In an optical disc apparatus for reproducing information recorded on a track of an optical disc, an optical head irradiates a light beam onto the track, detects a reflected light reflected by the track, and generates a reproduction signal based on the reflected light. A decoder circuit decodes the reproduction signal, and generates a decoded signal including information recorded on the track. A correlation detector circuit calculates a cross-correlation value between the reproduction signal and the decoded signal. A servo circuit detects a deviation amount of an irradiation position of the light beam onto the track, from the reproduction signal, and controls the irradiation position of the optical head based on the cross-correlation value and the deviation amount.

An optical disk drive and a digital servo method for the optical disk drive includes controlling functions of the optical disk drive with a microprocessor. Low-pass filtered and gain adjusted versions of individual photodetector output signals resulting from an illumination of an optical disk are received. Versions of the individual photodetector output signals are digitized to produce digital signals. A focus control signal and/or a tracking control signal is determined through at least one servo algorithm executed by a digital signal processor based on a focus error and/or tracking error, respectively, determined from the digital signals. The digital signal processor is an integrated circuit structured and arranged for manipulation of digital signals in accordance with programmed commands, and in a manner that operates faster than the microprocessor.

To provide an optical information recording and reproducing apparatus capable of correct positioning, in an optical information recording and reproducing apparatus which branches a light beam into reference light and signal light to cause interference and records an obtained interference fringe as a hologram on an optical information recording medium and reproduces the hologram recorded by applying the reference light onto the optical information recording medium, the apparatus has an image pickup element which detects reproduction light passing through an aperture 101 in reproduction light obtained by applying the reference light onto the optical information recording medium and generates a reproduction signal, photo detectors 104a, 104b, 104c, and 104d that are different from the image pickup element and detect reproduction light applied on a location on the periphery of the aperture 101, and a computing unit which computes a position error signal based on outputs from the photo detectors.

A recording and reproducing apparatus according to the present disclosure includes a first optical pickup configured to record information on either a land track and a groove track, with respect to a recording medium that is able to be recorded in the land track and the groove track, a second optical pickup configured to record information on a track different from a track recorded by the first optical pickup, and a controller configured to cause the first optical pickup to record information if tracks of both sides of a track that the first optical pickup follows are recorded, and to cause the second optical pickup to record information if tracks of both sides of a track that the second optical pickup follows are recorded.