| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical head device reading phase modulation type optical information which are three-dimensionally recorded. SOLUTION: Light beams emitted from a semiconductor laser 1 are collimated by a small diameter collimating lens 2 whose effective diameter of aperture is smaller than the effective diameter of aperture of an objective lens 5 and a part of the collimated light transmits a half mirror 3 to be converged on a phase type three-dimensional disk 4. Then, a part of light beams made incident on the objective lens 5 among light beams reflected and diffracted on the phase type three-dimensional disk 4 are reflected on the half mirror 3 and after the reflected light beams receive the change of an optical path toward a photodetector for signal detection 9, the light beams transmit a phase and intensity modulation plate 6 to be reconverged on a pin hold 8 by a recondensing lens 7 and the center part of the converged light beams are made incident on the photodetector 9. |
