Spectral Efficiency Comparison for Long-Haul Optical Dispersion Management Multi-Level Wavelength Division Multiplexing Systems

This article reports on a numerical investigation of the performance of long-haul dispersion management wavelength division multiplexing links in terms of Q-factor and spectral efficiency. To take into account the role of the phase and amplitude modulations, two well-known transmission formats were analyzed: return-to-zero differential quadrature phase shift keying and coherent 8 quadrature amplitude modulation. To optimize the spectral efficiency, the role of the pulse shape, investigating both Gaussian and Nyquist pulses, was also considered. Furthermore, the role of polarization is studied considering both polarization multiplexing and transmission of adjacent channels with orthogonal states of polarization. Such a study is carried out on a 700-km-long dispersion management link consisting of G.652 spans (100-km long) and by adopting a periodical compensation of the chromatic dispersion by means of fiber gratings.