INTEGRATED-OPTIC GRATING SCALE-DISPLACEMENT SENSOR USING LINEARLY FOCUSING GRATING COUPLERS

An integrated optic sensor was proposed and demonstrated for measuring displacement of a grating scale. The sensor is constructed by integrating a pair of linearly focusing grating couplers (LFGCs) and a pair of photodiodes (PDs) in a glass waveguide on an Si substrate. Two beams, radiated from the LFGC pair, overlap on the grating scale with each other. The beams diffracted by the grating scale interfere on the PDs, and the interference signals vary when the grating scale moves along its grating vector direction. The device was designed and fabricated, and the variation of output photocurrents was confirmed experimentally.