Image Number 3 for United States Patent #5408492.
An optical rotation sensor comprises a light amplification stimulated emission ring laser formed in a solid medium is provided with phase modulator devices which produce push-pull phase modulation of counterpropagating optical waves in the ring thereby enhancing bidirectional lasing in single longitudinal modes in each direction. A frequency selective output coupler couples a predetermined portion of the optical energy at the lasing frequency from the ring to an output waveguide. A substantially U-shaped output waveguide having legs extending away from the ring in opposite directions and toward a common position. Clockwise and counterclockwise light waves are coupled from the ring to the two separate legs of the output waveguide and are directed to the common position to create an interfering light pattern on photodetector apparatus. The interfering light pattern is indicative of the rate of rotation, as defined by the Sagnac effect. Signal processing circuitry connected to the detector derives navigation and flight control information from the detector. In one embodiment, the ring laser and input and output couplers are implemented in a rare earth-doped lithium niobate substrate. In another embodiment, the ring laser and the input and output waveguides are implemented in rare earth-doped optical fibers. In a further embodiment, the ring laser and input and output couplers as well as the phase modulators and the photodetector apparatus are implemented in a single semiconductor substrate and gain electrically supplied to the ring laser.