Remote Fiber Optic Angular-Orientation Sensor Using Phase Detection of Two Orthogonal Oscillating Polarization Vectors

Abstract

A method for remotely detecting the angular position of a rotatable code wheel is provided by generating two sine wave modulated light beams which are orthogonally polarized with respect to each other. The beams are combined and then directed through a polarization filter mounted on the code wheel. The combined beam incurs a phase shift with respect to a reference signal which depends upon the position of the code wheel. The combined polarized beam provides angular position resolution between zero and ninety degrees, but lacks quadrant resolution. Two other light beams are directed to a two channel digital mask pattern imprinted on the code wheel. The mask pattern encodes these latter beams with "on" or "off' pulses to provide quadrant resolution. The beams are converted to digital electric signals which are received by a programmable read oly memory (PROM). The PROM provides an output corresponding to the angular position of the code wheel to a display.