Instability and nonlinearity of the output characteristics of fiber ring interferometers

An analysis is reported of various configurations of the Sagnac interferometer, in particular a fiber ring interferometer converting an optical phase shift to the rf range. It is shown that this interferometer may exhibit a high linearity of the output characteristics without recourse to frequency splitting, but the processes occurring in modulation–demodulation systems result in an instability and nonlinearity of the output characteristics of the interferometer. An interferometer with an angular velocity resolution of the order of 10 ^–5 rad/s was used to show that the nonlinearity of the output characteristic of the interferometer used to convert the optical phase shift to the rf range amounted to 10 ^–2, which was approximately an order of magnitude poorer than the corresponding parameter obtained for a coarse laser sensor of the angular velocity.