| 摘要 |
PURPOSE: To provide an optical head device capable of considerably reducing the deterioration of a reproduced signal even when information recording density becomes high. CONSTITUTION: A light source 1 transmits a laser beam. A collimator lens 2 makes an incident laser beam parallel. A super-high resolution filter 3 shields the neighborhood of the central part of the cross section of the incident laser beam. A beam splitter 5 makes the incident laser beam transmit through and reflects a reflected light beam from an objective lens 12. The objective lens 12 converges the incident beam, forms the image on an information recording medium 7, makes the reflected beam from the information recording medium 7 parallel and makes it incident on the beam splitter 5. A re-converging lens 13 converges the reflected beam again. A pin hole 9 makes the vicinity of the center of the re-converged beam transmit through and removes the side lobe. A photodetector 10 receives the re-converged beam. The objective lens 12 makes the numerical aperture at the time of receiving light larger than the numerical aperture at the time of converging light. |
