Wavelength plate, optical element, and optical pickup

A wavelength plate to be placed in an optical path through which rays of a plurality of wavelengths travel back and forth, the plurality of wavelengths including a ray having a wavelength λ, the wavelength plate comprising:

• first and second phase shift layers stacked together, wherein,
• the first phase shift layer includes a two-dimensional array of a plurality of birefringent regions, the birefringent regions including first and second regions having different optic axis directions from each other, such that the relationship 150°<Δ1≦210° is true, where Δ1 is a retardation for the ray of the wavelength λ;
• and
• the second phase shift layer has a uniform optic axis direction, such that the relationship {(2n−1)×90°}−30°≦Δ2≦{(2n−1)×90°}+30° is satisfied (where n is an integer), where Δ2 is a retardation for the ray of the wavelength λ.

A wavelength plate to be placed in an optical path through which rays of a plurality of wavelengths travel back and forth, the plurality of wavelengths including a ray having a wavelength λ, the wavelength plate comprising:

• first and second phase shift layers stacked together, wherein,
• the first phase shift layer includes a two-dimensional array of a plurality of birefringent regions, the birefringent regions including first and second regions having different optic axis directions from each other, such that the relationship 105°≦Δ1≦165° is true, where Δ1 is a retardation for the ray of the wavelength λ;
• and
• the second phase shift layer has a uniform optic axis direction, such that the relationship {(2m−1)×90°}+45°−30°≦Δ2≦{(2m−1)×90°}+45°+30° is satisfied (where m is an integer), where Δ2 is a retardation for the ray of the wavelength λ.

A wavelength plate to be placed in an optical path through which rays of a plurality of wavelengths travel back and forth, the plurality of wavelengths including a ray having a wavelength λ, the wavelength plate comprising:

• first and second phase shift layers stacked together, wherein,
• the first phase shift layer includes a two-dimensional array of a plurality of birefringent regions, the birefringent regions including first and second regions having different optic axis directions from each other;
• the second phase shift layer has a uniform optic axis direction;
• and
• the relationship 240°≦Δ1≦300° is true, where Δ1 is a retardation of the wavelength plate for the ray of the wavelength λ.

An optical pickup comprising:

• at least one light source for radiating rays of a plurality of wavelengths, including a ray having a wavelength λ;
• converging means for converging a ray radiated from the light source onto an optical information medium;
• a photodetector for receiving light reflected from the optical information medium;
• and
• an optical element disposed in a portion commonly shared by an optical path of a ray traveling from the light source toward the optical information medium and an optical path of a ray traveling from the optical information medium toward the photodetector, wherein,
• the optical pickup includes a wavelength plate and a polarization filter,
• the wavelength plate comprising:
• a two-dimensional array of a plurality of birefringent regions, the birefringent regions including first and second regions having different optic axis directions from each other,
• wherein the relationship 240°≦Δ1≦300° is true, where Δ1 is a retardation of the wavelength plate for the ray of the wavelength λ.

An optical pickup comprising:

• a unit integrating:
• at least one light source for radiating rays of a plurality of wavelengths, including a ray having a wavelength λ, and
• a photodetector for receiving any one of the rays of the plurality of wavelengths reflected from an optical information medium;
• and
• an optical element disposed in a portion commonly shared by an optical path of a ray traveling from the light source toward the optical information medium and an optical path of a ray traveling from the optical information medium toward the photodetector, wherein,
• the optical pickup includes a wavelength plate and a polarization filter,
• the wavelength plate comprising:
• a two-dimensional array of a plurality of birefringent regions, the birefringent regions including first and second regions having different optic axis directions from each other,
• wherein the relationship 240°≦Δ1≦300° is true, where Δ1 is a retardation of the wavelength plate for the ray of the wavelength λ.

An optical pickup comprising:

• at least one light source for radiating rays of a plurality of wavelengths, including a ray having a wavelength λ;
• converging means for converging a ray radiated from the light source onto an optical information medium;
• a photodetector for receiving light reflected from the optical information medium;
• and
• an optical element disposed in a portion commonly shared by an optical path of a ray traveling from the light source toward the optical information medium and an optical path of a ray traveling from the optical information medium toward the photodetector, wherein,
• the optical pickup includes a wavelength plate and a polarization filter,
• the wavelength plate comprising:
• a two-dimensional array of a plurality of birefringent regions, the birefringent regions including first and second regions having different retardations from each other,
• wherein the retardation of the first regions for the ray of the wavelength λ is 270°+δ 1 (where 0°<δ 1≦30°), and the retardation of the second region for the ray of the wavelength λ is 270°−δ 2 (where 0°<δ 2≦30°).