Temporal cloak has been widely studied in recent years. It is an analogy with spatial cloak from the space-time duality associated with diffraction and dispersion. Different temporal cloak schemes have been proposed. One of the key elements to achieve temporal cloak is dispersion system. It is to create a temporal gap by modulating the group velocity, inside which an event occurs. Traditional ways to realize slow or fast light include EIT, CPO, photonic crystal waveguides and optical fibers. Normally, the temporal gap need to reach the lever of nanosecond, then event such as modulator can be practically operated in the temporal gap.

In this work, we demonstrated a tunable temporal gap based on simultaneous fast and slow light in electro-optic photonic crystals. The light experiences an anomalous dispersion near the transmission center and a normal dispersion away from the center, where it can be accelerated and slowed down, respectively. We also obtained the switch between fast and slow light by adjusting the external electric filed. The observed largest temporal gap is 541 ps, which is crucial in practical event operation inside the gap. The results offer a new solution for temporal cloak.

This work was published on Optics Express, 23(14), 18345-18350 (2015).