Optical head for recording and playing back optical information

Claim 1

An optical head for recording and playing back optical information, said optical head comprising: an illumination system which has a light source for providing a parallel beam, grating means for deriving three beams of light including 0-dimensional diffraction light, +1-dimensional diffraction light and -1-dimensional diffraction light from the parallel light beam, and means for guiding the three beams onto an optical information recording medium, and a photoreceiver system having an edge mirror, a first photodiode for receiving a half of the 0-dimensional diffraction light and all of the +1-dimensional diffraction light without being affected by said edge mirror, and a second photodiode for receiving the remaining approximately one half of the 0-dimensional diffraction light and all of the -1-dimensional diffraction light, both being reflected by the edge mirror, said photoreceiver system being further provided with: a first photoreceiver diode having a cell for receiving all of the +1 dimensional diffraction light and two cells for receiving half of the 0-dimensional diffraction light; a second photoreceiver diode having a cell for receiving all of the -1 dimensional diffraction light and two cells for receiving the remaining half of the 0-dimensional diffraction light; and signal generating means having a first operational circuit which produces and information signal by adding up outputs from cells for receiving the 0-dimensional diffraction light, and a focusing control signal by comparing outputs from cells for receiving the 0-dimensional diffraction light, and a second operational circuit which produces a tracking control signal by comparing outputs from the respective cells for receiving the +1 and -1 dimensional diffraction lights.