Page 49 - Market Analysis Report of Optical Communications Field in China & Global market 2021

Fiber Technology Review and Outlook

for Submarine Networks

Chen Hao, John Hedgpeth
Corning Incorporated

1. Introduction slope fiber were carefully selected and assembled to
minimize residual span dispersion and dispersion slope.
ubmarine networks are essential parts of today’s optical
communications infrastructure, which carries more than Fig. 1 Dispersion-managed fiber solution for direct detection system
99 percent of inter-continental data traffic. Driven by the
ever-increasing bandwidth demand from cloud & content
providers, the submarine fiber and cable market continues
to show strong demand and multiple tens of new submarine
cable projects are expected to be deployed in the next few
years.
In the past decade, fiber capacity has exponentially increased
thanks to the proliferation of fiber-based transmission
technologies. In the meantime, fiber attributes also have
evolved to keep pace with the transmission technology
innovations. For example, dispersion management fiber was
introduced for 10Gb/s and 40Gb/s direct-detection systems.
Large effective area (A ), ultra-low-loss fiber has been In the 2010’s, a breakthrough in speed of electronic
eff
widely deployed for 100Gb/s and above coherent detection components and digital signal processing (DSP) technology
systems. Today, to achieve a step increase of submarine allowed for an adoption of coherent detection with spectral-
cable capacity, the industry deploys more linear SDM (space efficient modulation. This allowed for the detection of
division multiplex) systems which maximizes overall cable signal phase, amplitude, state of polarization, and digital
capacity instead of focusing on single fiber pair capacity. compensation of PMD and fiber chromatic dispersion. This
In practice, SDM systems successfully reduce cost-per-bit led to the adoption of 100Gb/s, which marked an important
in the presence of electrical power constraint. As a result, milestone in the evolution of optical fiber communication
moderate A , lowest attenuation and smaller, 200 µm systems. In a coherent detection system, reach and
eff
outer diameter fiber becomes a preferred option for SDM performance is constrained by OSNR, which is a function of
systems. channel power, noise figure, and span attenuation. As shown
When the industry follows this trajectory to further in Figure 2, optical fiber with ultra-low loss, largest Aeff
enhance the cable capacity, it becomes necessary to and low nonlinear refractive index is essential for improving
considerrevolutionary SDM fiber types for next-generation system OSNR and transmission performance. Compared
SDM systems. Today, the industry still evaluates each SDM to Ge-doped fibers, silica-core fibers (such as Corning®
®
fiber type, and is yet to determine which SDM fiber options Vascade fibers) enable lower nonlinear refractive index (2.1
2
-20
could prevail in next-generation SDM submarine systems. x 10 m /W), lower attenuation (0.150dB/km), and large
2
In this paper, we will briefly review the technology trends of Aeff ( up to 150 µm ), providing further OSNR benefit and
the submarine transmission system and discuss innovative longer distance/higher capacity per fiber pair.
fiber options for SDM submarine systems.
Fig.2 Fiber attenuation and Aeff contributes to higher ONSR
2. Submarine Fiber of Yesterday
In the 2000s, direct detection systems (10Gb/s and
40Gb/s) were deployed. In those systems only signal
amplitude (optical power) was detected, and the
transmission performance was predominantly limited by
the accumulated Polarization mode dispersion (PMD)
and chromatic dispersion of fiber. Therefore, PMD and
chromatic dispersion needed to be minimized to enable long
(transoceanic) system reach, which was achieved by using 3. Today’s Fiber for SDM Submarine Linear
dispersion-managed fiber solutions and low PMD fibers Systems
(Figure1). Positive chromatic dispersion and dispersion In submarine systems, where repeatersare powered from
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