Ultra-narrowband nonlinear wavelength conversion using coupled photonic crystal nanocavities

Narrowband optical parametric processes are important for applications such as optical parametric oscillators [1] and sources of single photons suitable for the storage in quantum memories [2]. For the strong nonlinear interaction, it is desirable to have nanostructures that support multiple resonances. Recently, a photonic crystal (PhC) cavity was specially designed to have multiple resonant frequencies with a good spatial mode overlap [3]. Meanwhile, by arraying PhC cavities under the nearest-neighbour coupling condition we can obtain split resonant frequencies whose Q values are as high as that of the single cavity [4]. The energy conservation law for the nonlinear interaction can be fulfilled comparatively easily between resonances at around the centre frequency of the split modes, where the resonant frequencies have regular intervals. Using this structure, we demonstrate a nonlinear wavelength conversion via stimulated four-wave mixing (FWM) with a bandwidth of 500 MHz.