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

A communication system comprising:

• a transmitter device for encoding input data as an analog electrical signal;
• an optical transmitter coupled to the transmitter device, the optical transmitter configured to convert the analog electrical signal to an optical signal;
• an optical communication channel coupled to the optical transmitter;
• an optical front end coupled to the optical communication channel, the optical front end configured to receive the optical signal from the optical transmitter over the optical communication channel and to convert the optical signal to an analog electrical signal and
• a receiver device coupled to the optical front end, the receiver device including
• an analog front end to receive the analog electrical signal and to sample the analog electrical signal based on a sampling clock to generate a digital signal;
• an oscillator to generate the sampling clock;
• a digital signal processor to generate a timing matrix representing coefficients of a timing tone detected in the digital signal, the timing tone representing frequency and phase of a symbol clock of the digital 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 signal relative to the sampling clock, and to cause an oscillator to adjust at least one of the phase and frequency of the sampling clock based on the rotation control signal;
• a demodulator to demodulate the digital signal to generate a demodulated signal;
• and
• a decoder to decode the demodulated signal to generate a decoded output signal.