Optical performance monitoring based on asynchronous delay-tap sampling

The asynchronous delay-tap sampling technique is a promising in-service monitoring technique capable of measuring simultaneous impairments for multiple bit rates and formats. The two core components of the technique are the characterization of the signal with an asynchronously sampled phase portrait and the extraction of impairment features using statistical machine learning techniques. A major advantage of the technique is that a direct detection–based receiver with set bandwidths can be used for multiple formats and bit rates. Early proof-of-principle demonstrations, based on single transponder- and laboratory-generated impairments, have been further validated at 10-Gb/s with WDM system measurements. Key challenges for practical realization of the technique include a demonstration of robustness with respect to transponder variations and compatibility with ROADMs. One finds that robustness to transponder variations can be improved by training over multiple transponders. Similarly, the ability to distinguish dispersion in the presence of ROADM filter effects may be enhanced by including filter variations in the training set. Experience to date suggests that the remarkable ability of machine-learning techniques to discern patterns in extremely “unstructured” phase portraits holds promise for application of the technique to the monitoring of advanced 100-Gb/s formats and the “next generation” of impairments.