Trapping and delaying light with an ultrahigh-Q photonic crystal nanocavity

We have fabricated a photonic crystal (PhC) nanocavity based on a width-modulated line defect and investigated it in the time domain. The obtained quality factor (Q) was extremely high, 1.2×10⁶, which corresponds to a photon lifetime of 1 ns. The photon lifetime was directly measured in the time domain using the ring-down method-a technique that has the potential to provide detailed information about the temporal dynamics of PhC nanocavity systems. Indeed, we investigated the dynamic tuning of Q and the pulse transmission using a similar technique. In the pulse transmission experiment, the pulse exhibited ultraslow propagation with a group velocity of 5.8 km/s. The demonstration of slow light on a chip paves the way for the development of various quantum and classical integrated devices.