Experimental Test of a Closed-Form EGN Model Over C+L Bands

This paper focuses on a closed-form ultra-wide-band solution of the GN and EGN model integrals (CFM, for closed form model), collaboratively developed by CISCO and Politecnico di Torino. The version presented here is capable of handling the frequency-dependence of all main system and fiber parameters and accounts accurately for Interchannel Stimulated Raman Scattering (ISRS). In the paper, we first describe the CFM in detail and then we present a validation experiment carried out over a 5-span 128-channel C+L transmission line over SMF. The experiment was designed to explore transmission scenarios ranging from quasi-linear to deeply non-linear, with significant ISRS. We describe the thorough characterization of the link and the careful instrumentation of the set-up, necessary to minimize all errors that might compromise the significance of the measurements. The results are extensively discussed and show a good match between the CFM predictions and the measured performance. The CFM provides a closed-form solution of the GN and EGN model integrals, but other steps of system performance assessment are not closed-form. However, since GN/EGN integrals are by far the most computationally heavy element of the calculation, the overall speed-up granted by using the CFM is quite significant, about four orders of magnitude. The real-time system performance assessment capability thus achieved makes it possible to perform physical-layer-aware numerical optimization of system and link parameters, a critical aspect in multi-band and ultra-wide-band optical networks. Overall, we believe that both the speed and the reliability of the CFM make it a valuable tool with significant potential for practical application in the field.