This paper will discuss the collaboratively formed cross-industry Open Cables concept for characterizing optical performance of undersea cables with the intent of assessing and understanding their capacity potential. The paper proposes definitions of two critical nonlinear and linear performance metrics for Open Cables: GSNR (Gaussian Signal to Noise Ratio) and SNRASE (Signal to Noise Ratio Amplified Spontaneous Emission), including effects such as Guided Acoustic Wave Brillouin Scattering (GAWBS) and signal droop. Measurement methodologies for these metrics are proposed, with considerations for limitations and impact of the test conditions and characteristics of the transponders used. Expanded definitions are offered to enable variable baud-rate transponders to be used for measurement, with considerations for scaling of SNR values. Considerations for using these metrics for capacity assessment and applying these techniques to concatenated multi-segment systems are introduced. Recommendations on key parameters for system specification, system characterization and proposals for SNR-based performance budgeting tables are also discussed as foundational elements to enabling accurate estimation of the capacity potential of a subsea Open Cable.View details
ECOC 2020; 46th European Conference on Optical Communication, Brussels (2020), pp. 1-3
We report on a field-trial over the Curie cable connecting USA to Chile. We detected
environmental changes through measurements of polarization of light. Seismic waves stemming from
moderate-size earthquakes caused perturbations in the 0.5-3Hz range, suggesting that transcontinental
cables may be used to detect earthquakes.View details
Since many years, the Q-budget table (normalized by the ITU-T G.977) has been widely used to characterize the transmission performance of subsea cables: this table detailed the margin allowance breakdown for any modulated wavelength. The fiber achievable transmission capacity was then deduced from the wavelength spacing and the system operating bandwidth.
However, the emergence of coherent detection and Digital Signal Processing (DSP) capabilities has enabled the deployment of a wide range of modulation schemes featuring various bit rate, FEC encoding, constellation and spectral shaping, non-linear effect mitigation, thus leading to a transponder-dependent fiber transmission capacity. Combined to the recent trend of the industry to deploy “open” cables it is now time to define a new method to characterize the subsea fiber performance independently of the transponder type. This is emphasized by the introduction of Space Division Multiplexing (SDM) systems equipped with a high fiber pairs count, bringing the granularity at the fiber level: easy to swap, to sell and to manage. Cable capacity will be evaluated via the sum of fiber capacities deduced from any SLTE (Submarine Line Terminal Equipment) at any time with any margin.
The proposed method for non-dispersion-managed undersea systems, relies on the General Signal to Noise ratio (GSNR) to remove the effect of baud rate, which is changing rapidly in each generation of SLTE. These have been metrics already widely debated at conferences/publications. Topics such as accuracy, Gaussian Noise (GN) model, assumptions, and measurability, are discussed to clarify definitions and a methodology. Finally, the paper reviews and discusses fiber capacity based on a given GSNR-based performance budget and various transponder types.View details
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