| 摘要 |
PURPOSE:To obtain exact detecting signals of luminance power by increasing the photocurrent by use of two photodetectors when detecting a reproducing power, and correlatively decreasing the photocurrent by use of one photodetector when detecting a recording or erasing power. CONSTITUTION:Two photodetectors 11a and 11b, first and second ones, are used. When the luminance power is small but a reproducing power should be detected, the photocurrent is increased by utilizing the photocurrents received by both of the photodetectors 1a and 1b. When the luminance power is large for recording or an erasing power should be detected, the photocurrent received by the photodetector 1a, one of the two, is utilized. The variation of the photocurrent is then reduced when each power is detected, thus making it difficult for the circuit systems to be affected by the offset drifting or the like. The exact detecting signals for luminance powers can be obtained accordingly. |
