Strategies for spectrally efficient optical fiber communication systems with direct detection

In order to use the available optical bandwidth efficiently, efforts are under way to achieve spectral efficiencies of at least 0.8 bits/s/Hz. For such spectrally efficient systems (considering copolarized WDM-channels), we discuss the importance of filtering for different modulation formats, different channel bitrates from 10-160 Gbit/s and different dispersion map designs. It turns out that the optimisation strategy for spectrally efficient WDM systems shows considerable differences to that of single channel systems. The specific modulation format and the chosen channel bitrate turn out to be of minor importance, thus enabling simple analytic expressions for the achievable system performance.