A Planar Laser Diffraction Encoder in Littrow Configuration for 2D Nanometric Positioning

This paper presents a novel design of a planar encoder based on the principle of diffractive interferometry. The system is capable of measuring the two-dimensional displacement of the planar grating of any size. It adopts a specially designed optical path that can increase the alignment tolerance between the optical head and the grating. Given the merits of its simple optical configuration and compact size, it can effectively reduce the environmental disturbance and allow higher stability. The signal processing circuit and waveform subdivision software were also developed to effectively compensate for the waveform errors and count the position to 1nm resolution. Experimental results showed that even in the normal laboratory environment the standard deviation of measured values can be controlled to within 15nm for a long stroke up to 25mm on both axes.