Tailoring Flatband Dispersion in Bilayer Moiré Photonic Crystals

Abstract

In this study, the photonic dispersion in 1D moiré structures formed by stacking two photonic crystal slabs with slightly different periods, separated by a carefully controlled subwavelength optical spacer, is experimentally investigated. Angle-resolved reflectivity measurements reveal moiré bands arising from the interplay between intra- and inter-layer coupling mechanisms of guided modes mediated by the moiré superlattice corrugation. By precisely adjusting the refractive index contrast through the filling factor of the photonic crystals, intralayer coupling is continuously tuned while keeping interlayer coupling constant. Consequently, the evolution of moiré minibands into flatbands characterized by minimal dispersion bandwidth is experimentally demonstrated. All experimental results show good agreement with numerical simulations. The findings not only confirm theoretical predictions but also provide a practical approach for realizing photonic flatbands in silicon-based moiré superlattices operating in the telecom wavelength range. This work paves the way toward harnessing flatband physics in advanced optoelectronic applications such as lasers and optical sensors.