Asymmetric frequency multiplexing topological devices based on floating edge band

• Jiajun Ma, Chunmei Ouyang, Yuting Yang, Dongyang Wang, hongyi li, Li Niu, Yi Liu, Quan Xu, Yanfeng Li, Zhen tian, Jiaguang Han, and Weili Zhang
• received 01/12/2024; accepted 03/19/2024; posted 03/20/2024; Doc. ID 518426
• Abstract: Topological photonics provide a platform for robust energy transport regardless of sharp corners and defects. Recently, the frequency multiplexing topological devices have attracted much attention due to the ability to separate optical signals by wavelength and hence the potential application in optical communication systems. The existing frequency multiplexing topological devices are generally based on the slow light effect. However, the group velocity of such the resulting static spatial local mode or finely-tuned flat band is zero, making it difficult for both experimental excitation and channel out-coupling. Here, we propose and experimentally demonstrate an alternative prototype of asymmetric frequency multiplexing devices including topological rainbow and frequency router based on floating topological edge mode (instead of localized ones), hence the multiple wavelength channels can be collectively excited with a point source and efficiently routed to separate output ports. The channel separation in our design is achieved by the gradually tuned bandgap truncation on a topological edge band covering a wide range of frequencies. Wherein, a crucial feature lies in that the topological edge band is detached from bulk states and floating within the upper and lower photonic band gaps. More interestingly, due to the sandwiched morphology of the edge band, the top and bottom band gaps will each truncate into transport channels that support topological propagation towards opposite directions, and the asymmetrical transportation is first-time realized for the frequency multiplexing topological devices.