A method of receiving an optical signal through an optical communication system. The optical signal is transmitted by a transmitter of the optical communication system with a predetermined State of Polarization in a succession of signalling intervals. The SoP in each signalling interval is selected to excite two orthogonal eigenvectors of Polarization Mode Dispersion (PMD) of the optical communication system. The SoP in one signalling interval may be different from the SoP in at least one other signalling interval. Modulation of the optical signal is detected in two orthogonal polarization directions. Modulation components associated with one of the two orthogonal eigenvectors are selected and used to recover data.