Throughput comparison between 50-GHz and 37.5-GHz grid transparent networks [Invited]

With the introduction of Nyquist pulse shaping, it is possible to transmit a channel in a spectral window close to its baud rate. To increase the overall network spectral efficiency, the most promising solution seems to be the reduction of the channel spacing. Standardization bodies have proposed a flexible grid with 12.5 GHz of granularity. Hence, 100-Gb/s signals can be transported in a 37.5-GHz grid network. While a 37.5-GHz channel spacing brings an ideal extra-throughput of 33% compared to a 50-GHz spacing, this value ignores filtering-induced impairments occurring when a narrower channel spacing is adopted. In this paper, we numerically investigate the filtering penalty stemming from optical filters and its implications on the extra-throughput provided by 37.5- versus 50-GHz grid wavelength division multiplexing (WDM) networks for two different networks with two different traffic distributions. We show fully transparent network scenarios where the ideal 33% extra-throughput of 37.5-GHz channel spacing is drastically reduced or even vanishes because of filtering penalties.