Longitudinal Performance Monitoring Towards Hollow Core Fiber Systems via Node Nonlinearity

The advent of hollow core fibers (HCF) in optical communication systems presents both opportunities and challenges for established monitoring techniques due to their ultra-low nonlinearity compared to traditional solid core fibers (SCF). Longitudinal performance monitoring (LPM) is an effective diagnostic method that leverages nonlinear effects to detect and localize impairments such as polarization-dependent loss, multipath interference, and differential group delay (DGD). This work explores the possibility of LPM in HCF systems that incorporate SCF segments. Through both simulation and experimental demonstrations, we show that the nonlinearity inherent in the SCF segments within the link enables continued LPM operation by producing detectable signals. Using commercial transceivers, we validate monitoring of both longitudinal power profile and distributed DGD with HCF-emulating spans. The results confirm that the transmission impairments can still be monitored and localized in HCF systems by exploiting SCF nonlinearities. Our experimental findings demonstrate the adaptability and robustness of LPM for next-generation optical networks based on HCF technology.