Abstract: A unique sensor is used to detect a transmission impairment that may have affected incoming optical channel signals. The sensor, more specifically, selects a group of the incoming channel signals and generates a first power signal, P0, over the selected group of signals and generates a second power signals, P1, over a weighted version of the selected group of channel signals. The sensor then generates, as a function of the first and second power signals, P0 and P1, a signal indicative of whether the particular transmission impairment affected the levels of individual ones of the incoming channel signals. If so, then control apparatus offsets the impairment accordingly.

Abstract: An optical amplifier is adapted to cancel the Raman gain of an optical transmission path that degrades those optical signals occupying the low end of the bandwidth such that the power is transferred from the latter signals to the optical signals occupying the high end of the bandwidth. More specifically, the optical amplifier adjusts the gain that it applies to the optical signals so that it favors the signal components at the low end of the bandwidth.