FREE SPACE OPTICSFREE SPACE OPTICS(FSO)(FSO)

WIRELESS LINKS AT WIRELESS LINKS AT THE SPEED OF LIGHTTHE SPEED OF LIGHT

WISAM ABDURAHIMAN

INTRODUCTION2

In telecommunications, Free Space Optics (FSO) is an optical communication technology that uses light propagating in free space to transmit data between two points. The technology is useful where the physical connections by the means of fiber optic cable are impractical due to high costs or other considerations. Free Space Optics (FSO) communications, also called Free Space Photonics (FSP) or Optical Wireless, refers to the transmission of modulated visible or infrared (IR) beams through the atmosphere to obtain optical communications. Like fiber, Free Space Optics (FSO) uses lasers to transmit data, but instead of enclosing the data stream in a glass fiber, it is transmitted through the air.

Principle3

Free Space Optics (FSO) works on the same basic principle as Infrared television remote controls, wireless keyboards or wireless Palm devices. Unlike radio and microwave systems, Free Space Optics (FSO) is an optical technology and no spectrum licensing or frequency coordination with other users is required, interference from or to other systems or equipment is not a concern, and the point-to-point laser signal is extremely difficult to intercept, and therefore secure

FSO: Optical or Wireless?

Speed of fiber — flexibility of wireless.

Flexibility of wireless optical transmission at speeds of up to

1.25 Gbps and, in the future, is capable of speeds of 10 Gbps using

WDM.

Eliminates the need to buy expensive spectrum.

Requires no municipal license approvals worldwide.

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Optical Wireless Communications Technologyfor

Voice / Video / Data …at the Speed of Light!

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Free Space Optics is an optical wireless, line-of-sight, broadband (1.5 Mbps-2.5 Gbps)

How Free Space Optics (FSO) Works

•Free Space Optics (FSO) transmits invisible, eye-safe light beams from one "telescope" to another using infrared lasers

•The beams of light in Free Space Optics (FSO) systems are transmitted by laser light focused on highly sensitive photon detector receivers. These receivers are telescopic lenses able to collect the photon stream and transmit digital data

•Commercially available systems offer capacities in the range of 100 Mbps to 2.5 Gbps, and demonstration systems report data rates as high as 160 Gbps

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A laser transmitter which is safe when viewed by the eye is designated IEC Class 1M

. It is possible to design eye-safe laser transmitters at both the 800 nm and 1550 nm wavelengths but the allowable safe laser power is about fifty times higher at 1550 nm.

Eye-Safety 8

Principle advantages of FSO are:9

FSO systems offers a flexible networking solution

virtually unlimited bandwidth, low cost, ease and speed of deployment .

Freedom from licensing and regulation translates into ease, speed and low cost of deployment

The only essential for FSO is line of sight between the two ends of the link

• Easily upgraded• Roof-top or through window operation• No latency• Highly Secure (wide military

applications)• Compatible with WDM technology• Low power consumption• Immunity from interference• Microwave Backup link (optional )

Advantages contd…10

•)

Free Space Optics (FSO) Security

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FSO laser beams cannot be detected with spectrum analyzers or RF meters.

It requires a matching Free Space Optics (FSO) transceiver carefully aligned to complete the transmission. Interception is very difficult and extremely unlikely.

The laser beams generated by Free Space Optics (FSO) systems are narrow and invisible, making them harder to find and even harder to intercept and crack .

Data can be transmitted over an encrypted connection adding to the degree of security available in FSO network transmissions.

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The following protocols have been wirelessly transmitted by laser communication:

• Ethernet, Fast Ethernet, Gigabit Ethernet• FDDI• ATM (OC-3, OC-12, OC-24) Using WDM 160 Gbps in the lab

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There are literally dozens of distinct FSO models to choose from:

15 FSO system mounted inside

16 FSO systems mounted outside

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Atmospheric effects on FSO

Free Space Optics uses the infrared portion of the electromagnetic spectrum between visible light and microwaves

Atmospheric effects such as fog, snow, rain, smog, sand-storms and scintillation (thermal shimmer) all cause attenuation of the infrared signal as it passes through the atmosphere

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Simple Link Budget Example

Weather Loss Link Range

Clear 1 dB/km 50 km

Haze 5 dB/km 10 km

Fog 50 dB/km 1 km

Heavy Fog 350 dB/km 143 m

How to overcome ??19

TECHNICAL SPECIFICATIONS

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Transmission rates :100 - 715 Mbps

Operational range :3 dB/km: clear air: 400m to 5500m

10 dB/km: extreme rain: 400m to 2400m

Laser output power :560 mW

Free-space wavelength :1550 nm

CONCLUSION21

The broader market for FSO-based technology did not emerge until late 2000 when it became clear that fiber-optic cable would not reach into every building in the near future. Today, it is increasingly finding its way into a range of enterprise and service provider applications. The costs and challenges associated with trenching fiber in metropolitan areas can be prohibitive, yet bandwidth demands are increasing, particularly in the "last mile." In many cities, these demands are outstripping service providers' ability to deploy fiber-optic cable. Combined with shrinking capital budgets, other gaps and applications in service providers' networks must also be addressed through viable alternatives such as FSO-based, optical wireless products.

REFERENCES Free-space Optics: Propagation And Communication

-Olivier Bouchet, Herve Sizun, Christian Boisrobert Planar-integrated free-space optics: an integration technique for

3D microoptics -Jahns.J,Jarczynski.M. Adaptive Optics in Astronomy ,1999, Cambridge University

Press - Francois Roddier. millimeter Through Visible Frequency Waves Through Aerosols-

Particle Modeling, Reflectivity and Attenuation -Kontogeorgakis, Christos.

Free Space Optics. - Heinz Willebrand Optical Communication Dictionary - Lawrence Harte Deep space optical communications - Hamid Hemmati

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