FREE SPACE OPTIC COMMUNICATIONSFREE SPACE OPTIC COMMUNICATIONS

Presented By: Ankur S. Presented By: Ankur S. SharmaSharma

Course: ECEE-641 Fiber Course: ECEE-641 Fiber Optics and Optical Optics and Optical Communications ICommunications I

Instructor: Instructor: Dr. Timothy P. KurzwegDr. Timothy P. Kurzweg

PRESENTATION LAYOUT:PRESENTATION LAYOUT:

Introduction to the concepts of Free Space Optics (FSO).Introduction to the concepts of Free Space Optics (FSO). Propagation concepts, Link Budget calculations.Propagation concepts, Link Budget calculations. FSO: Last Mile Bottleneck Solution.FSO: Last Mile Bottleneck Solution. Configurations of FSO systems.Configurations of FSO systems. Chaining in FSO SystemsChaining in FSO Systems DATA security/ Safety considerations for FSO systems.DATA security/ Safety considerations for FSO systems. Signal Propagation impediments.Signal Propagation impediments. Advantages of FSO as regards to other widely used Advantages of FSO as regards to other widely used

systems.systems. Physical Applications of FSO systemsPhysical Applications of FSO systems Manufacturers/Players in field of FSO.Manufacturers/Players in field of FSO.

Requirements of a good Requirements of a good Transmission System:Transmission System:

High BandwidthHigh Bandwidth High BERHigh BER Low SNRLow SNR Power efficientPower efficient Provide Data Security.Provide Data Security. Low costLow cost Easy to install and maintainEasy to install and maintain..

Introduction to the concepts of Free Introduction to the concepts of Free Space Optics (FSO)Space Optics (FSO)

FSO is a line-of-sight technology FSO is a line-of-sight technology which uses LASERS and Photo which uses LASERS and Photo detectors to provide optical detectors to provide optical connections between two points—connections between two points—without the fiber.without the fiber.

FSO can transmit data, voice or FSO can transmit data, voice or video at speeds capable of video at speeds capable of reaching 2.5 Gbps. Products reaching 2.5 Gbps. Products capable of speeds upto 10 Gbps capable of speeds upto 10 Gbps are expected to hit the markets are expected to hit the markets within one year.within one year.

FSO units consist of an optical FSO units consist of an optical transceiver with a laser transceiver with a laser (transmitter) and a Photo detector (transmitter) and a Photo detector (receiver) to provide full duplex (bi-(receiver) to provide full duplex (bi-directional) capability.directional) capability.

FSO systems use invisible infrared FSO systems use invisible infrared laser light wavelengths in the laser light wavelengths in the 750nm to 1550nm range.750nm to 1550nm range.

FSO Major Sub SystemFSO Major Sub System

Free Space Optic Link Equation:Free Space Optic Link Equation:

• • Preceived = received powerPreceived = received power • • Ptransmit = transmit powerPtransmit = transmit power • • Areceiver = receiver areaAreceiver = receiver area • • Div = beam divergence (in radians)Div = beam divergence (in radians) • • Range = link lengthRange = link length

Denver, Colorado Fog/Snowstorm ConditionsDenver, Colorado Fog/Snowstorm Conditions

Theoretical Maximum Range:Theoretical Maximum Range:

LAST MILE BOTTLENECKSLAST MILE BOTTLENECKS Less then 5% of all buildings in the Less then 5% of all buildings in the

US have a direct connection to the US have a direct connection to the very high speed (2.5-10 Gbps) fiber very high speed (2.5-10 Gbps) fiber optic backbone, yet more than 75% optic backbone, yet more than 75% of businesses are within 1 mile of of businesses are within 1 mile of the fiber backbone. the fiber backbone.

Most of these businesses are Most of these businesses are running some high speed data running some high speed data network within their building, such network within their building, such as fast Ethernet (100 Mbps), or as fast Ethernet (100 Mbps), or Gigabit Ethernet (1.0 Gbps). Gigabit Ethernet (1.0 Gbps).

Yet, their Internet access is only Yet, their Internet access is only provided by much lower bandwidth provided by much lower bandwidth technologies available though the technologies available though the existing copper wire infrastructure existing copper wire infrastructure (T-1 (1.5 Mbps), cable modem (5 (T-1 (1.5 Mbps), cable modem (5 Mbps shared) DSL (6 Mbps one Mbps shared) DSL (6 Mbps one way) ), etc.way) ), etc.

The last mile problem is to connect The last mile problem is to connect the high bandwidth from the fiber the high bandwidth from the fiber optic backbone to all of the optic backbone to all of the businesses with high bandwidth businesses with high bandwidth networks.networks.

DSL and cable modems cannot provide true DSL and cable modems cannot provide true broadband services. Cable modems enjoy higher broadband services. Cable modems enjoy higher capacity, yet the channel is shared and the capacity, yet the channel is shared and the amount of bandwidth at any given time is not amount of bandwidth at any given time is not guaranteed.guaranteed.

Copper lines provide data rates to a fraction of 1 Copper lines provide data rates to a fraction of 1 Mbps.Mbps.

T1 lines can reach upto a few Mbps but are still T1 lines can reach upto a few Mbps but are still far away from the Gbps speed which the fiber far away from the Gbps speed which the fiber backbone can support.backbone can support.

The chart below shows how these technologies The chart below shows how these technologies address different market segments based on address different market segments based on technology, technical capabilities (reach, technology, technical capabilities (reach, bandwidth), and economic realities.bandwidth), and economic realities.

A high-bandwidth cost-effective solution to the last mile problem is to use free-A high-bandwidth cost-effective solution to the last mile problem is to use free-space laser communication (also known as or optical wireless) in a mesh space laser communication (also known as or optical wireless) in a mesh

architecture to get the high bandwidth quickly to the customers.architecture to get the high bandwidth quickly to the customers.

DATA SECURITYDATA SECURITY

To overcome the security in a network two conditions are necessary: To overcome the security in a network two conditions are necessary: (1) Intercept enough of the signal to reconstruct data packets and (1) Intercept enough of the signal to reconstruct data packets and

(2) Be able to decode that information(2) Be able to decode that information..

Preventing Interception of the SignalPreventing Interception of the SignalDirectional transmission:Directional transmission:Narrow divergence of the FSO Narrow divergence of the FSO transmit path (shown in red) as compared to a typical transmit path (shown in red) as compared to a typical Radio Frequency (RF) Radio Frequency (RF) path (shown in blue). The tightly collimated FSO beam ensures path (shown in blue). The tightly collimated FSO beam ensures that the signal energy is focused on the receiving unit, making interception of the beam that the signal energy is focused on the receiving unit, making interception of the beam extremely difficult.extremely difficult.

Another view of the narrow beam divergence inherent in Another view of the narrow beam divergence inherent in FSO transmission. (For clarity only one transit beam is FSO transmission. (For clarity only one transit beam is

shown.)shown.)

FSO SYSTEM CONFIGURATIONSFSO SYSTEM CONFIGURATIONS::

Signal Propagation Impediments:Signal Propagation Impediments: FogFog: The major challenge to FSO communications is fog. The primary way to counter : The major challenge to FSO communications is fog. The primary way to counter

fog when deploying FSO is through a network design that shortens FSO link fog when deploying FSO is through a network design that shortens FSO link distances and adds network redundancies. FSO installations in foggy cities such as distances and adds network redundancies. FSO installations in foggy cities such as San Francisco have successfully achieved carrier-class reliability.San Francisco have successfully achieved carrier-class reliability.

AbsorptionAbsorption: Absorption occurs when suspended water molecules in the terrestrial : Absorption occurs when suspended water molecules in the terrestrial atmosphere extinguish photons. This causes a decrease in the power density atmosphere extinguish photons. This causes a decrease in the power density (attenuation) of the FSO beam and directly affects the availability of a system.(attenuation) of the FSO beam and directly affects the availability of a system.

ScatteringScattering: Scattering is caused when the wavelength collides with the scatterer. The : Scattering is caused when the wavelength collides with the scatterer. The physical size of the scatterer determines the type of scattering. When the scatterer is physical size of the scatterer determines the type of scattering. When the scatterer is smaller than the wavelength, this is known as Rayleigh scattering. When the scatterer smaller than the wavelength, this is known as Rayleigh scattering. When the scatterer is of comparable size to the wavelength, this is known as Mie scattering.is of comparable size to the wavelength, this is known as Mie scattering.

Physical obstructionsPhysical obstructions: Flying birds can temporarily block a single beam, but this : Flying birds can temporarily block a single beam, but this tends to cause only short interruptions, and transmissions are easily and tends to cause only short interruptions, and transmissions are easily and automatically resumed.automatically resumed.

Building sway/seismic activityBuilding sway/seismic activity: The movement of buildings can upset receiver and : The movement of buildings can upset receiver and transmitter alignment.transmitter alignment.

SafetySafety: To those unfamiliar with FSO, safety is often a concern because the : To those unfamiliar with FSO, safety is often a concern because the technology uses lasers for transmission.technology uses lasers for transmission.

ScintillationScintillation: Heated air rising from the earth or man-made devices such as heating : Heated air rising from the earth or man-made devices such as heating ducts creates temperature variations among different air pockets. This can cause ducts creates temperature variations among different air pockets. This can cause fluctuations in signal amplitude which leads to image fluctuations at the FSO receiver fluctuations in signal amplitude which leads to image fluctuations at the FSO receiver end.end.

Rough Estimate of Power losses in the system Infrared ight (765 nm) :Rough Estimate of Power losses in the system Infrared ight (765 nm) : Clear, still air -1 dB/km -5 dB/km Clear, still air -1 dB/km -5 dB/km Scintillation 0 to -3 dB/km 0 Scintillation 0 to -3 dB/km 0 Birds or foliage Impenetrable 0 to -20 dB Birds or foliage Impenetrable 0 to -20 dB Window (double-glazed) -3 dB -1 dB Window (double-glazed) -3 dB -1 dB Light mist (visibility 400m) -25 dB/km -1 dB/km Light mist (visibility 400m) -25 dB/km -1 dB/km Medium fog (visibility 100m) -120 dB/km -1 dB/km Medium fog (visibility 100m) -120 dB/km -1 dB/km Thick fog (visibility 40m) -300 dB/km -1 dB/km Thick fog (visibility 40m) -300 dB/km -1 dB/km Light rain (25mm/hour) -10 dB/km -10 dB/km Light rain (25mm/hour) -10 dB/km -10 dB/km Heavy rain (150mm/hour) -25 dB/km -40 dB/km Heavy rain (150mm/hour) -25 dB/km -40 dB/km

ADVANTAGES OF FSO SYSTEMSADVANTAGES OF FSO SYSTEMS

No licensing required.No licensing required. Installation cost is very low as compared to Installation cost is very low as compared to

laying Fiber.laying Fiber. No sunk costs.No sunk costs. No capital overhangs.No capital overhangs. Highly secure transmission possible.Highly secure transmission possible. High data rates, upto 2.5 Gbps at present High data rates, upto 2.5 Gbps at present

and 10 Gbps in the near future.and 10 Gbps in the near future.

Applications Of FSO SystemsApplications Of FSO Systems Disaster management as was Disaster management as was

exhibited during the Sept 11 exhibited during the Sept 11 attacks.attacks.

Merill Lynch & Co. has set up FSO Merill Lynch & Co. has set up FSO system from its Vesey Street system from its Vesey Street office towers across the Hudson office towers across the Hudson River to an alternate site in New River to an alternate site in New Jersey.Jersey.

TeraBeam, a major producer of TeraBeam, a major producer of FSO equipment, successfully FSO equipment, successfully deployed FSO at the Sydney deployed FSO at the Sydney Summer Olympic Games.Summer Olympic Games.

A network of FSO devices is fast A network of FSO devices is fast coming up in Seattle which is coming up in Seattle which is touted as the Capital of Fog. touted as the Capital of Fog. Manufacturers believe that if an Manufacturers believe that if an FSO system can successfully FSO system can successfully work in Seattle then it can do so in work in Seattle then it can do so in any part of the world.any part of the world.

Affordably extend existing fiber Affordably extend existing fiber network.network.

Disaster recovery and temporary Disaster recovery and temporary applicationsapplications

Manufacturers/ Players in the Field of FSO:Manufacturers/ Players in the Field of FSO:

LightPointe: A San Diego based company which LightPointe: A San Diego based company which received contributions from Cisco Systems and received contributions from Cisco Systems and Corning to the tune of $33 million. It has raised a Corning to the tune of $33 million. It has raised a total of $51.5 million.total of $51.5 million.

AirFiber: Another San Diego based company AirFiber: Another San Diego based company which has received contributions from Nortel which has received contributions from Nortel Networks to the tune of $50 million. It has raised Networks to the tune of $50 million. It has raised a total of $92.5 million. a total of $92.5 million.

Terabeam: A Kirkland, WA based company has Terabeam: A Kirkland, WA based company has received funding from Luscent technologies to received funding from Luscent technologies to the tune of $450 million and has raised $585 the tune of $450 million and has raised $585 million to date.million to date.