IMPROVEMENT OF TEMPERATURE DEPENDENCE OF FARADAY ROTATION USING TWO LAYER EPITAXIAL FILMS IN (BiR)IG FOR OPTICAL ISOLATORS

Abstract

The temperature dependence of Faraday rotation in the practical temperature range was improved using the two-step-epitaxial method. Two series of compensation films to decrease the temperature dependence of Faraday rotation were attempeted: (1) Tb-garnet films (2) highly Ga-substituted (BiGd)₃ (FeGa)₅ O₁₂ films. The temperature coefficients of Faraday rotation at 45 degrees (≡ β deg/°C) were measured. In the case of series (2), (BiLuGd)IG/(BiGd)(FeGa)G films with β=0.00 deg/°C were obtained. The total film thickness was 0.58 mm at λ= 1.3 μm, and that was 0.89 mm at λ= 1.55 μm, respectively. The extinction ratio was 38 dB at both wavelengths. In the case of series (1), the Faraday rotation and compensation effect were smaller than those from Crosseley's model. Pb contamination and canting of Tb-sublattice magnetization are plausible causes of the disagreement.