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The output signal of a birefringent fiber gyroscope is analyzed, and sources of error due to polarization cross coupling in the fiber and fiber components are identified. Techniques to suppress such errors by modulating the fiber birefringence and balancing the optical power in the two polarization modes are proposed and demonstrated.

A novel demodulation scheme for interferometers with optical phase modulation is described. The optical phase shift is measured by mixing a train of square digital pulses with a photodetector current and adjusting the pulse spacing by using an electronic closed loop. The optical phase shift is tracked with deviation less than 0.007 rad, which can be easily corrected by using a look-up table. An experimental optically open-loop fiberoptic gyroscope that uses this demodulation shows a linear scale factor in good agreement with theory.In the interferometric fiber-optic gyroscope with optical phase modulation, the detector current is given by' ID(t) = 21 + Cos[nm Cos(w0mt) + OR]},( 1) where Io is the maximum detector current, Am is the amplitude of differential phase modulation, air = 27rfm is the modulation frequency, and OR is the rotation-induced Sagnac phase shift. In practical gyroscope systems, a wide dynamic range with good linearity is desirable. For this purpose many demodulation systems have been proposed. 2` These can be classified into two categories: closed-loop and open-loop systems.

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