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Free Space Optics : 

Free Space Optics Submitted By:- Kaustubh Goswami Guided by PROF. U. A. Rane DEPARTMENT OF ELECTRONICS AND TELECOMMUNICATION A SEMINAR ON

Contents: : 

Contents: Introduction. What is FSO? Significance of FSO Operation Advantages /Disadvantages Application Future Aspects Conclusion.

Free Space Optics (FSO)?? : 

Free Space Optics (FSO)?? A data transmission technology from one point to another point by using laser beam in free space is known as “free space optics”. Currently, It can allow upto 2.5 Gbps of data rate but can be increased to 10 Gbps using WDM FSO is based on connectivity between two stations consisting of optical transceiver to achieve full duplex communication

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

Introduction to the concepts of Free Space Optics (FSO) FSO is a line-of-sight technology which uses LASERS and Photo detectors to provide optical connections between two points without the fiber. FSO can transmit data, voice or video at speeds capable of reaching 2.5 Gbps. FSO units consist of an optical transceiver with a laser (transmitter) and a Photo detector (receiver) to provide full duplex (bi-directional) capability. FSO systems use invisible infrared laser light wavelengths in the 750nm to 1550nm range.

Requirements of a good Transmission System : 

Requirements of a good Transmission System High Bandwidth High BER Low SNR Power efficient Provide Data Security. Low cost Easy to install and maintain.

Technology: How it works? : 

Technology: How it works? FSO enables similar bandwidth transmission abilities as fiber optics, using similar optical transmitters and receivers It involves two FSO units (similar to BTS of wireless technology) each consisting of high power laser transmitters and receivers, a telescope is used in conjunction to guide the light and capture it at the receiving end. It is then typically interface with network switches, hub, bridge or router via multimode fiber

FSO Instruments : 

FSO Instruments Transmitter source: Semiconductor lasers and LEDs(short range). Solid-state lasers e.g. Yd:Yag (bulky, power) Gas lasers e.g. CO2 (bulky, lifetime) Quantum Cascade (QC) lasers (cooling for higher power operation) Operation within optical windows Basic Requirements: High power operation (average power,not peak power!) High modulation speed Operation over wide temperature range

Reciever Source : 

Reciever Source Detector: Basic Requirement: Compensation for lower power lasers (High gain) Capability to Reject Background noise(S/N ratio) High Acceptance Angle (NA)

Slide 9: 

Typical City-Wide Broadcast FSO Deployment

Technical Specification for laser : 

Technical Specification for laser Wavelength used are ~780nm to ~850 nm for short ranges and less intensity typically 20mw 1550nm (class 1M)for long range data links typically 640 mw . 1550 nm wavelength is safe for eye . 1550 nm wavelength is also being used for optical fiber communication so compatible also. Attenuation is less at longer wavelengths.

Slide 11: 

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

Slide 12: 

ADVANTAGES OF FSO SYSTEMS No licensing required. Installation cost is very low as compared to laying Fiber. No sunk costs. No capital overhangs. Highly secure transmission possible. High data rates, upto 2.5 Gbps at present and 10 Gbps in the near future.

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FSO As A Last-Mile Solution Low investment in infrastructure Typical fiber optical cable costs $ 200,000 per mile approximately for installation and support. FSO based networks can be implemented for a fraction of the cost Low delay in deployment of FSO based networks Typical deployment of a fiber based network takes well over an year, while FSO based networks may be deployed with no substantial over-heads License Free Bandwidth Unlike microwave links, optical bandwidth isn’t licensed – i.e , bandwidth is free. This amounts to lower operational costs Supports High Data Rates

Advantages of FSO Over Contemperory Technologies : 

Advantages of FSO Over Contemperory Technologies DSL and cable modems cannot provide true broadband services. Cable modems enjoy higher capacity, yet the channel is shared and the amount of bandwidth at any given time is not guaranteed. Copper lines provide data rates to a fraction of 1 Mbps.

Slide 15: 

FSO is a LOS technology where it is essential that interconnecting points must see each other without any physical obstruction. Some of the potential disturbances are:- Fog: Wavelength dependence of fog attenuation change with density Between 0.5-4um attenuation by dense fog increases with wavelength. Atmospheric Absorption: Molecular absorption (gases) Aerosol absorption (dust, smoke, water drops) Scattering: Rayleigh Scattering (gases) Mie scattering (aerosol, fog) Geometrical optics (snow, rain) Technological Challenges

Brief Description of Challenges : 

Brief Description of Challenges Fog: 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 distances and adds network redundancies. FSO installations in foggy cities such as San Francisco have successfully achieved carrier-class reliability. Absorption: Absorption occurs when suspended water molecules in the terrestrial atmosphere extinguish photons. This causes a decrease in the power density (attenuation) of the FSO beam and directly affects the availability of a system. Scattering: 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 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. receiver end.

Contd.. : 

Contd.. Physical obstructions: Flying birds can temporarily block a single beam, but this tends to cause only short interruptions, and transmissions are easily and automatically resumed. Building sway/seismic activity: The movement of buildings can upset receiver and transmitter alignment. Safety: To those unfamiliar with FSO, safety is often a concern because the technology uses lasers for transmission. Scintillation: Heated air rising from the earth or man-made devices such as heating ducts creates temperature variations among different air pockets. This can cause fluctuations in signal amplitude which leads to image fluctuations at the FSO

Denver, Colorado Fog/Snowstorm Conditions : 

Denver, Colorado Fog/Snowstorm Conditions

Slide 19: 

Scintillation: The variation of refractive index along the propagation path caused by slight temperature variations among different air pockets. Acts like series of small lenses that deflect the beam into and out of the transmission path causes amplitude fluctuations at the receiver. Can impact BER performance ,increases with distance .therefore for long distance communication Multiple beam technology is used.

Solution : 

Solution Active beam steering (sometimes involving MEMS) Multiple laser beams Automated power control.

Slide 21: 

Limitations Of FSO Unreliable Bandwidth availability : Variations in weather conditions affect available bandwidth Requires Line of Sight link Limited Range Need sophisticated mechanism for alignment of the transmitter and receiver Even slight mechanical disturbances may lead to loss of alignment, and may result in complete link break-down

Slide 22: 

Applications Of FSO Systems Disaster management as was exhibited during the Sept 11 attacks. Merill Lynch & Co. has set up FSO system from its Vesey Street office towers across the Hudson River to an alternate site in New Jersey. TeraBeam, a major producer of FSO equipment, successfully deployed FSO at the Sydney Summer Olympic Games. A network of FSO devices is fast coming up in Seattle which is touted as the Capital of Fog. Manufacturers believe that if an FSO system can successfully work in Seattle then it can do so in any part of the world. Affordably extend existing fiber network. Disaster recovery and temporary applications

Industrial Applications : 

Industrial Applications Short Range Applications Weather monitors; fog, snow, rain using light back-scatter Traffic counting and monitoring Optical Interconnects. Long Range Applications Deep space probe communications; distances measured in light-years Building to building computer data links; very high data rates. Ship to ship communications; high data rates with complete security. Telemetry transmitters from remote monitors; weather, geophysical. Electronic distance measurements; hand held units out to 1000 ft. Optical radar; shape, speed, direction and range. Remote telephone links; cheaper than microwave Wide Area Applications Campus wide computer networks City-wide information broadcasting Inter-office data links

Slide 24: 

Air Force Its potential for low electromagnetic emanation when transferring sensitive data Navy Secure communication with submerged submarines. Military Application of FSO

Slide 26: 

Markets For FSO The industry is expected to grow from approximately $120 million in 2000 to more than $2 billion annually by 2006, according to a study conducted by the Strategis Group, a Washington, D.C.- based telecommunications research firm. Companies working in FSO Terabeam Corp Lightpointe Nortel fSONA Communications Crinis Networks

Slide 27: 

Future Prospects Of FSO AirFiber Hybrid Free- space optic/Radio LightPointe Multi-beam sending process Terabeam carrier-grade FSO equipment and services

AirFiber : 

AirFiber AirFiber's products combine FSO with 60 GHz millimeter-wave radio, makes wireless communication possible in any weather.

Terabeam : 

Terabeam Terabeam's FSO products have advanced beam-steering features that update beam direction up to 300 times per second.

Light Point : 

Light Point Light Point's FSO products utilize a multi-beam sending process, which overcomes atmospheric degradations and temporary beam obstructions by overlapping redundant infrared beams.

Conclusion : 

Conclusion FSO is emerging as a trustworthy solution for bandwidth problemIt gives the maximum speed from 2.5 GBps to 160 GBps.

References: : 

References: Technical forum: http://www.mrv.com/technology http://www.freespaceoptics.org/index.cfm http://www.imagineeringezine.com/ Search from: http://www.sciam.com/ http://www.wcai.com

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Thank You!!!

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