Patent ID: 7711266

Claim:
A method of testing for Polarization Mode Dispersion (PMD) in-service on a fiber span between a first terminal in a network and a second terminal in the network, the method comprising: in a control system, selecting a plurality of available data channels from data channels of a data bandwidth within the fiber span; in a light system, transmitting test signals based on the plurality of available data channels; in a filter system, filtering the test signals to prevent interference with the unavailable data channels; in a multiplexer located in the first terminal, receiving data signals from a plurality of transmitters in the first terminal, receiving the test signals from the filter system, transmitting the data signals in the data channels of the data bandwidth within the fiber span, wherein the fiber span has a bandwidth that comprises a first subsection and a second subsection and wherein the data bandwidth comprises the first subsection of the bandwidth, and transmitting the test signals over the plurality of available data channels in the data bandwidth concurrently with transmitting the data signals, wherein the data signals occupy a subset of the data channels of the data bandwidth and the test signals occupy the plurality of available data channels in the data bandwidth; in a de-multiplexer located in the second terminal, receiving the data signals and the test signals; and in a PMD measurement system coupled to the de-multiplexer, measuring PMD of the fiber span based on the test signals.