David W. Boertjes

100G and beyond with digital coherent signal processing

The demand for increased bandwidth is ever present. Coherent technology coupled with advanced modulation formats and digital signal processing is a key enabler for optical communication systems at 100 Gb/s and beyond. This article reviews the attributes of coherent systems in light of the challenges faced by system designers to realize increased bit rates for next-generation optical systems.

Convex Channel Power Optimization in Nonlinear WDM Systems Using Gaussian Noise Model

Optimization of channel powers to maximize minimum margin or total capacity in WDM systems is studied. Using a Gaussian noise nonlinearity model, the signal-to-noise ratio (SNR) in each channel is expressed as a convex function of the channel powers. Using the SNR expression, convex optimization problems with objectives of maximizing the minimum channel margin or maximizing the fiber capacity minus a coding cap are formulated. Performance gains from software-based power optimization are observed in mesh networks and in point-to-point links having heterogeneous SNR requirements. By contrast, in systems with uniform amplifier noise and modulation formats, the optimized power allocation provides very little improvement over a traditional flat power allocation. In the 14-node NSFNET network, a margin gain of 1.5 dB on average is achieved through power optimization, as compared to a flat power allocation. Margin gains averaging 1.4 dB are found for subsets of this network with three to 13 nodes.

Field Trial of Short Term Capacity Optimization on a Live System

This field trial demonstrates margin-mining to produce additional short-term capacity. Algorithms for higher density modulation format viability in current system conditions are presented. Measurements show suitability of this capacity-maximizing approach for use in live systems.