Faraday effect and the modulation of infrared radiation in iron garnets

Iron garnets, which are transparent ferromagnetics possessing record high values of the magneto-optic figure of merit, were used to obtain pulsed magneto-optic light modulation. Modulators with a closed magnetic circuit were placed in a constant external magnetic field, perpendicular to the direction of light propagation. Light pulses of 1 and 10 μsec duration with rise times of the order of 0.2 μsec were obtained. There were no intensity oscillations after the end of a pulse, in contrast to piezoelectric resonance oscillations observed for pulses of this duration in electro-optic modulators. The modulation depth in Y₃Fe₅O₁₂ and Y₃Ga_0.8Fe_4.2O₁₂ modulators was 70% for control currents of respectively 80 and 4.5 mA.