Optical-frequency-comb generation and entanglement with low-power optical input in a photonic molecule

Abstract

Optical-frequency combs consisting of equally spaced sharp lines in frequency space have triggered substantial advances in optical-frequency metrology and precision measurements and in applications such as laser-based gas sensing and molecular fingerprinting. Here, we propose a scheme to generate a type of optical-frequency combs and convert them from one cavity to the other in a hybrid optical system composed of a pair of coupled photonic crystal cavities called a photonic molecule (PM) and a single semiconductor quantum dot (QD) embedded in one cavity of the molecule. Optical-frequency combs are formed by the interaction between a cavity mode and a continuous-wave (CW) two-tone driving laser consisting of a pump field and a seed field via QD-induced strong nonlinearity. In this situation, the initial input pump and seed CW lasers can interact among each other and produce optical higher-order sidebands with equal spacing via parametric frequency conversion provided by QD-induced nonlinear optical effects. Using numerical simulations, it is clearly shown that the beat frequency of the two-tone components plays an important role in determining the comb spacing and matched frequency combs can be formed in the PM. We also demonstrate that the present interacting QD-PM system can serve as a platform to generate large-scale quantum entanglement between two comb modes. The results obtained here may be useful for real experiments in a photonic crystal platform.