Flex-grid optical networks: spectrum allocation and nonlinear dynamics of super-channels

Flex-grid optical networks have evolved as a near-future deployment option to facilitate dynamic and bandwidth intense traffic demands. These networks enable capacity gains by operating on a flexible spectrum, allocating minimum required bandwidth, for a given channel configuration. It is thus important to understand the nonlinear dynamics of various high bit-rate super-channel configurations, and whether such channels should propagate homogenously (uniform channel configuration) or heterogeneously (non-uniform channel configuration), when upgrading the current static network structure to a flex-grid network. In this paper, we report on the spectrum allocation strategies based on the impact of inter-channel fiber nonlinearities, for PM-16QAM channels (240Gb/s, 480Gb/s and 1.2Tb/s) -termed as super-channels, propagating both homogenously, and heterogeneously with 120Gb/s PM-QPSK, 43Gb/s PM-QPSK, and 43Gb/s DPSK traffic. In particular, we show that for high dispersion fibers, both homogenous and heterogeneous spectrum allocation enable similar performance, i.e. the nonlinear impact of hybrid traffic is found to be minimal (less than 0.5dB relative penalties). We further report that in low dispersion fibers, the impact of spectrum allocation is more pronounced, and heterogeneous traffic employing 120Gb/s PM-QPSK neighbors enables the best performance, ~0.5dB better than homogenous transmission. However, the absolute nonlinear impact of co-propagating traffic is more significant, compared to high dispersion fibers, with maximum performance penalties up to 1.5dB.