| 摘要 |
PROBLEM TO BE SOLVED: To perform a recording and a reproducing to two kinds of optical disks by utilizing light quantities of laser beams efficiently. SOLUTION: A laser beam is generated by changing over radiant light sources 21A, 21B according to the kind of optical disks 41A, 41B. A laser beam of a first wavelength emitted from the radiant light source 21A is diffracted at a hologram optical element(HOE) 26 on which saw wave shaped ruggednesses having the step shape of four stages are formed in a concentric circular shape to be converged at a prescribed position of the optical disk 41A by a refractive type object lens 27. A laser beam of a second wavelength emitted from the radiant light source 21B transmits the HOE 26 to be converged at a prescribed position of the optical disk 41B by the refractive type object lens 27. Then, the laser beam (reflected light beam) reflected on the optical disks 41A, 41B is received by a photodetector 29 via an optical system and information are reproduced from the received reflected light beam. |
