| 摘要 |
PURPOSE:To eliminate the variance of a reproduced signal to attain a high SN ratio even if double refraction remains, by detecting reflected lights which are separated from each other by a polarizing beam splitter and a semitransparent mirror and using the sum of detection signals as the reproduced signal. CONSTITUTION:Laser light is irradiated to an information disc 16 through a collimate lens 12, a semitransparent mirror 31, a polarizing beam splitter 13, a 1/4 wavelength plate, and an object lens 15. The reflected light is reflected by the polarizing beam splitter 13 and the semitransparent mirror 31 and is detected by photodetectors 18 and 33. Since the reflected light passing through the 1/4 wavelength plate 14 becomes an elliptically polarized light generally by double refraction of the information disc 16, it is separated to reflected light and transmitted light by the polarizing beam splitter 13. Since the sum of these reflected light and transmitted light is the total quantity of reflected light and is constant, the amplitude of a detection signal 36 is always constant by addition of outputs of photodetectors 18 and 33 even in case of double refraction. |
