Multifunctional wavelength division multiplexer based on the topological rainbow in valley photonic crystals

The topological rainbow is a peculiar physical phenomenon, and has important application prospects in the fields of topological photonics and micro/nano-photon devices. Here, we design a multifunctional wavelength division multiplexer by using the gradient topological valley photonic crystals. By introducing a rotational degree of freedom, it can be achieved the different cutoff frequencies of the interface state dispersion at different spatial locations. This multifunctional wavelength division multiplexer comprises a lateral transmission channel and several vertical transmission channels. It can precisely separate the electromagnetic waves with different frequencies and capture different positions of the transmission channels, thus achieving the precise control of the multi-band electromagnetic waves.