Networks are increasing in their complexity, both in terms of cascaded filtering (e.g., via ROADMs in mesh networks) and multiple-bit/symbol modulation formats. For instance, intra-channel noise will increasingly be spectrally carved by filters, the signal bandwidths will frequently be as large as the effective channels widths, and different data rates will be used more and more on a given network. All these factors will affect wavelengths differently, as some wavelengths might have passed through a different number of ROADMs, data rates in a single fiber might vary from one wavelength to the next, etc. Nevertheless, OSNR remains a critical network performance parameter, which requires OSNR measurements optimized on a per-channel basis, like the WDM-aware technique. Purely polarization-based OSNR measurement techniques (e.g., polarization nulling) can perform well when networks and noise sources remain simple, but as demonstrated herein, the robustness and performance of WDM-aware measurement renders it well suited for advanced network architectures and modulation formats.
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