Optical element and optical pickup device comprising it

An optical pickup device comprising:

• a light source for irradiating light;
• a magneto-optical recording medium, receiving said irradiated light, for reflecting said irradiated light through an optical element to a photodetector;
• and
• a photodetector for receiving and detecting the reflected light from said magneto-optical recording medium and detecting the recording signals of said magneto-optical recording medium based on the Kerr angle of rotation,
• said optical element including,
• a flat, transparent base having a plurality of faces,
• a diffraction grating, formed on one of said plurality of faces, having grating lines arranged at a grating pitch approximately equal to the wavelength of a light incident to said diffraction grating, said incident light being of a predetermined wavelength, and
• said base being a substitute made of a material having an optical anisotropy property,
• a thickness of said substrate being predetermined such that a phase difference between phases of a P polarization and of an S polarization contained in said light incident to said diffraction grating, and a phase difference between the phases of said P polarization and said S polarization occurring upon said light propagating through said substrate, cancel out.

An optical element comprising:

• a flat, transparent base having a plurality of faces;
• a first diffraction grating, formed on one of said plurality of faces, having grating lines arranged at a grating pitch approximately equal to the wavelength of a light incident to said diffraction grating, said incident light being of a predetermined wavelength;
• and
• a second diffraction grating, formed on one of said plurality of faces different from that of said diffraction grating,
• said first diffraction grating and second diffraction grating being formed such that the grating pitch of the first diffraction grating and a grating pitch of the second diffraction grating are equal, and such that the grating lines of the first diffraction grating and the grating lines of the second diffraction grating are parallel with each other.

An optical element comprising:

• a flat, transparent base having a plurality of faces;
• a diffraction grating, formed on one of said plurality of faces, having grating lines arranged at a grating pitch is approximately equal to the wavelength of a light incident to said diffraction grating, said incident light being of a predetermined wavelength;
• and
• a phase compensating grating, formed on one of said plurality of faces different from that of said diffraction grating, having grating lines substantially orthogonal to the grating lines of the diffraction grating.

An optical pickup device comprising:

• a light source for irradiating light;
• a magneto-optical recording medium, receiving said irradiated light, for reflecting said irradiated light through an optical element to a photodetector;
• and
• a photodetector for receiving and detecting the reflected light from said magneto-optical recording medium,
• said optical element including,
• a flat, transparent base having a plurality of faces,
• a diffraction grating, formed on one of said plurality of faces, having grating lines arranged at a grating pitch approximately equal to the wavelength of a light incident to said diffraction grating, said incident light being of a predetermined wavelength, and
• a phase compensating grating, formed on one of said plurality of faces different from that said diffraction grating, having grating lines substantially orthogonal to the grating lines of the diffraction grating.

An optical element comprising:

• a flat, transparent base with an index of refraction n;
• and
• a grating, formed on said flat, transparent base, having a grating pitcha A approximately equal to the wavelength .alpha. of a light incident to said grating, said incident light being of a predetermined wavelength, wherein the index of refraction n of said flat, transparent base, the wavelength .alpha. of the incident light, and the grating pitch A of said grating, satisfy the equation,
• A.ltoreq..alpha./n.

A polarized light detecting unit comprising:

• a transparent substrate;
• a diffraction grating, formed on said transparent substrate, having a grating pitch approximately equal to the wavelength of a light incident to said diffraction grating, said incident light being of a predetermined wavelength for separating said incident light into two polarized lights having mutuallly orthogonal polarizations;
• a first photodetector, mounted integrally and substantially in parallel with said substrate, for receiving a zeroth-order diffracted light produced by said separation of incident light by said diffraction grating;
• and
• a second photodetector, located in the same plane as said first photodetector and mounted integrally with said first photodetector and said substrate, for receiving a first-order diffracted light produced by said separation of incident light by said diffraction grating, wherein the distance between said diffraction grating and said first and second photodetectors is no more than 10 mm.