Fiber Optic Gyroscope

This paper describes the development of Fiber Optic Gyroscope (FOG) for Space applications at LEOS. The sensor has all solid-state optical devices for the precise measurements of mechanical rotation. The basic phenomenon underlying optical rotation sensing is known as the Sagnac effect. In the Sagnac effect two identical light beams traveling in opposite directions around a closed loop path experience a phase difference when the loop is rotated about its normal axis, and this phase difference is proportional to the rotation rate. The potential advantage of this sensor compared to mechanical Gyro is no moving parts, rapid start up, lightweight, low power consumption and g insensitivity. Development model is a single axis sensor based on a multi turn, two-beam interferometer with a sensor head and processing electronics. Sensor head contains 500-meter polarization maintaining fiber wound on a bobbin acts as the sensing element. In the open loop system, processing electronics was implemented in Analog Demodulation using Lock-in amplifiers and 16 bits Rate output was generated. Short term bias stability of 0.27°/hour was achieved. To improve the performance, closed loop signal processing using Digital Serrodyne modulation approach was followed. This method offered good stability, high sensitivity and linearity over a large dynamic range. In the closed-loop system, all digital processing was implemented using Field Programmable Gate Array (FPGA) and both Rate and Incremental Angle outputs are available as 16 bit serial words. Whole system is assembled and tested. Angle Random Walk (ARW) measured is 0.012°/√hour and bias stability is 0.0378°/hour without any compensation techniques.