Laminated wave plate and optical pickup device using the same

1. A laminated wave plate including a first wave plate having a phase difference of Γ 1 and a second wave plate having a phase difference of Γ 2 with respect to a wavelength λ, the first wave plate and the second wave plate being bonded together so that an optical axis of the first wave plate and an optical axis of the second wave plate intersect each other to function as a quarter-wave plate as a whole, the laminated wave plate comprising following equations from (1) to (6):

Γ1=360°×( n 1+1)  (1);

Γ2=90°×(2 ×n 2+1)  (2);

ΔΓ1=(Γ12 a−Γ 11 a )/(λ12−λ11)  (3);

ΔΓ2=(Γ12 b−Γ 11 b )/(λ12−λ11)  (4);

cos 2θ1=1−(1−cos ΔΓ2)/[2×(1−cos ΔΓ1)]  (5); and

θ2=45° ±5°  (6),

wherein θ 1 is an optic axis orientation of the first wave plate, θ 2 is an optic axis orientation of the second wave plate, Γ 11 a is a phase difference of the first wave plate at the wavelength λ 11 , Γ 12 a is a phase difference of the first wave plate at the wavelength Γ 12 , Γ 11 b is a phase difference of the second wave plate at the wavelength λ 11 , Γ 12 b is a phase difference of the second wave plate at the wavelength λ 12 , and each of λ 11 <λ<λ 12 , n 1 , and n 2 is a natural number starting from 1.

2. The laminated wave plate according to claim 1 , wherein

n 1 =8;

n 2 =4;

ΔΓ 1 =4.34; and

ΔΓ 2 =1.09.

3. The laminated wave plate according to claim 1 , wherein

n 1 =10;

n 2 =5;

ΔΓ 1 =5.43; and

ΔΓ 2 =1.36.

4. An optical pickup device comprising:

a laser light source,

an objective lens to condense emitted light from the laser light source to an optical storage medium,

a light detector to detect the emitted light condensed by the objective lens and reflected by the optical storage medium, and

a laminated wave plate according to claim 1 installed in a light way from the laser light source to the optical storage medium or a light way from the optical storage medium to the light detector.

5. An optical pickup device comprising:

a laser light source,

an objective lens to condense emitted light from the laser light source to an optical storage medium,

a light detector to detect the emitted light condensed by the objective lens and reflected by the optical storage medium, and

a laminated wave plate according to claim 2 installed in a light way from the laser light source to the optical storage medium or a light way from the optical storage medium to the light detector.

6. An optical pickup device comprising:

a laser light source,

an objective lens to condense emitted light from the laser light source to an optical storage medium,

a light detector to detect the emitted light condensed by the objective lens and reflected by the optical storage medium, and

a laminated wave plate according to claim 3 installed in a light way from the laser light source to the optical storage medium or a light way from the optical storage medium to the light detector.

7. A laminated wave plate including a first wave plate having a phase difference of Γ 1 and a second wave plate having a phase difference of Γ 2 with respect to a wavelength λ, the first wave plate and the second wave plate being bonded together so that an optical axis of the first wave plate and an optical axis of the second wave plate intersect each other to function as a quarter-wave plate as a whole, the laminated wave plate comprising following equations from (1), (2), (7) and (8):

Γ1=360°×( n 1+1)  (1);

Γ2=90°×(2× n 2+1)  (2);

θ1=−5.5° ±5°  (7); and

θ2=45° ±5°  (8),

wherein θ 1 is an optic axis orientation of the first wave plate, θ 2 is an optic axis orientation of the second wave plate, and each of n 1 , and n 2 is a natural number starting from 1.

8. The laminated wave plate according to claim 7 , wherein

n 1 =8;

n 2 =4.

9. The laminated wave plate according to claim 7 , wherein

n 1 =10;

n 2 =5.

10. An optical pickup device comprising: a laser light source, an objective lens to condense emitted light from the laser light source to an optical storage medium, a light detector to detect the emitted light condensed by the objective lens and reflected by the optical storage medium, and a laminated wave plate according to claim 7 installed in a light way from the laser light source to the optical storage medium or a light way from the optical storage medium to the light detector.

11. An optical pickup device comprising: a laser light source, an objective lens to condense emitted light from the laser light source to an optical storage medium, a light detector to detect the emitted light condensed by the objective lens and reflected by the optical storage medium, and a laminated wave plate according to claim 8 installed in a light way from the laser light source to the optical storage medium or a light way from the optical storage medium to the light detector.

12. An optical pickup device comprising: a laser light source, an objective lens to condense emitted light from the laser light source to an optical storage medium, a light detector to detect the emitted light condensed by the objective lens and reflected by the optical storage medium, and a laminated wave plate according to claim 9 installed in a light way from the laser light source to the optical storage medium or a light way from the optical storage medium to the light detector.