Eigenstate of polarization in a fiber ring resonator and its effect in an optical passive ring-resonator gyro

Resonance characteristics of an optical fiber ring resonator are derived taking the effect of birefringence into account. We introduce the concept of the eigenstate of polarization to discuss the resonance characteristics resulting from the polarization fluctuation. Using this concept, the polarization problem in an optical passive ring-resonator gyro (OPRG) is discussed to reveal that this causes gyro drift. A way to reduce the drift is to use not polarizers but two polarization controllers. The precision required for polarization control is estimated; it is found difficult to do in practice. We discuss another configuration to solve the polarization problem in an OPRG without polarization controllers.