INTERFEROMETRIC ANGLE ENCODER

Four unusual features are combined in the construction of an interferometric angle encoder: (1) a robust optical configuration, (2) a three-port lenticular fringe receiver, (3) a hexaflash phase-analysis circuit, and (4) a recursive phase unwrapping and smoothing filter. Raw performance of the instrument is about 600 prad resolution at 2 MHz sample rate. That is about a factor of 25 away from the shot noise limit. Resolution is improved to about 13 prad by on-the-fly smoothing to a 500 Hz bandwidth and data acquisition of 32-bit values is implemented at up to 5376 samples per second. The overall range of the system can be up to 18-degrees.