Honeycomb lattice, possessing the same geometry as graphene, have been widely studied in condensed matter physics and photonics. Various platforms have been used to construct photonic honeycomb lattice, such as waveguide arrays, on-chip silicon photonics, semi-conductor microcavities, and metamaterials, showing potential applications in topological photonics, nonlinear optics and quantum optics. However, the current honeycomb systems hold difficulties in achieving arbitrary reconfigurability and experimental flexibility due to the fixed configurations after fabrication. Therefore, it is important to find an alternative platform with reconfigurability and flexibility for satisfying various potential applications in photonics.

Here, we demonstrate the construction of a two-dimensional honeycomb lattice by using a one-dimensional ring resonators array in the synthetic frequency space. Such a system is highly re-configurable with coupling parameters in the synthetic dimension flexibly controlled by external modulations. It has been used to simulate various physical phenomena associated with graphene, including Klein tunneling, valley-dependent edge states, effective magnetic field, as well as valley-dependent Lorentz force. Our work exhibits the capability for simulating quantum effects, valley-dependent effects, and topological edge states, pointing out the way to manipulate the frequency information of light with synthetic dimensions.

The research was published in “Danying Yu, Guangzhen Li, Meng Xiao, Da-Wei Wang, Luqi Yuan, and Xianfeng Chen, Communications Physics 4, 219 (2021)”

Link：https://www.nature.com/articles/s42005-021-00719-9