| 摘要 |
PROBLEM TO BE SOLVED: To contrive effective utilization of laser beam and reduction of the cost for the device in keeping compatibility with the conventional optical disk. SOLUTION: A polarizing beam splitter 5 for splitting an optical path of either of outgoing and return passages of an incident laser beam in accordance with its polarization state is provided between a laser 1 consisting of 1st and 2nd semiconductor lasers 1a and 1b for emitting different laser beams in wavelength and an objective lens 8, and a phase plate 4 for generating a prescribed phase difference between the laser beams to be incident upon the polarizing beam splitter 5 is provided between the polarizing beam splitter 5 and the laser 1. Then, the incident laser beam from the laser 1 upon the polarizing beam splitter 5 is reflected by a prescribed quantity of light by the polarizing beam splitter 5 to be incident upon a light quantity detector 14, so as not to make unnecessary laser beam incident upon the light quantity detector 14. Consequently, the laser beam is effectively utilized, and also a gain control circuit to be used for the light quantity detector 14 is unnecessitated to reduce the cost. |
