Roll-off factor control to increase the energy efficiency of a Nyquist-WDM pulse-shaping filter

We investigate the effect of adjusting the excess in bandwidth (roll-off factor) of a pulse-shaping filter on the performance of a long haul (N-WDM) 21 x 256 Gb/s PM-16QAM coherent system. After calibrating a simulator with the results obtained experimentally, taken with a roll-off set to 0.1, we varied the roll-off value from 0.1 to 1.0 in the simulation setup and verified its impact on the transmission in a linear regime. The simulated results were, then, combined with data obtained from the literature relating the number of taps of a FIR filter to its energy consumption. Within a given transmitted reach and as long as the system operates within the FEC limit, it is demonstrated that a less stringent specification for the roll-off can lead to a reduction on energy consumption without compromising the system performance. Such a geometric pulse-shaping technique allowed us to establish a 3-D figure of merit based on the resolution of the filter, given by the number of taps, the correspondent roll-off factor and the energy consumption.