Abstract
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.
Highlights
Recent growth in dynamic and bandwidth intense user-applications, cloud services, etc. has invoked high interest in flex-grid optical networks [1,2,3]
For the two fiber types, standard single mode fiber (SSMF) and large effective area fiber (LEAF), the maximum transmission distances were fixed at 1600km and 1120km, respectively, such that 1C transmission always achieves performance beyond soft forward error correction (FEC) threshold (Q-factor of ~6.25)
This effect is due to sheer number of channels considered in the super-channel configuration, i.e. 1C essentially means single-channel transmission or only intra-channel nonlinearities, 2C and 5C have the impact of inter-channel nonlinearities intrinsically included
Summary
Recent growth in dynamic and bandwidth intense user-applications, cloud services, etc. has invoked high interest in flex-grid optical networks [1,2,3]. The concept of flex-networks allows for simultaneous transmission of mixed bit rates, 10Gb/s, 40Gb/s, 100Gb/s, 200Gb/s, 400Gb/s, 1Tb/s, etc., employing different modulation schemes and baud-rates, essentially allowing for flexible channel bandwidth, and spectral grid allocation dependent on the considered channel configuration [8,9]. One of the key unknowns in such flex-networks is the interplay of nonlinear fiber impairments when different mix of modulation formats, data-rate, and spectral grid are propagated together. A preliminary study was reported in [10], investigating the nonlinear impact of 40Gb/s and 100Gb/s channels on a 400Gb/s PM-16QAM super-channel, a detailed analysis across various super-channel configurations, traffic allocations, and link configurations is still missing Another important issue is the fragmentation scenario in flexnetworks, due to spectrum allocation based on mixed traffic types, creating band-gaps across the spectrum, essentially reducing the capacity advantage [11,12]. For low dispersion fibers, the impact of spectrum allocation is more significant, and co-propagating traffic employing 120Gb/s PM-QPSK enables the most optimum performance, homogenous traffic still performs within ~0.5dB of the optimal solution
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