Abstract: In an information recording apparatus for recording predetermined information on a recording medium by means of a laser beam, an optical system and a light detector are arranged for detecting a reflected version of the laser beam from the recording medium, whereby the focusing of the laser beam on the recording medium is automatically controlled.

Abstract: In apparatus wherein a predetermined information signal is recorded on an optical disk by the use of a light beam; an information recording apparatus characterized by provision of a light detector for detecting reflected light caused by the reflection of the light beam by the optical disk, and a checking circuit for detecting the duration for which a maximum peak value of the output from the light detector exists, the recorded state of information on the optical disk being detected on the basis of the output from the detector by the checking circuit.

Abstract: An optical head comprising a lens disposed at a position for forming spot images of a semiconductor laser having a plurality of lasing points, in which beams from the semiconductor laser are focused on a disc on which predetermined information is recorded by light.

Abstract: An optical head comprising a semiconductor laser array which is used as a light source, and an optical system which guides laser beams from the array to a predetermined recording medium. The beam from one lasing point of the array is modulated by predetermined information and is used as a recording beam, while the beam from another lasing point is continuously oscillated and is used as a playback beam.

Abstract: In an optical information recording apparatus, a version of a recording light emitted from a light source and reflected by a recording medium is detected to control the recording light output power of the light source.

Abstract: An optical information recording and reproducing apparatus is disclosed in which a predetermined signal is recorded on a track of a rotating recording medium by a recording light beam and the recorded information is reproduced by a reproducing light beam. The information recorded on the last record track is reproduced by the recording beam and the reproducing beam and radiating position of the recording beam on the recording medium is displaced by a predetermined distance from the last record track.

Abstract: Optical information reconstructing apparatus comprising a disc having at least one surface on which groups of dots bearing information are concentrically or spirally arrayed, a mechanism for rotating the disc, a light source for projecting a light beam on the array of groups of dots, and at least one photodetector for detecting diffracted light waves from the groups of dots, characterized in that a semiconductor laser array is used as the light source and that the light emission is switched from one laser source to another in the laser array in tracking the information.