Laminated wave plate, optical pickup device, polarization converter, and projection display apparatus

1. A laminated wave plate comprising a first wave plate with a phase difference of Γ 1 =180° with respect to a designed wavelength λ 0 and a second wave plate with a phase difference of Γ 2 =180°, in which the first wave plate and the second wave plate are arranged and laminated so that optical axes thereof intersect each other,

wherein when in-plane bearing angles of optical axes of the first and second wave plates are represented by θ 1 and θ 2 , an angle formed by a polarization direction of the linearly-polarized beam incident on the laminated wave plate and a polarization direction of a linearly-polarized beam output from the laminated wave plate is represented by φ, and an optical axis adjustment amount is represented by a, the following expressions are satisfied:

θ 2 =θ 1 +φ/2;

θ 1 =φ/4+ a;

θ 2 =3φ/4− a ; and

0<a≦a max ,

wherein the maximum value a max of the optical axis adjustment amount satisfies the following expressions in the designed wavelength range of 400≦λ 0 ≦490 nm:

a max =A 0 +A 1 ·φ+A 2 ·φ 2 +A 3 ·φ 3 +A 4 ·φ 4 +A 5 ·φ 5 ;

A 0 =0.00001548;

A 1 =0.0427887;

A 2 =−0.000385;

A 3 =1.723×10 −6 ;

A 4 =−4.19×10 −9 ; and

A 5 =4.086×10 −12 ,

satisfies the following expressions in the designed wavelength range of 490≦λ 0 ≦520 nm:

a max =A 0 +A 1 ·φ+A 2 ·φ 2 +A 3 ·φ 3 +A 4 ·φ 4 +A 5 ·φ 5 +A 6 ·φ 6 +A 7 ·φ 7 ;

A 0 =0.00006705;

A 1 =17.699248;

A 2 =−0.16963;

A 3 =0.0006754;

A 4 =−1.4×10 −6 ;

A 5 =1.68×10 −9 ;

A 6 =−1.1×10 −12 ; and

A 7 =2.72×10 −16 , and

satisfies the following expressions in the designed wavelength range of 520≦λ 0 ≦800 nm:

a max =A 0 +A 1 ·φ+A 2 ·φ 2 +A 3 ·φ 3 +A 4 ·φ 4 +A 5 ·φ 5 +A 6 ·φ 6 ;

A 0 =0.00003014;

A 1 =5.4681617;

A 2 =−0.038557;

A 3 =0.0001094;

A 4 =−1.56×10 −7 ;

A 5 =1.106×10 −10 ; and

A 6 =−3.13×10 −14 .

2. The laminated wave plate according to claim 1 , wherein the designed wavelength is set to λ 0 =500 nm and the optical axis adjustment amount is set to the range of 2.8°≦a≦3°.

3. The laminated wave plate according to claim 1 , wherein the designed wavelength is set to λ 0 =510 nm and the optical axis adjustment amount is set to the range of 0°<a≦2.2°.

4. A laminated wave plate comprising a first wave plate with a phase difference of Γ 1 =180° with respect to a designed wavelength λ 0 and a second wave plate with a phase difference of Γ 2 =180°, in which the first wave plate and the second wave plate are arranged and laminated so that optical axes thereof intersect each other, the laminated wave plate converting an incident linearly-polarized beam into a linearly-polarized beam obtained by rotating a polarization plane of the incident linearly-polarized beam by a predetermined angle of 90° and outputting the converted linearly-polarized beam,

wherein when in-plane bearing angles formed by the polarization plane of the incident linearly-polarized beam and optical axes of the first and second wave plates are represented by θ 1 and θ 2 , the following expressions are satisfied:

22.5°<θ 1 <45.0°; and

45.0°<θ 2 <67.5°.

5. The laminated wave plate according to claim 1 , wherein the first and second wave plates are formed of quartz crystal.

6. An optical pickup device comprising:

a light source;

an objective lens focusing a beam emitted from the light source on a recording medium;

a detector detecting the beam reflected from the recording medium; and

the laminated wave plate according to claim 1 which is disposed in an optical path between the light source and the objective lens.

7. An optical pickup device comprising:

a light source;

an objective lens focusing a beam emitted from the light source on a recording medium;

a detector detecting the beam reflected from the recording medium; and

the laminated wave plate according to claim 4 which is disposed in an optical path between the light source and the objective lens.

8. A polarization converter comprising:

a flat light-transmitting substrate having a first main surface as a beam incidence surface and a second main surface as a beam output surface;

first and second thin optical films disposed in the substrate; and

a wave plate disposed on the second main surface of the light-transmitting substrate,

wherein the first and second thin optical films are alternately arranged in parallel with a gap therebetween to be tilted about the first and second main surfaces,

wherein the first thin optical film separates a beam input from the first main surface into a first linearly-polarized beam and a second linearly-polarized beam perpendicular to each other, transmits and outputs the first linearly-polarized beam from the second main surface, and reflects the second linearly-polarized beam,

wherein the second thin optical film reflects the second linearly-polarized beam reflected by the first thin optical film and outputs the reflected second linearly-polarized beam from the second main surface, and

wherein the wave plate is the laminated wave plate according to claim 1 which is disposed in a part of the second main surface outputting the first linearly-polarized beam transmitted by the first thin optical film or in a part of the second main surface outputting the second linearly-polarized beam reflected by the second thin optical film.

9. A polarization converter comprising:

a flat light-transmitting substrate having a first main surface as a beam incidence surface and a second main surface as a beam output surface;

first and second thin optical films disposed in the substrate; and

a wave plate disposed on the second main surface of the light-transmitting substrate,

wherein the first and second thin optical films are alternately arranged in parallel with a gap therebetween to be tilted about the first and second main surfaces,

wherein the first thin optical film separates a beam input from the first main surface into a first linearly-polarized beam and a second linearly-polarized beam perpendicular to each other, transmits and outputs the first linearly-polarized beam from the second main surface, and reflects the second linearly-polarized beam,

wherein the second thin optical film reflects the second linearly-polarized beam reflected by the first thin optical film and outputs the reflected second linearly-polarized beam from the second main surface, and

wherein the wave plate is the laminated wave plate according to claim 4 which is disposed in a part of the second main surface outputting the first linearly-polarized beam transmitted by the first thin optical film or in a part of the second main surface outputting the second linearly-polarized beam reflected by the second thin optical film.

10. A polarization converter comprising:

a flat light-transmitting substrate having a first main surface as a beam incidence surface and a second main surface as a beam output surface;

first and second thin optical films disposed in the light-transmitting substrate; and

a wave plate,

wherein the first and second thin optical films are alternately arranged in parallel with a gap therebetween to be tilted about the first and second main surfaces,

wherein the first thin optical film separates a beam input from the first main surface into a first linearly-polarized beam and a second linearly-polarized beam perpendicular to each other, transmits the first linearly-polarized beam, and reflects the second linearly-polarized beam,

wherein the second thin optical film reflects the second linearly-polarized beam reflected by the first thin optical film and emits the reflected second linearly-polarized beam from the second main surface, and

wherein the wave plate is the laminated wave plate according to claim 1 which is disposed and laminated on the beam output surface of the first thin optical film outputting the first linearly-polarized beam.

11. A polarization converter comprising:

a flat light-transmitting substrate having a first main surface as a beam incidence surface and a second main surface as a beam output surface;

first and second thin optical films disposed in the light-transmitting substrate; and

a wave plate,

wherein the first and second thin optical films are alternately arranged in parallel with a gap therebetween to be tilted about the first and second main surfaces,

wherein the first thin optical film separates a beam input from the first main surface into a first linearly-polarized beam and a second linearly-polarized beam perpendicular to each other, transmits the first linearly-polarized beam, and reflects the second linearly-polarized beam,

wherein the second thin optical film reflects the second linearly-polarized beam reflected by the first thin optical film and emits the reflected second linearly-polarized beam from the second main surface, and

wherein the wave plate is the laminated wave plate according to claim 4 which is disposed and laminated on the beam output surface of the first thin optical film outputting the first linearly-polarized beam.