Laminated wave plate and optical pickup using the same
View Patent ↗A conventional broadband quarter-wave plate has not completely solved the wavelength dependence and has different efficiencies of shifting the phase by 90° depending on the wavelengths, and therefore has a problem that it cannot fulfill the strict specifications on the optical characteristics which are demanded of a wave plate from a viewpoint of the optical efficiency and the like in an optical pickup device compatible with a plurality of different wavelengths. To provide a wave plate which completely functions as a quarter-wave plate with respect to a plurality of different wavelengths and an optical pickup using that wave plate to solve the problem, the present invention provides a laminated wave plate, wherein a wave plate with a phase difference α and a wave plate with a phase difference β with respect to monochromatic light with a wavelength λ are laminated in such a way that directions of optical axes of said plates intersect each other, so that the laminated wave plate, as a whole, functions as a quarter-wave plate, and which is characterized in that a relationship between the α and the β satisfies the following formulas: (3/2)×π≠α−2×π×( m −1) π≠β−2×π×( n −1), wherein: each of m and n is a positive integer.
1. A laminated wave plate comprising:
a first wave plate with a phase difference α and an azimuth angle θ 1 with respect to monochromatic light with a wavelength λ, and
a second wave plate with a phase difference β and azimuth angle θ 2 with respect to monochromatic light with a wavelength λ,
said first and second wave plate being laminated together in such a way that directions of optical axes of said plates intersect each other, so that
said wave-plate functions as a phase difference Γ with respect to lights of two wavelengths λ1 and λ2 which are different from each other;
characterized in that
said wavelength λ is λ=λ1 or λ=λ2,
a refractive index of normal ray of said first wave plate is N O1 , a refractive index of abnormal ray of said first wave plate is N e1 and a thickness of said first wave plate is d 1 ,
a refractive index of normal ray of said second wave plate is N o2 , a refractive index of abnormal ray of said first wave plate is N e2 , and a thickness of said first wave plate is d 2 ,
said phase differences α and β respectively satisfy following formulas (3) and (4):
α=2×π/λ×( N e1 —N o1 )× d 1 (3)
β=2×π/λ×( N e2 —N o2 )× d 2 (4)
said first wave plate satisfies a Mueller matrix A 1 of a following formula (5):
(
5
)
A
1
=
[
1
0
0
0
0
1
-
(
1
-
cos
α
)
sin
2
2
θ
1
(
1
-
cos
α
)
sin
2
θ
1
cos
2
θ
1
-
sin
α
sin
2
θ
1
0
(
1
-
cos
α
)
sin
1
-
(
1
-
cos
α
)
sin
2
2
θ
1
sin
α
sin
2
θ
1
2
θ
1
cos
2
θ
1
0
sin
α
sin
2
θ
1
-
sin
α
sin
2
θ
1
cos
α
]
said second wave plate satisfies a Mueller matrix A 2 of a following formula (6):
A
2
=
[
1
0
0
0
0
1
-
(
1
-
cos
β
)
(
1
-
cos
β
)
sin
2
θ
2
cos
2
θ
2
-
sin
β
sin
2
θ
2
sin
2
2
θ
2
0
(
1
-
cos
β
)
sin
1
-
(
1
-
cos
β
)
cos
2
2
θ
2
sin
β
cos
2
θ
2
2
θ
2
cos
2
θ
2
0
sin
β
cos
2
θ
2
-
sin
β
sin
2
θ
2
cos
β
]
(
6
)
an incident light input to said laminated wave plate is expressed by a Stokes vector T of a following formula (7):
T
=
[
t
1
t
2
t
3
t
4
]
(
7
)
an emitted light output from said laminated wave plate is expressed by a Stokes vector S of the following formula (8):
S
=
[
S
1
S
2
S
3
S
4
]
(
8
)
a relationship between said Stokes vector T and said Stokes vector S satisfies the following formulas (9) and (11):
[
S
1
S
2
S
3
S
4
]
=
A
2
·
A
1
[
t
1
t
2
t
3
t
4
]
(
9
)
S
=
A
2
·
A
1
[
1
1
0
0
]
(
11
)
wherein when said phase difference Γ of said laminated wave plate is expressed by a following formula (12):
Γ
=
arc
tan
S
3
S
1
2
+
S
2
2
(
12
)
said phase difference Γ in said wavelength λ1 and said wavelength λ2 satisfied a following formula:
Γ=(2× N− 1)×(π/2)
wherein N is a positive integer.
2. A laminated wave-plate comprising:
a first wave plate with a phase difference α and an azimuth angle θ 1 with respect to monochromatic light with a wavelength λ, and
a second wave plate with a phase difference β and an azimuth angle θ 2 with respect to monochromatic light with a wavelength λ,
said first and second wave plate being laminated together in such a way that directions of optical axes of said plates intersect each other;
characterized in that
said phase difference α is a multiple-order 255° and said phase difference β is multiple-order 130°, and
said azimuth angle θ 1 and said azimuth angle θ 2 satisfy:
θ1=25.5°±5°
θ1=25.5°±5°
θ2=79.8°±5°.
3. The laminated wave plate according to claim 2 , wherein said phase difference α is fourth-order 255°, and said phase difference β is second-order 130°.
4. The laminated wave plate
according to claim 2 or 3 , wherein said laminated wave plate functions as a quarter-wave plate with respect to wavelengths of 655 nm and 785 nm.
5. A laminated wave plate comprising:
a first wave plate with a phase difference α and an azimuth angle θ 1 with respect to monochromatic light with a wavelength λ, and
a second wave plate with a phase difference β and an azimuth angle θ 2 with respect to monochromatic light with a wavelength λ,
said first and second wave plate being laminated together in such a way that directions of optical axes of said plates intersect each other;
characterized in that
said phase difference α is a multiple-order 180°, and said phase difference β is multiple-order 270, and
said azimuth angle θ 1 and said azimuth angle θ 2 satisfy:
θ1=14°±5°
θ2=72°±5°.
6. The laminated wave plate according to claim 5 , wherein said phase difference α is fifth-order 180°, and said phase difference β is second-order 270°.
7. The laminated wave plate according to claim 5 or 6 , wherein said laminated quarter plate functions as a quarter-wave plate with respect to light with wavelengths of 655 nm and 785 nm.
8. A laminated wave plate comprising:
a first wave plate with a phase difference α and an azimuth angle θ 1 with respect to monochromatic light with a wavelength λ, and
a second wave plate with a phase difference β and an azimuth angle θ 2 with respect to monochromatic light with a wavelength λ,
said first and second wave plate being laminated together in such a way that directions of optical axes of said plates intersect each other;
characterized in that
said phase difference α is multiple-order 180°, and said phase difference β is multiple-order 270°, and
said azimuth angle θ 1 and said azimuth angle θ 2 satisfy:
θ1=7°±5°
θ2=52°±5°.
9. The laminated wave plate according to claim 8 , wherein said phase difference α is seventh-order 180°, and said phase difference β is first-order 270°.
10. The laminated wave plate according to claim 8 or 9 , wherein said laminated wave plate functions as a quarter-wave plate with respect to light with wavelength of 655 nm and function as a half-wave plate with respect to light with wavelength of 785 nm.
11. A laminated wave plate comprising:
a first wave plate with a phase difference a and an azimuth angle θ 1 with respect to monochromatic light with a wavelength λ, and
a second wave plate with a phase difference β and an azimuth angle θ 2 with respect to monocrhromatic light with a wavelength λ,
said first and second wave plate being laminated to each other in such a way that directions of optical axes of said plates intersect each other;
characterized in that
said phase difference α is a multiple-order 180°, and said phase difference β is multiple-order 180°, and
said azimuth angle θ 1 and said azimuth angle θ 2 satisfy:
θ1=12°±5°
θ2=57°±5°.
12. The laminated wave plate according to claim 11 , wherein said phase differenceα is seventh-order 180°, and said phase difference β is third-order 180°.
13. The laminated wave plate according to claim 11 or 12 , wherein said laminated wave plate functions as a half-wave plate with respect to light with wavelength of 655 nm and function as a 2/2-wave plate with respect to light with wavelength of 785 nm.
14. An optical pickup constructed in such a way that a first linearly polarized light with a first wavelength and a second linearly polarized light with a second wavelength pass through a wave plate, characterized in that said wave plate is the wave plate according to any one of claims 1 to 3 , 5 and 6 , 8 and 9 .
15. An optical pickup constructed in such a way that a first linearly polarized light with a first wavelength and a second linearly polarized light with a second wavelength pass through a wave plate, characterized in that said wave plate is the wave plate according to claim 4 .
16. An optical pickup constructed in such a way that a first linearly polarized light with a first wavelength and a second linearly polarized light with a second wavelength pass through a wave plate, characterized in that said wave plate is the wave plate according to claim 7 .
17. An optical pickup constructed in such a way that a first linearly polarized light with a first wavelength and a second linearly polarized light with a second wavelength pass through a wave plate, characterized in that said wave plate is the wave plate according to claim 10 .
18. An optical pickup constructed in such a way that a first linearly polarized light with a first wavelength and a second linearly polarized light with a second wavelength pass through a wave plate, characterized in that said wave plate is the wave plate according to claim 13 .