Highly efficient Cherenkov-type second harmonic generation in a Ta2O5/KTiOPO4 waveguide

Abstract
Highly efficient Cherenkov‐type second harmonic generation is investigated. The waveguide is composed of a KTiOPO4 substrate, a Ta2O5 thin‐film core and a SiO2 clad in the strip‐loaded configuration. The conversion efficiency strongly depends on the waveguide geometry, and it can be a maximum for a particular Ta2O5 film thickness with a Cherenkov angle of nearly 0°. This maximum efficiency is further increased by narrowing the waveguide width down to 1.8 μm. Consequently, a normalized conversion efficiency of 210%/W cm and a blue second harmonic power of 28 mW were achieved with the 4.5‐mm‐long waveguide.