Analogue-to-digital converter phase insensitive dispersion search method with large search step size for low computational cost

摘要

Accumulated chromatic dispersion (CD) estimation is crucial for frequency-domain equalisation in an optical coherent digital receiver. To solve the problems of small search step size and analogue-to-digital converter (ADC) sampling phase sensitivity from conventional CD searching algorithm, a CD searching method with modified shift parameters and waveforms is proposed in this study. The modified CD searching method allows a much larger search step size and can achieve faster CD estimation with low computational complexity. The performance of the modified CD searching method is also insensitive to ADC sampling phase. On the basis of simulation results, a very low search error probability is confirmed with a search step size of 50 km. About 1 K symbols are found to be enough for dispersion estimation. After the frequency-domain equaliser (FDE) with the estimated dispersion value, the residual dispersion length <;30 km can be well compensated with a 9-tap adaptive time-domain equaliser (TDE) with fast convergence. The overall error rate performance of the tunable electrical dispersion compensation is also studied and compared with lumped and distributed optical dispersion compensation for dynamically switched optical networks.