A Passive Phase Recovery Technique for Sagnac Interferometers Based on Controlled Loop Birefringence

We analyse the polarization and phase properties of the birefringent Sagnac interferometer in the case of a polarized source. We show that control of loop birefringence allows an arbitrary phase difference to be imposed upon the counter-propagating beams for any source polarization state, with control over the relative states of polarization of the recombining beams. We show how this may be achieved using one half-wave and two quarter-wave plates. We discuss the application of this method in fibre-optic sensors.