function to correct a spherical aberration generated by the light converging element due to a difference between the first wavelength λ

1 and the second wavelength λ

2 and/or a spherical aberration caused due to a difference between t1 and t2 and the spherical aberration correcting member has a function to correct a spherical aberration caused due to a difference between t1 and t3.

104. The optical pickup apparatus of claim 103, wherein the stepped structure is one of a superposition type diffractive structure, a diffractive structure and an optical path difference providing structure.

105. The optical pickup apparatus of claim 104, wherein an optical path difference provided to the first light flux by the stepped structure is multiplied the first wavelength with an integer.

106. The optical pickup apparatus of claim 105, wherein an optical path difference provided to the first light flux by the stepped structure is multiplied the first wavelength with an even number.

107. The optical pickup apparatus of claim 106, further comprising:

a second correcting optical system having an optical surface including a diffractive structure and an optical path difference provided to the first light flux by the diffractive structure is multiplied the first wavelength with an odd number.

108. The optical pickup apparatus of claim 106, further comprising:

a second correcting optical system having an optical surface including a optical path difference providing structure and an optical path difference provided to the first light flux by the optical path difference providing is multiplied the first wavelength with an odd number.

109. The optical pickup apparatus of claim 103, wherein a magnification ml of an optical system structured by the light converging element and the aberration correcting element for a light flux having the first wavelength λ

1 almost coincides with a second magnification m2 for a light flux having the second wavelength λ

2.

110. The optical pickup apparatus of claim 107, wherein a magnification ml of an optical system structured by the light converging element and the aberration correcting element for a light flux having the first wavelength λ

1 almost coincides with a second magnification m2 for a light flux having the second wavelength λ

2.

111. The optical pickup apparatus of claim 108, wherein a magnification ml of an optical system structured by the light converging element and the aberration correcting element for a light flux having the first wavelength λ

1 almost coincides with a second magnification m2 for a light flux having the second wavelength λ

2.

112. The optical pickup apparatus of claim 103, wherein the light converging element is optimized in terms of a spherical aberration for the first wavelength λ

1 and the protective substrate having the thickness t1.

113. The optical pickup apparatus of claim 110, wherein the light converging element is optimized in terms of a spherical aberration for the first wavelength λ

1 and the protective substrate having the thickness t1.

114. The optical pickup apparatus of claim 111, wherein the light converging element is optimized in terms of a spherical aberration for the first wavelength λ

1 and the protective substrate having the thickness t1.

115. The optical pickup apparatus of claim 103, wherein the light converging element and the aberration correcting element is supported such that a relative positional relationship therebetween is not changed.

116. The optical pickup apparatus of claim 113, wherein the light converging element and the aberration correcting element is supported such that a relative positional relationship therebetween is not changed.

117. The optical pickup apparatus of claim 114, wherein the light converging element and the aberration correcting element is supported such that a relative positional relationship therebetween is not changed.

118. The optical pickup apparatus of claim 103, wherein the spherical aberration correcting member is a liquid crystal phase controlling element comprising a liquid crystal layer to cause a phase change for a transmitting light flux due to an application of a voltage and electrode layers to face to each other so as to apply a voltage to the liquid crystal layer, and the liquid crystal phase controlling element corrects a spherical aberration due to a difference between the thickness t1 and the thickness t3 by conducting a phase control for the third light flux.

119. The optical pickup apparatus of claim 116, wherein the spherical aberration correcting member is a liquid crystal phase controlling element comprising a liquid crystal layer to cause a phase change for a transmitting light flux due to an application of a voltage and electrode layers to face to each other so as to apply a voltage to the liquid crystal layer, and the liquid crystal phase controlling element corrects a spherical aberration due to a difference between the thickness t1 and the thickness t3 by conducting a phase control for the third light flux.

120. The optical pickup apparatus of claim 117, wherein the spherical aberration correcting member is a liquid crystal phase controlling element comprising a liquid crystal layer to cause a phase change for a transmitting light flux due to an application of a voltage and electrode layers to face to each other so as to apply a voltage to the liquid crystal layer, and the liquid crystal phase controlling element corrects a spherical aberration due to a difference between the thickness t1 and the thickness t3 by conducting a phase control for the third light flux.

121. The optical pickup apparatus of claim 118, wherein the liquid crystal phase controlling element selectively conducts only a phase control for the third light flux.

122. The optical pickup apparatus of claim 119, wherein the liquid crystal phase controlling element selectively conducts only a phase control for the third light flux.

123. The optical pickup apparatus of claim 120, wherein the liquid crystal phase controlling element selectively conducts only a phase control for the third light flux.

124. The optical pickup apparatus of claim 103, wherein the spherical aberration correcting member is a movable lens unit comprising an actuator and a movable lens group capable of being moved in the optical axis direction by the actuator, and the movable lens unit corrects a spherical aberration due to a difference between the thickness t1 and the thickness t3 by changing a magnification of the light converging element.

125. The optical pickup apparatus of claim 116, wherein the spherical aberration correcting member is a movable lens unit comprising an actuator and a movable lens group capable of being moved in the optical axis direction by the actuator, and the movable lens unit corrects a spherical aberration due to a difference between the thickness t1 and the thickness t3 by changing a magnification of the light converging element.

126. The optical pickup apparatus of claim 117, wherein the spherical aberration correcting member is a movable lens unit comprising an actuator and a movable lens group capable of being moved in the optical axis direction by the actuator, and the movable lens unit corrects a spherical aberration due to a difference between the thickness t1 and the thickness t3 by changing a magnification of the light converging element.

127. The optical pickup apparatus of claim 125, wherein a magnification m3 of the light converging element for the third wavelength λ

3 satisfies the following formula (177);

−

0.15<

m3<

−

0.02  

 

(177)

128. The optical pickup apparatus of claim 126, wherein a magnification m3 of the light converging element for the third wavelength λ

3 satisfies the following formula (177);

−

0.15<

m3<

−

0.02  

 

(177)

129. The optical pickup apparatus of claim 103, wherein at least two light sources among the first, second and third light sources are made in one body.

130. The optical pickup apparatus of claim 127, wherein at least two light sources among the first, second and third light sources are made in one body.

131. The optical pickup apparatus of claim 128, wherein at least two light sources among the first, second and third light sources are made in one body.

132. The optical pickup apparatus of claim 129, wherein all of the first, second and third light sources are made in one body.

133. The optical pickup apparatus of claim 130, wherein all of the first, second and third light sources are made in one body.

134. The optical pickup apparatus of claim 131, wherein all of the first, second and third light sources are made in one body.

137. The optical pickup apparatus of claim 134, further comprising:

a third light source to emit a third light flux having a third wavelength λ

3 (λ

3>

λ

2) for conducting recording and/or reproducing information for a third optical information recording medium equipped with a protective substrate having a thickness t3 (t3≧

t2).

138. The optical pickup apparatus of claim 134, wherein the second optical surface has a function to refrain a longitudinal chromatic aberration caused due to wavelength dispersion when the first wavelength λ

1 fluctuates within a range of ±

10 nm.

139. The optical pickup apparatus of claim 134, wherein the second optical surface has a function to refrain a spherical aberration change caused due to wavelength dispersion when the first wavelength λ

1 fluctuates within a range of ±

10 nm.

140. The optical pickup apparatus of claim 137, wherein the first wavelength λ

1 (μ

m), the second wavelength λ

2 and the third wavelength λ

3 (μ

m) satisfy the formulas (2), (3) and (3′

) respectively,

0.39<

λ

1<

0.42  

 

(2) 0.63<

λ

2<

0.68  

 

(3) 0.75<

λ

3<

0.85  

 

(3′

)

141. The optical pickup apparatus of claim 140, further comprising a structure that at least two light fluxes among light fluxes having the first, second and third wavelengths λ

1, λ

2 and λ

3 enter with respective magnifications different from each other into the optical system.

142. The optical pickup apparatus of claim 141, wherein the optical pickup apparatus has a structure that at least two light fluxes among light fluxes having the first, second and third wavelengths λ

1, λ

2 and λ

3 enter with the almost same magnification into the optical system.

135. An optical pickup apparatus for conducting recording and/or reproducing information for plural different recording mediums with plural wavelength light fluxes, comprising:

a first light source to emit a light flux having a first wavelength λ

1;

a second light source to emit a light flux having a second wavelength λ

2 (λ

2>

λ

1);

an objective optical system for converging a light flux having the first wavelength λ

1 onto a recording plane of a first information recording medium equipped with a protective substrate having a thickness t1 and for converging a light flux having the second wavelength λ

2 onto a recording plane of a second information recording medium equipped with a protective substrate having a thickness t2 (t2≧

t1);

wherein the objective optical system comprises a first optical surface to provide substantially no optical path difference for an incident light flux having the first wavelength λ

1 and to provide an optical path difference for an incident light flux having the second wavelength λ

2 and a second optical surface to refrain a chromatic aberration change caused due to wavelength dispersion when the first wavelength λ

1 fluctuates within a range of ±

10 nm.

136. The optical pickup apparatus of claim 135, wherein the first wavelength λ

1 (μ

m) and the second wavelength λ

2 (μ

m) satisfy the formulas (2) and (3) respectively,

0.39<

λ

1<

0.42  

 

(2) 0.63<

λ

2<

0.68  

 

(3).

143. An optical pickup apparatus for conducting recording and/or reproducing information for plural different recording mediums with plural wavelength light fluxes, comprising:

a first light source to emit a light flux having a first wavelength λ

1;

a second light source to emit a light flux having a second wavelength λ

2 (λ

2>

λ

1);

an objective optical system for converging a light flux having the first wavelength λ

1 onto a recording plane of a first information recording medium equipped with a protective substrate having a thickness t1 and for converging a light flux having the second wavelength λ

2 onto a recording plane of a second information recording medium equipped with a protective substrate having a thickness t2 (t2≧

t1);

wherein the objective optical system comprises a plastic lens having a positive paraxial power, a first optical surface to provide substantially no optical path difference for an incident light flux having the first wavelength λ

1 and to provide an optical path difference for an incident light flux having the second wavelength λ

2, and a second optical surface to refrain a change of a spherical aberration caused due to a change of a refractive index of the plastic lens when environmental temperature changes.

144. The optical pickup apparatus of claim 143, wherein the first wavelength λ

1 (μ

m) and the second wavelength λ

2 (μ

m) satisfy the formulas (2) and (3) respectively,

0.39<

λ

1<

0.42  

 

(2) 0.63<

λ

2<

0.68  

 

(3).

145. The optical pickup apparatus of claim 143, further comprising:

a third light source to emit a third light flux having a third wavelength λ

3 (λ

3>

λ

2) for conducting recording and/or reproducing information for a third optical information recording medium equipped with a protective substrate having a thickness t3 (t3≧

t2).

146. The optical pickup apparatus of claim 143, wherein the second optical surface has a function to refrain a longitudinal chromatic aberration caused due to wavelength dispersion when the first wavelength λ

1 fluctuates within a range of ±

10 nm.

147. The optical pickup apparatus of claim 143, wherein the second optical surface has a function to refrain a spherical aberration change caused due to wavelength dispersion when the first wavelength λ

1 fluctuates within a range of ±

10 nm.

148. The optical pickup apparatus of claim 145, wherein the first wavelength λ

1 (μ

m), the second wavelength λ

2 and the third wavelength λ

3 (μ

m) satisfy the formulas (2), (3) and (3′

) respectively,

0.39<

λ

1<

0.42  

 

(2) 0.63<

λ

2<

0.68  

 

(3) 0.75<

λ

3<

0.85  

 

(3′

)

149. The optical pickup apparatus of claim 145, further comprising a structure that at least two light fluxes among light fluxes having the first, second and third wavelengths λ

1, λ

2 and λ

3 enter with respective magnifications different from each other into the optical system.

150. The optical pickup apparatus of claim 145, wherein the optical pickup apparatus has a structure that at least two light fluxes among light fluxes having the first, second and third wavelengths λ

1, λ

2 and λ

3 enter with the almost same magnification into the optical system.