Abstract: Chromatic dispersion (CD) processing apparatus comprises an equalizer loop comprising: a frequency domain equalizer (FDE) arranged to receive samples of an electrical representation of an optical communications signal having CD and to apply CD compensation to the samples, to form dispersion corrected samples having a residual CD value; a time domain equalizer arranged to receive the corrected samples and to generate a representation of a channel linear transfer function of the signal from the corrected samples, to generate and transmit a monitoring signal comprising said representation; optical performance monitoring apparatus arranged to receive the monitoring signal and to estimate the residual CD value; and a processor arranged to receive the estimated residual value and to compare it to a threshold value and to generate and transmit to the FDE an estimation signal comprising the estimated value unless it is less than the threshold.

Abstract: Chromatic dispersion (CD) processing apparatus comprises an equalizer loop comprising: a frequency domain equaliser (FDE) arranged to receive samples of an electrical representation of an optical communications signal having CD and to apply CD compensation to the samples, to form dispersion corrected samples having a residual CD value; a time domain equaliser arranged to receive the corrected samples and to generate a representation of a channel linear transfer function of the signal from the corrected samples, to generate and transmit a monitoring signal comprising said representation; optical performance monitoring apparatus arranged to receive the monitoring signal and to estimate the residual CD value; and a processor arranged to receive the estimated residual value and to compare it to a threshold value and to generate and transmit to the FDE an estimation signal comprising the estimated value unless it is less than the threshold.

Abstract: A method of monitoring a differential group delay (DGD) of an optical communications signal having a polarisation multiplexed modulation format is described. The method includes the operations of receiving a signal and performing analogue to digital conversion of the signal to generate a digitised signal corresponding to one polarisation of the signal and to generate another digitised signal corresponding to another polarisation of the signal, and applying a polarisation mode dispersion(PMD) compensation to each of the digitised signals. The method further includes the operations of obtaining an indication of the channel transfer function of the optical communications signal, determining a DGD in dependence on the indication of the channel transfer function, determining a delay between the PMD compensated digitised signals, subtracting the delay from the DGD to obtain a corrected DGD, and generating and transmitting a monitoring signal with an indication of the corrected DGD.

Abstract: A method of monitoring a differential group delay, DGD, of an optical communications signal having a polarisation multiplexed modulation format is described. The method includes the steps of receiving a signal and performing analogue to digital conversion of the signal to generate a digitised signal corresponding to one polarisation of the signal and to generate another digitised signal corresponding to another polarisation of the signal, and applying a polarisation mode dispersion, PMD, compensation to each of the digitised signals. The method further includes the steps of obtaining an indication of the channel transfer function of the optical communications signal, determining a DGD in dependence on the indication of the channel transfer function, determining a delay between the PMD compensated digitised signals, subtracting the delay from the DGD to obtain a corrected DGD, and generating and transmitting a monitoring signal with an indication of the corrected DGD.