| 摘要 |
PURPOSE:To increase the record capacity of a photomagnetic disk underwent a pre- group and pre-format by using a polarizing prism which separates the reflected light of the photomagnetic disk into two polarized beams orthogonal to each other and a differential amplifier and an addition amplifier which obtain the difference and the sum of the electric signals detected by two photodetectors, respectively. CONSTITUTION:The reflected light given from a disk 13 is reflected again by a half mirror 10, and a multi-split photodetector 23 detects both focusing and tracking error signals. The light reflected by a half mirror 11 is separated into two polarized beams or hogonal to each other by a polarizing prism 15 such as a Rochon prism, a wollaston prism, etc. These two beams are made incident to photodetectors 17 and 18, respectively via a convex lens 16 and converted into electric signals. The prism 15 is set by turning by 45 deg. around the center of the optical axis to the polarizing direction of the reflected light supplied from the mirror 11. The beams detected by the detectors 17 and 18 are converted into electric signals by head amplifiers 19 and 20. Then the difference is obtained by differential amplifier 24 those electric signals in order to detect a signal which is recorded in a photothermic and magnetic way. Then the sum is obtained by an addition amplifier 25 by adding said signals to detect a pre-format signal such as an address signal, a synchronizing signal, etc. |
