Patent ID: 7308200

Claim:
A method for use with a wavelength multiplexed optical communications system, comprising: increasing or decreasing optical power of an optical signal of each channel contained in a wavelength multiplexed optical signal by a predetermined amount, and determining whether each channel belongs to a linear area or a nonlinear area by obtaining a first Q value by adjusting power level down from a first power level, obtaining a second Q value by adjusting power level up from the first power level, comparing the first Q value with the second Q value and a result of the comparing indicating whether in a non-linear or linear area; and conducting pre-emphasis by increasing transmissive optical power of a transmitter when a channel whose Q value is to be improved belongs to a linear area, and decreasing the transmissive optical power of the transmitter when a channel whose Q value is to be improved belongs to a nonlinear area if the Q value is improved at a terminal of a receiver of the optical signal of each channel.