Multi-Tb/s Transmission Based on DMT-Modulated VCSELs in Metro Networks Assisted by Volterra Equalization

The effectiveness of Volterra equalization (VE) is analyzed to improve the performance of a metropolitan area network (MAN), characterized by directly-modulated (DM) vertical-cavity surface-emitting laser (VCSEL) sources combined with coherent detection, in order to target both high capacity and hundreds of km reaches. VE, which is a well-known nonlinear equalization technique, is used to cope not only with the distortion introduced by the real implementation of direct discrete multi-tone (DMT) modulation of the VCSEL, but also with the nonlinear impairments. A suitable experimentation, in case of 25-GHz spaced dense wavelength division multiplexed (DWDM) propagation, allows to validate a simulation tool, developed to provide a systematic analysis of the supported capacity per VCSEL, with and without VE. Simulations permit to analyze the effects of VE for different channel spacings (25, 50 and $100\,$ GHz) and for different standard single-mode fiber (SSMF) lengths (up to $200\,$ km), focusing on the evolution of the capacity per channel in case of different launch powers and optical signal-to-noise ratios. The dependence of the VE effectiveness is evaluated also in terms of spectral behavior. VE allows to achieve up to 13%-capacity increase, assuring 50 Gb/s rate per polarization per VCSEL, in case of DWDM transmission and after 200-km propagation, as targeted by the considered MAN applications.