We perform an experimental investigation of a maximum likelihood-based (ML-based) algorithm for bulk chromatic dispersion estimation for digital coherent receivers operating in uncompensated optical networks. We demonstrate the robustness of the method at low optical signal-to-noise ratio (OSNR) and against differential group delay (DGD) in an experiment involving 112Gbit/s polarization-division multiplexed (PDM) 16-ary quadrature amplitude modulation (16QAM) and quaternary phase-shift keying (QPSK). 
Experimental demonstration of the maximum likelihood-based chromatic dispersion estimator for coherent receivers