Topological rainbow trapping based on non- Hermitian twisted piecing photonic crystals

Topological rainbow trapping, which can separate and trap different frequencies of topological states into different positions, plays a key role in topological photonic devices. However, few schemes have been proposed to realize topological rainbow trapping effects in lossy photonic crystal systems, which has restricted their practical applications, since loss is ubiquitous in nanophotonic devices. Here, we propose a method to realize a topological rainbow based on non-Hermitian twisted piecing photonic crystals. Different frequencies of topological photonic states are separated and trapped in different positions without overlap in the lossy photonic crystals. Moreover, the frequencies of interface states can be modulated by loss, and a topological rainbow can also be achieved in both TE and TM modes. This work brings an effective method to realize robust nanophotonic multiwavelength devices in non-Hermitian systems.