Integrated lasers in crystalline double tungstates with focused-ion-beam nanostructured photonic cavities

Deeply etched Bragg gratings were fabricated by focused ion beam (FIB) milling in KGdxLu1-x(WO4)2:Yb3+ to obtain photonic cavity structures. By optimizing parameters such as dose per area, dwell time and pixel resolution the redeposition effects were minimized and grating structures more than 4 µm in depth with an improved sidewall angle of ~5 degrees were achieved. Fabry-Perot microcavities were defined and used to assess the optical performance of the grating structures at ~1530 nm. 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.