Abstract

The idea behind flexible optical transmission is to optimize the use of fiber capacity by flexibly assigning spectrum and data rate adapted to the needs of end-to-end connection requests. Several techniques have been proposed to this end. One such technique is based on the utilization of Nyquist-shaping filters with the aim of reducing the required channel spacing in flexible single-carrier and super-channel optical transmission systems. Nonetheless, the imperfect shape of the filters used at the bandwidth-variable transceivers and wavelength-selective switches compels the necessity to allocate a certain spectral guard band between (sub-)channels. Bearing this is mind, in this paper, we focus on the evaluation of the network-level performance, in terms of the filter characteristics and the WDM frequency-grid granularity, of flexible Nyquist-WDM-based transmission. We demonstrate that a granularity of 6.25 GHz offers a good compromise between network performance and filter requirements for spectrum assignment to single-carrier and super-channel signals. However, for subchannel allocation within a super-channel, granularities as fine as 3.125 GHz are required to take advantage of filters with resolutions in the region of 1–1.2 GHz. Finer filter resolutions and frequency slot granularities provide negligible performance improvement.

© 2015 IEEE

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