Digital Back-Propagation in Optical Fiber Communication Systems Considering Equalization Enhanced Phase Noise

The effect of equalization enhanced phase noise (EEPN) will be introduced in digital signal processing (DSP) based coherent optical communication systems. The EEPN will seriously degrade the transmission performance of a highcapacity optical transmission system. In this work, the influence of EEPN on the performance of dual- polarization 16-ary quadrature amplitude modulation (DP-16QAM) optical transmission system using the electrical dispersion compensation (EDC), the single-channel digital back-propagation (DBP), the partial-bandwidth DBP and the full-field DBP (FF-DBP) were comparatively evaluated with and without considering distortions from the EEPN. Deteriorations on achievable information rates (AIRs) and modulation error ratios (MERs) of optical communication systems due to EEPN have also been assessed. Numerical results indicate that the transmission performance of coherent optical systems can be significantly degraded by the EEPN, especially when FF-DBP is used for the nonlinearity compensation. The larger the linewidth of the local oscillator (LO) laser is, the more serious the degradation caused by EEPN is. This deterioration leads to a decrease in optimal launch powers, AIRs and MERs in the long-haul optical communication systems. In the DP-16QAM transmission system, because of the interference of the EEPN generated by the LO laser with a linewidth of 1 MHz, the degradations on the AIR and MER are 0.15 Tbit/s and 4.15 dB in the case of FF-DBP, respectively. It can also be concluded that, for coherent optical systems with long transmission distances and high symbol rates, the compensation bandwidth and the computational complexity of MC-DBP in the DSP module can be significantly reduced by using narrower-linewidth LO lasers.