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Ring Laser Gyroscopes

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Demand for higher resolution in inertial navigation (commercial and military) ... observed in 1600's by Christiaan Huygens in the behavior of pendulum clocks ... – PowerPoint PPT presentation

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Title: Ring Laser Gyroscopes


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
  • 1910s Sagnac experiments characterize
    rotational effects on a counter propagating beams
    of light
  • 1960s Sperry develops first commercial RLG
  • 1970s Honeywell develops first dithered RLG
  • 1980s RLGs 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 1600s 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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