Objective lens and optical information recording/reproducing apparatus

1. An optical information recording/reproducing apparatus for recording information to and/or reproducing information from an optical disc based on a predetermined standard by using a light beam having a wavelength of λ (unit: nm),

the optical information recording/reproducing apparatus comprising:

a biconvex objective lens that converges the light beam onto a recording surface of the optical disc and satisfies a condition:

0.48

<

d

·

(

n

-

1

)

f

2

<

0.75

(

1

)

where f represents a focal length (unit: mm) of the objective lens with respect to the wavelength λ, d represents a thickness (unit: mm) of the objective lens along an optical axis of the objective lens, and n represents a refractive index with respect to the wavelength λ;

a photoreceptor that receives the light beam reflected from the recording surface of the optical disc;

a detector that detects quality of a signal outputted by the photoreceptor based on the light beam reflected from the recording surface of the optical disc; and

an objective lens driving unit configured to tilt the objective lens in a direction to improve the quality of the signal based on a result of detection by the detector,

wherein the objective lens is configured such that an offence against a sine condition takes a local minimum value within a range larger than or equal to 20% and smaller than 80% of an effective beam radius with respect to the optical axis, the offence against the sine condition takes a maximum value within a range of 80% to 100% of the effective beam radius, and the maximum value of the offence against the sine condition falls within a range of 0.001 to 0.01.

2. The optical information recording/reproducing apparatus according to claim 1 ,

wherein:

at least one of surfaces of the objective lens is formed to be a phase shift surface having a phase shift structure including a plurality of refractive surface zones which are concentrically formed and are divided by minute steps, each of the steps being formed at a boundary between adjacent ones of the plurality of annular zones to give a predetermined optical path length difference to the light beam incident thereon;

when (Σφ 0.00-1.00 ) represents a sum of heights of all the steps formed in an effective beam diameter on the phase shift surface, and (Σφ 0.95-1.00 ) represents a sum of heights of the steps formed in a range of 95% to 100% of an effective beam radius with respect to the optical axis, the objective lens satisfies a condition:

0.1

<

(

∑

ϕ

0.95

-

1.00

)

(

∑

ϕ

0.00

-

1.00

)

<

0.5

.

(

2

)

3. The optical information recording/reproducing apparatus according to claim 2 ,

wherein the steps of the phase shift structure are defined by a following optical path difference function φ(h):

φ( h )=( P 2 ×h 2 +P 4 ×h 4 +P 6 ×h 6 +P 8 ×h 8 +P 10 ×h 10 +P 12 ×h 12 ) mλ

where P 2 , P 4 , P 6 . . . represent coefficients of the 2 nd order, 4 th order, 6 th order, h represents a height from the optical axis, and m represents a diffraction order at which diffraction efficiency is maximized.

4. The optical information recording/reproducing apparatus according to claim 1 , wherein the optical disc has a protective layer thickness of 0.05 to 0.15 (unit: mm).

5. The optical information recording/reproducing apparatus according to claim 1 , wherein a numerical aperture NA of the objective lens defined on an optical disc side lies within a range of 0.8 to 0.87 when the light beam having the wavelength λ is used.

6. The optical information recording/reproducing apparatus according to claim 1 , wherein the objective lens comprises a resin.

7. The optical information recording/reproducing apparatus according to claim 1 ,

wherein the refractive index n of the objective lens satisfies a condition:

1.4< n< 1.7  (5).

8. An optical information recording/reproducing apparatus for recording information to and/or reproducing information from an optical disc based on a predetermined standard by using a light beam having a wavelength of λ (unit: nm),

the optical information recording/reproducing apparatus comprising:

a biconvex objective lens that converges the light beam onto a recording surface of the optical disc and satisfies a condition:

0.48

<

d

·

(

n

-

1

)

f

2

<

0.75

(

1

)

where f represents a focal length (unit: mm) of the objective lens with respect to the wavelength λ, d represents a thickness (unit: mm) of the objective lens along an optical axis of the objective lens, and n represents a refractive index with respect to the wavelength λ;

a photoreceptor that receives the light beam reflected from the recording surface of the optical disc;

a detector that detects quality of a signal outputted by the photoreceptor based on the light beam reflected from the recording surface of the optical disc; and

an objective lens driving unit configured to tilt the objective lens in a direction to improve the quality of the signal based on a result of detection by the detector,

wherein the objective lens is configured such that an offence against a sine condition and a spherical aberration become equal to each other at a 100% point of an effective beam radius when a protective layer thickness of the optical disc lies within a range of 0.105 to 0.15 (unit: mm).

9. A biconvex objective lens for an optical information recording/reproducing apparatus for recording information to and/or reproducing information from an optical disc based on a predetermined standard, the optical disc having a protective layer thickness of 0.05 to 0.15 (unit; mm),

the biconvex objective lens having surfaces and satisfying a condition:

0.48

<

d

·

(

n

-

1

)

f

2

<

0.75

(

1

)

where f represents a focal length (unit: mm) of the objective lens with respect to a light beam having a wavelength λ used for recording information to and/or reproducing information from the optical disc, d represents a thickness (unit: mm) of the objective lens along an optical axis of the objective lens, and n represents a refractive index with respect to the wavelength λ,

wherein the objective lens is configured such that an offence against a sine condition takes a local minimum value within a range larger than or equal to 20% and smaller than 80% of an effective beam radius with respect to the optical axis, the offence against the sine condition takes a maximum value within a range of 80% to 100% of the effective beam radius, and the maximum value of the offence against the sine condition falls within a range of 0.001 to 0.01.

10. The biconvex objective lens according to claim 9 , wherein:

at least one of surfaces of the objective lens is formed to be a phase shift surface having a phase shift structure including a plurality of refractive surface zones which are concentrically formed and are divided by minute steps, each of the steps being formed at a boundary between adjacent ones of the plurality of annular zones to give a predetermined optical path length difference to the light beam incident thereon;

when (Σφ 0.00-1.00 ) represents a sum of heights of all the steps formed in an effective beam diameter on the phase shift surface, and (Σφ 0.95-1.00 ) represents a sum of heights of the steps formed in a range of 95% to 100% of an effective beam radius with respect to the optical axis, the objective lens satisfies a condition:

0.1

<

(

∑

ϕ

0.95

-

1.00

)

(

∑

ϕ

0.00

-

1.00

)

<

0.5

.

(

2

)

11. The biconvex objective lens according to claim 10 ,

wherein the steps of the phase shift structure are defined by a following optical path difference function φ(h):

φ( h )=( P 2 ×h 2 +P 4 ×h 4 +P 6 ×h 6 +P 8 ×h 8 +P 10 ×h 10 +P 12 ×h 12 ) mλ

where P 2 , P 4 , P 6 . . . represent coefficients of the 2 nd order, 4 th order, 6 th order, h represents a height from the optical axis, and m represents a diffraction order at which diffraction efficiency is maximized.

12. The biconvex objective lens according to claim 9 ,

wherein a numerical aperture NA of the objective lens defined on an optical disc side lies within a range of 0.8 to 0.87 when the light beam having the wavelength λ is used.

13. The biconvex objective lens according to claim 9 , wherein the objective lens comprises a resin.

14. The biconvex objective lens according to claim 9 , wherein the refractive index n of the objective lens satisfies a condition:

1.4< n< 1.7  (5).

15. An optical information recording/reproducing apparatus for recording information to and/or reproducing information from an optical disc based on a predetermined standard by using a light beam having a wavelength of λ (unit: nm),

the optical information recording/reproducing apparatus comprising:

an objective lens that converges the light beam onto a recording surface of the optical disc and satisfies a condition:

0.48

<

d

·

(

n

-

1

)

f

2

<

0.75

(

1

)

where f represents a focal length (unit: mm) of the objective lens with respect to the wavelength λ, d represents a thickness (unit: mm) of the objective lens along an optical axis of the objective lens, and n represents a refractive index with respect to the wavelength λ;

a photoreceptor that receives the light beam reflected from the recording surface of the optical disc;

a detector that detects quality of a signal outputted by the photoreceptor based on the light beam reflected from the recording surface of the optical disc; and

an objective lens driving unit configured to tilt the objective lens in a direction to improve the quality of the signal based on a result of detection by the detector;

wherein:

at least one of surfaces of the objective lens is formed to be a phase shift surface having a phase shift structure including a plurality of refractive surface zones which are concentrically formed and are divided by minute steps, each of the steps being formed at a boundary between adjacent ones of the plurality of annular zones to give a predetermined optical path length difference to the light beam incident thereon;

when (Σφ 0.00-1.00 ) represents a sum of heights of all the steps formed in an effective beam diameter on the phase shift surface, and (Σφ 0.95-1.00 ) represents a sum of heights of the steps formed in a range of 95% to 100% of an effective beam radius with respect to the optical axis, the objective lens satisfies a condition:

0.1

<

(

∑

ϕ

0.95

-

1.00

)

(

∑

ϕ

0.00

-

1.00

)

<

0.5

.

(

2

)

16. An objective lens for an optical information recording/reproducing apparatus for recording information to and/or reproducing information from an optical disc based on a predetermined standard, the optical disc having a protective layer thickness of 0.05 to 0.15 (unit: mm),

the objective lens including surfaces and satisfying a condition:

0.48

<

d

·

(

n

-

1

)

f

2

<

0.75

(

1

)

where f represents a focal length (unit: mm) of the objective lens with respect to a light beam having a wavelength λ used for recording information to and/or reproducing information from the optical disc, d represents a thickness (unit: mm) of the objective lens along an optical axis of the objective lens, and n represents a refractive index with respect to the wavelength λ;

wherein:

at least one of the surfaces of the objective lens is a phase shift surface having a phase shift structure including a plurality of refractive surface zones which are concentrically formed and are divided by minute steps, each of the steps being formed at a boundary between adjacent ones of the plurality of annular zones to give a predetermined optical path length difference to the light beam incident thereon;

when (Σφ 0.00-1.00 ) represents a sum of heights of all the steps formed in an effective beam diameter on the phase shift surface, and (Σφ 0.95-1.00 ) represents a sum of heights of the steps formed in a range of 95% to 100% of an effective beam radius with respect to the optical axis, the objective lens satisfies a condition:

0.1

<

(

∑

ϕ

0.95

-

1.00

)

(

∑

ϕ

0.00

-

1.00

)

<

0.5

.

(

2

)

17. A biconvex objective lens for an optical information recording/reproducing apparatus for recording information to and/or reproducing information from an optical disc based on a predetermined standard, the optical disc having a protective layer thickness of 0.05 to 0.15 (unit: mm),

the biconvex objective lens having surfaces and satisfying a condition:

0.48

<

d

·

(

n

-

1

)

f

2

<

0.75

(

1

)

where f represents a focal length (unit: mm) of the objective lens with respect to a light beam having a wavelength λ used for recording information to and/or reproducing information from the optical disc, d represents a thickness (unit: mm) of the objective lens along an optical axis of the objective lens, and n represents a refractive index with respect to the wavelength λ, and

wherein the objective lens is configured such that an offense against a sine condition and a spherical aberration are equal to each other at a 100% point of an effective beam radius when a protective layer thickness of the optical disc lies within the range of 0.105 to 0.15 (unit: mm).

18. The biconvex objective lens according to claim 17 ,

wherein:

at least one of surfaces of the objective lens is formed to be a phase shift surface having a phase shift structure including a plurality of refractive surface zones which are concentrically formed and are divided by minute steps, each of the steps being formed at a boundary between adjacent ones of the plurality of annular zones to give a predetermined optical path length difference to the light beam incident thereon;

when (Σφ 0.00-1.00 ) represents a sum of heights of all the steps formed in an effective beam diameter on the phase shift surface, and (Σφ 0.95-1.00 ) represents a sum of heights of the steps formed in a range of 95% to 100% of an effective beam radius with respect to the optical axis, the objective lens satisfies a condition:

0.1

<

(

∑

ϕ

0.95

-

1.00

)

(

∑

ϕ

0.00

-

1.00

)

<

0.5

.

(

2

)

19. The biconvex objective lens according to claim 18 ,

wherein the steps of the phase shift structure are defined by a following optical path difference function φ(h):

φ( h )=( P 2 ×h 2 +P 4 ×h 4 +P 6 ×h 6 +P 8 ×h 8 +P 10 ×h 10 +P 12 ×h 12 ) mλ

where P 2 , P 4 , P 6 . . . represent coefficients of the 2 nd order, 4 th order, 6 th order, h represents a height from the optical axis, and m represents a diffraction order at which diffraction efficiency is maximized.

20. The biconvex objective lens according to claim 17 , wherein the objective lens comprises a resin.