| 摘要 |
PURPOSE:To read recording information with only a 2nd higher harmonic and to decrease noises of the detection signal of a photodetector by providing a filter which cuts off primary light between a 1st separating means and a 1st photodetector. CONSTITUTION:The primary light after passing through a dichroic mirror 22 is made incident on the photodetection surface of a four-division photodetector 12 through, for example, a cylindrical lens 11. The 2nd higher harmonic reflected by the dichroic mirror 22 is converged by a condenser lens 10 on the photodetection surface of the photodetector 13 through a primary light cutoff filter 15. Thus, the primary light is cut off by plural filters and the recording information can be read with only the 2nd higher harmonic, so the high SN ratio is obtained at the time of the reproduction of an optical disk and noises of the detection signal of the photodetector are decreased. |
