Patent ID: 8401403

Claim:
A receiver, comprising: an optical module receiving a quadrature amplitude modulated optical signal; analog-to-digital conversion circuitry configured to convert the quadrature amplitude modulated optical signal into a digital signal; and timing recovery circuitry configured to provide a timing estimation of the digital signal utilizing a cyclic correlation; wherein the quadrature amplitude modulated optical signal comprises a polarization multiplexed signal with two polarizations X and Y, and wherein the cyclic correlation for each polarization is a function of an angle between X and Y and delay between X and Y; wherein the timing recovery circuitry is configured to form two new signals W and Z from X and Y to overcome nulls in the cyclic correlation, and wherein the timing estimation is provided utilizing cyclic correlations associated with each of the signals X, Y, W, and Z; and wherein the timing recovery circuitry is configured to compute a timing estimate A based upon the cyclic correlations associated with the signals X and Y and a timing estimate B based upon the cyclic correlations associated with the signals W and Z, and wherein the timing recovery circuitry is configured to select either the timing estimate A or the timing estimate B based upon a comparison involving two or more of the cyclic correlations associated with each of the signals X, Y, W, and Z.