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Free Space Optics
The Speed of Fiber
The Flexibility of Wireless
What is Free Space Optics (FSO)?
Free-space optics (FSO) is a line-of-sight
technology that uses lasers to provide
optical bandwidth connections that can
send and receive voice, video, and data.
Speeds can reach up to 2.5Gbps
and those speeds can be
transmitted up to 4km over any
protocol.
FSO provides a fiber optic
connection using air instead of
glass
Why FSO?
Requires no spectrum
licensing.
•Is easily upgradeable, and its
open interfaces support
equipment from a variety of
vendors.
•Requires no security
software.
•Is immune to radio frequency
interference or saturation.
•Can be deployed behind
windows, eliminating the need
for costly rooftop rights.
History
Its old technology! Originally developed for NASA and the
military in the 1960s, well before Fiber Optic Cables
How it Works
FSO technology is based on connectivity between FSO-based optical
wireless units, each consisting of a high-power optical source (i.e.
LASAR), plus a lens that transmits light through the atmosphere to
another lens receiving the information. At this point the receiving
lens connects to a
high-sensitivity
receiver via optical
fiber.
Challenges and Solutions
Fog: The primary challenge to FSO. The water droplets in fog can completely
hinder the passage of light through a combination of absorption, scattering, and
refraction.
The only solutions so far is to shorten distances and add redundancies
Absorption: Absorption occurs when water molecules in the
atmosphere extinguish light, leading to a decrease in the power
density of the FSO. Absorption occurs more readily at some
wavelengths than others.
Absorption can be overcome by using power appropriate to
atmospheric conditions, and use of FSO units with multiple beams.
Scattering: Caused when light beams hit particulates in the are and are
directed else ware. Multiple beams and network redundancies can combat this.
Challenges and Solutions
Physical obstructions: Flying birds or construction cranes can temporarily block
single-beam FSO systems.
Optical wireless products using multi-beam systems (spatial diversity) can also
counter temporary obstructions.
Scintillation: Heated air rising from the earth or man-made
devices such as heating ducts create temperature variations
among different air pockets. This can cause fluctuations in signal
amplitude which leads to "image dancing" at the FSO-based
receiver end
Multi-beam systems can also be used to limit Scintillation
problems
Building sway/seismic activity: The movement of buildings can
upset receiver and transmitter alignment. New FSO-based optical
wireless offerings use a large receivers, tracking, and multiple
beams to maintain connectivity.
For more information visit
www.freespaceoptics.org