Coupled microresonators are expected to play a key role in slow-light engineering and various types of light-matter interaction enhancement, especially if they are based on small and high-Q cavities. Although rapid progress has been made on microresonator performance, large-scale arrays of coupled resonators based on high-Q wavelength-sized cavities have not yet been realized. Here, we show large-scale (N>100) ultrahigh-Q coupled nanocavity arrays based on photonic crystals. This is the first demonstration of large-scale coupled resonator arrays based on wavelength-sized cavities, in which tight-binding sinusoidal dispersion is seen. We confirm that an ultrahigh value of Q (∼1×106) is maintained, even when N is large, and the resonators exhibit very low loss characteristics with regard to light propagation. The ultrahigh value of Q and small size has enabled us to achieve ultraslow light pulse propagation with a group velocity well below 0.01c and a long group delay.
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