High-index-contrast potassium double tungstate waveguides enabled by heterogeneous integration

Rare-earth-ion doped potassium double tungstate [KY(WO4)2] waveguide amplifiers are of interest due to high-gain amplification at high-bit rates with low noise figure. The fabrication of such waveguide amplifiers is conventionally based on overgrowing an active layer on a host KY(WO4)2 crystalline material. These devices exhibit low refractive index contrast, typically <0.02, consequently requiring large optical pump power to invert the active material. In this work, we have successfully demonstrated heterogeneous integration of KY(WO4)2 (n ≈ 2) with a silicon dioxide (n ≈ 1.44) carrier. Focused ion beam milling was used to fabricate high-index-contrast waveguides, permitting the realization of efficient amplifiers when doped with rare-earth-ions.