Optical pickup and optical information recording apparatus using the same
View Patent ↗An optical pickup includes a diffraction grating partitioned into three areas, in which the phase of periodic grating groove structure in an area is successively shifted from that in the adjacent area by 90°. In the generation of a differential push-pull signal, an amplification factor K for sub push-pull signals is varied depending on the type of the optical disk. By such composition of the optical pickup, amplitude deterioration of the tracking error signal accompanying displacement of the object lens is reduced.
1. An optical information recording/reproducing apparatus comprising:
an optical pickup including:
a laser light source,
a beam separation means which separates a laser beam emitted by the laser light source into a main beam and at least two sub beams,
a converging optical system which converges the main beam and the sub beams and forms three separate convergence spots on a recording surface of an optical information record medium on which guide grooves are formed at preset pitches, and
a photodetector which is placed to receive each of reflected beams of the three convergence spots from the optical information record medium with a photoreceptor surface divided into at least two faces;
a push-pull signal generation circuit which generates push-pull signals regarding the main beam and the sub beams respectively by executing proper operations to photoelectric signals obtained from the photoreceptor surfaces of the optical pickup;
a differential push-pull signal generation circuit which generates a differential push-pull signal by adding all or part of the push-pull signals regarding the sub beams together, amplifying the added signal by an amplification factor K, and subtracting the amplified signal from the push-pull signal regarding the main beam; and
an amplification factor control means which changes the amplification factor K depending on the interval between the guide grooves of the optical information record medium, wherein the amplification factor K satisfies an expression K=K 1 *K 2 , K 1 is a value obtained by dividing a light quantity detected at main beam spot by a sum of light quantities detected at two sub beam spots, and K 2 is a compensation coefficient for compensating for the difference between a modulation degree of a push-pull signal obtained from the main beam spot and a modulation degree of a push-pull signal obtained from the sub beam spots.
2. The optical information recording/reproducing apparatus according to claim 1 , wherein said compensation coefficient K 2 is changed depending on the type of the optical information record medium.