| 摘要 |
PURPOSE:To make stable focus control even for a recordable light disk etc. in which no information signal is recorded by providing a focus error detecting means basing on phase difference, a recordable light disk having a track and information for focus detection provided on the track and a focus error detecting means using optical method. CONSTITUTION:When a record carrier 1 moved to the position of a record carrier 1', reflected light moves to the light detecting section 11b of a light detector 11, and consequently, output comes out in a differential amplifier 14. Output of the differential amplifier 14 drives a linear motor 6 through an equalizer 16 and a driving amplifier 17, and operates to make output of the differential amplifier 14 '0', and the focus of an objective lens 5 on the record carrier 1 is maintained, and operation is made even if no special signal is recorded on the record carrier 1. The detecting means using phase difference phase compares output of a light detector 19 and output of the light detector 11 and detection is realized by inputting to an adder 15 to make the phase difference '0'. |
