Novel Non-Data-Aided Clock Recovery Method for DP-QPSK Systems With CMA Equalizers

We propose a novel non-data-aided clock recovery method for differential quadrature phase-shift keying optical systems based on the coefficients of the constant modulus algorithm (CMA) adaptive equalizer. The new technique exhibits a satisfactory performance under certain combinations of differential group delay (DGD) and state of polarization, in which the traditional Gardner algorithm fails. The robustness of the proposed algorithm against chromatic dispersion, DGD, and state of polarization variations is demonstrated experimentally.