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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {3}$</tex-math></inline-formula> × <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {3}$</tex-math></inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {11.0}$</tex-math></inline-formula> dB, crosstalks (CTs) below <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {-24.3}$</tex-math></inline-formula> dB, and extinction ratios (ERs) greater than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {13.6}$</tex-math></inline-formula> dB across the entire C-band (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {1.530}\mathbf {-1.565}$</tex-math></inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathrm{\mu }$</tex-math></inline-formula>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.