Three-axis fiber optic vector magnetometer

Abstract

A three-axis fiber optic vector magnetometer is provided for measuring both he direction and magnitude of a DC or low frequency magnetic field. The magnetometer includes an optical interferometer system including a sensing fiber arm disposed with three respective sensing portions perpendicular to one another and attached to a uni-directional sensor material. The interferometer system also includes a reference fiber arm and a laser light source for generating and introducing a laser light into both of the arms. Respective biasing devices generate a reference AC magnetic bias and a respective reference frequency in the three sensing portions. A detecting device detects a reference light signal from the reference fiber arm and the magnetically altered sensing light signal from the sensing fiber arm and forms an interferometer output signal. Respective separating devices then separate the respective magnetically induced interferometer signals at respective ones of the frequencies and produce a respective output signal indicative thereof. This output signal is thus indicative of the magnetic field strength in the respective direction and a vector sum of the strengths shows the magnetic field direction. Preferably, the sensor material is an annealed amorphous metallic glass strip and the separating means are lock-in amplifiers in their phase sensitive detection modes. The biasing devices are also preferably respective Helmholtz coils and a feedback system is provided for feeding back the output of the respective separating devices to the respective biasing devices.