Elimination of birefringence in garnet films for waveguide magneto-optic devices.

The linear birefringence of magneto-optic garnet thin films which interferes with the Faraday rotation in waveguide devices can be reduced to small values by growing multiple films to minimize the shape effect, annealing at high temperatures to reduce the growth-induced effect and growing the films in compression to control the photoelastic effect. The remaining birefringence can be reduced to zero by chemical etching the film until the effects exactly cancel each other at a particular wavelength. The etch-tuning procedure is demonstrated on a double Bi-YIG film at wavelengths of 1.51 and 1.32microns. Extinction ratios of 100 to 1 have been achieved at 45D and 90D Faraday rotations at both wavelengths.