Digital Longitudinal Monitoring of Fiber-optic Link Using Coherent Receiver

In fiber-optic communication systems, it is crucial for operators to accurately monitor various physical parameters along optical links to fully leverage the potential transmission capacity and conduct fault analysis.Digital longitudinal monitoring (DLM) has been intensively studied for its capability of monitoring various physical parameters, such as optical power, distributed along the fiber-longitudinal direction by solely processing signals received at coherent receivers.In this article, the fundamentals and recent advances in DLM are reviewed, including working principles, spatial resolution, and key experiments demonstrating its feasibility for use in operations.