Laminated wave plate and optical pickup device using the same
View Patent ↗A laminated wave plate that corresponds to a plurality of wavelengths including at least two wavelengths of λ A and λ B , and includes a first wave plate disposed on an incident side and a second wave plate disposed on an emitting side, the first wave plate and the second wave plate being laminated in such a manner that their optical axes are intersected each other, includes the following equations from (1) to (5): Γ A1 =360°+360°×2 N A (1); Γ A2 =180°+360°× N A (2); Γ B1 =360°×2 N B (3); Γ B2 =360°× N B (4); and N B =(Δ n B /Δn A )×(λ A /λ B )×(0.5+ N A ) (5), in which Γ A1 is a phase difference of the wavelength λ A at the first wave plate, Γ A2 is a phase difference of the wavelength λ A at the second wave plate, Γ B1 is a phase difference of the wavelength λ B at the first wave plate, Γ B2 is a phase difference of the wavelength λ B at the second wave plate, θ 1 is an in-plane azimuth of the first wave plate, θ 2 is an in-plane azimuth of the second wave plate, Δn A is a birefringent difference that is a difference (ne A −no A ) between a normal ray refractive index no A and an abnormal ray refractive index ne A of the wavelength λ A , and Δn B is a birefringent difference that is a difference (ne B −no B ) between a normal ray refractive index no B and an abnormal ray refractive index ne B of the wavelength λ B , under conditions of θ 1 =−21°, and θ 2 =45°.
1. A laminated wave plate corresponding to a plurality of wavelengths including at least two wavelengths of λ A and λ B , and including a first wave plate disposed on an incident side and a second wave plate disposed on an emitting side, the first wave plate and the second wave plate being laminated in such a manner that their optical axes are intersected each other, the laminated wave plate satisfying the following equations from (1) to (5):
Γ A1 =360°+360°×2 N A (1);
Γ A2 =180°+360°× N A (2);
Γ B1 =360°×2 N B (3);
Γ B2 =360°× N B (4); and
N B =(Δ n B/Δ n A )×(λ A /λ B )×(0.5+ N A ) (5),
wherein
N A is a positive integer
Γ A1 is a phase difference of the wavelength λ A at the first wave plate,
Γ A2 is a phase difference of the wavelength λ A at the second wave plate,
Γ B1 is a phase difference of the wavelength λ B at the first wave plate,
Γ B2 is a phase difference of the wavelength λ B at the second wave plate,
θ 1 is an in-plane azimuth of the first wave plate,
θ 2 is an in-plane azimuth of the second wave plate,
Δn A is a birefringent difference that is a difference (ne A -no A ) between a normal ray refractive index no A and an abnormal ray refractive index ne A of the wavelength λ A , and
Δn B is a birefringent difference that is a difference (ne B -no B ) between a normal ray refractive index no B and an abnormal ray refractive index ne B of the wavelength λ B , under conditions of θ 1 =−21°, and θ 2 =45°.
2. The laminated wave plate according to claim 1 , wherein a combination of (N A , N B ) is one of the following combinations from (a 1 ) to (a 4 ):
( N A , N B )=(2.0, 2.0) (a1);
( N A , N B )=(3.0, 3.0) (a2);
( N A , N B )=(8.0, 7.0) (a3); and
( N A , N B )=(9.0, 8.0) (a4).
3. The laminated wave plate according to claim 1 , wherein one of the wavelengths λ A and λ B is in a wavelength band from 390 nm to 410 nm.
4. An optical pickup device, comprising:
a laser light source;
an objective lens condensing laser light on a recording medium; and
a detector detecting light emitted after being condensed by the objective lens and being reflected by the recording medium,
wherein the laminated wave plate according to claim 1 is disposed on an optical path between the laser light source and the objective lens.