Optical data recording and reproducing apparatus including optical detector for detecting light beams reflected by a plane parallel plate and then diffracted by a diffraction grating

摘要

An optical data recording and reproducing apparatus in which a light beam is diffracted into three light beams. The three light beams are reflected by a first surface of a plane parallel plate and applied through an objective lens to a recording medium, which forms three signal light beams. The three signal light beams are reflected back to the plane parallel plate and partially reflected by a second surface of the plate. A first optical detector detects one of the three signal light beams, which corresponds to the main light beam of the 0-th order of diffraction. A second optical detector detects a light beam of the -1st order of diffraction corresponds to the auxiliary light beam of the +1st order of diffraction and a light beam of the +1st order of diffraction corresponding to the auxiliary light beam of the -1st order of diffraction. Accordingly, the second optical detector can output a tracking error signal without interference by the main light beam.