Ring resonator in a Sagnac interferometer as a birefringence magnifier

A novel birefringence magnification technique that uses a ring resonator in a Sagnac interferometer is proposed and demonstrated. An enhancement factor of 38 was obtained experimentally. The scheme can be used to increase measurement sensitivity to small birefringence and polarization mode dispersion and to decrease the threshold for nonlinear switching and laser mode locking by a Sagnac interferometer.