| 摘要 |
PURPOSE:To prevent the S/N ratio of a signal from being deteriorated by providing a light intensity adjustment means, cancelling the change of return light coefficient which is generated by the difference of the reflectance of a recording medium and always operating a laser with low noise. CONSTITUTION:Light emitted from a semiconductor 1 is made incident on an ND filter 10 being the light intensity adjustment means through a collimator lens 2 and a polarization beam splitter PBS 3 being a light wave separation means. The light emitted by the filter 10 is partially reflected on the recording medium 6, reflected on the PBS 3 through the filter 10 and made incident on a PIN detector 9 being a photoelectric conversion element. Then, in the case that the recording medium 6 has the low reflectance, the filter 10 is retreated from an optical path. In the case that the medium 6 has the high reflectance, the change of the coefficient of the light returned to the laser 1 is cancelled when the filter 10 having proper transmittance is installed to the optical path. Thus, the laser 1 is always operated under the state of the low noise and a reproduction signal having the high S/N ratio is obtained. |
