Linearization of open-loop fiber optic gyroscopes with Mean-Value demodulation scheme

Abstract

Interferometric Fiber Optic Gyroscopes (IFOGs) are the most used angular velocity sensors for high-performance inertial navigation systems, both in open-loop or closed-loop configurations. Although open-loop IFOGs present a lower cost than closed-loop ones, since it is not necessary to use multifunction integrated optic circuits, they cannot achieve the same performance level. In general, compared to closed-loop gyroscopes, the devices in open-loop configurations have lower linearity, lower scale factor stability, and lower dynamic range, being more attractive for medium-high performance applications, such as in the attitude control of small satellites. This work presents a technique to increase the linearity of open-loop IFOGs using the Mean-Value demodulation scheme, allowing the use of this device in a new range of applications that requires ultra-high linearity. The Mean-Value demodulation scheme, proposed by this research group in previous works, extracts the angular velocity information using time-domain analog demodulation of the Sagnac’s interferometer output signal. This work presents a way to improve the linearity through a new digital signal processing technique implemented in the electronic demodulation system. This technique was developed and evaluated by computer simulations and implemented in a physical open-loop IFOG. The sensor’s output presented a linearity 65 times better than without the proposed technique, achieving maximum nonlinearity error of 230 ppm, for a full scale of $\pm 15\deg/\mathrm{s}$. This novel technique also dispenses the need for individual calibration on open-loop IFOGs, a costly and time-dependent process.