Elimination of residual signals and reduction of noise in a low-frequency magnetic fiber sensor

Low-frequency sensitivities of interferometric magnetic fiber optic sensors have been limited by the presence of a large residual signal at the dither frequency which limits the dynamic range and upconverts low-frequency noise into sideband noise around the carrier. We present an operating regime that enables us to eliminate residual signals associated with the ac carrier. By choosing the proper carrier frequency and amplitude we obtain a nulled residual signal, strong magnetomechanical coupling, and an increase in signal-to-noise ratio of approximately 13 dB over previously reported results. A minimum detectable field of 45 pT/(Hz)1/2 at 0.1 Hz is demonstrated.