This is a presentation about FSO and its implementation and working.

1. FREE SPACE
OPTICAL
COMMUNICATION
B Y
JOSH WA V SU N N Y
R EG N O: VIT16C S021
SEMIN A R GU ID E:
ASST. PROF. VIMAL BABU P
C SE D EPA R TMEN T
1

2. Introduction
History
Existing System
Why Free Space Optics?
System Overview
Challenges
Advantages
Disadvantages
Applications
Conclusion
References
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INTRODUCTION
 Free Space Optical Communication (FSO) :-- The transmission of
visible and IR beams through the atmosphere, to obtain optical
communications.
“Free Space” means air, outer space or vacuum.
 Also called “Free Space Photonics(FSP)” or “Optical Wireless ”.
 Line of Sight(LOS) propagation.

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INTRODUCTION (CONTD.)
 Primarily 2 types :-
1) Using LED transmitter.
 Short range communication.
 Produces incoherent light.
2) Using LASER transmitter.
 Long range communication.
 Produces coherent light.

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HISTORY
 Ancient Greeks used a coded alphabetic signalling with torches.
In 1880, Alexander Graham Bell invented “photophone”.
Invention of LASERs in 1960s revolutionized Free Space Optics.
The USA, in the early 1980s, started using it in military communications.
Germany & France made significant advancements in satellite
communications.

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EXISTING SYSTEM
 Optical fiber communication.
 Long, thin strands of very pure glass encircled by plastic casing.
 Works under the principle of Total Internal Reflection(TIR).
 Costly.

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WHY FREE SPACE OPTICS?
 WHY NOT JUST BURY MORE FIBER?
 Cost.
 Rights of way.
 Permits.
 Trenching.
 Time.
 With FSO, especially through the
windows, no permits, no digging and
no fees..!

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WHY FREE SPACE OPTICS?(contd.)
 Very narrow and directional beam.
 Beams with very narrow diameter.
 Very close spacing of links without interference.
 No side lobes.
 Highly secure.
 Efficient use of energy.
 Ranges of 20m to about 4kms possible.

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WHY FREE SPACE OPTICS?(contd.)
 Deployment behind windows.
 Rapid installations without trenching and
permitting.
 Direct connection to the end user.
 Bypasses the building owner.

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WHY FREE SPACE OPTICS?(contd.)

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SYSTEM OVERVIEW & WORKING
 Uses a directed beam of light radiation b/w transmitter and receiver.
 An FSO unit consists of :-
1. Optical Transmitter.
2. Optical Receiver.
3. Transmission Medium.
 Uses lens on both transmitter & receiver.
 Maximum range is about 4 kms.

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SYSTEM OVERVIEW & WORKING (contd.)
A basic diagram of FSO

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SYSTEM OVERVIEW & WORKING (contd.)

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SYSTEM OVERVIEW & WORKING (contd.)

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SYSTEM OVERVIEW & WORKING (contd.)
1) Source :- Data to be transmitted.
2) Modulator :- Performs direct modulation of message
signal with the carrier signal.
3) Laser Driver :- A device that delivers constant current
to the laser diode for smooth operation.
4) Laser Diode :- Produces modulated laser beams for transmission.

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SYSTEM OVERVIEW & WORKING (contd.)
5) Atmospheric channel :- Medium through which LASER beam
propagates.
6) Photo Detector :- Converts received light signals into electricity or
voltage.
7) Amplifier :- Amplifies the converted signal for efficient demodulation.
8) Demodulator :- Demodulates the received signal to obtain the
transmitted message.

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SYSTEM OVERVIEW & WORKING (contd.)
9) Destination :- Receiving end of data which have
been transmitted.

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CHALLENGES FACED

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CHALLENGES FACED (contd.)
 Obstructions :- Obstructions in the path can hinder transmission.
 Fog :- Aerosol consisting of water droplets and ice.
 Absorption or scattering of optical signals due to airborne particles.
 Can result in complete outage.
 Can be alleviated by shortening link distances and adding n/w redundancies.

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CHALLENGES FACED (contd.)
 Scintillation :- Heated air rising from Earth or man-made devices
creates temperature variations in the atmosphere.
 Results in beam spreading and wandering.
 Almost mutually exclusive with fog attenuation.
 Results in increased error rates, but not complete outage.
 Building sway / Seismic activity :- Movement of building can upset
receiver and transmitter alignment.

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CHALLENGES FACED (contd.)
 Absorption :- Atmospheric absorption results in power attenuation
of the FSO beam.
 Scattering :- When the scatterer is smaller than the wavelength, it
is known as Rayleigh scattering. When the scatterer
is of comparable size with the wavelength, it is known
as Mie scattering.

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SECURITY
 FSO laser beams cannot be detected with spectrum analyzers
or RF meters.
 FSO laser transmissions are optical and travel along a line of
sight path that cannot be intercepted easily.
 The laser beams generated by FSO systems are narrow and
invisible, making them harder to find and even harder to
intercept and crack.

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ADVANTAGES
 Installation cost is very low when compared to optical fiber
communication.
 No licensing required like RF.
 Immunity from electromagnetic interference.
Deployment of FSO system is quicker and easier.
Data is highly secured.

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ADVANTAGES (contd.)
 No need of trenching and digging land.
 High data transmission rate of up to 2.5GB/s.
 Unregulated spectrum and hence huge bandwidth available.

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DISADVANTAGES
 Transmission rate is weather dependent.
 If sun goes directly behind the transmitter, it can intercept
the signal.
 Distance is limited.
 High launch power can cause eye hazards.

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DISADVANTAGES (contd.)
 Transmission rate is affected by environmental factors
like fog, snow, rainfall et cetera.
 Atmospheric barriers and physical obstructions can act
as a deterrent.

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APPLICATIONS
 Enterprise connectivity.
 It is used to communicate between spacecrafts as lower
chance of disturbances of signal.
 Military and government applications for secure data
transfer.
 Disaster management uses due to the ease in setting up
the network.

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CONCLUSION
 For future short range applications, FSO provides a promising and
viable supplemental technology to wireless systems and optical fiber.
 FSO provides a low cost, rapidly deployable method of gaining access
to fiber-quality connections.
 The growing requirements for efficient and secure communications
has led to an increased interest in FSO communication.

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REFERENCES
[1] S. Ghosh, K. Basu and S. K. Das, "An architecture for next generation radio access networks,"
IEEE Network, vol. 19, 20017, pp.35-42
[2] J. Hou and D. C. O'Brien, "Vertical handover-decision-making algorithm using fuzzy logic for the
integrated Radio-and-OW system," Wireless Communications, IEEE Transactions on, vol. 5, 2016, pp.
176-185.
[3] S. Ghosh. "Emergent technology based Radio Access Network (RAN) design framework for next
generation broadband wireless systems," M.S. thesis, Dept. Comp. Sci. and Eng., Univ. Texas at
Arlington, 2014.
[4] T. Kamalakis, I. Neokosmidis, A. Tsipouras, S. Pantazis and I. Andrikopoulos, "Hybrid free space
optical/millimeter wave outdoor links for broadband wireless access networks," in Personal, Indoor and
Mobile Radio Communications, IEEE 18th International Symposium on, 2018, pp. 1-5.

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