Stop-and-go algorithm for blind equalization in QAM single-carrier coherent optical systems

Coherent detection has recently allowed the adoption of high-order modulation formats in single-carrier optical systems where a simple feed-forward equalizer, in proper configuration, is able to perfectly compensate for fiber linear impairments, such as group velocity dispersion and polarization-mode dispersion. In this letter, the blind update of the equalizer taps is investigated with reference to a 16-ary quadrature amplitude modulation (QAM) format in the presence of different channel impairments. A novel algorithm is proposed, which represents an improvement of the stop-and-go, through the use of a powerful asynchronous detection strategy.