Sub-femtojoule all-optical switching using a photonic-crystal nanocavity

Although high-speed all-optical switches are expected to replace their electrical counterparts in information processing, their relatively large size and power consumption have remained obstacles. We use a combination of an ultrasmall photonic-crystal nanocavity and strong carrier-induced nonlinearity in InGaAsP to successfully demonstrate low-energy switching within a few tens of picoseconds. Switching energies with a contrast of 3 and 10 dB of 0.42 and 0.66 fJ, respectively, have been obtained, which are over two orders of magnitude lower than those of previously reported all-optical switches. The ultrasmall cavity substantially enhances the nonlinearity as well as the recovery speed, and the switching efficiency is maximized by a combination of two-photon absorption and linear absorption in the InGaAsP nanocavities. These switches, with their chip-scale integratability, may lead to the possibility of low-power, high-density, all-optical processing in a chip. All-optical switching energies as small as 0.42 fJ — two orders of magnitude lower than previously reported — are demonstrated in small photonic crystal cavities incorporating InGaAsP. These devices can switch within a few tens of picoseconds, and may therefore have potential for low-power high-density all-optical processing on a chip.