Realization of on-chip lasers in crystalline double tungstate waveguides using focused-ion-beam nanostructuring

We report our recent work on obtaining on-chip lasers in crystalline double tungstate waveguides using focused-ion-beam (FIB) nanostructuring. Photonic cavity structures were defined by forming deeply etched Bragg gratings in KGdxLu1-x(WO4)2:Yb 3+ using FIB milling. The FIB milling procedure was optimized and gratings more than 4 μm in depth with an improved total sidewall angle of about 5 were achieved. Their optical performance was assessed at 1530 nm in Fabry-Pérot microcavities realized on the waveguides. An on-chip integrated laser cavity at 980 nm was achieved by defining a FIB reflective grating and FIB-polished waveguide end-facet. With this cavity, an on-chip integrated waveguide laser in crystalline potassium double tungstate was demonstrated for the first time.