A novel miniature magnetic field sensor based on Faraday effect using a heterodyning fiber grating laser

An orthogonally polarized dual-frequency fiber grating laser is exploited to sense magnetic field in this paper. It shows that the fiber grating laser is sensitive to axial magnetic field through Faraday effect, which results in the beat frequency shift after photodetction of the laser output. The axial magnetic field induces a circular birefringence into the laser cavity, which combines with the intrinsic linear birefringence of the laser cavity to form an elliptical birefringence. The elliptical birefringence is then translated to the beat note frequency through heterodyning between the two orthogonally polarized laser outputs after photodetection. Because the fiber laser is as short as less than 2 cm, a novel miniature magnetic field sensor is then demonstrated.