Achieving greater transmission capacity in submarine optical cables is of great interest as data traffic demands continue to increase worldwide. A significant constraint unique to submarine cable ...systems is that of electrical power that must be delivered to the entire cable from the terminals at the landing points. Recently, much focus has been on how to maximize the overall cable transmission capacity within fixed electrical power feed constraints. Until recently, all repeatered submarine cable systems were built using the erbium-doped fiber amplifier C-band, but C+L-band systems are now being considered and deployed. In parallel, there has been intense interest in spatial division multiplexing technologies, such as multicore fibers, as potential means to enabling greater transmission capacity in terrestrial and submarine systems. In this work, we examine maximum submarine cable capacities for three types of systems based on single-core fibers with C-band only or C+L-band transmission, and general multicore fiber systems with C-band-only transmission. The analysis is performed on the basis of common fixed power constraints and received signal-to-noise requirements, and comparable fiber-core characteristics. Additional losses for devices, such as C/L-band splitters and fan-in/fan-out modules, are accounted, and their impact on maximum cable capacity is estimated. For multicore fiber systems, other potential effects, such as higher fiber attenuation and crosstalk between cores, are also analyzed and evaluated with respect to capacity impacts. We find that single-core C-band systems offer the highest cable capacity, provided cable designs can accommodate the number of fiber pairs suggested.
We analyze the potential suitability or strength of arguments for the application of multicore optical fibers in high capacity submarine cable systems via transmission and techno-economic modeling. ...We consider hypothetical multicore fibers (MCFs) with 2-4 weakly coupled cores and compare capacity and cost/bit against conventional single-core fibers (SCFs). The analysis is performed in the context of a trans-Atlantic link length system and we evaluate the relative fiber performance with three different, but related, system design approaches. Two SCF coating diameters are assessed in terms of how this parameter affects the cost/bit through fiber density in submarine cables and resulting cable cost. We find that MCFs may enable higher cable capacity when fiber pair limits are imposed, but likely not at lower cost/bit unless optimistic and best case assumptions are made with respect to MCF relative fiber cost. We also find that reduced diameter SCFs can deliver much of the density and cable cost savings that motivates interest in MCF without the challenges of a new eco-system as required by MCF. However, MCF may enable the design of the largest cable capacities such as 1 Pb/s or more that might not be attainable with SCFs without significant cable changes.
We assess the potential applicability and performance of multicore fibers (MCFs) against conventional single-core fibers (SCFs) in submarine transmission systems. In particular, we assume 4-core MCFs ...with nominally uncoupled cores and separate amplification of each MCF core with conventional erbium doped fiber amplifiers (EDFAs) using fan-in/fan-out (FI/FO) devices in the repeaters. We examine the effects of the number of physical fibers accommodated in the cable design, MCF and FI/FO crosstalk, FI/FO loss, span length, transceiver implementation penalty, and minimum required signal-to-noise ratio (SNR). The relative cable capacities offered by the MCF and SCF systems are evaluated under the different conditions. Then the relative cost/capacity for systems built with the two types of fiber are calculated using a system cost model for two conditions: 1) with maximum cable capacity and 2) for minimum overall cost/capacity. The potential role of multicore fibers (MCFs) in submarine cable systems is investigated in the context of electrical power limitations and physical fiber count limitations. Cable capacities are estimated based on ideal Shannon-limited capacity unless a transceiver implementation penalty, or gap-to-Shannon capacity, is applied. The systems are modeled assuming constant output power amplifiers as are commonly deployed in submarine systems. We find that MCFs offer the greatest cable capacity increase for low fiber count cables, but that the cost/capacity can be significantly higher. When minimization of cost/capacity is the design goal, MCF systems remain higher in this metric than SCF systems, while enabling only a small capacity increase at best.
Power efficiency is a key concept in submarine cable transmission systems because of fixed and limited electrical power supplies. Electrical power is provided by a DC voltage applied across the cable ...from power feed equipment (PFE) located at the terminal ends and is used to power all optical amplifiers throughout the entire link which may be many thousands of kilometers. We examine here via system modeling aspects of power efficiency in the context of maximizing this quantity, primarily with respect to the optimal generalized signal-to-noise ratio (GSNR). We explore the dependence on capacity metric, span loss, link length, and fiber attenuation. We also compare the optimal GSNR predicted using pump power as a measure of power consumption in a single fiber with total cable capacity predicted by application of a pump sharing model and the resulting electrical-to-optical conversion efficiency predicted as a function of amplifier output power, span loss, and repeater power available. We find that the cable capacity measure predicts somewhat higher optimal GSNR than the single fiber measure based on amplifier pump power. The optimal GSNR decreases with longer link length and optimal span loss is somewhat higher than previous results based on different analyses.
Submarine optical transmission systems are commonly operated with constant output power amplifiers. The Gaussian Noise (GN) model of propagation was generally developed in the context of constant ...gain amplification and accounts for amplified spontaneous emission (ASE) noise and nonlinear interference (NLI) noise. Recently, new models have been proposed and developed to predict signal-to-noise ratio (SNR) models for systems with constant output power amplification that account for the phenomenon known as signal droop, or more broadly, generalized droop (GD). Here we describe a GD model within the context of noises as generated in the GN model, and then further including other distributed noise generation such as might occur for crosstalk in multicore optical fibers. The model results in simple expressions for SNR, signal power, and noise powers as a function of the number of identical spans. We provide numerical modeling confirmation of the analytical model for different formats, and experimental transmission data that is fully consistent with the model.
The throughput of submarine transport cables is approaching fundamental limits imposed by amplifier noise and Kerr nonlinearity. Energy constraints in ultra-long submarine links exacerbate this ...problem, as the throughput per fiber is further limited by the electrical power available to the undersea optical amplifiers. Recent works have studied how employing more spatial dimensions can mitigate these limitations. In this paper, we address the fundamental question of how to optimally use each spatial dimension. Specifically, we discuss how to optimize the channel power allocation in order to maximize the information-theoretic capacity under an electrical power constraint. Our formulation accounts for amplifier physics, Kerr nonlinearity, and power feed constraints. Whereas recent works assume that the optical amplifiers operate in deep saturation, where power conversion efficiency (PCE) is high, we show that given a power constraint, operating in a less saturated regime, where PCE is lower, supports a wider bandwidth and a larger number of spatial dimensions, thereby maximizing capacity. This design strategy increases the capacity of submarine links by about 70% compared to the theoretical capacity of a recently proposed high-capacity system.
We address the potential application of G.654.C optical fiber for O-band transmission in the wavelength range of 1270 nm to 1330 nm. Fiber samples at the extreme upper end of the cable cutoff ...manufacturing distribution are chosen for modeling and experimentation. Modeling of multipath interference (MPI) generation in bend conditions representative of cable deployment suggests minimal to negligible penalty and transmission experiments at 100 Gb/s and 400 Gb/s with commercial IMDD transceivers demonstrate longer transmission with increased power margin compared to standard G.652 fiber due to lower O-band attenuation and no adverse impacts from MPI.
The demand for information capacity in data center networks has grown exponentially during past decades. Such growth promotes consideration for adoption of coherent transmission technologies in this ...application space to achieve current and future high data rate requirements at 400G, 800G, and higher. Coherent systems offer higher capacity than direct detection systems using more degrees of freedom to carry information, but with higher system complexity. To meet the cost and power consumption requirements for data center transceivers, coherent-lite technologies have been proposed. Among them, self-homodyne coherent (SHC) is a promising candidate which allows the use of low cost lasers and simplifies digital signal processing (DSP). We study SHC systems and focus on the use of multicore fiber (MCF) to obtain small channel skew, which allows for further simplification of DSP. We observe and manage stimulated Brillouin scattering (SBS) effects in the local oscillator path. We analyze the optimal power split ratio between the data path and the local oscillator path to maximize data capacity. Moreover, we compare the channel skew and transmission performance between multicore fiber and ribbon fiber. SHC with MCF delivers high data capacity with significant complexity reduction, which may be a promising solution for data center links.
Power efficiency of long-haul optical fiber transmission has emerged as a critical challenge to cost-effectively increasing submarine cable capacity. Building on previous experimental work and ...informed by physical system modeling and optimization, we report on extensive amplified transmission experiments characterizing the metric of fiber capacity per unit pump power over a range of amplifier powers and link distances relevant to power-limited spatial-division-multiplexed submarine systems. We compare experimental results with modeling incorporating optical amplifier physics as well as generalized droop, demonstrating excellent agreement over the range of powers and distances tested. We predict the performance gains achievable by further optimizing the system design and implementation within tolerances ideally achieved in deployed submarine systems, and estimate fiber pair counts and total cable capacities achievable for the link distances investigated. Our results suggest the utility of amplifier pump powers as low as 20 mW and output powers as low as 6.5 dBm in reaching Pb/s cable capacities.
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