Laminated wave plate and optical device using the same

Abstract

[Problems to be Solved] To obtain a laminated quarter-wave plate having a bandwidth of a plurality of wavelengths to be a phase difference of 90 degrees broadened [Means to Solve the Problem] A laminated wave plate of the present invention includes a first wave plate having a phase difference of Γ1 and a second wave plate having a phase difference of Γ2 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 are intersected 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×(n1+1) . . . (1); Γ2=90×(2×n2+1) . . . (2); ΔΓ1=(Γ12a−Γ11a)/(λ12−λ11) . . . (3); ΔΓ2=(Γ12b−Γ11b)/(λ12−λ11) . . . (4); cos 2θ1=1−(1−cos ΔΓF)/2(1−cos ΔΓ1) . . . (5); and θ2=45°±5° . . . (6), wherein θ1 is an optic axis orientation of the first wave plate, θ2 is an optic axis orientation of the second wave plate, and each of λ11≦≦λ≦λ12, n1, and n2 is a natural number starting from 1.

1 . A wave plate in which a first wave plate of a phase difference of Γ1 and a second wave plate of a phase difference of Γ2 with respect to a wavelength λ, are arranged such that their optical axes cross each other, wherein linearly-polarized light incident is converted into circularly-polarized light, or
 circularly-polarized light incident is converted into linearly-polarized light, 
 the 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 θ1 is an optic axis orientation of the first wave plate, θ2 is an optic axis orientation of the second wave plate, and each of n1, and n2 is a natural number starting from 1. 
 
     
     
         2 . The wave plate according to  claim 1 , wherein
   n1=8;     n2=4.   
     
     
         3 . The wave plate according to  claim 1 , wherein
   n1=10;     n2=5.   
     
     
         4 . An optical pickup device comprising: a light source, an objective lens to condense emitted light from the 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 wave plate according to  claim 1 . 
     
     
         5 . An optical pickup device comprising: a light source, an objective lens to condense emitted light from the 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 wave plate according to  claim 2 . 
     
     
         6 . An optical pickup device comprising: a light source, an objective lens to condense emitted light from the 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 wave plate according to  claim 3 .