Optical waveguide facet preparation using programmable focused ion beam sculpting

One of the many processing steps for photonic device fabrication is the preparation of low-loss optical facets for fiber-chip, and chip-chip coupling. This article presents a method for facet preparation using focused ion beam (FIB) sculpting. The technique is demonstrated using commercially prepared silicon nitride waveguides. The facets exhibit coupling loss dominated by modal mismatch and are consistent with high optical quality in terms of micro-roughness and optical scattering. The process takes 30 s per facet using a FIB current of 15 nA. Higher beam currents result in the deformation of the waveguide facet with concomitant increased coupling loss. A proof-of-concept automated process is demonstrated in which 22 facets are prepared without user oversight. The programmable nature of this approach suggests a material-agnostic FIB process for facet preparation of waveguides for systems of chips integrated on a single carrier. The FIB process also has the potential to prepare alignment locators for fibers or other elements requiring optical integration.