Adjusting Polarization To Reduce Error in an Interferometer

An unconventional and highly effective technique has been devised to reduce cyclic errors that arise in the operation of a displacement-measuring heterodyne optical interferometer. The cyclic errors are attributable largely to undesired small exchanges of power between light beams that are nominally in mutually orthogonal polarization states (such exchanges are denoted generally as polarization leakage). Unlike some prior techniques for reducing cyclic errors, the present technique does not require additional optical or electronic signals, additional signal processing, or use of optical components other than those of the interferometer itself. Optionally, the present technique can be used in conjunction with the prior techniques to reduce errors further.