Ofc Summer Training Report

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PATIKRA, NARNAUL-HARYANA 123002

SUMMER TRAINING REPORT

Submitted in partial fulfillment for the award of degree ofBachelor in Technology

IN

Electronics & Communication Engineering(Session 2013-2014)

Submitted by:Subhash Kumar Yadav

12ECEL26, 5th Semester

Done at:


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Department of Electronics & Commn. Engg. Narnaul-Haryana 123002

CERTIFICATE

Certified that this is the bonafied reportof Summer Internship entitled OPTICALFIBRE CABLES done by Subhash KumarYadav of fifth Semester inELECTRONICS & COMMUNICATION

ENGINEERING in the YaduvanshiColllege of Engineering & Technologyduring the academic year 2013-2014 and

CERTIFICATE


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submitted for practical examinationconducted by M.D.U University Rohtak.

Guided by:-

Mr.Rahul (Lecturer E.C.E Dept.)ACKNOWLEDGEMENT

I am thankful to the Company D.S Enterprises forproviding necessary facility to carry out my trainingsuccessfully.

I take this opportunity to thank Mr. Pradeep,PRINCIPAL, and YADUVANSHI COLLEGE OFENGINEERING & TECHNOLOGY for granting us thepermission to carry out the summer training.

I am extremely thankful to Mr. Sudhir Yadav H.O.D,Electronics and Communication department, for her

timely advices and all the facilities he provided us,to carry out this report and finish it successfully.


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I express my profound gratitude for the pragmaticguidance rendered to us our guide Mr. Rahul Yadav,My Training Incharge & Lecturer in Electronics and

Communication Department. They have alwaysbeen a source of inspiration and have been guidingus constantly through all our ups and downs of ourendeavor in completing out this report, for which Iam greatly indebted to them.

PREFACEIndustrial training is one of the most importantcomponents in the fulfillment of any engineeringcourse conducted at any level at any college. Eachand every one of us would always have an addedadvantage if I have a chance to come face to facewith the equipments and the processes I am being

taught in my engineering course.

The main purpose of the training program is toexpose the trainees to practical experience of theactual industrial conditions in which they arerequired to work in future.

I deem it a privilege to have undergone training inan organization, which has allowed me to see theactual working of the Telecommunication industry.At the department Managed Service Division.


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I have been given the chance to be familiar withnew technologies.

Subhash Kumar Yadav

ABSTRACT

Communication is an important part of our daily life.The communication process involves information

generation, transmission, reception andinterpretation. As needs for various types ofcommunication such as voice, images, video anddata communications increase demands for largetransmission capacity also increase.

This need for large capacity has driven the rapiddevelopment of light wave technology; a worldwide

industry has developed. An optical or light wavecommunication system is a system that uses lightwaves as the carrier for transmission. An opticalcommunication system mainly involves three parts.

Transmitter, receiver and channel.


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In optical communication transmitters are lightsources, receivers are light detectors and the

channels are optical fibers. In opticalcommunication the channel i.e., optical fibers playan important role because it carries the data fromtransmitter to the receiver. Hence, here we shalldiscuss mainly about optical fibers.

CONTENTS History

Introduction & Justification of need ofFiber.

Facts & Myths about Fiber Optics.

Physics Behind Optical Fiber

Construction of Fibers

Classification of Optical FibersBased on the materials usedBased on number of modesBased on refractive index


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Modes And Propagation Of Light InFibers

Optical Fiber Cables

Joint of Fiber Fiber Splices

Fusion Splices

Equipment Required for OFC Joint

Electric Field With In Fiber Cladding

Repeaters And Regenerators

Light Sources

Detecting the Signal.

Comparison with other Medias.

Advantages Over Conventional Cables

Application of the Optical FiberCommunication

Features.

Essential Features of an Optical Fiber

Problems & Impairments found in OFCCommunication.

Conclusions

Bibliography

History of Optical andFiber in

Telecommunications


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The beginning of optical communications is ratherinteresting. It has always been a belief that if youwant to know where things are going, you have to

understand where they have been. A little history willhelp. Optical communications systemsdate back to the optical telegraph invented byFrench engineer Claude Chappe in the 1790s.He useda series of semaphores mounted on towers, withhuman operators relaying messages from one towerto the next. Of course, in order for this to work, thepeople had to be close enough together to visually

see the other messengers motions. This was not agreat service for evening transmission and had someproblems with weather conditions (for example, fog,heavy rain, heavy snow, and so on). The systemdepended on a line-of-sight operation; hence, thetowers needed elevation to extend the coverage(albeit, a limited distance between repeaters) andclose proximity.

However, the opticaltelegraph did perform better than hand carriedmessages. Alas, by the mid-nineteenth century thesystem was replaced by the electric telegraph,leaving a scattering of telegraph hills as its legacy.The use of electrical transmissions was better suitedfor communications over distances.

Optical communication systems date back to the1790s, to the optical semaphore telegraph inventedby French inventor Claude Chappe. In 1880,Alexander Graham Bell patented an optical telephonesystem, which he called the Photophone. However,


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his earlier invention, the telephone, was morepractical and took tangible shape. The Photophoneremained an experimental invention and never

materialized. During the 1920s, John Logie Baird inEngland and Clarence W. Hansell in the United Statespatented the idea of using arrays of hollow pipes ortransparent rods to transmit images for television orfacsimile systems.

In 1954, Dutch scientist Abraham Van Heel andBritish scientist Harold H. Hopkins separately wrotepapers on imaging bundles. Hopkins reported on

imaging bundles of unclad fibers, whereas Van Heelreported on simple bundles of clad fibers. Van Heelcovered a bare fiber with a transparent cladding of alower refractive index. This protected the fiberreflection surface from outside distortion and greatlyreduced interference between fibers.

Abraham Van Heel is also notable for anothercontribution. Stimulated by a conversation with the

American optical physicist Brian O'Brien, Van Heelmade the crucial innovation of cladding fiber-opticcables. All earlier fibers developed were bare andlacked any form of cladding, with total internalreflection occurring at a glass-air interface. AbrahamVan Heel covered a bare fiber or glass or plastic witha transparent cladding of lower refractive index. Thisprotected the total reflection surface from

contamination and greatly reduced cross talkbetween fibers. By 1960, glass-clad fibers hadattenuation of about 1 decibel (dB) per meter, fine formedical imaging, but much too high forcommunications. In 1961, Elias Snitzer of American


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Optical published a theoretical description of a fiberwith a core so small it could carry light with only onewaveguide mode. Snitzer's proposal was acceptable

for a medical instrument looking inside the human,but the fiber had a light loss of 1 dB per meter.Communication devices needed to operate over muchlonger distances and required a light loss of no morethan 10 or 20 dB per kilometer.

By 1964, a critical and theoretical specification wasidentified by Dr. Charles K. Kao for long-rangecommunication devices, the 10 or 20 dB of light loss

per kilometer standard. Dr. Kao also illustrated theneed for a purer form of glass to help reduce lightloss.

In the summer of 1970, one team of researchersbegan experimenting with fused silica, a materialcapable of extreme purity with a high melting pointand a low refractive index. Corning Glass researchersRobert Maurer, Donald Keck, and Peter Schultz

invented fiber-optic wire or "optical waveguide fibers"(patent no. 3,711,262), which was capable of carrying65,000 times more information than copper wire,through which information carried by a pattern oflight waves could be decoded at a destination even athousand miles away. The team had solvedthe decibel-loss problem presented by Dr. Kao. Theteam had developed an SMF with loss of 17 dB/km at

633 nm by doping titanium into the fiber core. ByJune of 1972, Robert Maurer, Donald Keck, and PeterSchultz invented multimode germanium-doped fiberwith a loss of 4 dB per kilometer and much greaterstrength than titanium-doped fiber. By 1973, John


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MacChesney developed a modified chemical vapor-deposition process for fiber manufacture at Bell Labs.This process spearheaded the commercial

manufacture of fiber-optic cable.In April 1977, General Telephone and Electronicstested and deployed the world's first live telephonetraffic through a fiber-optic system running at 6 Mbps,in Long Beach, California. They were soon followed byBell in May 1977, with an optical telephonecommunication system installed in the downtownChicago area, covering a distance of 1.5 miles (2.4

kilometers). Each optical-fiber pair carried theequivalent of 672 voice channels and was equivalentto a DS3 circuit. Today more than 80 percent of theworld's long-distance voice and data traffic is carriedover optical-fiber cables.

INTRODUCTION

Optical fibers are arguably one of the worlds mostinfluential scientific developments from the latterhalf of the 20th century. Normally we are unawarethat we are using them, although many of us dofrequently. The majority of telephone calls andinternet traffic at some stage in their journey will be


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transmitted along an optical fiber. Why has thedevelopment of fibers been given so much attentionby the scientific community when we have

alternatives? The main reason is bandwidth fiberscan carry an extremely large amount of information.More indirectly, many of the systems that we eitherrely on or enjoy in everyday life such as banks,television and newspapers as (to name only a verylimited selection) are themselves dependent oncommunication systems that are dependent onoptical fibers.

Fiber Justification:Many reasons exist for the initial introduction offiber, but some of the strongest reasons are asfollows:

1. Bandwidth compared with copperTaken in bulk, it would take 33 tons of copper totransmit the same amount of information handledby 1/4 pound of optical fiber.

2. StrengthThe tensile strength of the fiber is greater than thatof steel.

3. Speed of transmission

Fiberoptic networks operate at speeds up to 10Gbps, as opposed to 1.54 megabits per second(Mbps) for copper. Soon, a fiberoptic system will beable to transmit the equivalent of an entire


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encyclopedia of information in 1 second. Fiber cancarry information so fast that you could transmitthree television episodes in 1 second.

4.Immunity to electrical and radiofrequencyinterference Fiberoptic cables have a greaterresistance to electromagnetic noise from items suchas radios, motors, or other nearby cables. Becauseoptical fibers carry beams of light, they are free ofelectrical noise and interference.5. Less weight in installationFiberoptics have a greater capacity for information,which means that smaller cables can be used. Anoptical fiber cable the size of an electrical cord canreplace a copper cable hundreds of times thicker.


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Facts about FiberopticsEveryone has a story to tell when asked about fiber.

Many of the myths and facts get confused andconfusing. Thus we should understand just whyeveryone is so excited about the use of fiber optics.Lets start with the facts first:

1. Optical fiber will be the backbone of the informationsuperhighway, transporting voice, video, and data tobusinesses, schools, hospitals, and homes. Demands

for information continue to increase so much that themaximum available transport rates are doublingapproximately every two years. Because of this rapidgrowth, electronic functions in communicationsnetworks eventually will be replaced by photonicfunctions, which provide higher information-carryingcapacity.

2. Fiberoptics are needed because coaxial television

cables are capable of carrying more information thancopper wire (unshielded twisted-pair wire). Computerand telephone companies need something with whichto compete with the CATV companies. This also meansthat the fiber wires will allow the telephone companiesto offer newer services. A new service being offered toconsumers known as very-high-bit-rate digitalsubscriber line (VDSL) will bring telephony, TV, Internetaccess, and high-speed future services to the door. Yet

this will depend on fiber to really achieve the result.Currently, the telephone companies are using a hybridfiber and coaxial (HFC) service to offer VDSL.


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3. Currently, all new undersea cables are made ofoptical fibers. This is crucial to the economic installationof high-density transmission systems. The cost of thefiber as opposed to the cost of copper makes theundersea cable more attractive and readily available.Look at the cost reductions in getting a trans-Atlanticcircuit since the introduction of fiber. Costs literallydove down to more affordable communications forcorporate connectivity internationally.

4. Many believe that 98 percent of copper wire will bereplaced by fiber optic cable, including at the local loop

to the residence. This belief is one we can all take tothe bank. Copper has many problems in distributionand maintenance. Fiber becomes far more economical.Logic, therefore, points to the deployment of more fiberto every facet of communications. Fiber optic cableinstalled in place of copper wire that already requiresreplacing is less expensive. Because it only needsrepeaters to amplify the signals every six miles insteadof every mile for copper, the cost of installation is much

less.

5. Optical fiber phone lines cannot be bugged or tappedeasily. If one were to attempt to tap into the fiber, thecable would be broken in the process. This would tripalarms on the link and cause maintenance andsurveillance personnel to take notice. Moreover, torejoin the cable is more difficult, eliminating the novicefrom the process of tapping into a fiber system. By

breaking into the cable, the light flow is disrupted(Figure 1-9). By splicing the cable improperly, loss andtransmission impairments become highly problematic.Actually, the lights reflections and refractions can be


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changed significantly, causing character changes in thecable. Therefore, only skilled personnel today can splicethe cables properly.

6. A fiber is thinner than a human hair. Fibers are 8 to10 microns or 50 to 62.5 microns thick. One micron (1_m) is 1/250th the thickness of a human hair. Thisthickness (thinness) represents the advantages of theglass itself. It is lighter and easier to handle. It isimmune to the mechanical problems of copper. Itcarries thousands of times the information of copperwire.

7. As radio spectrum becomes scarcer and the need formore information-carrying capacity increases, manyutility companies are finding it cost-effective to installfiber optic communications networks.

Fiber Myths

Many common misconceptions about optical fibertechnology slip into any discussion. Optical fiber, opticalsystems, optical networks, optical technologywhat doesthis opto jargon mean? The myths include the following:1. Fiber is the most expensive wiring option. Actually, fiberis exceptionally cost competitive when compared withcoaxial cable and copper twisted-pair cable for mostapplications. Over the long term, fiber is actually the leastexpensive option. The biggest chunk of new network costsis usually installation, so it makes sense to take advantage

of the opportunity to meet tomorrows requirements byinstalling fiber today.

2. Unshielded twisted-pair cable can be used for high-speeddata applications. When you transmit above 100 Mbps,


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fiber is the only medium that can be used confidently. As astopgap measure, some high-speed copper wire systemsare being offered today. However, these systems mayrequire rewiring with special wire, such as a specially rated

version of shielded twisted-pair cable. Even with thisspecial copper wire, questions still remains as to whetherthe system can transmit 100 Mbps over typical distances.

3. Only high-speed systems need fiber. Fiber can be usedeffectively for any system. When demands dictate, newelectronics can be installed as upgrades to higher speeds.Error-free transmission capability is a critical aspect of anymodern communications system. Many present-day and

virtually all future communications networks will requirethe extensive bandwidth and flexibility of optical fiber.

4. Fiber is highly technical and very difficult to handle.Installing fiber optic networks is predictable andstandardized. Because fiber cable is smaller, lighter, andmore flexible than other types of cable, some installers feelthat it is actually easier to install fiber.

5. Fiber is extremely fragile. Glass fiber is actually strongerthan steel. With an average tensile breaking strength of600,000 pounds per square inch, fiber exceeds the strengthrequirements of all of todays communications applications.

The Physics behind Fiber OpticsA glass tunnel through which light travels is created.When the light hits the cladding, it interacts withand reflects back into the core. Because of thisdesign, the light can bend around curves in

The fiber and this makes it possible for the light totravel greater distances without having to berepeated. This is illustrated in the below figure.


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The light that travels along the fiber is made up of abinary code that pulses on and off and determineswhat information a given signal contains. Theadvantage of fiber is that these on/off pulses can be

translated to video, computer, or voice data dependingon the type of transmitter and receiver used.A

fiberoptic cable has two parts: the core (center orinside) and a cladding (outside covering). These twoparts of the fiber work together to cause somethingcalled total internal reflection, which is the key to fiberoptics. The light beam is focused on the core of thefiber, and it begins its journey down the fiber. Soon,

because of a turn in the fiber or the direction at whichthe light originally entered the fiber, the light reachesthe outside edge of the core. Normally, it would simplyexit the fiber at this point, but this is where thecladding helps. When the light hits the cladding (whichis made of a material selected especially because itreacts differently to light than the core material),instead of going on straight, it reflects. This creates atunnel effect in which the light bounces its way down

the fiber until it exits at the other end of the fiber.

The light spectrum used in fiber


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Construction of Fiber


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In fibers, there are two significant sections thecore and the cladding. The core is part where thelight rays travel and the cladding is a similar

material of slightly lower refractive index to causetotal internal reflection. Usually both sections arefabricated from silica (glass). The light within thefiber is then continuously totally internally reflectedalong the waveguide.

Figure : Structure of Fiber


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When light enters the fiber we must also considerrefraction at the interface of the air and the fibercore. The difference in refractive index causesrefraction of the ray as it enters the fiber,allowing rays to enter the fiber at an angle greaterthan the angle allowed within the fiber as shown inthe figure 3

This acceptance or critical angle(theta), theta, is acrucial parameter for fiber and system designers.

More widely recognized is the parameter NA(Numerical Aperture) that is given by the followingequation:

NA = Sin qa = ?(n12 n22)


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CLASSIFICATION OF OPTICALFIBERS:-

Optical fibers are classified into three types basedon the material used, number of modes andrefractive index.5.1. Based on the materials used:-a. Glass fibers:

They have a glass core and glass cladding. Theglass used in the fiber is ultra pure, ultratransparent silicon dioxide (SiO2) or fused quartz.Impurities are purposely added to pure glass toachieve the desired refractive index.

b. Plastic clad silica:This fiber has a glass core and plastic cladding. Thisperformance though not as good as all glass fibers,

is quite respectable.c. Plastic fibers:


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They have a plastic core and plastic cladding. Thesefibers are attractive in applications where highbandwidth and low loss are not a concern.

5.2. Based on the number of modes:-a. Single Mode fiber:

When a fiber wave-guide can support only the HE11mode, it is referred to as a single mode wave-guide.In a step index structure this occurs w3hen thewave-guide is operating at v


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It is a fiber in which more than one mode ispropagating at the system operating wavelength.Multimode fiber system does not have theinformation carrying capacity of single mode fibers.However they offer several advantages for specificsystems. The larger core diameters result in easiersplicing of fibers. Given the larger cores, higher

numerical apertures, and typically shorter linkdistances, multimode systems can use lessexpensive light sources such as LED s . Multimodefibers have numerical apertures that typically rangefrom 0.2 to 0.29 and have core size that range from35 to100 micro-meters.

5.3. Based on refractive index:-a. Step index fiber:

The step index (SI) fiber consists of a central core

whose refractive index is n1, surrounded by a ladingwhose refractive index is n2, lower than that ofcore. Because of an abrupt index change at the core


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cladding interface such fibers are called step indexfibers.

b. Graded index fibers:

The refractive index of the core in graded indexfiber is not constant, but decreases gradually fromits maximum value n1 to its minimum value n2 atthe core-cladding interface. The ray velocitychanges along the path because of variations in therefractive index. The ray propagating along the fiberaxis takes the shortest path but travels most slowly,as the index is largest along this path in medium oflower refractive index where they travel faster. It istherefore possible for all rays to arrive together atthe fiber output by a suitable choice of refractiveindex profile.5.4 Based on installation methods Cable canbe classified as:-a. Duct cableb.Direct buried cablec.Aerial cabled.Premise Cable


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Fiber Cable Conditions: When optical fibers are to be installed in a working

environment their mechanical properties are of primeimportance. In this respect the unprotected optical fiberhas several disadvantages with regard to its strengthand durability. Bare glass fibers are little and havesmall cross sectional areas which make them very


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susceptible to damage when employing normaltransmission line handling procedures. It is thereforenecessary to cover the fibers to improve their tensilestrength and to protect them against externalinfluences.

Fibers themselves are very small, with an outsidediameter of 125 microns due to the cladding. Althoughthey are also very strong under tension (greater tensilestrength than steel), they break very easily whensubjected to lateral pressure or any kind of roughhandling. Therefore, to use fiber in hostile

communications environments, the fiber needs to beenclosed in a cable. Depending on the location andtype of installation, fiber cables vary widely in theircharacteristics. They are made to satisfy a specificneed. The goal of using a cable is to protect the fiberfrom things that can harm it. Several risks poseproblems for the installers and operators of fiber basednetworks, including the following:1. Tensile stress: Fiber itself is very strong under

tension. Stress causes a significant increase in lightattenuation and creates a number of other problems.One has to be careful not to stress the cable too much.The fibers also can stretch, causing a change in thereflective and refractive indices and creating majorproblems.

2. Bends: Tight bends in the fiber cause signal lossbecause the light escapes through the cladding

material. Crimping the cable also causes signal lossbecause the micro bends create the wrong angle ofincidence for the light to bounce down the fiber. Byplacing the fibers in a cable, the bending radius is


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better maintained because of the additional materialsinside the cable (strengthening members and othercladding components)...

3. Physical damage: The type of protection used incables varies with the risks posed. Indoor conditionsinclude the risk of rodent damage. The cables are afood supply that rodents cannot resist. They will chewthrough the outer cladding (and then some); causingdamage and loss of reflective materials (the light willescape from inside the fibers). Rodent damage is notlimited to indoor installations. Gophers, rabbits,

termites, and fire ants all may eat through cables.

4. Backhoe fade: This risk comes from heavy earth-moving equipment such as backhoes and plows. Amajor hazard for outdoor cables is cable-layingmachines. In most countries, the cables are laid alongrights-of-way. The contractors used by all the majortelecommunications providers cut the cables they arehired to install. Many of the cable cuts are from the

same contractors that initially laid them in the firstplace.

5. Damage during installation: Cable also mustwithstand the stresses of being installed. Theinstallation crews have a job to do, and they do it. Theyhave little regard for the stresses, tugs, and snags theyput in the cable. Their job is to install x amount of cableper day, and they do just that. Consequently, they

bend, stretch, and snag/cut the cabling in the processof installing it.


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6. Water: Water is the worst enemy of an optical fibersystem. Waterproofing the cable is often moreimportant than worrying about some of the other risks.Over time, the fibers begin to degrade because of achemical reaction between the glass and water. Theglass can change its absorption rate, and this cancause significant loss of signal strength. The change inthe composition of the glass causes it to cloud andchanges the refractive and reflective characteristics.Basically, this means that water is a big problem. Asaccess holes flood, the water can permeate through theouter jacket of fiber cables and cause these problems.

Water also causes micro cracking in the glass fibers,producing light scatter.

FIBER JOINTS TYPES:Optical fiber links, in common with any linecommunication system, have a requirement for bothjointing and termination of the transmission medium.The number of intermediate fiber connections or jointsis dependent upon the link length, the continuouslength of the fiber cable that may be produced by thepreparation methods and the length of the fiber cablethat may be practically installed as a continuoussection on the link. It is therefore apparent that fiber tofiber connection with low loss and minimum distortion(i.e. modal noise) remains an important aspect ofoptical fiber communicationsystem.

Before optical fibers splicing and joining are

done certain preparations are made with fiber or fibercables as case may be to achieve best results at theend surface. First of all the protective plastic thatcovers the glass cladding is stripped from each fiber


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end, which is then cleaved with a special tool,producing a smooth and flat end.

1. Fiber splices: These are semi permanent orpermanent joints which find major use in most opticalfiber telecommunication system (analogous toelectrical soldered joints).

2. Demountable fiber connectors or simpleconnectors: these are removable joints which alloweasy, fast, manual coupling and uncoupling of fibers(analogous to electrical plugs and sockets).

The above fiber to fiber joints are designed ideally tocouple all the light propagating in one fiber into theadjoining fiber. By contrast fiber couplers are branchingdevices that split all the light from main fiber into twoor more fibers or, alternatively, couple a proportion ofthe light propagating in the main fiber into main fiber.

FIBER SPLICES:-A permanent joint formed between two individualoptical fibers in the field or factory is known as afiber splice. Fiber splicing is frequently used toestablish long haul optical fiber links where smallerfiber lengths need to be joined, and there is no

requirement for repeated connection anddisconnection. Splices may be divided into twobroad categories depending upon the splicingtechnique utilized. These are fusion splicing orwelding and mechanical splicing.


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Fusion splicing is accomplished by applyinglocalized heating(e.g. by a flame or an electric are )

at the interface between two butted, prealignedfiber ends causing them to soften and fuse.

Mechanical splicing, in which the fibers are held inalignment by some mechanical means, may beachieved by various methods including the use oftubes around the fiber ends (groove splices).

A requirement with fibers intended for splicing isthat they have smooth and square end faces. Ingeneral this end preparation may be achieved usinga suitable tool which cleaves the fiber as illustrated.

FUSION SPLICES:-The fusion splicing of single fibers involves the

heating of the two prepared fiber ends to theirfusing point with the application of sufficient axialpressure between the two optical fibers. It istherefore essential that the stripped (of cabling and


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buffer coating) fiber ends are adequately positionedand aligned in order to achieve good continuity ofthe transmission medium at the junction point.

Hence the fiber are usually positioned and clampedwith the aid of an inspection microscope.

Flame heating sources such as micro plasmatorches (argon and hydrogen) and oxhydric microburners (oxygen, hydrogen and alcohol vapour)have been utilized with some success. However, themost widely used heating source is an electric arc.

This technique offers advantages of consistent,

easily controlled heat with adaptability for useunder field conditions. A schematic diagram of thebasic two fibers is welded together. Shows adevelopment of the basic are fusion process whichinvolves the rounding of the fiber ends with a lowenergy discharge before pressing the fiberstogether and fusing with a stronger arc. Thistechnique, known as perfusion, removes the

requirement for fiber end preparation which has adistinct advantage in the field environment. Apossible drawback with fusion splicing is that theheat necessary to fuse the fibers may weaken thefiber in the vicinity of the splice. It has been foundthat even with careful handling; the tensile strengthof the fused fiber may be as low as 30 % of that ofthe uncoated fiber before fusion.


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EQUIPMENT REQUIRED FOR OFCJOINT:

1) Optical fiber fusion splicer specification (splicermachine) AC input 100 to 240v, frequency 50/60Hz DC input 12V/A

2) Fiber cutter It converts irregular shaped fiber end into

smooth & flat end.3) Chemicals used in OFC joint

HAXENE: To remove jelly from the fiber ACETONE: For cleaning the OFC ISO PROPENOT: For smoothness of optical

glass.4) Sleeve: - To enclose fiber joint.5) Tool Kit6) Joint kit.

Joint encloser. Buffer

Adhesive tape.7) Generator /12V Battery8) Cotton clothes for fiber cleaning.


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REPEATERS AND REGENERATORS:-Optical repeaters are purely optical devices that areused simply to combat attenuation in the fiber;typically spans of 80km upwards are now possible.

The recent introduction of soliton transmissionmethods has increased the allowed distancebetween repeaters and systems spanning 130km

without a repeater are now possible.

Regenerators are devices consisting of bothelectronic and optical components to provide 3RRegeneration Retiming, Reshaping,

Regeneration,retiming and reshaping detect thedigital signal that will be distorted and noisy (partly

due to the optical repeaters), and recreate it as aclean signal as shown in figure.

This clean signal is then regenerated (opticallyamplified) to be sent on. It should be noted thatrepeaters are purely optical devices whereasregenerators require optical-to-electrical (O/E)conversion and electrical-to-optical (E/O)conversion. The ultimate aim of many fiber systemresearchers is to create a purely optical networkwithout electronics, which would maximizeefficiency and performance. Many aspects of such a


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system are in place, but some still require the O/Eand E/O conversion.

Figure7 - A digital signal before (noisy and attenuated) and afterregeneration

The most common optical amplifier currently in useis the EDFA (Erbium Doped Fiber Amplifier). Theseconsist of a coil of fiber doped with the rare earthmetal erbium. A laser diode pumps the erbiumatoms to a high-energy state; when the signalreaches the doped fiber the energy of the erbium

atoms is transferred to the signal, thus amplifying it.

Light Sources:-Two types of light source are used with fibers, LEDsand Laser Diodes.

LEDs can operate in the near infrared (the mainwavelengths used in fibers are 1300nm and

1550nm, along with 850nm for some applications);they can emit light at 850nm and 1300nm. Theyalso have the advantages of long lifetimes andbeing cheap. Unfortunately they are large comparedto the cross-section of a fiber and so a large amountof light is lost in the coupling of an LED with a fiber.

This also reduces the amount of modal controldesigners have over incident light.

Laser diodes can be made to emit light at either1300nm or 1550 nm, and also over a small spectralwidth (unlike LEDs), which reduces chromaticdispersion. Their emitting areas are extremely small


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and so the angle of incidence of light on a fiber canbe accurately controlled such that


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must be used to calculate the bandwidth of adetector.

There are many further complications in detectors,including noise equivalent power that indicates howclean a signal from a detector is. An analysis ofhow analogue and digital signals are processedafter the initial detector is also interesting.

Advantages of Fiber over OtherForms of Media:

1. Lower errors: BER approximates 1015, 16 for

fiber, whereas copper will be in the 103,4 for UTPto 108 for coaxial cable.


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2. Attractive cost per foot: Cost per foot for fiber isnow approximately $0.20 compared with $0.13 forcopper (Category 5+)

3. Performance: Immune from RFI and EMI withoutextra cost of shielding on copper

4. Ease of Installation: Ease of installation due tolower weight and thickness

5. Distances: Greater distance with fewer repeaters.Now can achieve 30 to 200 miles without repeaters.Copper and radio are limited to less than 30 miles.UTP digital transmission systems require repeatersevery mile.

6. Bandwidth improvements: Fiber is nearing 1.6Tbps, copper achieves 100 Mbps, and coax cancarry up to 1 Gbps.

7. Capable of carrying analog and digital: Using TDMand WDM, the fiber is both digital and frequencymultiplexed, increasing capacity.

8. Safety.: Fiber is a dielectric and does not carryelectricity. It presents no sparks or fire hazards. Itdoes not cause explosions, which occur due tofaulty copper cable.

APPLICATION OF THE OPTICAL FIBERIN COMMUNICATION:-


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TRUNK NETWORKThe trunk or toll network is used for carrying telephone

traffic between major conurbations. Hence there isgenerally a requirement for the use of transmissionsystems which have a high capacity in order tominimize costs per circuit. The transmission distancefor trunk systems can vary enormously from under 20km to over 300 km, and occasionally to as much as1000 km. Therefore transmission systems which exhibitlow attenuation and hence give a maximum distance ofunrepeatered operation are the most economicallyviable. In this context optical fiber systems with theirincreased bandwidth and repeater spacing offer adistinct advantage.

JUNCTION NETWORK:The junction or interoffice network usually consists ofroutes within major conurbations over distances oftypically 5 to 20 km. However, the distribution of

distances between switching centers (telephoneexchanges ) or offices in the junction network of largeurban areas varies considerably for various countries.

MILITARY APPLICATION:In these applications, although economics areimportant, there are usually other, possiblyoverriding, considerations such as size, weight,deployability, survivability (in both conventional andnuclear attack and security. The special attributes ofoptical fiber communication system therefore oftenlend themselves to military use.


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MOBILES:One of the most promising areas of milita5ry

application for optical fiber communication is withinmilitary mobiles such as aircraft, ships and tanks. Thesmall size and weight of optical fibers provide andattractive solution to space problems in these mobileswhich are increasingly equipped with sophisticatedelectronics. Also the wideband nature of optical fibertransmission will allow the multiplexing of a number ofsignals on to a common bus. Furthermore, theimmunity of optical transmission to electromagnetic

interference (EMI) in the often noisy environment ofmilitary mobiles is a tremendous advantage. This alsoapplies to the immunity of optical fiber to lighting andelectromagnetic pulses (EMP) especially withinavionics. The electrical isolation, and therefore safety,aspect of optical fiber communication also provesinvaluable in these applications, allowing routingthrough both fuel tanks and magazines.

COMMUNICATION LINKS:The other major area for the application of optical fibercommunication in the military sphere includes bothshort and long distance communication links. Shortdistance optical fiber systems may be utilized toconnect closely spaced items of electronics equipmentin such areas as operations rooms and computerinstallations. A large number of this system havealready been installed in military installations in theunited kingdom. These operate over distances fromseveral centimeters to a few hundred meters attransmission rates between 50 bauds and 4.8 kbits-1.In addition a small number of 7 MHz video links


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operating over distances of up to 10 m are in operation.There is also a requirement for long distancecommunication between military installations whichcould benefit from the use of optical fibers. In boththese advantages may be gained in terms ofbandwidth, security and immunity to electricalinterference and earth loop problems over conventionalcopper systems.

CIVIL APPLICATION:The introduction of optical fiber communicationsystems into the public network has stimulated

investigation and application of these transmissiontechniques by public utility organizations which providetheir own communication facilities over moderatelylong distances. For example these transmissiontechniques may be utilized on the railways and alongpipe and electrical power lines. In these applications,although high capacity transmission is not usuallyrequired, optical fibers may provide a relatively lowcost solution, also giving enhanced protection in harsh

environment, especially in relation to EMI and EMP.Experimental optical fiber communication systemshave been investigated within a number oforganizations in Europe, North America and Japan. Forinstance, British Rail has successfully demonstrated a 2Mbits-1 system suspended between the electricalpower line gantries over a 6 km route in Cheshire. Also,the major electric power companies have shown agreat deal of interest with regard to the incorporation

of optical fibers within the metallic earth of overheadelectric powerlines. fibers are now the standard.

TELECOMMUNICATION:


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Optical point to point cable link between telephonesubstations.

LOCAL AREA NETWORKS (LAN's):Multimode fiber is commonly used as the "backbone" tocarry signals between the hubs of LAN's from wherecopper coaxial cable takes the data to the desktop.Fiber links to the desktop, however, are also common.

CABLE TV:As mentioned before domestic cable TV networks useoptical fiber because of its very low power

consumption.

CCTV:Closed circuit television security systems useoptical fiber because of its inherent security, as wellas the other advantages mentioned above.

Problems and Impairments Foundin Fiber Systems

1. Attenuation: Like an electrical signal moving oncopper, the light pulse will attenuate on the fiber. Thesignal gets weaker because a certain portion of thelight is absorbed by the glass. The actual frequencydetermines the amount and speed of absorption.Attenuation is stated in the form of decibels (dB).

2. Dispersion: When the pulse is sent down the fiber,

it spreads out during the transmission. The short pulsebecomes longer and joins with the pulse behind it. Thismakes it difficult (or impossible) for the receivingequipment to separate the pulses. There are differentforms of dispersion, including


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MaterialA range of frequencies is produced by the LEDand laser. The materials used to create the fiber cable usedifferent refractive indices; therefore, each wavelengthmoves at a different speed inside the fiber cable. This

means that some wavelengths arrive before others and asignal pulse disperses over a broader range. This is alsocalled smearing.Waveguidethe center core creates the waveguide (itguides the wave inside the core). The shape and therefractive index inside the core can create the dispersion orspreading of the pulse.ModalMultimode fiber creates many different modes(paths) for the light to travel down the fiber. The length of

the path can be different depending on the mode taken,meaning the light beams may take different paths ofdiffering lengths. Portions of the light may arrive out ofsequence. This means that the spreading over time causesthe fiber receiver to have to deal with this. The longer theroute, the bigger is the problem.

3. Noise:Modal noise is usually associated withmultimode fiber. The mismatch of the connectors and

the modes in a cable can cause loss of some of themodes. This causes signal loss, which is defined asnoise.4. Polarization:Optical fibers in normal systems arecylindrical and symmetric. Light traveling on the fibercan change in its polarity (positive to negative). At thehigher speeds, this may pose problems.


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BASIC OPTICALCOMMUNICATION LINK

TPYE OF FIBRES

SINGLE MODE


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Based on installation methods Cablecan be classified as:

Duct cable

Direct buried cable

Aerial cable

Premise Cable

Limitations of Fiber Optics

Communication over optical fiber is limited by twofactors:

Loss Dispersion

1. LOSSES DUE TO ATTENUATION

Reasons for Attenuation:

Because of the following factors:


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Rayleigh scattering (Attenuation decreasedwith wavelength)

Attenuation absorption peaks associated with

the hydroxyl ion (OH

-)

Attenuation to increase at wavelength above1.6 micron due to bending induced loss andsilica absorption

Attenuation for SM fiber is typically 0.20 to 0.35dB/Km.

2. Loss Mechanisms.


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Density Fluctuations

Loss due to external reasons: Micro Bending Macro Bending

Macro Bending:


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If the radius of a bend is relatively large (say 10 cm or so) there

will be almost no loss of light. However, if the bend radius is

very tight (say 1 cm) then some light will be lost.

Micro Bending:

Micro Bends


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Micro-bends can be an important source of loss. If the fiber is

pressed onto an irregular surface you can get tiny bends in the

fiber as illustrated in the figure

Modal Dispersion:

$ Modal dispersion is the spreading of optical signals indifferent modes

$ Multimode fiber has large number of modes and eachmode travel with different velocities, which results in

modal dispersion

$ Multimode fiber is not used for long distancecommunication due to this large modal dispersion

coefficient

$ Graded-index multimode fiber have less modaldispersion coefficient, thus can be used for longer

distance than multimode fiber

Chromatic Dispersion


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$ Different frequency components within the optical pulse(different wavelength) travels with different group

velocities

$ Chromatic dispersion occurs only in single mode fibersince which has one mode of propagation$ High chromatic dispersion broadens the optical pulses

in time and lead to inter-symbol interference that can

produce an unacceptable bit error rate

Date post:	14-Apr-2018
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