Next‐Nearest‐Neighbor Coupling Topological Protection of On‐Chip Modes with Orbital Angular Momentum

Inspired by topological insulators, topological photonics has attracted the attention of researchers since its discovery. Many phenomena like topological state bring numerous new opportunities to the entire photonics. Previous studies have proved that topological systems can protect photonic orbital angular momentum (OAM). In this work, two Su–Schrieffer–Heeger (SSH) waveguide chains are combined, and the interface waveguide is designed to generate next‐nearest‐neighbor coupling (NNC) between itself and the waveguides in the SSH chains. It is discovered that with NNC, more modes are topologically protected. Laguerre‐Gaussian (LG) modes are typical OAM light beams, which are composed of several Hermite‐Gaussian (HG) modes. With NNC and special design of the waveguide, which is located at the interface, it is proven that SSH chains can protect more OAM modes. This model is named the NNC‐SSH model. Thus, this study expands the field of topological photonics and presents a new idea of topological protection, which has a very high potential in many fields such as OAM multiplexing.