Strong coupling between distant photonic nanocavities via dark whispering gallery modes.

The strong coupling between photonic nanocavities at arbitrary positions is important for the realization of photonic integrated circuits. However, the coupling between nanocavities is mainly through the evanescent field, which limits the distance between nanocavities and hinders the scalability of photonic circuits. Here, we propose a scheme to realize the strong coupling between two distant nanocavities beyond the limitations of evanescent field coupling. Two distant identical one dimensional photonic crystal cavities (1DPhCCs) more than 8 µm apart are bridged by a microring which supports whispering gallery modes (WGMs). We demonstrate that the two 1DPhCCs can be strongly coupled even though the microring is largely detuned from them. The supermodes between the two 1DPhCCs are formed while the proportions of the WGM in the microring are suppressed at large detuning. The light energy mainly oscillates between the two 1DPhCCs, leaving the WGM in the microring as a dark mode. Such a scheme can realize strong coupling between distant nanocavities without much difficulties in experiments, which provides advantages for the realization of next-generation photonic circuits.