How many supercells are required for unconventional light confinement in moiré photonic lattices?

Abstract

Moiré structures are receiving increasing attention in nanophotonics as they support intriguing optical phenomena. In the so-called “magic configuration,” one-dimensional moirés give rise to fully dispersionless energy bands known as “flatbands,” where the light is tightly localized within each supercell of the periodic moiré. The goal of this investigation is to determine to what extent the confinement of light, observed in periodic structures, is preserved in microcavities of finite size. Here we analyze the optical response of finite moiré structures consisting of one, two, or more supercells of 1D moiré. Our calculations reveal that for a single-supercell cavity, the magic configuration does not impact the electric field confinement at the wavelength of the flatband modes. However, when three or more supercells are connected, we show that the coupling between supercells is canceled at the “magic configuration,” resulting in highly confined modes with a quality factor greater than 106 and exhibiting the characteristics of a quasi-bound state in the continuum where optical losses are eliminated through a destructive interference process.