Chromatic dispersion processing apparatus and method

A method of processing chromatic dispersion of an optical communications signal, the method comprising:

• receiving samples of an electrical representation of an optical communications signal having a chromatic dispersion;
• compensating the received samples for a value of chromatic dispersion, to form dispersion corrected samples having a residual chromatic dispersion value;
• generating a representation of a channel linear transfer function of the optical communications signal from the dispersion corrected samples;
• estimating the residual chromatic dispersion value from the representation of the channel linear transfer function;
• comparing the estimated residual value to a threshold value and unless it is less than the threshold value, adding the estimated residual value to a value of chromatic dispersion previously compensated for, to form a subsequent value of chromatic dispersion;
• and
• repeating the compensating, generating, estimating, and comparing operations for respective subsequent values of chromatic dispersion until the estimated residual value is less than the threshold value.

An optical monitoring apparatus comprising:

• an optical detection apparatus arranged to receive an optical communications signal and to generate an electrical representation of the optical communications signal;
• an analog to digital conversion apparatus arranged to generate samples of the electrical representation;
• and
• a chromatic dispersion processing apparatus comprising an equalizer loop comprising:
• a frequency domain equaliser arranged to receive samples of an electrical representation of an optical communications signal having a chromatic dispersion, and further arranged to apply chromatic dispersion compensation to the samples, to form dispersion corrected samples having a residual chromatic dispersion value;
• a time domain equaliser arranged to receive the dispersion corrected samples and to generate a representation of a channel linear transfer function of the optical communications signal from the dispersion corrected samples, and further arranged to generate and transmit a monitoring signal comprising the representation of the channel linear transfer function;
• an optical performance monitoring apparatus arranged to receive the monitoring signal and to estimate the residual chromatic dispersion value from the representation of the channel linear transfer function;
• and
• a processor arranged to receive the estimated residual value and to compare the estimated residual value to a threshold value, and further arranged to generate and transmit to the frequency domain equaliser an estimation signal comprising the estimated residual value unless the estimated residual value is less than the threshold value.

An optical receiver comprising:

• an optical detection apparatus arranged to receive an optical communications signal and to generate an electrical representation of the optical communications signal;
• an analog to digital conversion apparatus arranged to generate samples of the electrical representation;
• and
• a digital signal processing apparatus comprising a chromatic dispersion processing apparatus comprising an equalizer loop comprising:
• a frequency domain equaliser arranged to receive samples of an electrical representation of an optical communications signal having a chromatic dispersion, and further arranged to apply chromatic dispersion compensation to the samples, to form dispersion corrected samples having a residual chromatic dispersion value;
• a time domain equaliser arranged to receive the dispersion corrected samples and to generate a representation of a channel linear transfer function of the optical communications signal from the dispersion corrected samples, and further arranged to generate and transmit a monitoring signal comprising the representation of the channel linear transfer function;
• an optical performance monitoring apparatus arranged to receive the monitoring signal and to estimate the residual chromatic dispersion value from the representation of the channel linear transfer function;
• and
• a processor arranged to receive the estimated residual value and to compare the estimated residual value to a threshold value, and further arranged to generate and transmit to the frequency domain equaliser an estimation signal comprising the estimated residual value unless the estimated residual value is less than the threshold value.

A non-transitory computer-readable storage medium having computer code stored therein, which when executed by a processor, cause the processor to perform operations comprising:

• receiving samples of an electrical representation of an optical communications signal having a chromatic dispersion;
• compensating the received samples for a value of chromatic dispersion, to form dispersion corrected samples having a residual chromatic dispersion value;
• generating a representation of a channel linear transfer function of the optical communications signal from the dispersion corrected samples;
• estimating the residual chromatic dispersion value from the representation of the channel linear transfer function;
• comparing the estimated residual value to a threshold value and unless it is less than the threshold value, adding the estimated residual value to a value of chromatic dispersion previously compensated for, to form a subsequent value of chromatic dispersion;
• and
• repeating the compensating, generating, estimating, and comparing operations for respective subsequent values of chromatic dispersion until the estimated residual value is less than the threshold value.