Novel Design of a 7-Core Photonic Crystal Fiber-Based Mode Multiplexer/Demultiplexer for High-Capacity Optical Communication

We present a novel broadband mode multiplexer/demultiplexer (MUX/DMUX) based on a seven-core photonic crystal fiber (PCF). The structural parameters of the device were optimized using the Finite Difference Eigenmode (FDE) and Eigenmode Expansion (EME) methods. Numerical simulations confirm that the design effectively supports seven linearly polarized modes (LP01, LP11, LP12, LP21, LP31, LP51, and LP61) within the main core. The fundamental LP01 mode propagates directly through the central core, while higher-order modes are efficiently coupled via the side cores. The proposed MUX/DMUX achieves exceptional mode conversion efficiency (MCE), exceeding 94.4% for LP11, 91.0% for LP12, 90.3% for LP21, 89.0% for LP31, 87.3% for LP51, and 85.0% for LP61. With an ultra-compact footprint of only 2.3 mm and an operational bandwidth spanning 1330–2000 nm, the device demonstrates outstanding performance metrics, including ultra-low insertion loss (IL) ranging from 0.03 dB (LP01 at 1.55 μm) to 0.71 dB (LP61 at 2.0 μm), maintaining IL below 0.75 dB across all modes and wavelengths. Moreover, the crosstalk (CT) remains suppressed below –27.5 dB over the entire 670 nm bandwidth. These results, combining record-low IL values with high mode conversion efficiency in a millimeter-scale footprint, establish a new benchmark for PCF-based MUX/DMUX devices, making them highly suitable for next-generation mode-division multiplexing (MDM) systems. .