Remotely-Interrogated Three-Axis Fiber Laser Magnetometer

A fiber optic magnetic field sensor node designed for seabed-mounted surveillance arrays, incorporating three orthogonally mounted magnetic field sensors and a microelectomechancial systems inclinometer, is described. Each sensor comprises a current carrying nonmagnetic bridge, which experiences the Lorentz force generated in a magnetic field. A metalized fiber laser attached to the bridge measures the induced strain. The operating principle and fundamental performance of the sensor as well as relevant performance parameters are described. Measured data illustrating the sensor and node performance in laboratory tests are presented. Less than 2 nanoTesla/Hz
^1/2
resolution at frequencies from 0.002 to 10 Hz is achieved with only 75 mA-rms of current. The sensor node is separated from the interrogation electronics with a 1-km fiber optic cable (extendable to 10 km) and qualified to an operating depth of 100 m. Methods to further improve the magnetometer performance are also discussed.