Inverse Design of Nonlinear Polaritonic Metasurfaces for Second Harmonic Generation

Enabling strong nonlinear optical phenomena requires carefully designed photonic devices to maximize light- matter interactions. In recent years, topology optimization has become an increasingly popular tool to optimize photonic devices, due to its efficiency in dealing with extremely large parameter spaces. The focus has largely been on two-dimensional linear optical devices, particularly in integrated photonic settings, with a limited number of studies extending topology optimization to nonlinear effects in dielectric structures. Here, we apply topology optimization to metal-multiple quantum well-metal structures supporting intersubband transitions. In past years, the combination of photonic engineering and material design has enabled extremely efficient ultrathin second harmonic generating metasurfaces, based on L-and T-shaped resonators. Topology optimization enables novel designs that exceed the state-of-the-art nonlinear metasurfaces to date, with the promise of further improvement. The same approach may be extended to other frequency mixing phenomena, such as sum-frequency or difference-frequency generation.