Magneto-optical garnet waveguides on semiconductor platforms: Magnetics, mechanics, and photonics

Garnet films with thicknesses of 100-1000 nm and waveguides with widths of 700-2000 nm were grown onto Si to characterize the mechanical stresses that occurred upon crystallization (700-800°C) by rapid thermal annealing. These magneto-optical garnet films and also photonic crystals have proposed uses in magnetic flux indicator films, integrated photonic devices, such as isolators, circulators, and polarization transformers, because their Verdet constants per unit loss are orders of magnitude better than other magneto-optical materials. However, garnet does not match Si-based materials mechanically with thermal expansion coefficients of 10.4 ppm/°C. These waveguides were optimized to have low losses in the near infrared, including the telecommunication wavelengths (1.0-2.3 dB/mm at 1.3 μm and 0.9-1.7 at 1.55 μm). The waveguide losses increased with waveguide width. Finite difference time domain simulations were used to estimate the number, effective index, and profile of modes in each guide. The polarization and localization of modes near guide surfaces effectively explain the trend in losses versus width. With Faraday rotations of 0.2 dB/m and 1.0 dB/mm loss, this integrated garnet has great potential for a multitude of photonic devices, including isolators, circulators, and mode converters.