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Ring Laser Gyroscopes

Ring Laser Gyroscopes. Micah Larson April 21, 2005. Why use an RLG (Sagnac interferometer)? . Demand for higher resolution in inertial navigation (commercial and military) Frictionless and therefore do not resist changes in orientation unlike their mechanical predecessors

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Ring Laser Gyroscopes

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  1. Ring Laser Gyroscopes Micah Larson April 21, 2005

  2. Why use an RLG (Sagnac interferometer)? • Demand for higher resolution in inertial navigation (commercial and military) • Frictionless and therefore do not resist changes in orientation unlike their mechanical predecessors • Small (relative to scope of application) as well as durable and accurate

  3. Historical Background • 1910’s: Sagnac experiments characterize rotational effects on a counter propagating beams of light • 1960’s: Sperry develops first commercial RLG • 1970’s: Honeywell develops first dithered RLG • 1980’s: RLG’s begin to replace mechanical gyros in inertial navigation

  4. Basic Composition • Equilateral triangular glass block • Three mirrors • One allows 1% transmission • Mirrors are manufactured such that there is 1ppm loss • He-Ne laser fill gas • Laser source (anode-cathode current drive) • Readout sensor

  5. Basic Operation • Two counter propagating (clockwise and counter-clockwise) beams travel around laser cavity • While undergoing rotation, a fringe interference pattern is detected at the readout sensor • Sagnac Effect

  6. Sagnac Frequency Splitting • Two rotating beams undergo frequency shifts, the corotating beam is seen as more red, counterrotating beam seen as more blue • Frequency splitting coupled with the time and phase difference previously described determine RLG resolution • Larger gyroscope = greater resolution

  7. Lock-In • When experiencing low angular rotation rates, it becomes possible for multiple gyros to “Lock-in” to the same frequency independent of angular velocity • Eliminates the effects of Sagnac frequency splitting • Similar to phenomenon observed in 1600’s by Christiaan Huygens in the behavior of pendulum clocks • Gyros lock in is due to optical coupling from backscatter as opposed to mechanical coupling • Dithering at a higher frequency avoids lock in

  8. Applications • Inertial navigation • Control systems • Large scale applications (Large RLGs) • Measuring variations in the angular rotation rate of Earth

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