The optical response of bilayer moiré photonic structures can be precisely controlled by varying the lattice geometry. Bilayer moiré photonic crystal slabs exhibit flat bands in the optical band structure, where the optical modes have zero group velocity. They also give rise to momentum-independent light-trapping of Bloch waves in both transverse and vertical directions, leading to high quality-factors ([Formula: see text]) and small mode volumes ([Formula: see text]). The large Q and small V lead to a large Purcell enhancement ([Formula: see text]), providing opportunities for low-threshold lasing, enhancement of optical nonlinearities, and quantum information processing.

Recently, twisted bilayer photonic materials have been extensively used for creating and studying photonic tunability through interlayer couplings. While twisted bilayer photonic materials have been experimentally demonstrated in microwave regimes, a robust platform for experimentally measuring optical frequencies has been elusive. Here, we demonstrate the first on-chip optical twisted bilayer photonic crystal with twist angle–tunable dispersion and great simulation-experiment agreement. Our results reveal a highly tunable band structure of twisted bilayer photonic crystals due to moiré scattering. This work opens the door to realizing unconventional twisted bilayer properties and novel applications in optical frequency regimes.

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