Technique of reducing the kerr effect and extending the dynamic range in

Abstract

A Brillouin fiber optic gyroscope includes an intensity modulator in the optical loop which periodically attenuates the Brillouin light waves counterpropagating in the optical loop so that the counterpropagating Brillouin waves each propagate as square waves. The use of square wave modulation for the counterpropagating light wave reduces the cross-effect of the Brillouin waves to substantially the same magnitude as the self-effect so that the non-reciprocal Kerr effect is substantially reduced or eliminated. In order to support the counterpropagating square waves, the optical loop is pumped with pump light having frequency components selected to pump the optical fiber to provide Brillouin light at frequencies necessary to generate square waves in the counterpropagating Brillouin light waves. In addition, the Brillouin light must be generated at the correct intensity and phase relationship to form the square wave. Because the relationship between the pump light and the generated Brillouin light is a non-linear function, the relative magnitudes of the frequency components of the pump light are selected to be different from the relative magnitudes of the Brillouin light so that when the pump light is applied to the optical loop, the transfer function results in the correct magnitudes for the frequency components of the Brillouin light. The intensity modulator assures that the Brillouin light is maintained in the proper phase relationship to maintain a square waveform.