An apparatus for and method of pre-emphasising the launch power profile of a section in an optical network. The method comprises the steps of measuring the output power at the output of the section, determining the predicted output power associated with a flat launch power profile using design characteristics of the section and determining the total power deviation between the measured output power and the predicted output power. The method also comprises the steps of determining the signal to noise ratio deviation and the nonlinear phase shift deviation as a function of the total power deviation, and pre-emphasising the launch power profile based on a function of the calculated signal to noise ratio deviations of each span and the calculated nonlinear phase shift deviations of each span, such that the sum of the nonlinear phase shift deviations and the sum of the signal to noise ratio deviations of each channel are reduced by an equal amount.
DYNAMIC EVALUATION OF THE OPTICAL MULTIPLEX SECTION PER-CHANNEL PRE-EMPHASIS POWER