| 摘要 |
PURPOSE:To obtain both an information and a focus error signal, by providing three semiconductor lasers which differ in distance from a light emission point to a recording medium and have self-coupling effect. CONSTITUTION:The quantity of return light of laser luminous flux to a semiconductor laser varies with a spot diameter on a disk, so the quantity of the output light of the semiconductor laser varies and photodetectors 7a, 7b and 7c near an opening end on the opposite side of the semiconductor laser detect variation in output light due to self-coupling effect. Outputs of the photodetectors 7a, 7b and 7c are led to a differential amplifier 11 to perform automatic focusing. Semiconductor lasers 1a-1c are arranged differing in distance from a disk surface and spots 15a-15c on the disk surface have different diameters. |
