Faraday-rotation-based miniature magnetic field sensor using polarimetric heterodyning fiber grating laser

A polarimetric heterodyning fiber grating laser is proposed to sense a magnetic field. When a magnetic field is parallel to the fiber grating laser, a circular birefringence is induced into the laser cavity. An elliptical birefringence results due to the circular birefringence and the intrinsic linear birefringence of the laser cavity. The elliptical birefringence is translated to the beat note frequency between the two orthogonally polarized laser outputs after photodetection. Confirmed by experiment results, it shows that the beat note frequency shift is proportional to the square of the magnetic field magnitude. Because the fiber laser is as short as less than 2 cm, a miniature magnetic field sensor is then demonstrated in principle.