A POLARIMETRIC CURRENT SENSOR USING AN ORTHOGONALLY POLARIZED DUAL-FREQUENCY FIBER LASER

We demonstrate a novel Er3+-doped fibre laser operating in orthogonall y polarized dual-frequency modes and its application to electric curre nt sensing with frequency read-out. A Faraday rotating mirror and spat ial hole burning effects in a gain medium and in a saturable absorber are utilized to control the lasing mode and polarization. The polariza tion mode beat frequency changes linearly in response to the non-recip rocal circular birefringence induced by an external magnetic field. Wh en the laser was applied to sensing an alternating electric current wi th a simple phase-locked loop signal processing scheme, the slope coef ficient of 8.0 kHz A(p-p)(-1), per turn and the noise equivalent curre nt of 460 mu A(rms) HZ(-1/2) per turn were obtained. The new current s ensor is immune to perturbations in the lead fibres.