Differential laser gyro employing reflection polarization anisotropy

Claim 1

A differential laser gyro system comprising a ring laser optical cavity having an optical path including an odd number of mirrors and a laser gain medium disposed in said cavIty; a Faraday cell disposed in said optical path; a pair of quarter wave plates disposed on opposite ends of said Faraday cell, said quarter wave plates and said Faraday cell comprising an optical path segment wholly between two of said mirrors, whereby the traveling waves incident upon each of said mirrors from either direction is plane polarized in mutually perpendicular planes; the length of said optical cavity being chosen with respect to the line frequency of said laser gain medium so as to provide a cavity length including an integral number of wavelengths within the oscillation-sustaining frequency range of said laser gain medium in said optical cavity, whereby the frequency of electromagnetic radiation in one orientation of plane polarization differs from the frequency of electromagnetic radiation in a perpendicular sense of polarization, the parameters of said laser gyro system being chosen so that there is provided a pair of laser gyros operating in said cavity separated in frequency, each implemented in a polarization which is distinct from the other, each having a bias which is opposite to but substantially equal in magnitude to the bias of the other; and differential read out means for providing an output proportional to the difference between outputs of the two laser gyros.