A compact optical encoder with micromachined photodetector

A compact optical encoder has been fabricated using a micromachining techni que for the measurement of linear displacement. The index grating for detec ting the Moire signal from the superimposed gratings consists of transmissi on type silicon grids, which are etched through by the reactive ion plasma. An array of line photodetectors is installed on the silicon grids by ion i mplantation. A scale grating is illuminated by the light passing through th e slits of the transmission index grating, and thus the light source can be placed just behind the index grating. Therefore the structure of the propo sed optical encoder is compact. In the experiment, the second order grating imaging phenomenon under incoherent illumination has been applied to the d isplacement sensing. The encoder signal with a high contrast is obtained at a large air gap between the two gratings.