Fiber optic magnetic field sensor based on domain wall motion in garnet film waveguides

A novel fiber optic magnetometer based on the Faraday effect in a magnetic garnet thin-film ridged waveguide is described. The single-mode film has planar magnetization aligned parallel and antiparallel to the light propagation direction by a gradient bias field, and a single domain wall crosses the light path. The motion of this wall in response to an applied field changes the Faraday rotation in the film. Operation of this field or current sensor in both the transmission mode and the single fiber reflection mode has been demonstrated. Optical output varying linearly with ac or dc fields up to 15 Oe, with a minimum detectable field of 0.05 Oe, has been observed. This domain wall motion scheme in a zero birefringence waveguide can also be used in a polarization controller.