Inspect WDM system quality using existing receiver circuitry

Paula Noaker Powell

Statistical monitoring of optical performance in WDM systems allows forecasting the bit-error rate and monitoring signal changes in a relatively short time compared to techniques based on frame evaluation. The major problem until now has been the complexity and thus cost of the monitoring equipment. Researchers at Siemens AG (Munich, Germany) think a relatively low-cost solution lies in embedding monitoring circuitry within a system`s existing receiver circuitry.

Performance monitoring with statistical characteristics involves deriving a histogram that shows the frequency versus amplitude of signals from an eye diagram. The Siemens receiver equipment uses a decision circuit to synchronously distinguish the events above and below a set threshold, thus allowing the derivation of a histogram without the signal sampling required by other techniques. To provide an undisturbed working channel, the researchers also include a second decision circuit for measurement purposes. The key feature of this channel is a variable decision threshold. In recent simulations and experiments, the Siemens researchers demonstrated that their technique can distinguish dispersion from noise by the behavior of the statistical characteristics, and that this behavior can then be used to monitor and adjust the dispersion of a WDM system. For details, contact Rainer Wiesmann at

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