OPTICAL ABSORPTION OF Bi-SUBSTITUTED IRON GARNET LPE FILMS FOR 0.8 μm OPTICAL ISOLATOR

Bi-substituted gadolinium iron garnet grown by an LPE method on Ca,Zr,Mg-doped GGG substrate is a promising material for use in 0.8 μm wavelength band optical isolator. We have investigated the effect of Mg2+ -, Si4+ -, and In3+ -doping to the melt and film annealing on optical absorption. The experimental result shows that optical sbsorption coefficient of as-grown films at 0.8 μm decreased with decreasing Mg2+ -doping and increasing Si4+ -doping levels. The absorption coefficients also decreased by annealing at 800°C down to 52-55 cm-1. The effect of annealing on optical absorption would be mainly caused by reduction of Fe3+ absorption at 0.7 μm. For Mg2+ -doped films annealed at 800°C in N2 atmosphere, high figure of merit of 27.3 deg/dB (1.65 dB loss for 45 degree rotation) was attained. The results of In3+ -doping are mentioned, too.