RECIPROCAL REFLECTION INTERFEROMETER FOR A FIBEROPTIC FARADAY CURRENTSENSOR

A reciprocal fiber-optic reflection interferometer for remote measurem ent of electrical current through the Faraday effect is described. The effects of polarization cross coupling because of nonideal elements a re eliminated with a low-coherence source. Nonreciprocal birefringence phase modulation is employed for detection of the Faraday phase shift . The theoretical predictions are confirmed by measurements with a pie ce of straight fiber as the sensing element in a 100-turn solenoid. Cu rrents from 0 to 40 A have been measured with a linear response and a noise limit of approximately 0.015 A/square-root Hz.