Fiber-optic Michelson magnetic field sensor based on a mechanical amplifier structure

A magnetic field sensor based on a mechanical amplifier structure is proposed and experimentally demonstrated. The sensor is composed of a 3×3 coupler-based Michelson interferometer. The magnetic field transducer is a mechanical amplifier structure, in which a TbDyFe rod is wrapped by the polarization-maintaining (PM) fiber. The deformation produced by the TbDyFe rod is amplified and transferred to the PM fiber, causing the fiber length to change. The time-varying phase shift caused by the applied magnetic field is recovered by a passive demodulation method. Experimental results show that the average magnetic field sensitivity of the sensor is 0.4471 V/µT (rms), corresponding to a phase shift sensitivity of 0.2581 rad/µT (rms) and minimum detectable magnetic field of 0.0755 nT/√Hz (rms). The maximum response time is 22.77 ms. The proposed magnetic sensor has a simple design with fast response time and is preferable for detecting weak magnetic fields.