Fiber optic gyroscope is an important development in the field of fiber optic sensors. It is now considered an alternative
technology to the mechanical and laser gyroscopes for the inertial guidance and control applications. The advantages of
FOG over mechanical gyroscopes are many like instantaneous operation, wide dynamic range, no g-sensitivity,
maintenance free, and capability to withstand high shock and vibration and so on. The advantages over laser gyroscopes
include cost effectiveness, light weight, low power consumption and improved ruggedness. The optical gyroscope
principle was first demonstrated by Sagnac in 1913. Optical gyroscopes implemented so far use Sagnac effect, which
states that an optical path difference induced by counter propagating beams in a rotating reference frame is proportional
to the absolute rotation.
The main requirement of a FOG is perfect reciprocity, i.e. in the absence of rotation, the counter propagating
beams inside the fiber must travel identical paths thus resulting in zero phase shift. The phase shift in a Sagnac
interferometer not only comprises of a non-reciprocal sources that set practical performance limits. These non-reciprocal
sources generate random time varying output resulting in a bias drift even under zero rotation rates, which causes serious
problems in present day gyroscope. In a FOG the reciprocal configuration ensures the bias stability, signal processing is
used to obtain maximum sensitivity, a broad band source is used to eliminate the effect of back scattering, polarization
coupling and Kerr effect and the closed loop operation is used to linearize the scale factor and improve its stability.