3 × 3 coupler based interferometric magnetic field sensor using a TbDyFe rod

An all-fiber magnetic field sensor by using a TbDyFe rod as the sensing element for the measurement of the weak alternating magnetic field is presented and experimentally demonstrated. The sensor is constructed with a 3 × 3 coupler based Mach-Zehnder interferometer, and the time-varying phase shift induced by the applied magnetic field is recovered by using a passive demodulation method. The experimental results show that the sensor exhibits excellent linearity and reversibility within 0-75 μT (residual mean square), and a high sensitivity of 69.83 mrad/μT (residual mean square) with a resolution of 2.14 nT/√Hz (residual mean square) at 200 Hz is experimentally achieved. The frequency response and the temperature characteristic of the sensor are also investigated.