| 摘要 |
PURPOSE:To separate and reproduce a clock signal and an information signal by detecting an intensity-modulated reflected light to reproduce the clock signal and detecting differentially reflected lights in the first and the second directions as rotation directions of the plane of polarization to reproduce the information signal. CONSTITUTION:A photomagnetic disc device inverts the magnetization direction of a vertically magnetized film on an optical disc to record signals. The reflected light from the magnetic film is divided into two by a half mirror, and divided reflected lights are detected by individual photodetectors after passing individual detectors provided for upward magnetization and downward magnetization, and signals are reproduced by the differential output. A pregroup 1 of the photomagnetic disc consists of address bits 2 having lambda/4 depth and a group 3, and the information signal is recorded on the group 3 with an amplitude sufficiently shorter than lambda/8 with lambda/8 depth as the center. Thus, the rotation of the disc is controlled to a certain linear speed by the clock signal formed on the group 3 to reproduce the information signal by the differential detection method.
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