| 摘要 |
PROBLEM TO BE SOLVED: To perform a recording and a reproducing with a high S/N with respect to two kinds of thicknesses of disks even without making the output of a semiconductor laser excessively large. SOLUTION: A semiconductor laser having the wavelength of 635nm and a light receiving element are incorporated in a module 1 and a semiconductor laser having the wavelength of 785nm and a light receiving element are incorporated in a module 2. The exit light from the module 1 is transmitted through a wavelength filter 3 to be made to be parallel beams in a collimator lens 4 and are transmitted through a hologram optical element 5 to be condensed on a disk 7 by an objective lens 6. The reflected light traces a reverse optical path to be detected by the light receiving element in the module 1. The exit light from the module 2 is reflected by the wavelength filter 3 to be made to be parallel beams in the collimator lens 4 and a minus 1-st order diffracted light by a hologram optical element 5 is made incident on the objective lens 6 as a divergent light to be condensed on a disk 8. The reflected light traces a reverse optical path to be detected by the light receiving element in the module 2. |
