Transcript EE 566 Optical Communication

Free Space Optic (FSO)
EE 566
Optical Communication
Ming Li
[email protected]
Why choose this topic?
Why still choose this topic?
September 11, 2001, New York
 Every
thing was destroyed
including normal fiber link
Wall street stock
market was closed
because the
communication was
destroyed

Two of these units were used between
building to re-establish a high speed
communication link.
FSO
communication between Merrill Lynch
Brokerage and Wall Street in New York following the
terrorist attack that destroyed normal fiber optic link
History of Free Space Optics

The transmission of information using
light is actually not a new idea.
Great
Wall
In the late nineteenth century, Alexander
Bell expanded his "phone-phone"
communication which modulated by
sunlight.
Birth of Laser FSO Communications
Gemini-7
In the mid-1960's
NASA initiated
experiments to
utilize the laser as a
means of
communication
between the ground
and space.
Satellite Laser Communication
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Space-to-Ground Lasercom Link
2000 km Link Distance
1 Gbps Transmission Rate
Chinese First Maned Spaceship
Military Application of FSO
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Air Force
Its potential for low
electromagnetic
emanation when
transferring sensitive
data
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
Navy
Secure
communication
with submerged
submarines.
Technology from Space
Lasercom
Advantage of FSO
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Wireless communicate from A to B
Low costs ($10K to $20K)
High bit rate (10 Mbps to 2.5 Gbps)
Set up a link in a few days
The lasers used are eye safe, so
even a butterfly can fly unscathed
through a beam
Application of FSO
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Connectivity Solutions
'Last-Mile' Network Solutions
Temporary Network Provision
Cable Free Connectivity in the Finance
Sector
CCTV Security Applications
GSM Microcell Connectivity
Industrial estates, Science parks and university
campus environments typically exhibit a common
problem – a number of separate buildings, separated
by roads or other obstacles, between which
communications links are frequently in demand.
Cable digging, increasingly unpopular in cities, is
regulated by the local authority who may restrict redigging frequency of roads - and the cost may be
prohibitive in any case, especially if a river or railway is in
the way.
FSO vs RF
RF 2.4 GHz systems were typically
running at 2-4 Mbps due to
interference issues in the unlicensed
frequency ranges
FSO provided 10 Mbps of throughput for
less than unlicensed RF
FSO was less cost, more secure, and
seemed simpler
Challenge of FSO

Challenge #1—hitting the
target
Challenge #2—interrupted
signals
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Hitting the target
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Getting a laser beam to hit the mark
in a laboratory setting is easy, but in
the real world it is much harder.
1)Atmospheric turbulence
2)Fog
3)Building movement
Atmospheric attenuation
and scatter
6.5 dB/km
150 dB/km
225 dB/km
300m distance to tall building
Solution
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Active beam steering (sometimes
involving MEMS),
Multiple laser beams,
Automated power control, and
calculated laser beam divergence.
Pulsed laser beams start out just
centimeters wide and can diverge to 1
meter or more over typical link
distances—like using a really big bullet
to hit a small target.
Challenge #2—
interrupted signals
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An email is beaming across the
FSO connection just as a bird flies
through, blocking the signal.
Solution #2—no lost
data
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No fear. FSO linkheads essentially "talk" to
one another, and just as people repeat words
in conversation, data can be retransmitted in
the event of a temporary beam blockage.
Several companies even have redundant
radio-frequency links that simultaneously
transmit the FSO signal. When the radio or
the FSO signal is blocked, the counterpart is
automatically used—no loss of data, and no
delay.
Companies and rapidly
advancing FSO technology
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AirFiber
Hybrid Free- space optic/Radio
LightPointe
Multi-beam sending process
Terabeam
carrier-grade FSO equipment and services
AirFiber
www.airfiber.com
San Diego, California, was founded in 1998
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AirFiber's products
combine FSO with
60 GHz millimeterwave radio, makes
wireless
communication
possible in any
weather.
LightPointe
www.lightpointe.com
San Diego, California, was founded

LightPointe's FSO
products utilize a
multi-beam sending
process, which
overcomes
atmospheric
degradations and
temporary beam
obstructions by
overlapping
redundant infrared
beams.
Terabeam
www.terabeam.com
Kirkland, Washington, was founded in 1997

Terabeam's
FSO products
have
advanced
beam-steering
features that
update beam
direction up to
300 times per
second.
Conlusion
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FSO is just starting to be applied to
solve the Internet “last-mile”
interconnectivity problem. Some
believe that it may be the unlimited
bandwidth solution for the metro
urban core of downtown building-tobuilding communication, as well as the
optimal technology for home-to-home
and office-to-office connectivity.
Reference
http://www.lightpointe.com/
http://www.freespaceoptic.com/
http://www.fsonews.com/
http://www.cablefreesolutions.com/
http://www.thefoa.org/
http://www.free-space-optics.org/
http://www.freespaceoptics.com/
http://www.opticsreport.com/