Digital Precoding for Improved Transmission in Multi-Mode Fiber Using Photonic Lanterns

Few-mode fiber (FMF) systems present a cost-effective alternative to wavelength division multiplexing (WDM) systems for increasing the data throughput in short-range intensity-modulated and direct detection (IM/DD) networks. A 2-mode fiber can deliver similar performance to a 2-wavelength system but with fewer components. However, FMF systems are limited by crosstalk (XT), which due to the short distance, primarily comes from the MUX/DEMUX components rather than the fiber itself. This XT is more static in nature. Photonic lanterns (PLs), commonly used as mode MUX/DEMUX, provide lower losses compared to other multiplexers [1]. This paper investigates an air-clad mode-selective three-fiber PL for two LP mode groups [2], offering a low-cost solution but still with notable XT. To compensate for XT without resorting to receiver-side MIMO, digital precoding can be adopted as suggested in [3]. In this paper, precoding based on the zero-forcing (ZF) technique is proposed and experimentally demonstrated to mitigate the effect of XT and its variation.