Electric current sensors employing spun highly birefringent optical fibers

The theory of highly elliptically birefringent fibers fabricated by spinning a linearly birefringent fiber during the draw is described. These fibers are particularly interesting for application as Faraday-effect fiber current monitors, since, in contrast to conventional fibers, they can be wound in small multiturn coils while retaining their sensitivity. The fiber and its application in three optical schemes are modeled using Jone calculus and are also experimentally investigated. A simple optical configuration is proposed, combining the elliptically birefringent fiber and a broad-spectrum light source. An accurate, compact, and robust current monitor is obtained. The sensor is characterized by a measurement repeatability of ±0.5%, a temperature drift of 0.05%/°C and a sensitivity of 1 mA RMS/Hz^1/2. Further, the performance of this sensor with optimized fiber length for a given measurement bandwidth is predicted