Reconfigurable and Non-Blocking Mode Distributor for Enhanced MIMO Operation in MDM Optical Networks

The increasing demand for higher data transmission rates has pushed conventional optical networks close to their capacity limits. Mode division multiplexing (MDM) has emerged as a promising solution, enabling multiple spatial modes to propagate through few-mode fibers (FMF). In this work, we propose and experimentally demonstrate a novel reconfigurable, non-blocking mode distributor for MDM systems. Unlike traditional multi-mode interference (MMI) coupler-based designs, our device employs Mach-Zehnder interferometers (MZIs) and asymmetric directional couplers (ADCs) to simultaneously deliver three spatial modes to distinct output ports with dynamic reconfigurability. The device functions as a $\mathbf {3}$ × $\mathbf {3}$ all-optical multiple-input-multiple-output (MIMO) mode switch, where each spatial mode can carry its own set of wavelength-division-multiplexed (WDM) data channels. Experimental results show that the device achieves insertion losses (ILs) below $\mathbf {11.0}$ dB, crosstalks (CTs) below $\mathbf {-24.3}$ dB, and extinction ratios (ERs) greater than $\mathbf {13.6}$ dB across the entire C-band ($\mathbf {1.530}\mathbf {-1.565}$ $\mathrm{\mu }$m). Additionally, the device is polarization-insensitive, supporting polarization division multiplexing (PDM) to potentially double the data capacity. These features make it a strong candidate for enhancing performance in high-throughput MDM optical networks.