Reciprocal and quasi-reciprocal Brillouin fiber-optic current sensors

A novel current sensor based on the interaction between two counter-propagating Brillouin fiber-optic lasers has been investigated. Polarization problems specific to current sensors are addressed and are solved by means of a mechanically twisted fiber-ring resonator including a polarization controller. The two proposed reciprocal and quasireciprocal configurations shows a linear response with a sensitivity of 126 Hz/A that is very close to the maximum sensitivity obtained by using fibers without linear birefringence. The limitations of the reciprocal configuration due to the lock-in range, the Kerr effect induced by the pump walk-off and by the pump intensity fluctuations are fully characterized. These limitations are compared with the limitations due to thermal drifts of the quasireciprocal configuration which allows direct detection of the current direction.