Polarization independent nonlinear fiber sagnac inteferometer

In general, the propagation of light in a twisted, birefringent fiber evolves with a period and phase change non-linearly dependent on the initial polarization state. We show both analytically and numerically that a critical value for the ratio of twist rate to birefringence can he chosen so that the period and nonlinear phase change are no longer sensitive to the input polarization state. This makes possible the design of a input-state independent Sagnac interferometer for mode-locked laser applications. (C) 2000 Published by Elsevier Science B.V.