Symbol timing estimation for coherent polarization multiplex optical receivers

A method for retrieving symbol timing information in a POLMUX system, comprising the steps of

• polarisation splitting a received POLMUX signal into two received polmux signal components (x, y;
• Xt, Yt) with orthogonal polarizations;
• rotating the orthogonal polmux signal components (x, y;
• Xt, Yt) by fixed rotation parameters (Rot0, Rot1, Rot2) obtaining at least three pairs of rotated signal components (X0, Y0;
• X1, Y1;
• X2, Y2) with different polarizations;
• squaring the obtained rotated signal components (X0, Y0;
• X1, Y1;
• X2, Y2) and determining a rotated signal component (X1) having the best phase information quality;
• selecting both corresponding rotated squared signal components (X1, Y1) of the determined signal component (X1) for further processing;
• deriving phase information (Phi_x, Phi_y) of both selected signal components (X1, Y1);
• and
• combining the derived phase information (Phi_x, Phi_y) to achieve the symbol timing information for correcting the phase or calculating an optimized timed signal.