Abstract

A pair of parallel mirrors that fold the beams of a Michelson interferometer serve as the mobile rotor of an angle encoder. The device remains in interferometric alignment for severe perturbations to all six degrees of freedom of the rotor and the path difference is purely a function of one angle that has a physical range of a third of a radian. For a 12-cm spacing of the parallel mirrors, a He-Ne laser produces a million fringes per radian. The interferometer conveniently adapts to a lenticular receiver giving three phase fringe signals suitable for a hexflash phase analyzer that provides a raw resolution of 1/1536 fringe (i.e., 650-prad rotor motion) with submicrosecond sampling time allowing good slew capability. A digital polar innovation filter unwraps and averages the samples in real time to maintain an extensive fringe count with even finer resolution.

© 1989 Optical Society of America