Observation of ultra-low-light-level all-optical switching

Photonic circuits require elements that can control optical signals with other optical signals. Ultra-low-light-level operation of all-optical switches opens the possibility of photonic devices that operate in the single-quantum regime, a prerequisite for quantum-photonic devices. We describe a new type of all-optical switch that exploits the extreme sensitivity to small perturbations displayed by instability-generated dissipative optical patterns. Such patterns, when controlled by applied perturbations, enable control of microwatt-power-level output beams by an input beam that is over 600 times weaker. In comparison, essentially all experimental realizations of light-by-light switching have been limited to controlling weak beams with beams of either comparable or higher power, thus limiting their implementation in cascaded switching networks or computation machines. Furthermore, current research suggests that the energy density required to actuate an all-optical switch is of the order of one photon per optical cross section. Our measured switching energy density of ~4.4 × 10 photons per cross section suggests that our device can operate at the single-photon level with modest system improvement.