Joint-polarization phase recovery algorithms for DP-16-QAM coherent optical systems

Dual-Polarization 16-QAM coherent systems are a spectrally efficient alternative to future optical networks with metropolitan dimensions. However, the close-packed constellation of the 16-QAM modulation format also has drawbacks, such as an increased susceptibility to phase noise generated in the transmitter and local oscillator lasers. This paper evaluates basic phase recovery algorithms developed for DP-16-QAM systems, using computer simulations and the offline post-processing of experimental data. Special attention is given to joint-polarization algorithms, which use the phase information of both polarization orientations to jointly produce a single estimate of the phase noise, thus relaxing the requirements for transmitter and local oscillator lasers.