Magneto-optic sensors based on iron garnets

As an alternative to bulk transducers, iron garnet films offer cost, fabrication, and performance advantages. Though films can be used in polarimetric systems, a simpler approach exploits the diffraction arising from serpentine domains in thin films. When a saturating field perpendicular to the film is applied, the light is not diffracted and couples into a receiving fiber with high transmission. The diffractive thin-film sensor requires no polarizer, but only a source, detector, 2x2 coupler, lens, and reflective film. It been applied to rotation sensing where magnetized teeth change the transducer transmission so that motion is sensed. Recently, we demonstrated an even simpler system that eliminates the 2x2 coupler and detector. In this system, light retroreflected back to the laser is detected by monitoring the laser terminal voltage as constant current is applied. The method exhibits polarization effects that may require compensation, but has been recently demonstrated using a thin-film magneto-optic sensor.