The Sagnac interferometer as a two-parameter sensor

We show the Sagnac interferometer as a two-parameter sensing device where nonreciprocal and reciprocal effects can be independently and simultaneously monitored. Phase shifts induced by nonreciprocal effects affect differently the counterpropagating beams in the loop and are accurately detected by a phase sensitive detection scheme. A probe for reciprocal effects is built by introducing a birefringence modulator inside the polarization-maintaining loop with its axes rotated with respect to the axes of the loop fiber. The resulting quadrature component of the demodulated signal is proportional to the phase shift induced by reciprocal effects at the probe site, making the interferometer suitable for dual parameter sensing. Demonstration of a electric/magnetic field sensor is presented. >