Dynamically encircling an exceptional point in a non-Hermitian system can lead to chiral behaviors, but this process is difficult for on-chip $\mathcal{P}\mathcal{T}$-symmetric devices which require accurate control of gain and loss rates. Here, we experimentally demonstrated encircling an exceptional point with a fixed loss rate in a compact anti-$\mathcal{P}\mathcal{T}$-symmetric integrated photonic system, where chiral mode switching was achieved within a length that is an order of magnitude shorter than that of a $\mathcal{P}\mathcal{T}$-symmetric system. Based on the experimental demonstration, we proposed a topologically protected mode (de)multiplexer that is robust against fabrication errors with a wide operating wavelength range. With the advantages of simplified fabrication and characterization processes, the demonstrated system can be used for studying higher-order exceptional points and for exotic light manipulation.

• Received 11 May 2022
• Accepted 6 October 2022

DOI:https://doi.org/10.1103/PhysRevLett.129.273601