Page 56 - SAMENA Trends - July-August 2022

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When Telecom Fiber can Sense

Somewhere in the Circum-Pacific Belt, campuses to massive distances spanning on sensors working at pre-determined
the ocean floor is rocked by a powerful continents and oceans. However, the story points, distributed sensing leverages on
earthquake. It triggers a giant tsunami that does not end here. Subsea and terrestrial the cable itself to sense the environment.
gathers speed, bearing down on populated cables are emerging in a new avatar, To put it simply, a DAS interrogator
islands, coastal towns and cities. Now bringing with it huge benefits across a connected to one end of the fiber sends out
imagine, the tremors being detected in range of applications. optical pulses and looks at the light that
milliseconds and the alert conveyed to an Fiber optic sensing comes back from every single microscopic
onshore monitoring center at the speed of The telecom sector is rapidly ditching piece of the fiber, a process known as
light. The alarm is raised and the authorities copper wire in favour of fiber optic cables – Rayleigh Backscatter. By gathering up
swing into action, evacuating people from thin strands of pure glass - each no thicker these tiny pieces of light and watching
vulnerable locations in good time. In such than a human hair, that facilitates the how they change thousands of times per
a scenario, one would be inclined to laud transmission of light over long distances. second due to vibrations in the vicinity, the
ocean-bottom seismometers (OBS) for Every piece of data that is sent or received interrogator identifies unique signatures
saving the day but what if it was an entirely on computers and almost every phone and marks each type of event. DAS is a
different system. As the world enters the call we make is transmitted along fiber. dedicated sensor that detects acoustic
digital age and the Internet becomes Even mobile phone communications events around the fiber. It needs dedicated
ubiquitous, a key facilitator of this rely on it. Only the last few kilometers hardware and, sometimes, even dedicated
transformative change remains hidden is carried through the air. For the past fiber - not used for telecommunications.
from our eyes. Buried in the seabed and in 60 years engineers have been exploring “DAS does not play an active role in data
trenches or laid in ducts under city streets the possibility of using fiber as sensors. transmission or communications per
and buildings, by roads and railways, a “Engineers and scientists have understood se but can be positioned alongside the
web of fiber optic cables come together to the extraordinary opportunity of optical communication line or network to protect
form data superhighways, processing over fiber sensing since the early days. The first the fiber asset or localize cuts,” says Dan
95 percent of global telecommunications. patent of fiber optic sensing dates to 1960, Danskin, Commercial Manager – DAS at
Touted as the “backbone” of the Internet and for decades, the most imaginative Alcatel Submarine Networks (ASN). In
there are currently around 486 active or minds have been exploring the many addition to DAS, there are non-dedicated
under-construction subsea cables with exciting possibilities that it has to offer,” sensors carrying out a different task, but
over 1,300 landings, stretching for more says Matteo Lonardi, Research Engineer which retains the capability of intelligent
than a million kilometers. Their terrestrial at Nokia Bell Labs. The most important sensing. Combined with fiber, coherent
counterparts boast even longer distances. technology driving fiber optic sensing is transponders are the fundamental block
Optical fibers are the Internet's core and Distributed Acoustic Sensing (DAS) which of any modern optical transmission. They
enable the immense communication of allows for real time measurements along convert electrical signals into light and vice-
people, devices, and computers from just the full length of a cable. As opposed to versa, transmitting and receiving hundreds
a few meters away like in data centers and conventional instruments which depend of gigabits per second, thanks to coherent
modulation and digital signal processing.
When receiving light signals, transponders
will carry out several advanced algorithms
to remove all the channel corruption
added during transmission over fiber to
reconstruct the original sent message.
Moreover, in current and future generations
of transponders within Nokia 1830 PSS
products, on top of transmitting and
receiving hundreds of gigabits per second,
the transponder will carry out advanced
monitoring, sensing, and analytics based
on all the light propagation information
retrieved while performing digital signal
processing. A coherent transponder does
not have the sole purpose of sensing,
yet it uses advancements in digital
signal processing to extract sensing and
monitoring information without needing
dedicated hardware or fiber.

56 JULY-AUGUST 2022