A performance study of dielectric metalens with process-induced defects

Metalenses based on dielectric nanostructures operating in the transmission mode are of great practical significances. As large-area, multifunctional metalenses are increasingly demanded at higher volumes nowadays, the quality and efficiency of the nanofabrication processes for these lenses are made even more important. Yet, no fabrication is without defects or errors. Using numerical calculation by finite-difference time-domain (FDTD) method, we study, in simulation, a set of common fabrication-induced errors such as inclined sidewall, critical dimension (CD) bias and process defects, and analyze their influences on the optical performances of two types of metalenses - one made of amorphous silicon and the other of silicon nitride. The study concludes that the lens behavior generally relies on the resonant nature of the nanostructure array. While most types of defects discussed in this work linearly decrease the focusing efficiency, a few would also influence the quality of the focal spot. Potential solutions to mitigate the effect of the process-induced defects are also investigated. The study provides the particular knowledge to understand the actual metalens performance when fabricated.