Abstract: An optical disk apparatus capable of automatically setting a pickup lens suitable for an optional optical disk selected from a plurality of optical disks having different thicknesses. Current flowing through an actuator is detected with a detector circuit, A/D converted, and supplied to a controller. The controller detects the in-focus positions at the surface and reflection film of an optical disk in accordance with an FOK signal and an FZC signal, calculates the current values flowing through the actuator at the in-focus positions, and judges the thickness of the optical disk in accordance with a difference between the current values.

Abstract: An optical disk recording/reproducing apparatus for recording data to and reproducing data from an optical disk engraved with a groove having a wobble waveform corresponding to a signal obtained by FM modulating a carrier serving as a rotation synchronizing signal by address information where the width of the groove may be a half of a track pitch and the depth thereof may be 1/6 to 1/8 of a recording/reproducing laser beam wavelength. Circuitry may be provided for obtaining a push-pull signal from a main spot of a recording/reproducing laser beam and for using the push-pull signal as a tracking error signal. Further circuitry is provided for changing the polarity of the push-pull signal to perform a tracking control at the groove center or at the land center. Circuitry is also provided for recording or reading, while the main spot is controlled to be at the groove center, data on or from the groove center and reading the address information from the push-pull signal of the main spot.

Abstract: Data is recorded at a double density on a CLV disk. Sub-spots are shifted by a half track pitch from a main spot. A push-pull signal obtained from the main spot is used as a tracking signal. The polarity of the push-pull signal is changed to perform the tracking control at the groove center or at the land center. While the main spot is controlled to be at the groove center, address information is read from the push-pull signal of the main spot. While the main spot is controlled to be at the land center, address information is read from the push-pull signal of a sub-spot.

Abstract: A laser driver circuit of an optical disk recording/reproducing apparatus includes a laser output detecting unit for detecting a digital average value of a laser output, first and second memories for storing a digital value of a current to be supplied to a laser diode, first and second D/A converters for converting the digital values stored in the first and second memories into analog values, and a current supplying unit for supplying a current proportional to an output of the first D/A converter or a current proportional to a sum of outputs of the first and second D/A converters to the laser diode.

Abstract: A carrier frequency extracted as a tracking error signal from a disk with an optical pickup by a push-pull method is passed either through a high-pass filter having its cut-off frequency changing proportionally with the disk revolution number or corresponding to the carrier frequency at the disk ordinary revolution, or through a band-pass filter having its center frequency changing proportionally with the disk revolution number or corresponding to the carrier center frequency at the disk ordinary revolution. Therefore, the carrier frequency can be efficiently separated from the EFM signal during recording while allowing to use one beam in reading a tracking error signal and recording an EFM signal, and allowing a compatibility with presently used CD players.