Rotational Interferometry for High-Resolution Angle Measurement

A high-resolution incremental angle encoder based on optical interferometry is described. The basic concept employs a Michelson configuration where one arm of the interferometer is directed tangentially to a reflector moving about the axis of rotation. The resulting optical path difference encodes angular motion as a linear translation of the interferometer fringe pattern, which can be detected and processed by conventional electronics. This instrument possesses a large angular range and very high angular precision which can be adjusted through the length of the lever arm. Design parameters and tradeoffs, error sources, limitations, and results of performance measurements are presented.