DETECTOR FOR CONVERGED SOPT POSITION OF OPTICAL INFORMATION RECORDING AND REPRODUCING DEVICE

摘要

PURPOSE:To obtain a stable focus error signal by scanning a recording medium with a converged spot after blinking successively plural light emitting sources and detecting and analyzing the interference fringes produced by the diffraction of an information track to produce the focus error signal. CONSTITUTION:The light sources 21-23 are successively blinked via a control circuit 24 with a frequency higher than the frequency band of an information signal. Then the converged light spots are projected on the converged spots 25-27 set on the information track 5 of an information recording medium 3 via an objective lens 9. Thus the track 5 is scanned. The diffracted light of the track 5 is reflected by a translucent mirror 7 via the lens 9 and made incident on a focus error detecting photodetector 28. The outputs signals of the photodetector 28 are sampled and held by a sampling/holding circuit synchronously with the blinking of sources 21-23. The output of the sampling/holding circuit undergoes the arithmetic processing through an arithmetic circuit. Then a focusing error signal is obtained.