Experimental Analysis and Modeling of Single-Sided vs Dual-Sided Filtering in Flex-Grid Switched Optical Networks

Flex-grid WSS filters embedded in Reconfigurable Add-Drop Multiplexers (ROADM) can selectively filter portions of the spectrum down to the GHz granularity enabling flexibility in optical channel add-drop operations. In this scenario, the signal's quality of transmission (QoT) can be severely impaired due to filters cascade by both single-sided (SS) and dual-sided (DS) passband narrowing, due to filters' deviation from nominal frequency or multi-carrier transceivers switching. We experimentally observe lower penalties in the SS filtering case and their interplay w.r.t. ASE noise placement. We also propose an experimental calibration method able to directly estimate the overall signal QoT degradation suitable to integration in digital twins' lightpath computation engines and network planners.