How does an optical submarine cable work?
The optical technologies of submarine cables consist in
sending information in the form of light pulses along a fiber, which gives
access to speeds higher than analog technologies. bolts
In what year was the first optical submarine cable put in
place?
The first optical transatlantic cable (TAT 8) was put into
service in 1988 between the United States, France and Great Britain. Between
1988 (TAT 8) and 2002 (APPOLO), the capacities of similar submarine cables will
be multiplied by a factor of 5,000 (and by a factor of 40,000 over a wider reference
period, from 1988 to 2009).
During the 20 th century, the capacities of optical cables ,
coupled with their speed of evolution, will lead to prematurely abandoning all
analog cables. Transmission satellites, previously used in addition to analog cables,
will also be outdated, before being reserved for certain sectors (television,
telephone services in sparsely populated areas, etc.).
Intercontinental wireless networks will also be gradually
marginalized. Thanks to the use of optical technologies, submarine cables
quickly ensured 99% of intercontinental data exchanges.
Submarine optical cables exhibit exponential transport
capabilities
An optical submarine cable is made up of a protective sheath
(1 and 2 on the diagram below), a metal reinforcement (3, 4, 5 and 6), an
insulating sheath (7) and pairs of optical fibers (8).
Cross-section of an optical fiber submarine cable and
description of the data path
Each pair of optical fibers is activated by multiplexers. A
multiplexer is a device that cuts and encodes each incoming piece of data in
the form of light rays, injected into the fiber at distinct wavelengths (up to
160 wavelengths or "colors" in the early 2000s. pair of optical
fibers then transmits these wavelengths to a demultiplexer, which recovers the
signal and retranslates it in the form of data that can be used by the
terrestrial segment.
The wavelengths of light s are transmitted through a window,
that is to say via an interval of frequencies (one also speaks of “bandwidth”).
Any bandwidth has several characteristics:
Signal attenuation: measures the loss of signal for each km
traveled.
Bandwidth: measured in nm, it is proportional to the
capacity accessible on a transmission system, measured in bit / s.
The speed: represents the capacities transmitted on each
color (2.5 to 400 Gbit / s).
In 2014, most long-distance networks used windows 1,550 nm
wide, which made it possible to limit loss while ensuring a substantial
transmission capacity.
The capacity of a cable is cast-off to estimate the amount
of data it can transmit. It is conventionally measured by speed bands:
E1 : 2Mbit/s
DS3 : 45 Mbit/s
STM1 : 155 Mbit/s
STM4 : 622 Mbit/s
STM16 : 2 500 Mbit/s
STM64 : 10 000 Mbit/s
How efficient is the transmission of an undersea cable?
The efficiency of the transmissions depends on the number of
colors passing through each optical fiber. This number varies according to the
type of multiplexer used: SDH ( Synchronous Digital Hierarchy ) multiplexers
allow the waves to be temporally multiplexed; "WDM" type multiplexers
( Wavelength Division Multiplexing ) allow wave frequencies to be multiplexed.
In practice, the complementary use of these technologies significantly improves
the capacities of optical fibers:
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