Abstract
C+L open line systems represent a cost-effective way to scale backbone network capacity. In this article, we review challenges and opportunities for C+L line systems stemming from Google's experience in designing, deploying, and operating a global C+L open optical network. We discuss business, operational, and technical aspects of C+L systems, and describe best practices for designing C+L links. Finally, we compare C and C+L systems, showing how the latter not only conceal capacity penalties but can even increase, depending on the deployed fiber types, the total system capacity with respect to two parallel C-band only systems.
Highlights
G OOGLE’S backbone optical network is designed to provide connectivity to Google’s datacenters for Internet and cloud computing services connecting billions of users globally
In dispersion uncompensated transmission scenarios, it has been widely shown that fiber propagation impairments caused by the interplay of loss, chromatic dispersion, and Kerr nonlinearity can be well approximated as an additive Gaussian noise on any single frequency, named nonlinear interference (NLI) [53], [54], in presence of stimulated Raman scattering (SRS) [29], [55]
In order to illustrate the expected signal-to-noise ratio (SNR) performance of a C+L system we look at two scenarios each utilizing G.652 and an erbium doped fiber amplifier (EDFA) based C+L node
Summary
G OOGLE’S backbone optical network is designed to provide connectivity to Google’s datacenters for Internet and cloud computing services connecting billions of users globally. Google’s long-haul network has reached a global scale, and has grown dramatically by approximately two orders of magnitude in capacity [2]–[4] Such growth has been enabled by the advancement of optical communication technologies [5] in particular the advent of transponders based on polarization multiplexed, multilevel modulation formats with digital signal processing (DSP) enabled coherent receivers [6]–[9] that allowed to scale single channel capacity, trading off spectral efficiency with sensitivity requirements. The simplest form of SDM, i.e. the deployment of parallel single mode fibers, is currently adopted in submarine cables [14], while multi-band (C+L) open line systems [4], [15] are globally deployed in the terrestrial long-haul network. Such challenges are related to propagation impairments, frequency dependent optical fibers characteristics, optical component limitations, and the interplay between all of them
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