| 摘要 |
PROBLEM TO BE SOLVED: To suppress variations in detecting sensibilities for every device and fluctuations of detecting sensibilities due to operationg environments and the secular change of the characteristic of a detecting element by detecting the position of an objective lens as two signals having the phase difference of 90 deg.C and arithmetically processing two signals and making the processed result the position detection signal of the objective lens. SOLUTION: A light emitting element 90, photodetectors 91a, 91b and a fixed slit 93 are provided on a base 80 and a movable slit 92 is provided on a lens holder 20. Opening parts 92a whose width are P/2 are provided in the movable slit 92 with an interval P and opening parts 93a, 93b whose widths are P/2 are provided by being shifted by P/2 in the moving dirtection of the movable slit 92. When the moving amount of the slit 92 is defined as (x), output signals S1, S2 of the photodetectors 91a, 91b respectively become S1=A sin(2πx/ P), S2=A cos(2πx/P). Here, signals which are not depended on an amplitude A are obtained by detecing the moving amount of the objective lens, based on S1/S2 and S1/(S1<1> +S2<2> )<1/2> .
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