Effect of orthogonal-mode random coupling on polarization characteristics of single-mode fiber lightguides (SMFL) and SMFL-based ring interferometers. Part III. Zero drift in ring interferometers with nonmonochromatic-radiation depolarizers

A method is proposed for calculation of the zero drift and Fedding interference signal at the output of a fiber ring interferometer with a circuit made of a weakly anisotropic single-mode fiber lightguide (SMFL) and a depolarizer made of an anisotropic SMFL with a nonmonochromatic radiation source. The fiber is divided into sections equal to the depolarization length in the SMFL. Four FRI circuits all of whose parameters are the same with the exception of the location of the depolarizer are compared theoretically for the first time. Numerical estimates are made. It is shown that an FRI with a Lyot depolarizer located between the polarizer and the circuit is best from a practical point of view. The required precision of assembly of the elements of the Lyot depolarizer is considerably lower than that in the other FRI circuits.Institute of Applied Physics, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 12, pp. 1567–1575, December, 1994.