Consistent with the present invention, a tunable laser emits a monitoring
signal which is combined with the WDM channels typically at the transmit
side of a WDM system. At each monitoring point along the WDM system, the
WDM channels are filtered out, the monitoring signal is sensed, and
desired systems parameters (e.g., gain flatness, dispersion, PMD and OSNR)
are measured. Accordingly, a single tunable element, i.e., the tunable
laser, can be provided, thereby reducing costs. Moreover, system
performance can be ascertained regardless of whether WDM channels are
present.
