Multi-channel frequency router based on valley-Hall metacrystals

Topological photonics has revolutionized the manipulation of electromagnetic waves by leveraging various topological phases proposed originally in condensed matter, leading to robust and error-immune signal processing. Despite considerable efforts, a critical challenge remains in devising frequency routers operating at a broadband frequency range with limited crosstalk. Previous designs usually relied on fine-tuning of parameters and are difficult to be integrated efficiently and compactly. Here, targeting the demand for frequency-selective applications in on-chip photonics, we explore a topological approach to photonic frequency router via valley-Hall metacrystals. Diverging from the majority of studies focusing on zigzag interfaces, our research shifts the attention to armchair interfaces within an type-A type-B type-A (ABA) sandwich-like structure, where a single column of type-B unit cells acts as a replacement in the background type-A metacrystal. Essentially, through tuning a single geometric parameter of the type-B unit cells, this configuration gives rise to interface states within a customized frequency band, enabling signal routing with limited crosstalk to meet specified demands. Moreover, this concept is practically demonstrated through a photonic frequency router with three distinct channels, experimentally exhibiting robust wave transmissions with excellent agreement with the design. This investigation manifests possible applications of the armchair interfaces in valley-Hall photonic systems and advances development of photonic devices that are both compact and efficient. Notably, the approach is naturally compatible with on-chip photonics and integration, which could benefit telecommunications and optical computing applications.