Chromatic dispersion estimation methods using polynomial fitting in PDM-QPSK or other multilevel-format coherent optical systems

Abstract

We propose a polynomial fitting algorithm based method for non-data-aided chromatic dispersion (CD) estimation in single carrier (SC) coherent optical systems with arbitrary modulation formats, and compare it with our previously proposed CD estimation method which is also based on the polynomial fitting algorithm but requires special modulation formats thus is a data-aided CD estimation method for systems with PDM-QPSK or other multilevel modulation formats. For the data-aided CD estimation method, an extra chirp-free OOK signal is transmitted. The curve of the average phase at the frequency±f as a function of the frequency f is measured at the coherent receiver. The accumulated CD is then estimated with a polynomial fitting algorithm. In the simulation of a 50Gbaud 50%-RZ OOK system through 12.5×80km standard single mode fiber (SSMF), the estimation errors are within±50ps/nm in 20 tests when the launch power is from −5dBm to −1dBm. Non-data-aided CD estimation for arbitrary modulation formats is achieved by measuring the differential phase between frequency f±fs/2 (fs is the symbol rate) in digital coherent receivers. The estimation errors are within±200ps/nm, in a 50Gbaud PDM-QPSK system through 10×80km SSMF with the launch power from −3dBm to −1dBm. The estimation accuracy can be potentially improved by averaging multiple results. The data-aided CD estimation method has an inherently bigger estimation range than that of the newly proposed non-data-aided method, while the newly proposed non-data-aided method can tolerate a much larger frequency offset between the transmitter and the local oscillator. These methods are promising for future optical fiber networks with dynamic optical routing and coherent detection.