Resonator Fiber Optic Gyro with Bipolar Digital Serrodyne Scheme Using a Field-Programmable Gate Array-Based Digital Processor

A field-programmable gate array-based digital processor is proposed and demonstrated experimentally for a resonator fiber optic gyro (R-FOG) with a bipolar digital serrodyne phase modulation scheme, which we previously proposed especially for R-FOG signal processing and its noise reduction. The processor has multi functions. First, it suppresses both the fast-and slow-drift components in the difference between the laser frequency and the resonator's resonant frequency. The fast-drift with a small amplitude is compensated for by a proportional controller with an oversampling function to reduce the quantization error, while the slow-drift with a large amplitude is tracked using an up/down counter. Second, it automatically adjusts the amplitude of the waveform for bipolar digital serrodyne phase modulation for waves travelling both in the resonator clockwise and counterclockwise. Bipolar laser frequency alternation required to track the resonator's resonant frequency is ideally realized by adjusting the phase modulation amplitude. This automatic adjustment also realizes an additional function for reducing the gyro drift caused by backscattering in the fiber resonator, which was originally implemented in the shape of the waveform for bipolar digital serrodyne phase modulation. Third, the FPGA generates a gyro output with open-loop operation. The R-FOG performance is demonstrated to be improved by applying these three functions with the FPGA. (C) 2011 The Japan Society of Applied Physics