communication system without fibers.doc

8/20/2019 communication system without fibers.doc

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INTRODUCTION

Communication, as it has always been relied and simply depended upon speed. The

faster the means! The more popular, the more effective the communication is!

Presently in the twenty-first centaury wireless networking is gaining because of speed

and ease of deployment and relatively high network robustness. Modern era of optical

communication originated with the invention of "#$ in %&'( and fabrication of low-

loss optical fiber in

%&)*.

+hen we hear of optical communications we all think of optical fibers, what have for

u today is PTC CMM/CT "0"T#M +T1/T 23#$" or in

other words +$# 2$## PTC".

2ree space optics or 2" 4lthough it only recently and rather suddenly sprang in to

public awareness, free space optics is not a new idea. t has roots that &* back over 5*

years-to the era before fiber optic cable became the preferred transport medium for high speed communication. 2" technology has been revived to offer high band width

last mile connectivity for today6s converged network re7uirements.

HISTORY OF FREE SPACE OPTICS (FSO)

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The engineering maturity of 2ree "pace ptics 82"9 is often underestimated, due to a

misunderstanding of how long 2ree "pace ptics 82"9 systems have been under development.

1istorically, 2ree "pace ptics 82"9 or optical wireless communications was first demonstrated by

le:ander ;raham 3ell in the late nineteenth century 8prior to his demonstration of the telephone!9.

3ell6s 2ree "pace ptics 82"9 e:periment converted voice sounds into telephone signals and

transmitted them between receivers through free air space along a beam of light for a distance of some

3ell considered this optical technology 4

and not the telephone 4 his preeminent invention because it did not re7uire wires for transmission.

lthough 3ell6s photophone never became a commercial reality, it demonstrated the basic

principle of optical communications. #ssentially all of the engineering of today6s 2ree "pace

ptics 82"9 or free space optical communications systems was done over the past ?* years or

so, mostly for defense applications. 3y addressing the principal engineering challenges of 2ree

space ptics 82"9, this aerospace@defense activity established a strong foundation upon which

today6s commercial laser-based 2ree "pace ptics 82"9 systems are based.

FSO! FREE SPACE OPTICS

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2ree space optics or 2", free space photonics or optical wireless, refers to the

transmission of modulated visible or infrared beams through the atmosphere to obtain

optical communication. 2" systems can function over distances of several kilometers.

2" is a line-of-sight technology, which enables optical transmission up to A.' ;bps of data, voice and video communications, allowing optical connectivity without deploying

fiber optic cable or securing spectrum licenses. 2ree space optics re7uire light, which

can be focused by using either light emitting diodes 8#B9 or "#$"8light

amplification by stimulated emission of radiation9. The use of lasers is a simple concept

similar to optical transmissions using fiber-optic cables, the only difference being the

medium.

s long as there is a clear line of sight between the source and the destination and

enough transmitter power, communication is possible virtually at the speed of light.

3ecause light travels through air faster than it does through glass, so it is fair to classify

2" as optical communications at the speed of light. 2" works on the same basic

principle as infrared television remote controls, wireless keyboards or wireless palm

devices.

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FSO TRANSMITTER

FSO RECEIVER

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Internal Components o Transree"#er

TRANSRECEIVER

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RE$EVANCE OF FSO IN PRESENT DAY COMMUNICATION

Presently we are faced with a burgeoning demand for high bandwidth and differentiated

data services. etwork traffic doubles every &-%A months forcing the bandwidth or data

storing capacity to grow and keep pare with this increase. The right solution for the

pressing demand is the untapped bandwidth potential of optical communications.

ptical communications are in the process of evolving ;iga bits@sec to terabits@sec and

eventually to pentabits@sec. The e:plosion of internet and internet based applications

has fuelled the bandwidth re7uirements. 3usiness applications have grown out of the

physical boundaries of the enterprise and gone wide area linking remote vendors,

suppliers, and customers in a new web of business applications. 1ence companies are

looking for high bandwidth last mile options. The high initial cost and vast time

re7uired for installation in case of 2C speaks for a wireless technology for high

bandwidth last mile connectivity there 2" finds its place.


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HO% FREE SPACE OPTICS (FSO) CAN HE$P YOU

2"6s freedom from licensing and regulation translates into ease, speed and low cost of

deployment. "ince 2ree "pace ptics 82"9 transceivers can transmit and receive

through windows, it is possible to mount 2ree "pace ptics 82"9 systems inside

buildings, reducing the need to compete for roof space, simplifying wiring and cabling,

and permitting 2ree "pace ptics 82"9 e7uipment to operate in a very favorable

environment. The only essential re7uirement for 2ree "pace ptics 82"9 or optical

wireless transmission is line of sight between the two ends of the link

2or Metro rea etwork 8M9 providers the last mile or even feet can be the

most daunting. 2ree "pace ptics 82"9 networks can close this gap and allow new

customers access to high-speed M6s. Providers also can take advantage of the

reduced risk of installing an 2ree "pace ptics 82"9 network which can later be

redeployed.

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ORI&IN OF FSO

t is said that this mode of communication was first used in the ( th centaury by the

;reeks. They used fire as the light source ,the atmosphere as the transmission medium

and human eye as receiver.

2" or optical wireless communication by le:ander ;raham 3ell in the late %& th

centaury even before his telephone! 3ells 2" e:periment converted voice sounds to

telephone signals and transmitted them between receivers through free air space along a

beam of light for a distance of some


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THE TECHNO$O&Y OF FSO

The concept behind 2" is simple. 2" uses a directed beam of light radiation between

two end points to transfer information 8data, voice or even video9. This is similar to

2C 8optical fiber cable9 networks, e:cept that light pulses are sent through free air instead of 2C cores.

n 2" unit consists of an optical transceiver with a laser transmitter and a receiver to

provide full duple: 8bi-directional9 capability. #ach 2" unit uses a high power optical

source 8 laser 9 plus a lens that transmits light through the atmosphere to another lens

receiving information. The receiving lens connects to a high sensitivity receiver via optical

fiber. Two 2" units can take the optical connectivity to a ma:imum of ?kms. asers are

one of the most significant inventions of the A*th century - they can be found in many

modern products, from CB players to fiber-optic networks. The word laser is actually an

acronym for ight mplification by "timulated #mission of $adiation. lthough stimulated

emission was first predicted by lbert #instein near the beginning of the A*th century, the first

working laser was not demonstrated until %&


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basic laser uses a mirrored chamber or cavity to reflect light waves so they

reinforce each other. n e:citable substance 4 gas, li7uid, or solid like the original ruby laser

4 is contained within the cavity and determines the wavelength of the resulting laser beam.

Through a process called pumping, energy is introduced to the cavity e:citing the atoms

within and causing a population inversion. population inversion is when there are more

e:cited atoms than grounded atoms which then leads to stimulated emission. The released

photons oscillate back and forth between the mirrors of the cavity, building energy and

causing other atoms to release more photons. ne of the mirrors allows some of the released

photons to escape the cavity resulting in a laser beam emitting from one end of the cavity.

%*


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%OR'IN& OF FSO SYSTEM

ptical systems work in the infrared or near infrared region of light and the easiest way

to visualiDe how the work is imagine, two points interconnected with fiber optic cable

and then remove the cable. The infrared carrier used for transmitting the signal is

generated either by a high power #B or a laser diode. Two parallel beams are used,

one for transmission and one for reception, taking a standard data, voice or video

signal, converting it to a digital format and transmitting it through free space . These

receivers are telescopic lenses able to collect the photon stream and transmit

digital data containing a mi: of nternet messages, video images, radio signals or

computer files.

Today6s modern laser system provide network connectivity at speed of


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+E##;T1

Currently available 2" hardware are of two types based on the operating wavelength

4 (** nm and %''* nm. %''* 2" systems are selected because of more eye safety,

reduced solar background radiation and compatibility with e:isting technology

infrastructure.

Commercially available systems offer capacities in the range of %** Mbps to A.' ;bps,

and demonstration systems report data rates as high as %


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n the transmitting section, the data is given to the modulator for modulating signal and

the driver is for activating the laser. n the receiver section the optical signal is detected

and it is converted to electrical signal, preamplifier is used to amplify the signal and

then given to demodulator for getting original signal. Tracking system which

determines the path of the beam and there is special detector 8CCB, CM"9 for

detecting the signal and given to pre amplifier. The servo system is used for controlling

system, the signal coming from the path to the processor and compares with the

environmental condition, if there is any change in the signal then the servo system is

used to correct the signal.

%5

Modulator Briver aser Transmit optic

Bata in

Be-

modulator

preamplifier detector $eceive optic

Bata out

preamplifier "pecial

detector

Tracking optic

Processor "ervo systems

#nvironmental

condition


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APP$ICATIONS OF FSO

ptical communication systems are becoming more and more popular as the interest

and re7uirement in high capacity and long distance space communications grow. 2"

overcomes the last mile access bottleneck by sending high bitrate signals through the air

using laser transmission.

pplications of 2" system is many and varied but a few can be listed.

%. Metro Area Netor* ( MAN )+ 2" network can close the gap between the last

mile customers, there by providing access to new customers to high speed M6s

resulting to Metro etwork e:tension.

A. $ast M"le Aess + #nd users can be connected to high speed links using 2". t

can also be used to bypass local loop systems to provide business with high speed

connections.

5. Enterpr"se onnet"#"t, + s 2" links can be installed with ease, they provide a

natural method of interconnecting segments that are housed in buildings

separated by public streets or other right-of-way property.

?. F"-er -a*.p + 2" can also be deployed in redundant links to backup fiber in

place of a second fiber link.

'. a*/a.l + 2" can be used to carry cellular telephone traffic from antenna towers

back to facilities wired into the public switched telephone network.


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CONC$USION

+e have discussed in detail how 2" technology can be rapidly deployed to provide

immediate service to the customers at a low initial investment, without any licensing

hurdle making high speed, high bandwidth communication possible. Though not very

popular in ndia at the moment, 2" has a tremendous scope for deployment companies

like C"C, ;1T PT# few other have made huge investment to promote this

technology in the market. t is only a matter of time before the customers realiDed, the

benefits of 2" and the technology deployed in large scale.

$#2#$#C#

%9 +ww. ightpointe.com

A9 www.freespaceoptics.org

59 www.freespaceoptics.com

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http://www.freespaceoptics.org/http://www.freespaceoptics.com/http://www.freespaceoptics.org/http://www.freespaceoptics.com/


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CONTENTS

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