| 摘要 |
PURPOSE:To reduce noise and to increase the signal amplitude over to the extent of a high frequency band by dividing laser light into three beams of light at the time of recording and reproducing information with the laser light, irradiating a discoid recording medium with the respective beams, detecting their reflected beams with three photodetectors to be sent to a differential amplifier and utilizing this output for recording and reproducing. CONSTITUTION:A beam 12 from a semiconductor laser 11 is allowed to pass through a diffraction grating 14 via a collimation lens 13 and divided into three beams, and after passing through a polarization beam splitter 15 and a 1/4-wavelength plate 16, the beams are converged by an objective lens 17 as three spots to irradiate the information disk 18. Then, the reflected beams are led to follow the original light path and reflected by the splitter 15 to go through a focusing lens system 19 and then received by three photodetectors 110-112. Afterward, their individual outputs are amplified by preamplifiers 113-115, whereas a 1st and 2nd outputs 113 and 114 are delayed by delay circuits 116 and 118 to be given to a gain control circuit 117, while a 3rd output 115 is sent as it is to a gain control circuit 119. Then, their difference is taken by the differential amplifier 122 to make the light beams follow a track. |
