Optical tracking system utilizing three photo-detectors

摘要

In apparatus for optically reproducing information recorded on an optical recording medium, an optical pickup device is arranged such that three light beams obtained by a diffraction grating are focused to apply first to third light spots to the medium so that the center of the second spot is positioned between (N-1)th and Nhu th tracks and the center of the third spot is positioned between Nth and (N+1)th tracks with the center of the first spot being positioned the center of the Nth track. First to third photo detectors are provided to receive reflected beams from the first to third light spots and the output signals thereof are supplied to a circuit for reproducing the information of the Nth track. In the reproducing circuit, after the output signals are synchronized with each other, the output signals of the second and third photo detectors are supplied to an adder and the sum signal is processed by an adjusting circuit so that the amplitude of a signal component of the (N-1)th and (N+1)th tracks becomes equal to that of a signal component thereof obtained by the first detector. A reproduced signal can be obtained by subtracting the processed signal from the output signal of the first detector.