A novel reflective fiber interferometer with non-reciprocal phase modulation adapted from Sagnac-type fiber
interferometers is used to measure the differential optical phase shift in polarimetric fiber sensors. The sensitive part
consists of two birefringent fiber sections with balanced differential group delay. A key element is a 45°-Faraday-rotator
that swaps the polarization states of the orthogonal light waves after their round trip through the two fiber sections.
An integrated-optic birefringent phase modulator at the detector end of the sensor introduces the non-reciprocal phase
modulation. The application of the interferometer to voltage sensing is experimentally demonstrated.