C. Seidel and G.F. Trommer
Fibre-optic gyroscope, modelling, interference, coherence, polarization
Although much research has been done on fibre-optic gyroscopes (FOG), these sensors often show bias errors, that is, the offset rotation rate varies with temperature and other environmental parameters. A low-coherence light source is used to avoid undesirable interferences between error signals. Nevertheless, in the standard FOG design it is possible that unintentionally optical paths match, which may cause bias errors. The parasitic interferences may originate from reflections and polarization cross-coupling, whether intended or not. The authors present a new simulation tool for modelling interferometric fibre optic sensors with inclusion of polarization and coherence effects. It allows, for the first time, modelling of the FOG signal quantitatively considering temperature dependence, light source parameters, and all perturbations and interferences between them with the corresponding degree of coherence. The authors analyze the gyroscope design, which leads to a localization of a bias error source that has not yet been described. This problem may occur in every FOG with an integrated optics circuit (IOC) and a Lyot depolarizer. Reflection paths from the IOC match phase differences gained in the depolarizer and lead to temperature- dependent bias errors. Guidelines for an optimum design avoiding the perturbing interferences are given.
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