Optical head utilizing diffraction grating

Claim 1

An optical type head device comprising: a light source for emitting a light beam, a beam splitter having a first surface which reflects the light beam emitted from said light source to direct it toward the data storing surface of an optical type data storing medium and a second surface which reflects the light beam reflected by said data storing surface, a condensor lens means for converging the light beam reflected by said beam splitter on said data storing surface as light spots, and a light detector for receiving for photoelectric conversion said light beam reflected by said second surface and passing through said first surface, characterized in that a diffraction grating is provided to separate said light beam emitted from said light source into a plurality of diffracted subbeams consisting of a zero-order subbeam so that a focussing error of the spot of said zero-order subbeam on said optical type data storing medium is detected by the fact that light spot of the zero-order subbeam is deformed on said light detector, and a positional error of the spot of said zero-order subbeam with respect to a data track on said optical type data storing medium is detected by the position of the spots of said subbeams other than the zero-order subbeam.