Optical disk apparatus

An optical disk apparatus comprising:

• a light source for emitting light of a wavelength λ1 and light of a wavelength λ2 (where λ1≠λ2);
• an objective lens for converging the light onto a signal surface of an optical disk;
• a polarized beam diffraction element for diffracting the light reflected from the optical disk;
• a photodetector for detecting the light diffracted from the polarized beam diffraction element;
• and
• a wavelength plate disposed between the optical disk and the polarized beam diffraction element, wherein,
• an imaginary line L on the beam splitter is defined, the line L being perpendicular to a radial direction of the optical disk, and intersecting an optical axis of the objective lens;
• the beam splitter at least has a region a1, a region a2, a region a3, a region A1, a region A2, and a region A3, such that
• the region a1, the region a2, and the region a3 are on a same side of the line L on the beam splitter, and
• the region A1, the region A2, and the region A3 are substantially symmetrical regions to the region a1, the region a2, and the region a3, respectively, with respect to the line L;
• the photodetector at least has two regions b and B;
• light of the wavelength λ1 entering the region a3, the region a1, and the region A2 of the beam splitter produces 1st order diffracted light which is projected onto the region b of the photodetector, and light of the wavelength λ1 entering the region A3, the region A1, and the region a2 of the beam splitter produces 1st order diffracted light which is projected onto the region B of the photodetector;
• light of the wavelength λ2 entering the region a3 of the beam splitter produces 1st order diffracted light which is projected onto the region B of the photodetector, and light of the wavelength λ2 entering the region A3 of the beam splitter produces 1st order diffracted light which is projected onto the region b of the photodetector;
• and
• based on a difference between a detection signal from the region b and a detection signal from the region B, the optical disk apparatus generates a tracking error signal for the optical disk or a correction signal for correcting the tracking error signal.

An optical disk apparatus comprising:

• a light source for emitting light of a wavelength λ1 and light of a wavelength λ2 (where λ1≠λ2);
• an objective lens for converging the light onto a signal surface of an optical disk;
• a polarized beam diffraction element for diffracting the light reflected from the optical disk;
• a photodetector for detecting the light diffracted from the polarized beam diffraction element;
• and
• a wavelength plate disposed between the optical disk and the polarized beam diffraction element, wherein,
• an imaginary line L on the beam splitter is defined, the line L being perpendicular to a radial direction of the optical disk, and intersecting an optical axis of the objective lens;
• the beam splitter at least has eight regions a1, a2, a3, A1, A2, A3, and A4 such that
• the region a1, the region a2, the region a3, and the region a4 are on a same side of the line L on the beam splitter, and
• the region A1, the region A2, the region A3, and the region A4 are substantially symmetrical regions to the region a1, the region a2, the region a3, and the region a4, respectively, with respect to the line L;
• the photodetector at least has six regions b, B, b′, B′, b″, and B″;
• light of the wavelength λ1 entering the region A2 and the region a1 of the beam splitter produces 1st order diffracted light which is projected onto the region b of the photodetector, and light of the wavelength λ1 entering the region a2 and the region A1 of the beam splitter produces −1st order diffracted light which is projected onto the region B of the photodetector, the optical disk apparatus generating a tracking error signal for the optical disk based on a difference between a detection signal from the region b and a detection signal from the region B;
• light of the wavelength λ2 entering the region a3 and the region a4 of the beam splitter produces −1st order diffracted light which is projected onto the region b′ of the photodetector, and light of the wavelength λ2 entering the region A3 and the region A4 of the beam splitter produces −1st order diffracted light which is projected onto the region B′ of the photodetector, the optical disk apparatus generating a difference signal based on a difference between a detection signal from the region b′ and a detection signal from the region B′;
• and light of the wavelength λ2 entering the region a3 further produces 1st order diffracted light which is projected onto the region b″ of the photodetector, and light of the wavelength λ2 entering the region A3 further produces 1st order diffracted light which is projected onto the region B″ of the photodetector, the optical disk apparatus generating a correction signal based on a difference between a detection signal from the region b″ and a detection signal from the region B″;
• the optical disk apparatus generates a tracking error signal for the optical disk by adding to the difference signal a value obtained by multiplying the correction signal by an arbitrary coefficient.