Optical moiré bound states in the continuum

Trapping electromagnetic waves within the radiation continuum holds significant implications in the field of optical science and technology. Photonic bound states in the continuum (BICs) present a distinctive approach for achieving this functionality, offering potential applications in laser systems, sensing technologies, and other domains. However, the simultaneous achievement of high Q-factors, flat-band dispersions, and wide-angle responses in photonic BICs has not yet been reported, thereby impeding their practical performance due to laser direction deviation or sample disorder. Here, we theoretically demonstrate the construction of moir & eacute; BICs in one-dimensional photonic crystal (PhC) slabs, where high-Q resonances in the entire moir & eacute; flat band are achieved. Specifically, we numerically validate that the radiation loss of moir & eacute; BICs can be eliminated by aligning multiple topological polarization charges with all diffraction channels, enabling the strong suppression of far-field radiation from the entire moir & eacute; band. This leads to a slow decay of Q-factors away from moir & eacute; BICs in the momentum space. Moreover, it is found that Q-factors of the moir & eacute; flat band can still maintain at a high level with structural disorder. In experiments, we fabricate the designed 1D moir & eacute; PhC slab and observe both high-Q resonances and a slow decrease of Q-factors for moir & eacute; flat-band Bloch modes. Our findings hold promising implications for designing highly efficient optical devices with wide-angle responses and introduce a novel avenue for exploring BICs in moir & eacute; superlattices. Trapping electromagnetic waves within the radiation continuum has significant implications in lasers and sensing. Here the authors achieved a moir & eacute; BIC in a photonic crystal slab, demonstrating simultaneous flat-band dispersing and high-Q features within a wide-angle regime.