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FSO (Free Space Optics)

By,
Bhavik Trivedi

29 October 2013

1
Outlines
•
•
•
•
•
•
•
•

Concept
Why Free Space Optics?
Origin & Technology of FSO
Working
Challenges
Applications
Merits...
Concept

[1]

• FSO - optical communication technology that
uses light propagating in free space to transfer
data.
• Line ...
FSO Transmitter

FSO Receiver

Fig. 1 FSO Transmitter & Receiver images [4]

4
Beam Divergence (Frequency) Effect

Fig. 2 Beam Divergence effect [3]
5
Why Free Space Optics? [6]

Why Not Just Bury More Fiber?
• Cost
• Rights of Way

• Permits
• Trenching
• Time
With FSO, e...
Why Free Space Optics? [6]

How FSO Works

7
Why Free Space Optics? [6]

Very Narrow and Directional Beams
•
•
•
•
•
•

Beams only a few meters in diameter at a kilome...
Why Free Space Optics? [6]

Deployment Behind Windows
• Rapid installations without trenching and
permitting
• Direct conn...
Origin

[1]

• Firstly used by Greeks in 8th century.
• According to them fire as the light source, the
atmosphere as tran...
Origin (cont.)

[1]

• Bell converted voice sounds into telephone
signals and transmitted them between
receivers through f...
Technology

[1]

• Uses a directed beam of light radiation
between transmitter and receiver.
• An FSO unit consists of
1) ...
Working

[2]

• FSO work on simple optical transmission
system.
• Modern Laser system provide network
connectivity speed f...
Working (cont.)

[2]

• It works in Tera Hertz (THz) spectrum.
• Wavelength:
• FSO can operate into two wavelengths:
1) 80...
Working (cont.)

[2]

Fig. 3 Sub-systems used in a typical free-space optics unit [2]

15
Challenges [6]

Sunlight

Environmental factors

16
Challenges [6]

Atmospheric Attenuation - FOG
• Absorption or scattering of optical
signals due to airborne particles
• Pr...
Challenges [6]

Low Clouds, Rain, Snow and Dust
• Low Clouds
– Very similar to fog
– May accompany rain and snow

• Rain
–...
Challenges [6]

Scintillation
• Beam spreading and wandering due to propagation through air
pockets of varying temperature...
Applications
•
•
•
•
•
•

[1]

Metro Area Networks (MAN)
Last Mile Access
Enterprise connectivity
Fiber backup
Backhaul
Se...
Merits

[1]

• Flexible network solution over conventional
broadband services.
• Straight forward deployment- no licenses
...
Demerits
•
•
•
•
•
•
•

[1]

Fog
Physical obstructions
Scintillation
Solar interference
Scattering
Absorption
Building swa...
References
[1] Free-space optical communication - Wikipedia, http://en.wikipedia.org/wiki/Free
space_optical_communication...
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Free space optics (FSO)

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Free space optics (FSO)

  1. 1. FSO (Free Space Optics) By, Bhavik Trivedi 29 October 2013 1
  2. 2. Outlines • • • • • • • • Concept Why Free Space Optics? Origin & Technology of FSO Working Challenges Applications Merits & Demerits References 2
  3. 3. Concept [1] • FSO - optical communication technology that uses light propagating in free space to transfer data. • Line of sight technology. • Bandwidth up to 2.5 Gbps. • Uses LED or Laser as a light source. 3
  4. 4. FSO Transmitter FSO Receiver Fig. 1 FSO Transmitter & Receiver images [4] 4
  5. 5. Beam Divergence (Frequency) Effect Fig. 2 Beam Divergence effect [3] 5
  6. 6. Why Free Space Optics? [6] Why Not Just Bury More Fiber? • Cost • Rights of Way • Permits • Trenching • Time With FSO, especially through the window, no permits, no digging, no fees 6
  7. 7. Why Free Space Optics? [6] How FSO Works 7
  8. 8. Why Free Space Optics? [6] Very Narrow and Directional Beams • • • • • • Beams only a few meters in diameter at a kilometer Allows VERY close spacing of links without interference No side lobes Highly secure Efficient use of energy Ranges of 20m to more than 8km possible 8
  9. 9. Why Free Space Optics? [6] Deployment Behind Windows • Rapid installations without trenching and permitting • Direct connection to the end user • Bypasses the building owner – No roof rights – No riser rights 9
  10. 10. Origin [1] • Firstly used by Greeks in 8th century. • According to them fire as the light source, the atmosphere as transmission medium and an eye as a receiver. • 19th century, Alexander Graham Bell – done experiments - which were later called as Photophone. 10
  11. 11. Origin (cont.) [1] • Bell converted voice sounds into telephone signals and transmitted them between receivers through free space along a beam of light for a distance of some 600 feet. • But Photophone never became commercial reality. • Though it demonstrated the basic principle of optical transmissions. 11
  12. 12. Technology [1] • Uses a directed beam of light radiation between transmitter and receiver. • An FSO unit consists of 1) Optical transceiver 2) Laser transmitter and receiver • Uses lens on transmitter and receiver. • Maximum range is about 4 kms. 12
  13. 13. Working [2] • FSO work on simple optical transmission system. • Modern Laser system provide network connectivity speed from 660 Mbps onwards. • Two beams are kept narrow. • The receiver detectors are either PIN diodes or Avalanche Photodiode. • FSO transmits invisible light beams between two beams. 13
  14. 14. Working (cont.) [2] • It works in Tera Hertz (THz) spectrum. • Wavelength: • FSO can operate into two wavelengths: 1) 800 nm 2) 1550 nm • 1550 nm wavelengths are more preferred due to its advantages over 800 nm. 14
  15. 15. Working (cont.) [2] Fig. 3 Sub-systems used in a typical free-space optics unit [2] 15
  16. 16. Challenges [6] Sunlight Environmental factors 16
  17. 17. Challenges [6] Atmospheric Attenuation - FOG • Absorption or scattering of optical signals 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 17
  18. 18. Challenges [6] Low Clouds, Rain, Snow and Dust • Low Clouds – Very similar to fog – May accompany rain and snow • Rain – Drop sizes larger than fog and wavelength of light – Extremely heavy rain (can’t see through it) can take a link down – Water sheeting on windows • Heavy Snow – May cause ice build-up on windows – Whiteout conditions • Sand Storms – Likely only in desert areas; rare in the urban core 18
  19. 19. Challenges [6] Scintillation • 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. 19
  20. 20. Applications • • • • • • [1] Metro Area Networks (MAN) Last Mile Access Enterprise connectivity Fiber backup Backhaul Service acceleration 20
  21. 21. Merits [1] • Flexible network solution over conventional broadband services. • Straight forward deployment- no licenses required • Low initial investment • Ease of installation • Re-deployability • High bit rates and low error rates 21
  22. 22. Demerits • • • • • • • [1] Fog Physical obstructions Scintillation Solar interference Scattering Absorption Building sway / Seismic activity 22
  23. 23. References [1] Free-space optical communication - Wikipedia, http://en.wikipedia.org/wiki/Free space_optical_communication [2] Vikrant Kaulgud, Free space optics Bridges the last mile, Electronics for U, June 2003 pp. 38-40. www.electronicsforu.com/electronicsforu/articles/hits.asp?id=822 [3] Hemmati, H., Free-space optical communications program at JPL, Jet Propulsion Lab., California Inst. of Technol., Pasadena, CA, USA, IEEE Lasers and Electro-Optics Society, pp. 106 - 107, vol.1, Nov. 1999. [4] John Kaufmann, Free Space Optical Communications: An Overview of Applications and Technologies, Boston IEEE Communications Society Meeting, December 1, 2011. [6] John Schuster, Free Space Optics (FSO) Technology Overview, Chief Technology Officer, Terabeam Corporation. www.fcc.gov/realaudio/presentations/2002/.../technology_overview.ppt‎ [5] Andy Emmerson, Fiberless Optics, Everyday practical electronics, April 2003, pp. 248. [6] www.fsona.com [7] www.freespaceoptic.com 23

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