Focused-ion-beam nanostructured photonic cavities for integrated lasers in crystalline double tungstate channel waveguides

In this work, the authors report utilization and optimization of the focused ion beam (FIB) milling technique for fabrication of grating structures to obtain integrated active photonic devices. The ridge waveguides in the KGLW:Yb³⁺ layers were aligned along the Ng optical axis of the material to make use of the large emission cross-section of the active ions when operated in TE polarization. The active film thickness was 1.92 μm, etched down by a depth of 1.2 μm using Ar⁺ milling. The resulting ridge waveguides had widths varying between 5 and 8 μm. Finally, a 1-μm-thick Si₃N₄ film was deposited by plasma-enhanced chemical vapour deposition as a top cladding layer to increase the overlap of the optical mode with the active waveguide region.