Optical element, aberration correcting element, light converging element, objective optical system, optical pickup device, and optical information recording reproducing device
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-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.
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 t 1 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 t 2 (t 2 ≧t 1 ) 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.
2. The optical system of claim 1 , 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.
3. The optical system of claim 2 , 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.
4. The optical system of claim 3 , wherein φ 1 and φ 2 represented with formulas (9) and (10) satisfy formulas (11) to (13):
φ1 =d 2( N λ1−1)/λ1 (9)
φ2 =d 2( N λ2−1)/λ2 (10)
INT(φ1)≦20 (11)
0≦|INT(φ1)−φ1|≦0.4 (12)
0≦|INT(φ2)−φ2|≦0.4 (13)
where INT(φi) (i=1, 2) is an integer obtained by rounding the value of φI,
λ 1 is the first wavelength (μm),
λ 2 is the second wavelength (μm),
d 2 is a depth (μm), 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.
5. The optical system of claim 4 , 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(φ1)=5 p (14)
INT(φ2)=3 p (15).
6. The optical system of claim 5 , wherein the optical system consists of a single optical element.
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 (μm) and the second wavelength λ 2 (μm) satisfy the formulas (2) and (3) respectively,
0.39<λ1<0.42 (2)
0.63<λ2<0.68 (3).
9. The optical system of claim 1 , wherein the optical system consists of a single optical element.
10. 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 .
11. The optical system of claim 10 , wherein the first wavelength λ 1 (μm) and the second wavelength λ 2 (μm) satisfy the formulas (2) and (3) respectively,
0.39<λ1<0.42 (2)
0.63<λ2<0.68 (3).
12. 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 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.
13. The objective optical system of claim 12 , 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.
14. The objective optical system of claim 12 , 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.
15. The objective optical system of claim 12 , 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 B 2 and B 4 are different from each other,
ϕ
b
=
λ
/
λ
B
×
n
×
∑
j
=
1
B
2
j
h
2
j
where λ is a wavelength of an incident light flux, λ B is a production wavelength, h is a height (mm) in a direction perpendicular to the optical axis, B 2j is a optical path difference function coefficient, and n is the diffraction order.
16. The objective optical system of claim 13 , wherein the light converging element is constructed with a plastic lens structured with one group one lens and a paraxial power P 1 (mm −1 ) of the aberration correcting optical system for the first wavelength λ 1 satisfies the following formula (20)
P1>0 (20).
17. The objective optical system of claim 13 , wherein the light converging element is constructed with a plastic lens structured with one group one lens and a ratio of a paraxial power P 1 (mm −1 ) of the aberration correcting optical system for the first wavelength λ 1 to a paraxial power P 2 (mm −1 ) of the light converging element for the first wavelength λ 1 satisfies the following formula (21)
| P 1 /P 2|≦0.2 (21).
18. The objective optical system of claim 17 , 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<νd<60 (23)
−10×10 −5 (° C. −1 )< dN 405 /dT <−8×10 −5 (° C. −1 ) (24)
where N 405 is a refractive index for a wavelength 405 nm at a temperature of 25° C., νd is Abbe's constant for d-line, and dN 405 /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.
19. The objective optical system of claim 17 , wherein the light converging element is made of a material in which particles having a diameter not larger than 30 μm are dispersed in a plastic material.
20. The objective optical system of claim 17 , wherein the light converging element is a glass lens.
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 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.
22. The objective optical system of claim 21 , 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.
23. The objective optical system of claim 21 , 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.
24. The objective optical system of claim 23 , 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.
25. 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 t 1 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 t 2 (t 2 ≧t 1 );
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.
26. The optical pickup apparatus of claim 25 , wherein the first wavelength λ 1 (μm) and the second wavelength λ 2 (μm) satisfy the formulas (2) and (3) respectively,
0.39<λ1<0.42 (2)
0.63<λ2<0.68 (3).
27. The optical pickup apparatus of claim 25 , 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 t 3 (t 3 ≧t 2 ).
28. The optical pickup apparatus of claim 25 , 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.
29. The optical pickup apparatus of claim 25 , 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.
30. The optical pickup apparatus of claim 27 , wherein the first wavelength λ 1 (μm), the second wavelength λ 2 and the third wavelength λ 3 (μm) satisfy the formulas (2), (3) and (3′) respectively,
0.39<λ1<0.42 (2)
0.63<λ2<0.68 (3)
0.75<λ3<0.85 (3′).
31. The optical pickup apparatus of claim 30 , 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.
32. The optical pickup apparatus of claim 31 , 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.
33. 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 t 1 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 t 2 (t 2 ≧t 1 );
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.
34. The optical pickup apparatus of claim 33 , wherein the first wavelength λ 1 (μm) and the second wavelength λ 2 (μm) satisfy the formulas (2) and (3) respectively,
0.39<λ1<0.42 (2)
0.63<λ2<0.68 (3).
35. The optical pickup apparatus of claim 33 , 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 t 3 (t 3 ≧t 2 ).
36. The optical pickup apparatus of claim 33 , 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.
37. The optical pickup apparatus of claim 33 , 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.
38. The optical pickup apparatus of claim 35 , wherein the first wavelength λ 1 (μm), the second wavelength λ 2 and the third wavelength λ 3 (μm) satisfy the formulas (2), (3) and (3′) respectively,
0.39<λ1<0.42 (2)
0.63<λ2<0.68 (3)
0.75<λ3<0.85 (3′).
39. The optical pickup apparatus of claim 35 , 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.
40. The optical pickup apparatus of claim 35 , 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.