POSITION DETECTING DEVICE

摘要

PURPOSE:To obtain a highly accurate position detecting device by reflecting coherent light by means of a diffraction grating the aperture function of which becomes anti-symmetrical with respect to an axis intersecting the scanning direction of the coherent light at right angles. CONSTITUTION:Gratings G and G' each of which has a width L and in which aperture functions e and areas of '1' (a) and (b) are alternately arranged at pitches (p) in a grating-like state are arranged so that the aperture functions can become anti-symmetrical with respect to an anti-symmetrical axis (t) intersecting the scanning direction (x) of coherent light. Therefore, the intensity of reflected light generated when the incident light of the coherent light passes the axis and detect signals produced by the reflection are minimized and the intensity distribution width of the detect signal when the incident light passes the axis is used as the intensity distribution width of the incident light by comparing the detect signal with signals detected by the reflected light before and after the incident light passes the axis. Namely, the intensity and distributed state of reflected light for detecting position reflected by an optical element by using the incident light is reflected equivalently to the incident light and accurate position detection is performed.