OPTICAL INFORMATION REPRODUCING DEVICE

摘要

PURPOSE:To obtain a stable focusing error signal by dividing a focusing error signal by the addition signal of the modulation factors of electric signals obtained from reflected lights of two auxiliary light beams. CONSTITUTION:Auxiliary light sources 5' and 5'' are arranged on the opposite sides across the main optical axis of a light source 5 and displaced at right angles to the main optical axis. The light beams from the auxiliary light sources are modulated by tracks of a recording medium 1 and converged on detectors 8 and 8'. When the defocusing quantity Z is 0, the playback signal modulation factor of a detector 8 has a maximum value A and both the playback modulation factors of the detectors 8' and 8'' have a value B. When the medium is below the focusing point (Z>0), the modulation factor E is less than the modulation factor F and a focusing error is obtained from the modulation factor difference, thereby correcting the degree of convergence of a lens 7. When the focusing error signal is divided by the modulation factor of one electric signal of the auxiliary light, the stable focusing error signal can be obtained without being affected by a track crossing signal.