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15 December 1978 Sources of Error in a Discrete Component Sagnac Optical Rate Sensor
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The objective of this paper is to temper the recent performance claims for optical rate sensors employing passive non-resonant cavities (Sagnac effect) with some results obtained in our laboratory. Over the period from 1971-1975 the authors investigated an all-discrete component embodiment of the above rate sensor employing mirrors in the cavity, beamsplitters for input/output, and an external HeNe gas laser. Unique to the Lear Siegler effort was the fact that the countertravelling beams were cross-polarized when combined. Inertial rates could then be sensed as ellipticities in the resultant beam via a highly sensitive ellipsometer. Sources of random error signals (false rate) unique to the ellipsometer and electronics were minimized and contributed less than 80°/hr of false rate in an 8" square cavity. However, the multilayers on the mirrors and beamsplitters produced non-reciprocal phase changes between the countertravelling beams whenever the latter became even slightly non-concentric. This non-concentricity may be due to a laser beam angular deviation (wobble) or to a ring element tilt. A typical HeNe laser with a confocal or hemispherical cavity has a 3x10 radbeam wobble. This, coupled with the multilayer sensitivity, yields false rates in the 0.1-1°/sec range. In addition, the laser beam wobble directly produced a geometric non-reciprocal phase which amounted to over 25°/sec. To reduce these errors we suggested using a solid state CW laser diode source and a multiturn single mode fiber ring. Unfortunately, such elements were not available to us at that time so further experimental effort at Lear Siegler was discontinued. However, analysis performed by us showed that various error sources would still limit the performance of this hybrid model to about 1-5°/hr. What is needed, therefore, is an all-integrated-optics embodiment of the sensor.
© (1978) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Ronald J. Fredricks and Wilbur A. Carrington "Sources of Error in a Discrete Component Sagnac Optical Rate Sensor", Proc. SPIE 0157, Laser Inertial Rotation Sensors, (15 December 1978);

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