Seminar on Free Space Optics

1. FREE SPACE
OPTICS
BY SABARINATH
S
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2. WHAT IS FSO?
• FSO stands for Free Space Optics
• Optical Communication Technology
• An LOS technology via Free Space
• No requirement of the optical
fiber cable
• Offers optical transmission up to
10Gbps
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3. HISTORY
• Firstly, Used by Greeks in 18th century.
• 19th Century- Abraham Graham Bell—done experiments —
Photophone
• Light beams to broadcast voice conversations across the air
• Idea of FSO was established but not commercialized 3
Fig: Bells Photophone Transmitter, 1880 Photograph

4. FSO DATA LINKS
The total attenuation A(λ) induced by the atmosphere can be
calculated as follows:
Α(λ) = αfog(λ)+ αsnow(λ)+ αrain(λ)+ αscattering(λ), [dB/km]
where αx(λ) is the attenuation produced by the given weather
parameters and λ is an operational wavelength.
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5. WORKING
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6. CHALLENGES
• Weather Conditions
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7. Absorption
• Occurs when photons are extinguished by suspended
water molecules
• Reduces the power density, wavelength dependant
In general Beer's law describes atmospheric attenuation:
τ=exp[-(αabs+βscat)L]
L: Distance between the transmitter and receiver
αabs: Atmospheric absorption
βscat: Scattering coefficients
αabs= σabs Nabs.
σabs :Effective absorption cross-section
Nabs :Concentration of gas molecule
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8. Scattering
• No energy loss in scattering, only a directional redistribution of energy
• Two main scattering: Rayleigh & Mie
• Scattering type depends on the relationship between the size of scattering
particles and the wavelength
Total scattering coefficient is given by:
βscat=βm+βa
where βm and βa denote Rayleigh and Mie scattering.
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9. Scintillation
• Temperature variations caused by
heated air rising from the earth or
man-made devices
• Cause signal amplitude fluctuations
• Beam wander and beam spreading
are two other turbulence effects
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Fig: Propagation of a laser beam through turbulent atmosphere

10. CONVENTIONAL v/s FREE SPACE OPTICS
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*DSL-Digital Subscriber Line
10 Gbps

11. FUTURE SCOPE
• NASA's Laser Communication Relay
Demonstration will test laser
communications from
geosynchronous orbit to Earth
• Record-breaking data rates of 200
Gbps from a low-Earth orbit small
satellite to a ground station.
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12. ADVANTAGES
• Operates in an unregulated frequency spectrum, the FCC has not mandated
licenses
• FSO has high transmission rates of up to 2.5 Gbps
• FSO has no interferences with other transmissions
• It is fast, low-cost, and easy installation
• FSO is highly immune to interception and jamming
• Good commercial availability
• User-adjusted capacity with an option of data link reconfiguration.
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13. APPLICATIONS
• Metro Area Networks (MAN)
• Enterprise Connectivity
• Backhaul
• Service acceleration
• Military applications
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15. THANK YOU
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