Passive interferometric interrogation of a magnetic field sensor using an erbium doped fiber optic laser with magnetostrictive transducer

• Power and wavelength stability of the erbium-doped fiber optic laser was ensured by modulating both mirrors (FBGs—Fiber Bragg Gratings) with the same magneto-restrictive element.
• High resolution of the interferometric readout system was provided by the laser high SNR (Signal to Noise Ratio) and narrower bandwidth.
• Laser wavelength variation was read using a passive interferometer producing three outputs with 120 degrees phase difference between them.
• High flexibility on performing customizations such as gain adjustment and compensation of the interferometer drift caused by environmental fluctuations was ensured by implementing the demodulation algorithm in software. Two distinct demodulation algorithms are implemented and its performance evaluated.
• Sensitivity of the laser response to AC magnetic fields was controlled by tuning the DC magnetic field from 0 to 16.47 mT.

An erbium doped (Er3+) fiber optic laser is proposed for magnetic field measurement. A pair of FBGs glued onto a magnetostrictive material (Terfenol-D rod) modulates the laser wavelength operation when subject to a static or a time dependent magnetic field. A passive interferometer is employed to measure the laser wavelength changes due to the applied magnetic field. A data acquisition hardware and a LabVIEW software measure three phase-shifted signals at the output coupler of the interferometer and process them using two distinct demodulation algorithms. Results show that sensitivity to varying magnetic fields can be tuned by introducing a biasing magnetic field. A maximum error of 0.79% was found, for magnetic fields higher than 2.26 mTRMS.