Method for determination of the polarisation nonreciprocity in a fibre ring interferometer

A method is proposed for observation of the polarisation nonreciprocity of fibre ring interferometers (FRIs) by placing a rotating polariser at the ou tput of an interferometer ahead of a photodetector. It is demonstrated theo retically and experimentally that the absence of a signal for any position of the transmission axis of the polariser at the FRI output is a criterion of the absence of the polarisation nonreciprocity. It is suggested that the coaxial alignment of the anisotropic FRI components be monitored during as sembly to ensure the polarisation nonreciprocity on the basis of the absenc e of a signal at the output of a rotating polariser. It is also shown that, when the conditions for the polarisation nonreciprocity are fulfilled, the signal from the output of a beam splitter located flush against the fibre loop output carries information about the phase characteristics of the beam splitter.