Aerospace & Defense Technology - August 2024 - 27

RF & Microwave Technology
Fortunately, as computer scientists were creating the internet,
the field of photonics was developing a method of using light to
transmit data much faster and over much longer distances than
what is possible with electricity conducted through copper wires.
Fiber Optics Enabled the Growth of the Internet
The first continuously operating helium-neon gas laser was
demonstrated in 1960, and a decade later, scientists at Corning
Glass Works invented ultra-transparent glass that could be
mass-produced into low-loss optical fiber. By 1977, fiber optics
began to carry traffic over public telephone networks. And in
1986, Sprint deployed the first nationwide 100 percent digital
fiber-optic network.
Optical fibers can transmit up to 60 Terabits per second,
more than 700 times faster than copper. And the data quality
is superior because the optical signal is not subject to electromagnetic
interference and radio-frequency interference (EMI/
RFI), crosstalk, and impedance problems that cause signal distortion
and loss with copper.
A watershed moment came in 1986. The invention of the erbium-doped
fiber amplifier (EDFA) significantly increased the distance
an optical signal could be transmitted before requiring an
electronic repeater, making fiber optics practical and economical
for intercontinental undersea cables. Previously, submerged
copper cables operated at only 140 megabits per second and
required powered electronic repeaters at frequent intervals.
The first transatlantic fiber optic cable went into operation
in 1988 - a year before Tim Berners-Lee proposed what became
the World Wide Web, causing a further explosion of internet
traffic. Today, submerged optical cables carry 95 percent of the
world's data traffic. Each single fiber has a bandwidth in excess
of 1 terahertz, one thousand times greater than what is possible
with copper wire.
Free Space Optical
Fiber optics enables significantly higher data transmission
rates, over longer distances, compared to copper wire. But
fiber optics is limited by the length of the strand of fiber.
What if the benefits of optical data transmission could be
untethered from this physical limitation, extending thousands
of miles through space?
Laser communications, also known as Free Space Optical
(FSO) communications, utilizes much of the technology
developed for fiber optics to wirelessly transmit data through
air, vacuum, or outer space. FSO is reliable over vast distances
when the light propagates in space for inter-satellite and
deep space links.
Unfortunately, here on Earth, atmospheric factors such as
fog, rain, dust, heat, and even birds pose significant challenges
to Free Space Optics (FSO) technology. These factors lead to
signal failures and unacceptable error rates and limit the feasibility
of long-distance point-to-point optical links between
terrestrial terminals.
Space Lasers Vastly Outperform RF
In the early 2000s, companies like Terabeam, AirFiber, and
CableFree invested significant sums in FSO as an alternative to
fiber optics. However, none of these ventures could overcome
the challenges posed by atmospheric conditions to establish
commercially viable services.
Terrestrial laser internet service is experiencing a resurgence,
with deployments in 13 countries, including Australia,
Kenya, and Fiji. In June 2023, Alphabet, the parent company
of Google, unveiled its ambitious plans for large-scale implementations
in regions of India and Africa, where fiber optics
is difficult to deploy, aiming to provide up to 20 Gbps bidirectional
throughput within a 20 km range.
7000
6000
Driven by
5000
4000
3000
2000
1000
Proliferated Constellations
of Low Earth Orbit (LEO)
Satellites
LEO
Exponential Growth
of Satellites
Other
GEO
Analyzing the growth of satellites since the year 2000. (Image: Kaman
Precision Products)
Aerospace & Defense Technology, August 2024
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Aerospace & Defense Technology - August 2024

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