Ultrafast and low-power photonic crystal all-optical switching with resonant cavities

We theoretically investigate and discuss the response time, switching contrast, and pump power of all-optical switching in a nonlinear photonic crystal structure with high quality factor (high-Q) cavity. For the response time of all-optical switching, the drop and rise time are considered, respectively. Moreover, we find that when the duration of pump pulse is shorter than the lifetime, the response curve of all-optical switching is asymmetric, and the drop time is determined by both the lifetime of high-Q cavity and duration of pump pulse, and the rise time is mainly determined by lifetime of high-Q cavity. In contrast, when the duration of pump pulse is much longer than the lifetime, the dynamic response curve is symmetric, and both the drop and rise time are determined by the duration of pump pulse. On the other hand, the pump power can be significantly reduced by using a setup where the probe beam is located at the high-Q cavity mode with very narrow linewidth. Furthermore, if the central wavelength of pump pulse is also set to match with this or another high-Q cavity mode, the pump power will be reduced further due to the large field enhancement within the photonic crystal, and more importantly there is no extra prolonged response time of all-optical switching. By this method, the pump power as low as 210 KW/cm² is observed in our model structure with the quality factor of only 32 096 for the ordinary polystyrene material.