Elimination of birefringence in garnet films for magneto-optic waveguide 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 multilayer 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 chemically etching the film until the effects exactly cancel each other at a particular wavelength. This etch-tuning procedure is demonstrated on a two-layer bismuth-yttrium iron garnet (Bi-YIG) film at wavelengths of 1.51 and 1.32 μm. Extinction ratios of 100 to 1 have been achieved at 45° and 90° Faraday rotations at both wavelengths.