Topological coupling and decoupling of photonic crystal waveguides: Application to topological wavelength demultiplexing

Photonic crystal waveguides (PCWs) coupling has broad applications in the realm of optical communications and optical integration. However, conventional PCWs couplers suffer inevitable backscattering that leads to energy loss and signal distortion due to local perturbation and sharp bends. This paper investigates topological coupling and decoupling of PCWs based on valley photonic crystals by the coupled-mode theory. The topological power transfer between the neighbouring PCWs can be existed or eliminated due to the coupling or decoupling. As a potential application of our work, a topological wavelength demultiplexer is designed and numerically demonstrated. The proposed device not only exhibits high transmission at three communication wavelengths but also is robust against sharp bend, structural disorder and defects due to the topological properties of structure. This method can be extended to novel designs of topological coupling devices of PCWs.