Highly efficient control of laser frequency is provided. An optical channel
monitor is coupled to a composite WDM signal resulting from the multiplexing of
outputs from multiple laser sources. The monitor determines the frequency of each
laser and this measurement is used to provide feedback for laser frequency control.
In this way a single optical channel monitor can provide frequency control for
numerous WDM channels, greatly reducing the cost and space required. Monitoring
capability may be provided to individual channels as needed.