Fiber-Optic Rotation Sensors: Alternate Configurations and Modes of Operation.

This is a theoretical and experimental study of rotation sensors which utilize the Sagnac effect in ring inerferometers fabricated from optical fibers. The effects of fiber birefringence and polarization of light on the performance of such sensors are of great importance and these effects have been investigated using a mathematical formalism particularly suited for treating these properties. This formalism has been applied to a variety of polarization conditions and to various kinds of phase modulation techniques. The predictions of this formalism are compared with experiment in certain cases and are found to be in good qualitative agreement. Based on these results, a new type of phase modulated rotation sensor which uses two modulation frequencies is proposed to overcome some of the problems characteristic of some kinds of operation. The principles of operation of reentrant pulsed fiber rotation sensors have also been examined. This is the case where a single pulse circulates around the fiber many times. Considerations of system optimization for various cases are treated and presented. Experimental results obtained with two types of such reentrant rotation sensors are presented and discussed. Mathematical formulas have also been derived for the rotation rate error in single pass and reentrant rotation sensors in terms of the uncertainties in the system parameters due to noise. In the case of reentrant rotation sensors, several mathematical algorithms for processing the signal have been treated. Computer calculations have been made on the rotation error as a function of the rotation rate and the number of recirculations, for a passive reentrant rotation sensor which uses a cycle counting detection algorithm. The rotation rate error as a function of recirculations and also for low rotation rates has been calculated and proposals have been made for reducing these errors. The theory should also be capable of treating other conditions of operation for a rotation sensor.