Optical fiber magnetic field sensor

The invention discloses an optical fiber magnetic field sensor. The optical fiber magnetic field sensor is formed by a light source, a coupler, a Y-shaped waveguide, a polarization beam splitter, an optical fiber ring, a 90-degree faraday optical rotation reflecting mirror and a photoelectric detector; light emitted from an SLD (Super Luminescent Diode) light source reaches the Y-shaped waveguide to form two beams of linearly polarized light after the light passes through the coupler; the two beams of linearly polarized light pass through the polarization beam splitter, and the polarization beam splitter enables one beam of linearly polarized light and the other beam of polarized light to be transmitted in a polarization maintaining optical fiber in an orthographic mode after the polarization direction of the linearly polarized light is rotated by 90 degrees; phase difference can be generated when the linearly polarized light and the polarized light pass through the optical fiber in an axial magnetic field; polarization modes can be mutually exchanged after the two beams of polarized lights carrying phase information are reflected through the 90-degree faraday optical rotation reflecting mirror; phase difference can be generated again when the two beams of polarized lights return to the optical fiber in the axial magnetic field; the two beams of linearly polarized lights in the orthographic mode are divided into two beams of linearly polarized light which are transmitted in a parallel mode after reversely passing through the polarization beam splitter, and interference can be generated when the two beams of linearly polarized light which are transmitted in the parallel mode reach the Y-shaped waveguide; light carrying interference phase information can be detected by a signal processing circuit after returning to the detector.