1. FREE SPACE OPTICAL
COMMUNICATION
PRESENTED BYNIDHI P TIGGA
& MRINAL

2. Introduction to the concepts of Free
Space Optics (FSO)


FSO was initially
developed by NASA
and US military.
FSO is a line-of-sight
technology which
uses LASERS and
Photo detectors to
provide optical
connections between
two points—without
the fiber.

3. Introduction to the concepts of Free
Space Optics (FSO)
 It uses optical communication technology.
 Uses invisible beams of light to provide
optical bandwidth connections.
 FSO can transmit data, voice or video at
speeds capable of reaching 1.25 Gbps.

5. How Free Space Optics /
Laser Communications
Works
 It's based on connectivity between FSO-
based optical wireless units.
 Provide full-duplex (bi-directional)
capability.
 Each optical wireless unit uses an optical
source, plus a lens or telescope.
 Receiving lens or telescope connects to a
high-sensitivity receiver via optical fiber.

6. Free Space Optic Link Equation:





• Preceived = received power
• Ptransmit = transmit power
• Areceiver = receiver area
• Div = beam divergence (in radians)
• Range = link length

7. Denver, Colorado Fog/Snowstorm Conditions

8. Preventing Interception of the Signal

9. Another view of the narrow beam divergence inherent in
FSO transmission.

10. Signal Propagation Impediments:

Fog: The primary way to counter fog when deploying
FSO is through a network design that shortens FSO link
distances and adds network redundancies.

Absorption: This causes a decrease in the power
density (attenuation) of the FSO beam and directly
affects the availability of a system.

Scattering: 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.

11. Signal Propagation Impediments(contd):

Physical obstructions: Flying birds can temporarily
block a single beam, but it tends to cause short
interruptions, and transmissions are easily and
automatically resumed.

Building sway/seismic activity: The movement of
buildings can upset receiver and transmitter alignment.

Scintillation: Heated air rising from the earth or manmade 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 end.

12. S.NO
System Infrared Light (765 nm)
Power Losses
1
Clear, still air
-1 to -5 dB/km
2
Scintillation
0 to -3 dB/km 0
3
Birds or foliage Impenetrable
0 to -20 dB
4
Window (double-glazed)
-3 to -1 dB
5
Light mist (visibility 400m)
-25 to -1 dB/km
6
Medium fog (visibility 100m)
-120 to -1 dB/km
7
Thick fog (visibility 40m)
-1 to -300 dB/km
8
Light rain (25mm/hour)
-1 to -10 dB/km
9
Heavy rain (150mm/hour)
-25 to -40 dB/km

13. ADVANTAGES OF FSO SYSTEMS
 Installation cost is very low as compared to
laying Fiber.
 No sunk costs.
 Highly secure transmission possible.
 High data rates
 Immunity to electromagnetic interference.
 License free long-range operation (in
contrast with radio communication)

14. DISADVANTAGES OF FSO SYSTEMS
 Beam dispersion
 Atmospheric absorption
 Rain
 Fog (10..~100 dB/km attenuation)
 Snow
 Pollution / smog
 Pointing stability in wind