Multiple Second‐Order Topological Photonic Systems for Multichannel Beam Splitting and Wavelength Demultiplexing

Abstract

Although second‐order topological photonic systems have been extensively investigated in the last several years, topological edge and corner states have been considered mainly in the systems with single topology. Herein, multiple topological photonic systems consisting of two different types of topologically nontrivial unit cells and their trivial counterparts which are related to each other under a relevant continuous transformation are presented. The dispersing characteristics of edge states are diverse at different topological interfaces of the system and can be controlled with relevant structural parameters, resulting in novel mechanism for multichannel topological beam splitting. Interestingly enough, second‐order topological corner states exist even in the structure of nontrivial photonic crystals surrounded by another nontrivial one unlike the previous cases with trivial surroundings, which can be confirmed from the spectral charge distributions. This enables us to obtain both spatially and spectrally separated multiband‐like corner states as well as edge ones in a multiple topological photonic system, which can be used for wavelength demultiplexer. The results in this work will trigger extensive studies on multiple topology for wide photonic applications.