Optical magnetic field sensors with high linearity using Bi-substituted rare earth iron garnets

Optical magnetic field sensors with high linearity were developed. Bi-substituted rare earth iron garnets were prepared using the liquid phase epitaxy method for use as the Faraday rotators of the sensors. The linearity error of the sensor output was obtained within 1.0% for alternating magnetic fields of up to 300 Oe. The sensor optical system has a new converged beam optical system using ball lenses. The linearity of these sensors is much better than that of sensors using a collimated beam optical system with graded index lenses. Sensors using the collimated beam optical system are nonlinear, since only the zeroth-order beam diffracted by the garnet maze domains is detected. Sensors using the converged beam optical system have high linearity because of the detection of diffracted beams up to the second-order. The experimental results agreed well with the calculated results.