Femtosecond pump and probe beams were used to study the transmittance properties of the photonic crystal as a function of the time-delay between the two beam pulses.

When the pump pulse is moved far away from the probe pulse in the temporal sequence, the probe pulse propagates through the photonic crystal. The transmittance of this pulse maintains its maximum value and switching is in the "ON" state. When the pump and probe pulses are at a zero time delay, the transmittance of the probe pulse drops to its minimum value and the switching is in the "OFF" state.

Image Credit: Qihuang Gong