Nonlinear all-optical switch based on a white-light cavity

It is well known that there is a bottleneck for nonlinear all-optical switching, namely, the switching power and the switching time cannot be lowered simultaneously. A lower switching power requires a resonator with a high quality (Q) factor, but leads to a longer switching time. We propose to overcome this bottleneck by replacing the nonlinear cavity in such an all-optical switch by a white-light cavity. This can be done by doping three-level atoms in the ring resonator and applying incoherent pump and coherent driving fields on it. The white-light cavity possesses broadband resonance in a linear region. Therefore, for the incident pulse, a broad range of frequency components can take part in the nonlinear process, and so it requires lower power to achieve switching compared to the conventional ring resonator. On the other hand, the refractive index of a white-light cavity has negative dispersion, leading to a fast group velocity. This results in a shorter time to build up the resonant response, yielding a short switching time.