| 摘要 |
PURPOSE:To reduce the deterioration in the error rate even in a base having double refraction by providing a difference circuit generating a difference between outputs of two photodetectors, an envelope circuit generating an envelope from the outputs and a comparator circuit comparing the output of the difference circuit. CONSTITUTION:The emitted light from a semiconductor laser 1 forms a spot on a recording medium 6 formed on a base 5 through a collimate lens 2, two beam splitters 3, and a condenser lens 4. The reflected light from the recording medium 6 is split by the beam splitter 3, the polarized plane is rotated by 45 deg. by a 1/2 wavelength plate 7, divided into two beams by a polarized beam splitter, they are detected by two photodetectors 9, and the outputs are led to a difference circuit 14. The output of the difference circuit 14 subjected to envelope detection by an envelope circuit 16 and the signal is digitized at a comparator circuit 15 by using the envelope output. Thus, the increase in the error rate is less even with a base having a large double refraction.
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