Mode-order conversion in a Mach-Zehnder interferometer based on Chern insulators.

Abstract

Mode-order conversion devices can provide a flexible platform to achieve mode coupling and optimizing in mode division multiplex (MDM) that can eliminate the restrain of capacity and density in photonic integration and communication. However, mode-order converters based on traditional photonic crystal (PC) waveguides are susceptible to defects, which always render device incapacitation in mode-order conversion. Herein, a mode converter designed by the Mach-Zehnder interferometer (MZI) structure is proposed to manipulate the conversion of topological edge states (TESs) based on Chern insulators consisting of gyromagnetic PCs. The back-and-forth conversion between fundamental and high-order modes is numerically demonstrated based on phase modulation in our proposed device, in which each mode can be immune to defects. This unique approach for converting the mode order of TES exploits a new perspective in MDM to design a high-performance multimode device, leading to potential applications in photonic integrated circuits (PIC), on-chip processors, and optical fiber communication.