| 摘要 |
PURPOSE:To facilitate the assembly of an optical head by providing a reflection type hologram between a light source and a condensing means, and photodetecting a diffracted light reflected by this hologram by a front monitor use photo-detector. CONSTITUTION:A beam reflected by a recording medium 4 passes through an objective lens 3, made incident on a diffraction hologram 21, '0'-order and + or -first order diffracted beams are generated, and a '0'-order beam returns to a semiconductor laser 1. On the other hand, a + or - first order beam is converged to an error signal use photodetector 5 placed on a substrate 7, brought to photoelectric conversion, and a focus and tracking error signal and an information signal are obtained. On the other hand, a '0'-order beam emitted from the laser 1 and reflected by a reflection type hologram 22 is converged to a front monitor use photodetector 8, and brought to photoelectric conversion. An output of the photodetector 8 is sent to an APC circuit, and a light emission output of the laser 1 is adjusted automatically. In such a way, a front light of a light source can be monitored, and the APC which is not influenced by a back talk noise caused by a return light can be realized. |
