Magneto-Optical Sensing Utilizing the Faraday Effect in Bulk Cd₁₋ₓMnₓTe

A magnetic field sensor utilizing the Faraday effect in bulk Cd1-xMnxTe was investigated. The magnetic field sensitivity was found theoretically as a function of various system parameters and compared with experiment. The magneto-optical Verdet constant of Cd.5Mn.5Te was measured at a wavelength of 633 nm, and found to be 0.15° cm-1Gauss-1. The optical absorption was measured to be 0.9cm-1, and the refractive index 3.1; all values agreed well with published measurements. A polarization preserving fiber was used to link the Cd.5Mn.5Te sensor in a polarization-rotated reflection scheme in order to cancel environmentally induced linear birefringence fluctuations which contribute to system noise. The linear birefringence fluctuations were modeled as a gaussian distributed random variable and included in the formulation of the sensing system\u27s signal-to-noise ratio. Since the standard deviation of the birefringence fluctuations was not known a priori, its value was chosen to match theory with experiment, and then compared with data fro recently published papers examining the statistics of linear birefringence fluctuations in polarization-preserving fibers; published values of the standard deviation of birefringence fluctuations for a given environmental perturbation compared reasonably with values inferred from our experimental data. Experimental results showed a marked improvement in the magnetic sensor\u27s signal-to-noise ratio using this method of polarization-rotated reflection