2. Outlines
• Concept
• Why Free Space Optics?
• Origin & Technology of FSO
• Working
• Challenges
• Applications
• Merits & Demerits
• References
3. Concept
• 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.
6. Why Free Space Optics?
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
8. Why Free Space Optics?
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
9. Why Free Space Optics?
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
10. Origin
• 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.
11. Origin (cont.)
• 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.
12. Technology
• 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.
13. Working
• 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.
14. Working (cont.)
• 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.
17. Challenges
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
18. Challenges
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
19. Challenges
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.
20. Applications
• Metro Area Networks (MAN)
• Last Mile Access
• Enterprise connectivity
• Fiber backup
• Backhaul
• Service acceleration
21. Merits
• 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
22. Demerits
• Fog
• Physical obstructions
• Scintillation
• Solar interference
• Scattering
• Absorption
• Building sway / Seismic activity
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 ofApplications 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
