Etch‐tuned ridged waveguide magneto‐optic isolator

Isolation ratios as large as 3000 to 1 (−35 dB) at wavelengths near 1.55 μm have been measured on ridged waveguide Faraday rotation isolators. These are the best results ever reported for any waveguide isolator. Single‐mode, triple‐layer bismuth yttrium iron garnet films were chemically etched to reduce the linear birefringence of the active top layer to zero at 1.49 μm. Ion implantation enhanced etching was used to create ridges 8 μm wide and 0.5 μm high. Using fiber coupled light from a tunable color center laser, isolation ratios of −25 dB or better were achieved over a wavelength range of ±0.03 μm near 1.5 μm. A silica overlayer was used to increase the effective thickness of the active layer and raise the optimum wavelength from 1.49 to 1.55 μm.