Dynamic evaluation of the optical multiplex section per-channel pre-emphasis power

An apparatus for pre-emphasising the launch power profile of a section in an optical network, the section comprising a plurality of fibre optic spans, each span being separated by an amplifier, the apparatus comprising:

• measuring means arranged to measure, for each channel of the section, the output power at the output of the section;
• predicted output power determining means arranged to determine, for each channel of the section, the predicted output power associated with a flat launch power profile using design characteristics of the section;
• total power deviation determining means arranged to determine, for each channel of the section, the total power deviation between the measured output power and the predicted output power;
• signal to noise ratio deviation determining means arranged to determine, for each channel of each plurality of fibre optic spans, the signal to noise ratio deviation as a function of the total power deviation;
• nonlinear phase shift deviation determining means arranged to determine, for each channel of each plurality of fibre optic spans, the nonlinear phase shift deviation as a function of the total power deviation;
• and
• pre-emphasis control means arranged to pre-emphasise 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.