Carrier Frequency Offset Estimation in the Eigenvalue Domain

eigenvalue transmission is a promising technique to overcome Kerr nonlinear limits in optical communication systems. The optical eigenvalue associated with the nonlinear Schrodinger equation is invariant during fiber-based nonlinear dispersive transmission. However, the effect of carrier frequency offset (CFO) induces an eigenvalue shift in the presence of the CFO for digitally coherent receivers. The CFO estimation method using eigenvalues capable of achieving highly accurate estimations and can be applied to an eigenvalue transmission system has been proposed. However, a detailed analysis of the eigenvalue-based CFO estimation method is yet to be examined. This study examines the estimation accuracy and limitations of the CFO estimation method through numerical simulations and experiments. The eigenvalue-based method achieves estimation accuracy of less than 10 kHz when the time window size W = 6.4 ns and sampling rate R-s = 20 GSa/s in numerical simulations. Moreover, the estimation error is proportional to energy loss when the time window size W and sampling rate R-s are limited. Through experiments, we achieve a fine estimation accuracy below 1 MHz when W = 12.8 ns and R-s = 5 GSa/s, although the accuracy is limited by the noise effect.