Current sensor using heterodyne detection

Based on the Faraday effect for measuring ac current, we describe a fiber-o ptic sensor that uses laser-diode intensity modulation to perform heterodyn e signal detection. The sensor output at the carrier frequency is used as a reference signal to normalize the results. The sensing element consists of a few coils low-birefringence fibers between polarizers. We built the curr ent sensor described above and tested its performance-sensitivity and noise -as functions of the angle between polarizers. (C) 1999 Optical Society of America.