Adiabatic frequency shifting is demonstrated by tuning an ultrahigh-Q photonic crystal nanocavity dynamically. By resolving the output temporally and spectrally, we showed that the frequency of the light in the cavity follows the cavity resonance shift and remains in a single mode throughout the process. This confirmed unambiguously that the frequency shift results from the adiabatic tuning. We have employed this process to achieve the dynamic release of a trapped light from an ultrahigh-Q cavity and thus generate a short pulse. This approach provides a simple way of tuning Q dynamically.
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