Fluctuations of the phase shift between opposite waves in a fiber ring interferometer

A study is made of the influence of homogeneous steady-state fluctuations of the permittivity of an optical fiber on the phase shift between opposite waves propagating in the fiber. The first order of perturbation theory is employed in deriving expressions for the spectral intensity of fluctuations of the phase shift. It is shown that the error in the determination of the angular velocity due to these fluctuations may be considerable.