A Novel Mode-Division Multiplexer/Demultiplexer with Ultra-Large Bandwidth and Ultra-Low Insertion Loss Based on Five-Core Photonic Crystal Fiber

A novel mode-division multiplexer/demultiplexer (MUX/DMUX) based on a five-core photonic crystal fiber (PCF) is proposed in this study. The structural parameters of MUX/DMUX were optimized using finite-difference eigenmode (FDE) and eigenmode expansion methods. The numerical simulation results show that the device can simultaneously multiplex five modes of LP01, LP11, LP21, LP31, and LP12 in the main core with an ultra-low insertion loss. At 1.55 μm, the mode conversion efficiency and insertion loss of the five modes were greater than 93.5% and less than 0.29 dB, respectively. The proposed MUX/DMUX is compact, with a length of only 1.84 mm. In addition, the device can operate efficiently with crosstalk of less than -11.34 dB over an ultra-wide bandwidth of 620 nm (from 1.33–1.95 μm, covering E-, S-, C-, L-, U-bands), offering great potential in future mode-division multiplexing systems.