O Introduction to the concepts of Free Space Optics
O Propagation concepts, Link Budget calculations.
O FSO: Last Mile Bottleneck Solution.
O Configurations of FSO systems.
O Chaining in FSO Systems
O DATA security/ Safety considerations for FSO
O Signal Propagation impediments.
O Advantages of FSO as regards to other widely used
O Physical Applications of FSO systems
O Manufacturers/Players in field of FSO.
Requirements of a good Transmission System:
O High Bandwidth
O High BER
O Low SNR
O Power efficient
O Provide Data Security.
O Low cost
O Easy to install and maintain.
Introduction to the concepts of Free Space
O FSO is a line-of-sight technology which uses LASERS and
Photo detectors to provide optical connections between two
points—without the fiber.
O FSO can transmit data, voice or video at speeds capable of
reaching 2.5 Gbps. Products capable of speeds upto 10
Gbps are expected to hit the markets within one year.
O FSO units consist of an optical transceiver with a laser
(transmitter) and a Photo detector (receiver) to provide full
duplex (bi-directional) capability.
O FSO systems use invisible infrared laser light wavelengths
in the 750nm to 1550nm range.
LAST MILE BOTTLENECKS
O Less then 5% of all buildings in the US have a direct connection to
the very high speed (2.5-10 Gbps) fiber optic backbone, yet more
than 75% of businesses are within 1 mile of the fiber backbone.
O Most of these businesses are running some high speed data
network within their building, such as fast Ethernet (100 Mbps), or
Gigabit Ethernet (1.0 Gbps).
O Yet, their Internet access is only provided by much lower
bandwidth technologies available though the existing copper wire
infrastructure (T-1 (1.5 Mbps), cable modem (5 Mbps shared) DSL
(6 Mbps one way) ), etc.
O The last mile problem is to connect the high bandwidth from the
fiber optic backbone to all of the businesses with high bandwidth
O DSL and cable modems cannot provide true broadband
services. Cable modems enjoy higher capacity, yet the channel
is shared and the amount of bandwidth at any given time is not
O Copper lines provide data rates to a fraction of 1 Mbps.
O T1 lines can reach upto a few Mbps but are still far away from
the Gbps speed which the fiber backbone can support.
O The chart below shows how these technologies address
different market segments based on technology, technical
capabilities (reach, bandwidth), and economic realities.
A high-bandwidth cost-effective solution to the last mile problem is to use
free-space laser communication (also known as or optical wireless) in a
mesh architecture to get the high bandwidth quickly to the customers.
To overcome the security in a network two conditions are
O (1) Intercept enough of the signal to reconstruct data
O (2) Be able to decode that information.
Narrow divergence of the FSO transmit path (shown in
red) as compared to a typical Radio Frequency (RF) path
(shown in blue). The tightly collimated FSO beam ensures
that the signal energy is focused on the receiving unit,
making interception of the beam extremely difficult.
Preventing Interception of the Signal
Another view of the narrow beam divergence inherent in FSO
transmission. (For clarity only one transit beam is shown.)
Signal Propagation Impediments:
O Fog: It is the major challenge to reduce the effect, FSO distance
must be reduced.
O Absorption: Attenuation occurs due to absorption and
O Scattering: Caused by suspended particles. When the scatterer is
smaller than the wavelength, this is known as
Rayleigh scattering. When the scatterer is of
comparable size to the wavelength, this is known
as Mie scattering.
O Physical obstructions: Flying birds can temporarily block a
O Building sway/seismic activity: The movement of buildings
can upset Rx-Tx alignment.
O Scintillation: Heated air rising from the earth or man-made
devices such as heating ducts creates temperature variations
among different air pockets. This can cause fluctuations in signal
amplitude which leads to image fluctuations at the FSO receiver
O Rough Estimate of Power losses in the system Infrared ight (765 nm) :
O Clear, still air -1 dB/km -5 dB/km
O Scintillation 0 to -3 dB/km 0
O Birds or foliage Impenetrable 0 to -20 dB
O Window (double-glazed) -3 dB -1 dB
O Light mist (visibility 400m) -25 dB/km -1 dB/km
O Medium fog (visibility 100m) -120 dB/km -1 dB/km
O Thick fog (visibility 40m) -300 dB/km -1 dB/km
O Light rain (25mm/hour) -10 dB/km -10 dB/km
O Heavy rain (150mm/hour) -25 dB/km -40 dB/km
ADVANTAGES OF FSO SYSTEMS
O No licensing required.
O Installation cost is very low as compared to laying Fiber.
O No sunk costs.
O No capital overhangs.
O Highly secure transmission possible.
O High data rates, upto 2.5 Gbps at present and 10 Gbps in the
Applications Of FSO Systems
ODisaster management as was exhibited
during the Sept 11 attacks.
OMerill Lynch & Co. has set up FSO system
from its Vesey Street office towers across
the Hudson River to an alternate site in
OTeraBeam, a major producer of FSO
equipment, successfully deployed FSO at
the Sydney Summer Olympic Games.
OA network of FSO devices is fast coming
up in Seattle which is touted as the Capital
of Fog. Manufacturers believe that if an
FSO system can successfully work in
Seattle then it can do so in any part of the
OAffordably extend existing fiber network.
ODisaster recovery and temporary
Manufacturers/ Players in the Field of FSO:
O LightPointe: A San Diego based company which received
contributions from Cisco Systems and Corning to the tune of $33
million. It has raised a total of $51.5 million.
O AirFiber: Another San Diego based company which has
received contributions from Nortel Networks to the tune of $50
million. It has raised a total of $92.5 million.
O Terabeam: A Kirkland, WA based company has received
funding from Luscent technologies to the tune of $450 million
and has raised $585 million to date.
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