In-service crosstalk monitoring, tracing and lightpath re-optimization for space-division multiplexing optical networks.

In recent years, to enlarge the single-mode fibers (SMFs) transmission capacity, researchers focused on the dimension of space, which is a new degree of freedom that is being considered for optical fiber communication beyond WDM. Space-division multiplexing (SDM), including mode-division multiplexing (MDM) using multimode fibers (MMFs) or few-mode fibers (FMFs), and core multiplexing using multicore fibers (MCFs), has attracted much recent attention. In an SDM system, high-density spatial channels are tightly packed into a single fiber, thus making crosstalk among cores or modes a critical challenge due to fiber imperfections, bending, and twisting. Previous studies have mostly been confined to the routing algorithms for crosstalk reduction but few focuses on the in-service crosstalk monitoring, tracing and quality-of-transmission (QoT)-oriented lightpath re-optimization. In this paper, we proposed novel in-service crosstalk monitoring and tracing (CMT) method and algorithm using fine-grained optical time slice monitoring channels for crosstalk reduction in SDM optical networks. Benefitting from the large amount of fine-grained channels provided by optical time slices, it becomes possible for every source node to allocate a dedicated monitoring time slice carrying the traffic and path information for each connection. Crosstalk monitoring and tracing can be realized by extracting the information contained in these monitoring time slices. Simulation results shows that the proposed CMT method and algorithm can obtain acceptable performance in large-scale network scenarios. Furthermore, we also proposed a quality-of-transmission (QoT)-oriented lightpath re-optimization mechanism based on in-service crosstalk monitoring and tracing to maintain a high level of QoT. Finally, we designed a prototype experiment to validate our proposed in-service crosstalk monitoring method. Results show that this method can realize in-service crosstalk monitoring, tracing and lightpath re-optimization over a seven-core fiber based transmission system, and the crosstalk with a minimum value of -37.9 dB can be monitored and successfully traced.