Single Mode Fiber Optic Sensor For High Currents

We are developing a pulsed current sensor that will be less intrusive than present sensors and that we hope will remain linear to much higher current levels. Polarized laser light is transmited by a low-birefringence, single mode optical fiber that encircles the current carrier. We observe the Faraday rotation of the polarization plane in the current-induced magnetic field. We have measured a Verdet constant of about 260/sup 0//MA for 633 nm light in Lightwave Technologies, Inc., Model F1506C fiber, and we have detected currents of up to 12 MA in pulses 0.5 to 40 ..mu..s long. Our major problems have involved signal noise from stray plasma light getting into the fiber and shock-induced birefringence that rotates the polarization slightly. Future plans are to try to Sagnac interferometer to reduce the sensitivity to shock waves.