This document provides an overview of free space optical communication (FSO). It begins with an introduction that defines FSO as the transmission of visible and infrared beams through the atmosphere to achieve optical communications. It then discusses the history and existing fiber optic systems. The document outlines the advantages of FSO such as low cost, high security, and rapid deployment. It also discusses challenges like weather effects and limitations in range. Applications mentioned include enterprise connectivity, military/government use, and disaster management. The conclusion states that FSO provides a promising supplemental technology to wireless and fiber optic networks.

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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