Tailoring Flatband Dispersion in Bilayer Moir\'e Photonic Crystals

In this study, we experimentally investigate the photonic dispersion in one-dimensional moir\'e structures formed by stacking two photonic crystal slabs with slightly different periods, separated by a carefully controlled subwavelength optical spacer. Angle-resolved reflectivity measurements reveal moir\'e bands arising from the interplay between intra- and inter-layer coupling mechanisms of guided modes mediated by the moir\'e superlattice corrugation. By precisely adjusting the refractive index contrast through the filling factor of the photonic crystals, we continuously tune intralayer coupling while keeping interlayer coupling constant. Consequently, we experimentally demonstrate the evolution of moir\'e minibands into flatbands characterized by minimal dispersion bandwidth. All experimental results show good agreement with numerical simulations. Our findings not only confirm theoretical predictions but also provide a practical approach for realizing photonic flatbands in silicon-based moir\'e 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.