Timing recovery for optical coherent receivers in the presence of polarization mode dispersion

A non-transitory computer-readable storage medium storing instructions for timing recovery, the instructions when executed by a processor causing the processor to perform steps including:

• receiving an input signal sampled based on a sampling clock, the input signal received over an optical communication channel;
• generating a timing matrix representing coefficients of a timing tone detected in the input signal, the timing tone representing frequency and phase of a symbol clock of the input signal and the timing tone having a non-zero timing tone energy;
• computing a rotation control signal based on the timing matrix, the rotation control signal representing an amount of accumulated phase shift in the input signal relative to the sampling clock;
• and
• controlling a numerically controlled oscillator to adjust at least one of the phase and frequency of the sampling clock based on the rotation control signal.

A receiver, comprising:

• an analog front end for receiving an analog input signal and generating a digital input signal sampled based on a sampling clock, the analog input signal received over an optical communication channel;
• a digital signal processor to generate a timing matrix representing coefficients of a timing tone detected in the digital input signal, the timing tone representing frequency and phase of a symbol clock of the digital input signal and the timing tone having a non-zero timing tone energy, the digital signal processor further to compute a rotation control signal based on the timing matrix, the rotation control signal representing an amount of accumulated phase shift detected in the digital input signal relative to the sampling clock;
• and
• a numerically controlled oscillator control block to adjust at least one of the phase and frequency of the sampling clock based on the rotation control signal.