Abstract: A method and device for monitoring of the plural discrete wavelengths which carry data channels in a WDM optical signal. An input fiber provides a WDM optical signal to a splitter for dividing the signal into two portions. The first portion is provided to a dispersive delay line for delaying, in a temporally staggered manner, the channels of the WDM signal, following which the staggered signal is provided to an optic detector and converted to a first resulting electrical signal. The second portion of the WDM signal is either first converted to an electric signal and then provided to an adjustable electronic delay for delaying all components in the electrical signal by the same delay interval to produce a second resulting electrical signal, or is first provided to an adjustable optical delay for delaying the channels in the second portion by the same delay interval and then converting the delayed signal to the second resulting electrical signal.