| 摘要 |
PURPOSE:To make highly accurate and stable focus control without influenced by detection error in a geometric optical focus detecting means by correcting the position of laser luminous flux to correct minute focus deviation of laser luminous flux and the surface of a recording carrier detected by lag of time interval. CONSTITUTION:As a light detector 10 is placed in the far field of reflected light, lag of timing that makes the difference of light intensity maximum is not caused even if there is some positional deviation. Accordingly, by detecting lag of timing of pulse signals 101, very accurate and stable detection of focus error can be made excluding influences of positional deviation of an optical system, fluctuation of the level of the quantity of light and quantity of electricity etc. A focus error correction signal 102, output of a low pass filter 25, is added by an adder 31 to a focus error signal 110, and focus detection error by geometric optical means is corrected. Accordingly, a light spot can be focused accurately on the surface of a record carrier 8 even when positional deviation and adjustment deviation exist in an optical system consisting of a convergent lens 11, a knife edge 12 and a focus error detector 13. |
