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FREE SPACE OPTICAL COMMUNICATION

(FSO)

Submitted By : Shantanu Praksah Naik

Branch : ECE( 3rd year)

Roll no : CSJMA10001390102

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PRESENTATION OVERVIEW

Introduction to FSO ?

Why FSO Today ?

Free-space optics subsystems

Working of FSO

Basic Architectures

Free Space Optics Applications

Challenges

Eye Safety

FSO Advantages

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Why FSO Today

Why Not Just Bury More Fiber?

No Trenching as in laying fiber optics

Less Installation Time

Low Cost

High data rates, up to 2.5Gbps at

present and 10 Gbps in the nearfuture.

Requires no RF spectrum licensing.

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FREE-SPACE OPTICS SUBSYSTEMS

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How FSO Works1 Network traffic converted into

pulses of invisible light

representing 1s and 0s

2Transmitter projects the

carefully aimed light pulsesinto the air

3 A receiver at the other end of

the link collects the light using

lenses and/or mirrors

Received signal converted back

into fiber or copper and

connected to the network

4

Reverse direction data transported

the same way. FULL DUPLEX5

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Basic Architectures

1. POINT TO POINT ARCHITECTUREIn this architecture two places are

connected using FSO technology

2. MESH ARCHITECTURE

Composed of a series of interconnected nodes

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3. POINT-TO-MULTIPOINT ARCHITECTUREA single node serves as an originator and multiple

links emanate from it.

4. MULTIPLE PTP ARCHITECTURESuitable to create an extensive link path

between distant buildings

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FSO CORE APPLICATIONS

METRO NETWORK EXTENSIONSFSO can be deployed to extend an existing metro ring or

to connect new networks

ENTERPRISE CONNECTIVITY

The flexibility of FSO allows it to be deployed in manyenterprise applications

FIBER COMPLEMENTFSO may also be deployed as a redundant link to back-up

fiber

DWDM SERVICESIndependent players aiming to build their own fiber rings

may use FSO to complete part of the ring

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CHALLENGES IN WORKINGSunlight

Building

Motion

Alignment

WindowAttenuation

Fog

Each of these factors can attenuate (reduce) the signal. However, there

are ways to mitigate each environmental factor.

Scintillation

RangeObstructions

Low Clouds

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Challenges

Atmospheric Attenuation - FOG

Absorption or scattering of opticalsignals due to airborne particles

Primarily FOG but can be rain, snow,

smoke, dust, etc.

Can result in a complete outage

FSO wavelengths and fog droplets

are close to equal in size (Mie

Scattering)

Typical FSO systems work 2-3X

further than the human eye can see

High availability deployments require

short links that can operate in the fog

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ChallengesSCINTILLATION

Scintillation is the spatial variation in light intensity caused byatmospheric turbulence

Beam spreading and wandering due to propagation through air

pockets of varying temperature, density, and index of refraction.

Almost mutually exclusive with fog attenuation.

Results in increased error rate but not complete outage.

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Challenges

Building Motion

Type Cause(s) Magnitude Frequency

Tip/tilt Thermal

expansion

High Once per day

Sway Wind Medium Once everyseveralseconds

Vibration Equipment (e.g.,HVAC), doorslamming, etc.

Low Many timesper second

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Challenges

Building Motion Thermal Expansion

Results from Seattle

Deployment:

15% of buildingsmove more than 4

mrad

5% of buildings move

more than 6 mrad

1% of buildings move

more than 10 mrad

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Challenges

Compensating for Building Motion Two Methods

1. Automatic Pointing and Tracking

Allows narrow divergence beams for greater link margin

System is always optimally aligned for maximum link margin

Additional cost and complexity

1. Large Divergence and Field of View

Beam spread is larger than expected building motion Reduces link margin due to reduced energy density

Low cost

0.2 1 mrad divergence

= 0.2 to 1 meter spread at 1 km

2 10 mrad divergence

=2 to 10 meter spread at 1 km

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EYE SAFETY AND FREE SPACE OPTICS

Laser beams with wavelengths in the range of 400 to 1400 nm

emit light that passes through the cornea and lens and is

focused onto a tiny spot on the retina (NOT SAFE)

wavelengths above 1400 nm are absorbed by the cornea and

lens, and do not focus onto the retina(SAFE)

Any FSO system can be designed eye safe independent of the

wavelength used

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FREE SPACE OPTICS (FSO)

ADVANTAGES

Requires no RF spectrum licensing.

Is immune to radio frequency interference or saturation.

Very secure due to high directionality and narrow ness of

beams

Zero chances of network failure.

Full Duplex Operation

Can be deployed behind windows, eliminating the need for

costly rooftop rights

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CONCLUSION

FSO network can be rapidly deployed to provide

immediate service to the customers. Though not

very popular at the moment FSO has a tremendous

scope for deployment. FSO adds the wireless

feature to OFC and thus provide a boon in the field

of high bandwidth requirements.

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REFERENCES

[1] Willebrand, S. Ghuman Baksheesh. Free Space

Optics : Enabling Optical Connectivity in Todays

Networks Publisher Sams Publishing

[2] Clark Gerald R. Free Space Optics : Extending the

Metro Optical Networks. Publisher : LightPointe.

[3] http://www.wikipedia.org

[4] http://www.lightpointe.com

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THANK YOU