Rare-earth iron-compound (Terfenol)-based optical phase modulator/magnetometer for use in fiber optic smart-structure sensors

A new fiber optic magnetostrictive phase modulator/magnetometer utilizing the highly magnetostrictive rare-earth iron compound TbxDy1-xFe2 is demonstrated to have a high sensitivity, dynamic range, minimum field detectability, and a better structural suitability than metallic glasses. The experimental linear phase shifting coefficient was 1.102 rad/Vp-m with the corresponding phase shift normalized to the magnetic field of 0.306 rad/G- m. A minimum detectable phase shift of better than 1 (mu) rad was obtained, which corresponds to 2 (mu) G/m for a 4 Hz bandwidth and 1 (mu) G/Hz1/2 per meter of fiber interaction length. The projected minimum detectable magnetic field for 30 meters is thus seen to be 3 pT/Hz1/2.