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The Fibreoptic Industry AssociationUFOs Explained 2002: Issue 3UFOs Explained 2002: Issue 3 © © Brand-Rex LimitedBrand-Rex Limited

Optical fibres Optical fibres

explained!explained!Solving the mystery of Solving the mystery of Unexplained Fibre OpticsUnexplained Fibre Optics

FIAThe Fibreoptic Industry Association

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The original content of "UFOs Explained" has been suppliedcourtesy of Brand-Rex Ltd, www.brand-rex.com, and copyright

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UFO’sUFO’s No, they’re not No, they’re not over your over your head head. If any mention of fibre optics has yourunning for the hills, panic not; help is athand. It’s only a mystery because no onehas bothered to explain it to you.

Well, that’s where this little book,produced by the Fibreoptic IndustryAssociation, can help. It won’t make you aworld-leading authority, but it will get youon the first few rungs of the ladder andhelp you to talk knowledgeably on thesubject.

And that’s important. Sooner or later,you’ll want to put fibre optics to work inyour own business or industry, so it makesthe best possible sense to start learningabout it here and now.

You’ll be surprised to discover howstraightforward and logical it all is. Yes,it’s an exciting new technology. And yes, itholds terrific promise for the future. Butfibre optics are already here and inwidespread use. They’re making life easierand a lot more convenient for you right now.

Pick up a ‘phone, visit the bank, stop off ata petrol station, and it’s almost certainyou’re in contact with fibre optictechnology. So join us as we begin toexplore the world of optical fibres. It’s sosimple, you’ll soon feel confident toembrace the technology without feeling outof your depth.

This light-hearted but useful introduction to fibreoptics was originally published by Brand-Rex (formallyBICC Brand-Rex). The Fibreoptic Industry Associationhave updated parts of the text and reformatted thedocument for the purposes of electronic publication.

The Fibreoptic Industry Association take thisopportunity to thank Brand-Rex for their permission topublish this document. Also we would like to thank thetechnical staff at Brand-Rex for the time and effortin obtaining an electronic version of the text andgraphics. Particular thanks go to Barry Elliott and IanTorr.


tomorrow’s cable.tomorrow’s cable.that information is all too easily corrupteddue to electrical machinery, thunderstormsor ‘noisy’ power lines. The problem justdoesn’t exist for optical fibres.

Security, too, is an important point. Signalscarried by optical fibres are practicallyimmune to detection; they’re effectivelyinvulnerable to eavesdroppers.

Low attenuation is another key benefit.(‘Low attenuation’ is a term you’ll comeacross time and time again in the world offibre optics, so you might as well know whatit means from the start). It’s simply a wayof describing low transmission loss. Whichmeans that a message can be trusted to golong distances from sender to recipient,intact, without needing a boost fromregenerators along the way.

You need another good reason? How aboutsafety. Optical fibre cables will not –indeed, cannot – produce sparks. Whichmakes them highly desirable in areas wherea stray spark could result in a big bang.

Today’s cable,Today’s cable,Fibre optic technology has been with us for severalyears and has by now proved its superiority. Opticalfibre systems offer so many advantages, it’s easy to seewhy copper cables can’t compete.

For one thing, optical fibre cables are much easier (andtherefore cheaper) to install, being far smaller in sizeand lighter to handle.

But the biggest advantage is that optical fibres cancarry far more information than any copper cable. Avirtue of the highest importance, you’ll agree, in an agewhere the flow of data transmission has increased froma trickle to a torrent.

Then again, optical fibres are completely free fromelectromagnetic interference. Even though copper cablecan only handle a limited amount of information bycomparison,


InformationInformationat light speed.at light speed.Copper cables carry messages by electricity.Optical cables carry messages by light.

But what’s so new about light being used totransmit signals? Our forefathers lit warningbeacons when invaders threatened. TheAncient Greeks used the heliograph, a movablemirror that reflected the sun’s rays and couldflash coded signals across great distances.Lighthouses are still in service, and trafficlights (when obeyed) are still keeping deathoff the roads.

In optical fibres, we’re using light in analtogether more sophisticated way. We’re alsousing an altogether different kind of light, butwe’ll get round to that later.

First, you need to know about radio waves andlight waves, and why the latter is a farsuperior transmitter of data. It all becomesclear as you cast an eye over theelectromagnetic spectrum.

You will not be surprised to see radio wavesthere, but the presence of light waves maypuzzle you. The truth is, radio waves,microwaves, infra-red, visible light, ultra-violet, X-rays and gamma-rays are all forms ofelectromagnetic radiation. Just one big happyfamily, waltzing along at the speed of lightwhich, as we all know, is 300,000,000 metres(186,000 miles) per second.

There are two ways of measuring these waves –-wavelength… the distance between waves-and frequency… the number of waves persecond

All waves are different; they have differentlengths and frequencies. The shorter thewavelength, the higher the frequency. Now,radio has a long wavelength. Take for instanceBBC Radio 1 on 98.9MHz. This means the waveis repeated every 3 metres. Compare that witha visible lightwave which is repeated thousandsof times over a single millimetre.

Look again at our model of the electro-magnetic spectrum, and you’ll “see thelight” even more clearly. Frequency isexpressed in hertz (or Hz) -remember wesaid Radio 1 operates on 98.9MHz, and thepart of the spectrum available forcommunication ranges from 10kHz to

over 100,000 million kHz – a range ofwavelengths from 30,000m to one millionthof a metre.

You’ll notice that particular frequencieshave been given different bands. The widthof any individual band shows how muchinformation carrying capacity is available atthat particular frequency.

The higher the frequency, the bigger theinformation carrying capacity, orbandwidth. And lightwaves offer some ofthe highest frequencies of them all.

The moral of the story? Becauselightwaves offer such a high bandwidthcapacity they have far more space availablefor signals. We need all this extra room orcapacity to handle the thousands of speechchannels, multiplicity of TV signals, andreams of data produced by the flood ofinformation technology.

That’s why light-carrying optical fibres areset to revolutionise the entire field ofcommunication and data transmission.


The light that’sThe light that’sout of sight!out of sight!In the last page or two we’ve learned thatoptical fibres use light to transmit signals, andwe’ve discovered that lightwaves can carry farmore information than radio waves.

We hinted earlier that optical fibres make useof a different kind of light to the ordinary,everyday kind that you’re familiar with.

We need a kind of light that can be guidedalong a solid rod of the finest purity glassadvanced technology can produce. Ordinarylight wouldn’t do at all.

To explain. In fibre optics, messages are firstconverted from electrical impulses intolightwaves. The lightwaves travel through thefibre (which, as we said, is a rod of extra-ordinarily pure glass) until it reaches thereceiving end. At this stage the message isconverted back into electricity by a piece ofelectronic equipment called a ‘receiver.’

It turns out that receivers are at their bestwhen dealing with a kind of light called infra-red. It also turns out that the special glassused in fibre optics – about which more later –is also at its best with infra-red.

Fascinating stuff, infra-red. It’s invisible tothe human eye in the same way that ‘dogwhistles’ are inaudible to the human ear. Yetyou can use it to produce highly dramaticcolour or black-and-white images on speciallysensitised films, using an infra-red filter overthe camera lens to black out all otherwavelengths.

Gun-sights that ‘see in the dark’ have beenmodified to pick out infra-red radiating fromtarget objects. Thermal cameras operate onthe same principle to detect heat leakingthrough an uninsulated roof. Hospital scannersuse infra-red to explore possible damage in thedeepest recesses of the human body or brain.

And if you have a remote-controltelevision, it’s good old infra-red thatsquirts from your handset to the TV toswitch channels or Ceefax.

But it’s in fibre optics that infra-redreally comes into its own – pumping voice,video and data transmissions downthousands of kilometres of optical fibre –and never an unwanted signal to annoy orconfuse.

Mind you, we can find a little job forvisible light too. It has it’s uses as aguidelight for motorway signs, jazzyadvertising displays, and medicalendoscopes.

That’s enough theory for the moment.Right now, it’s time we looked at opticalfibres at work today. Join us overleaf…

And you thoughtAnd you thoughtfibre optics were new!fibre optics were new!In a whole range of communications anddata transmission installations, optical fibrecables are already making majorcontributions. On these pages, we’ll runthrough a selection of applications whereoptical fibre cables have been chosen – andexplain the reasons for that choice.

Data TransmissionOptical fibre cables are the products ofadvanced technology; designed in and forthe computer age. They are better suitedfor the purpose than older copper-basedtypes. The unique combination of highbandwidth and low transmission loss meanshigher data rates and more freedom forthe user to decide where to locatecomputers and their peripherals.

TelemetryTelemetry is the process of monitoring thebehaviour of electronically operatedmachinery over long or short distances byremote control. Here again, hightransmission capacity plus low transmissionloss are the chief benefits. But there’sanother big plus point that has particularappeal to industrial users; optical fibrecables are not susceptible to interferencefrom heavy electrical equipment. Signalintegrity is thus assured.

Closed Circuit TVMonitoring a wide range of industrialapplications, CCTV cameras often have tooperate in harsh or hostile environments.Faultless performance can only be assuredby the combination of high bandwidth andzero crosstalk characteristics of opticalfibre cables. (Crosstalk refers to unwantedsignals caused by adjacent conductors incopper cables).


TelecomThe degree of high bandwidth that onlyoptical fibres can provide is cruciallyimportant in the world oftelecommunications. But keeping loss ofsignals down to the barest minimum isequally essential. Optical fibres serve bothneeds by supporting high transmissioncapacity with low transmission loss. Ofcourse, cables are often routed throughunderground ducts where space can beseverely limited.

Because of the small physical size of opticalfibres, many more can be incorporated intoa cable reducing the overall space requiredin underground ducts.

The emergence of optical fibre technologyhas enabled both existing telecomoperators and newly emerging competitorsto build high quality, high capacitynetworks.

Today telephone companies, cable TVoperators, electricity utilities and railwaycompanies all rely on optical fibres in orderto carry the majority of theircommunication services, including telephony,high speed data and television pictures.

MilitarySecurity of communications is a question ofprime importance in the military field.Optical fibre cables, offering completeimmunity to signal detection, are clearly theideal solution. The low size and weight ofthese cables answers the need for compact,lightweight equipment in battlefieldconditions. The key benefits of hightransmission capacity coupled with lowtransmission loss pay off in optimumperformance under the harshest ofoperating conditions.

Hazardous AreasOn top of all their otheradvantages, optical fibres haveanother inherent benefit thatmakes them particularly suitedfor use in hazardous areas such aspetrol stations and installation in

the oil, gas and petrochemical industries –being non-metallic, they are incapable ofproducing sparks. Thus, the risk of ignitionin fire-prone areas is greatly reduced.

Why now?The hunger for more information! Takejust one area, data transmission. As theswell becomes a tidal wave, the availabilityof a transmission medium which offersmuch higher signal capacity and much lowersignal losses – amongst the many otheradvantages – can only increase theeffectiveness of the entire process whilepushing the limits of technology back stillfurther.

Conventional copper cable systems are hardpressed to keep up with the mounting speedof development in communication andinformation technology. They were neverdesigned to handle the range of tasksthey’re now being called upon to perform.In many cases, they’ve already reached thelimit of their operating parameters. Putsimply, they just can’t cope.

Fibre optics technology, on the other hand,is a child of the high-tech age; born tothrive in the fast-changing world ofelectronics. It is both an essential part ofthis rapid advance, and the means by whichrelated user-industries can keep pace.

Cost–effective?Yes! To begin with, sand (of which morelater), the basic raw material of an opticalfibre, is cheaper than copper, but moreseriously, increased production volume and

advancing technology have brought the costof adopting fibre optics down substantially.The sound financial sense of investing inmodern technology with plenty of growthpotential, rather than one which isbecoming increasingly obsolete, is obvious:more for your money.

Future capacityOptical fibre cables positively encourageyou to install capacity now which caters forfuture demand. The savings to be made inthis way are even more pertinent thanpresent costs. Remember this if you’recabling a new building, or digging a cabletrench for the installation of otherservices.


A glass full of light.A glass full of light.Having read this far, you know more thanmost people about optical fibre cables. Youknow that they offer a host of superiorbenefits. You’ve seen some of the importantcontributions they’re making incommunications and data transmission rightnow. And you’re aware that they offerterrific potential for the future.

Now you’re ready to discover just what anoptical fibre is, and how it’s made.

Put simply, an optical fibre is a solid rod ofglass finer than a strand of human hair. Thefibre is surprisingly very flexible. In thesame way that electricity travels along wires,infra-red light is guided along the fibre in acontinuous beam, or as digital on/off pulses.

The finished optical fibre looks simpleenough… the making of one is anything but.To begin with, you can’t use any old glass.Only glass of the most exceptional purity willdo. Glass so pure that a solid block of thestuff 5km thick would be as transparent as apristine window pane – and without any ofthe distortions and impurities that cause asheet of ordinary glass to look green whenyou examine it edge on.

As already mentioned, the major ingredient is

sand. But, again, notthe kind that fills yoursandals and sandwichesat the beach. This is aspecial kind of sandcalled silica.

Why do we need a silica glass so pure?

Because its purpose is to transmit infra-red light reliably and efficiently over longdistances. Ordinary glass would lose thesignal beyond recovery within a fewmetres; impurities would scatter the lightin the fibre, rather as light is lost in fog.In the optical fibre, we have at lastconquered the problem of ‘conducting’light without any hindrance from fog, rainor dust.

The manufacturing process takes place inthe driest, cleanest environment thattime, money and a heck of a lot ofpatience can buy. A speck of dust or astray fingerprint, and the job’s destroyed.

Remember, an optical fibre is the wispieststrand of silica glass, and solid all the waythrough. Yet things are going on in there

that would make the hair rise on your head. Yousee, light is not merely zipping along in any kind ofan orderly fashion. It’s positively bouncing andbending, dashing this way and that.

Frantic is the word for it.

Now, mind, it’s strictly controlled. Every bounceand bend is predetermined. Let’s get to the heartof the matter. The innermost core of the opticalfibre is silica glass of the highest density. Infra-red light is guided along the core. Being glass, you’dexpect the light to shoot out of it in all directions.But it doesn’t, because …

From the core the silica glass graduates to form aslightly less dense outer cladding. Light isreflected back from the outer cladding to the core,and continues its travels, bouncing along from sideto side, from cladding to core. Protection isprovided by …

A plastic coating, covering the optical cladding andcore, preventing external dust particles andmoisture from attacking the glass.


Different fibreDifferent fibretypes.types.What the blazes gets into light when it getsinside an optical fibre? What possesses it togo leaping about like a wild thing?

Well it’s all done for a purpose. For reasonstoo technical to go into, light follows adifferent path along different types of opticalfibre. It never get the chance to choose itsown path, because it’s guided every step of theway from transmitter to receiver. Nothingwild or random about it.

(By the way, if you want to make yourselfunderstood when the talk turns to opticalfibres, don’t say ‘path’ - say mode. It meansthe same thing).

Now, you’ll be asking yourself, how do you setabout guiding light so it bends and bouncesalong the right mode? It’s all down to thatwonderful stuff, silica glass. And the awesomedegree of control that goes into forming it intoan optical fibre.

The glass itself is given different degrees ofoptical density at certain points. When thelight passes from a high density region into alow density region, it bends or bounces. Andvice versa.

In other words, higher and lower densities inthe same rod of silica glass control the waylight behaves.

Optical engineers, of course, never use plainwords like ‘bending’ and ‘bouncing’. Theyprefer ‘refraction’ and ‘reflection’. It’ll do youno harm to learn the difference between thetwo.

When light hits a reflective surface, like amirror, it bounces back. That’s reflection.When light passes from one medium through toanother of a different density, it bends.That’s refraction. Pour yourself a nice glass ofwater, stand your door-key in it, and watchhow the key appears to bend as itsimage passes from water to your eye.

Now we’ll look at the different types ofoptical fibre on the market right now.

First, there’s Single Mode Fibre. As the namesuggests, light can only follow one mode in thistype of fibre. That’s because the core isexceptionally narrow. Single mode fibresoffer the greatest information carryingcapacity of all the fibre types, and can supportthe longest transmission distances.

Multimode Fibres normally have a wide coreand give light a wide choice of modes. Thereare two kinds to consider…

In Step Index Multimode Fibres, an abrupt anddefinite change occurs between areas of lowand high density. The shift from one level ofdensity to another causes light to bounce.

In Graded Index Multimode Fibres, the changebetween low and high density areas within thefibre happens gradually. Light is gently bentrather than bounced. This type of fibreoffers two advantages over step indexmultimode: longer transmission distances andhigher bandwidth.

When optical engineers talk about thesedifferences, you’ll hear them use the phrase‘refractive index profile’. Do not be alarmed.It’s simply a way of showing, in diagram form,the different levels/variation of density withinthe fibre. Which is something you nowunderstand. (Unless you skipped the last threeparagraphs).

You may be wondering why we go to all thebother. Why can’t we manage with just onekind of optical fibre?

Well, think of all the industries that are eitherusing or are about to use optical fibre systems.Think of the different jobs they’ll have toperform.

Computer Engineering, Data Transmission,Remote Control Engineering, High VoltageEngineering, Chemical Processes, SurveillanceSystems, High Security Systems, Aviation andSpace Technology…

You’d hardly expect areas of such diversity toget by on just one standard fibre type, wouldyou?

That’s why the potential user is given a choiceof fibres, each one designed to satisfy aparticular set of requirements.

(The fact that such a choice is widely availablesimply underlines what we’ve been telling youall along; that fibre optics is a well-established, up-and-running technology).


Light sources.Light sources.As you know by now, optical fibres are so thin,so fine, you can pass a whole bunch of themthrough the eye of a darning needle. Itfollows, then, that the light source used tosend light along them also has to be incrediblyslender.

In short, we need the minutest light sourcecapable of concentrating the highest amountof power down the fibre.

A light bulb couldn’t do it. For one thing, itscatters light far and wide withoutdiscrimination.

Fortunately, we have a choice of two light

sources (or transmitters) which areeminently suitable for the job. We can useeither small light-emitting diodes (LEDs), orLASER ‘chips’.

You’re familiar with LEDs – the littleindicator lights on hi-fi systems, cardashboard indicators, and so forth.

LASER chips, like LEDs, are made from tinychemical crystals which generate light whenexcited by electricity. They’re a lot moreexpensive than cheap and cheerful LEDs, andare used only when the very purest infra-redlight is needed to provide extra high data-rate performance.

Unlike ordinary light, LASER light canconsist of single wavelengths concentratedinto a straight beam. The chip itself is nobigger than a grain of sand.

Travelling lightInfra-red, carrying a payload ofinformation, is pulsed at speed down opticalfibre. Light becomes a ‘pulse’ when a lightsource (transmitter) is switched on and off.LEDs and LASER chips are the onlydevices available capable of switching onand off fast enough.

Connecting an optical fibre to a LED or aLASER chip is a task that calls for the mostcritical precision. Alignment must beabsolutely spot-on, or the light transmittedwill be scattered and lost – along with allthe data the light is carrying.

The message starts out as an electricimpulse which excites the LED, or LASERchip, into emitting flashes of infra-red.These flashes – more correctly, coded‘pulses’ – have to be introduced directly intothe optical fibre. These pulses of lightbounce along the fibre until they reachjourney’s end – the receiver. The receiveris a photodetector which converts thetransmitted light back into an electronicimpulse, which is then decoded back intothe original message.

And that’s how optical fibre works. Astrand of silica glass, pure and fine – ahighly concentrated light source pulsingsignals through at one end in the form ofinfra-red – and a receiver at the other endto take in the light pulse and convert itback into the original signal.


All talking together.All talking together.All talking togetherHopefully you now know how we can transmit asingle message through our fibre but if weneeded a single fibre for each message itwould be very expensive. Remember how lightis electromagnetic radiation just like radiowaves but with a much shorter wavelength?Well just as radio waves can be used totransmit many programmes simultaneously soour optical fibres can carry lots of messages atthe same time. In this way we are making useof all that enormous bandwidth that isavailable in the optical part of the spectrum.

To find out how we can simultaneously sendlots of messages (we call this multiplexing) wefirst need to consider in a bit more detail howwe send a single message, such as the spokenvoice, into the flashes of light that travel downthe fibre. First of all we speak into amicrophone which converts our voice into anelectrical signal whose strength varies with

sound pressure. We then take this signal and8000 times a second, we sample it and decidewhich of 256 voltage levels each sample isclosest to. Now instead of transmitting theoriginal voltage levels we send the 8 digitbinary number that corresponds to it. If forinstance it was closest to 56 we would send00111000. As we do this 8000 times a secondthis means that for each voice channel we haveto send 8 x 8000 = 64,000 ones or noughts (wecall them bits) every second.

All this may seem like a lot of trouble to go tobut this new digital format can also be used tocarry other messages, such as TV signals, andit is of course the way that computers talk toeach other naturally. Once in this form it iseasy to transmit it on our fibre by simplyturning our LASER off and on. As we shall seelater it’s also possible to decode it almostperfectly in most cases.

Time multiplexingNow that we have our signal in this digitalformat if we want to send two signals simultaneously then we simply interleave the signals as shown. Of course this new message must only take as long to send as each of theoriginal messages so each ‘bit’ can only be halfas long and the transmission speed will be128,000 bits/s.

We can keep on doing this and it is not unusualto interleave almost 32,000 channels and tosend over 2,500,000,000 bits every second inthis way.

Wavelength multiplexingOur fibres need to carry not just voicemessages but faxes, computer messages, TVsignals, internet traffic etc. etc. There is nowso much demand for capacity (bits) that if wejust use time multiplexing each of the bitsbecomes so small that it is getting difficult tosend them without distortion. This has led to anew technique called ‘wavelength multiplexing’to be developed.

Instead of just using one we use a number ofLASERs, each one of which transmits at adifferent wavelength (colour). In this way wecan increase the capacity of our fibre withoutmaking the bits any smaller. By using an opticalfilter at the decoder we can select whichwavelength to listen to, much as we can tuneinto a particular radio station.

Another big advantage of wavelengthmultiplexing is that it allows us to route signalsto different places without using anyelectronics.

The picture shows how station A transmits tostation B using red light and to station C withgreen light, with optical filters being used toroute the two signals where the fibres splitinto two


OvercomingOvercomingtransmission loss.transmission loss.If you remember we said that only the purestglasses were used to make fibres and thismeant that 5km of optical fibre is as clear as anormal pane of glass. But what happens if wewant to transmit our signal over even longerdistances? The equivalent of how many panesof glass (we call this transmission loss) can oursignal travel through before it is too weak tobe able to be decoded accurately?

The answer can be as great as 400km (thedistance from London to Paris) depending uponexactly how much information we want to send.That’s a long way for the light from one LASERchip to travel and if we care to make it traveleven further then it’s going to need a littlehelp. To explain how, we are going to have tounderstand how our decoder works and tomeet the big villain of the piece: NOISE.

Decoding lightYou don’t need to read a book like this to tellyou that it’s easier to hear a person near toyou than someone who is 10m away. The reasonis that the weaker the signal the more it getslost in all the other everyday noises that aregoing on around us. Our light decoder has thesame problem – it always generates some noiseof its own which means it cannot decode anymessages that come from too far away.

So how can we overcome the dreaded noise?Well, when we send our messages using pulsesof light then, as long as there’s not too muchnoise, we can decode whether a pulse has beensent or not. In fact, with digital signals, wecan do this so well that we think there’ssomething wrong if we make even a single errorin decoding a billion pulses of light. So one wayof overcoming noise is to add something we calla regenerator into our optical fibre justbefore the signal gets too weak to be reliablydecoded. This decodes the message almostperfectly and then retransmits it at a highersignal level using a LASER chip. Because we dothis almost perfectly each time, we cancontinue to do this over and over again andsend our signal half way round the world ifrequired. We call this process regeneration.

Optical amplifiersRegeneration is fine if we are only transmittinga single wavelength of light and we knowexactly how many bits per second ofinformation we are sending. It is, however, acomplicated process in that we keep having toturn our signal from being optical to electricaland vice versa. This has led to thedevelopment of the optical amplifier in whichthe weak light is amplified directly without theneed for the intermediate electronics. Opticalamplifiers ‘boost’ incoming noise as well assignal and even add a small amount of noisethemselves so they have to be spaced a bitcloser together than regenerators. They are,however, extremely versatile and can amplifymany wavelengths at once (we would need aseparate regenerator for each wavelength)making them ideal for systems carrying morethan one wavelength of light.

Optical fibre cables.Optical fibre cables.The way forward

Optical fibre cables are now even found onhigh voltage power lines. These are used forcontrolling the electricity network and to buildtelecommunication systems.

A composite steel/aluminium andoptical cable can replace anearth wire

A non-metallic cable can bewrapped on an existing earth wire

A non-metallic self-supporting cable can besuspended from thetowers between phaseconductors


Making anMaking anoptical cable.optical cable.As we told you earlier, the merest touch of acareless finger, no matter how well scrubbed,could ruin the fibre for keeps. It sounds likesacrilege therefore to talk of burying itunderground, pushing it through sewers, orlaying it on areas where it is likely to bedoused with petrol or assaulted by corrosivechemicals.

You’re right! It wouldn’t be reasonable to sendthem naked into the field. Protection fromrough handling and onerous environments is anabsolute must.

The cable-maker builds protection around anoptical fibre by building a cable around it. It’srather like cladding a knight in armour, ordressing a fireman in protective gear.

Cables are essential to any activity requiringthe use of electrical power. Without a cable toconnect powered equipment to a power source,the equipment’s redundant and we needn’t havebothered discovering electricity.

Is the cable to be used indoors or outdoors?Will it be buried underground, or even at sea?Does it need self-suspension qualities for anoverhead installation? Will it be subject tovibration, crushing or high pressure? Does itneed protection from chemicals, bacteria,rodents? Is a cable needed that generatesless smoke and toxic gases in an outbreak offire? The questions are seemingly endless, butall must be answered if the cable-maker is toselect the correct materials and method ofconstruction.

Whatever the challenge, the experiencedcable-maker will have the ideal solution inhis/her standard or non-standard cable ranges.

The first thing he does when he/she rolls uphis/her sleeves is to put a kind of jacket onthe fibre. Called in the trade a ‘buffer jacket’,it’s the fibre’s first line of defence against theunfriendly elements. There are two basicmethods:

Either: Tight Buffers, i.e. plastic coatingsdrawn over the fibres.

Or: Loose Buffers, i.e. fibre with the freedomto move within a cavity, a common form being afibre in a loose tube.

Now, while fibre optics is a fairly recenttechnology, cable-making has been a wellestablished activity for over a century. Therehave been changes, of course; cable-makersare forever introducing new and innovativetechniques. But, essentially, most of thematerials and techniques used in the making ofconventional copper cables can be applied toadvanced optical fibre cables.

The cable-maker wants to know what job thecable is expected to perform and what sort ofworking conditions it’s expected to endure.Only then can he/she select the rightmaterials.

It could well be that a special cable type willbe required. So every cable-maker worth hisor her salt keeps a range of non-standardcables, just in case.

To ease any strain on the precious opticalfibres, he’ll add strain members made of steel,glass or synthetic yarns.

What other materials might we need? Fillingcompounds, perhaps, to keep water out.Metallic tapes, if a really impenetrable waterbarrier is called for. Metallic barriers, such aslead, to keep out corrosive chemicals. Thecable maker may decide to use binding tapes tobunch a number of cable elements together –carefully used, this method can isolate thecable core from any movement in the outerjacket.

Outer jacket? That’s the plastic sheath thatcovers and protects the innards of a cable.And it’s no ordinary plastic, we hasten to add.It could be a flame retardant polymer forindoor use, or polyethylene for outdoors.

Armouring could be essential, especially toprovide extra protection for the cable whileit’s being installed. The most common formsare steel wire and steel tape, which improvethe cable’s resistance to crushing and anunkind cut from a spade.


You’ve solvedYou’ve solvedthe mystery.the mystery.So now you know. Fibre optic technology isn’tover your head after all. It never was; you justwanted someone to explain it for you.

And you can’t start learning too early. Opticalfibre cables are already thoroughlyestablished in industries throughout America,Britain and the rest of the world. Fibre opticsis a ‘now’ technology.

But you’re wondering if there’s an applicationfor fibre optics in your own field. Theanswer’s a resounding “Yes” if you’re involvedwith computer engineering, data transmission,the oil and petrochemical industries,telemetry, telecoms, surveillance systems,CATV, or aviation and space technology.

In all these areas, the advantages of fibreoptics have proved to be far superior to thoseoffered by any other transmission system.The exceptionally large bandwidth, forexample, has the potential to carry 100,000times more information than a coaxial cable.

Voice, data and television signals may all becombined together and transmitted over asingle optical link with little loss of signal.

Optical fibres are almost completely immune toall forms of electromagnetic interference, andthere’s never any crosstalk between fibres.

FIA Information sourcesFIA Information sourcesVisit the Web-site:

www.fia-online.co.uk

e-mail the Secretariat:[email protected]

Telephone: +44 (0) 1763 273039

Members are able to access, free of charge,copies of all the FIA Technical Supportdocuments. Non-members are able to purchasethe documents from the Secretariat.

It’s virtually impossible to tap into an existingfibre optic link. This provides a level ofsecurity unobtainable with coaxial basedsystems.

The small size and light weight of optical fibrecables leads to lots of room for extra capacityin underground cables ducts.

In areas where the danger of explosion exists,optical fibre cables are incapable of emittingsparks.

As the input and output circuits connected to afibre are only optically coupled, no electricalconnection takes place. This results in totalelectrical isolation, making it possible tomonitor and control high voltage installations.And since glass does not conduct electricity,there’s no risk of adverse effects from anearby lightning strike.

The end of this book isn’t the end of all thehelp and advice you can get from the FIA.We’re always ready and willing to share ourknowledge, and we’ll gladly put you on ourmailing list to keep you in the know.


ArmourExtra protection for a cable. Improvesresistance to cutting and crushing. The mostcommon form is steel wire.

AttenuationA term which refers to a decrease intransmission power in an optical fibre. Usuallyused as a measurement, e.g. ‘low attenuation’means low transmission loss.

BandwidthThe amount of space in a given part of theelectromagnetic spectrum needed to carry ourcommunication signals, i.e. ‘greater bandwidths’means more usable space.

BifurcatorAn adaptor with which a loose tube containingtwo optical fibres can be split into two singlefibre cables. See Loose Tube.

BufferMaterial surrounding the fibre to protect itfrom physical damage.

CladdingThe outermost region of an optical fibre, lessdense than the central core. Acts as an opticalbarrier to prevent transmitted light leakingaway from the core.

CoreThe central region of an optical fibre, throughwhich signal-carrying infra-red light istransmitted. Manufactured from high densitysilica glass. See Silica Glass.

ElectromagneticRadio waves and light are waves of energyassociated with electric and magnetic fields,and are forms of radiation occurring within theelectromagnetic spectrum.

Fibre OpticsIt’s what this book’s all about.

FrequencyThe number of times a signal occurs in a givenperiod usually measured in Hertz or cycles persecond. See Hertz.

Graded Index(More precisely, graded index profile.) A termdescribing how the refractive index of glassused in this type of optical fibre altersgradually from the core to the optically lessdense outer cladding. See Core; see Cladding.

HertzThe unit of frequency, equivalent to one cycleper second, named after the wireless pioneerHeinrich Hertz.

Kilohertz Megahertz Gigahertz (kHz) (MHz) (GHz)One thousand One million One thousand Hertz. Hertz. million Hertz.

A useful glossary of terms

How to tell a How to tell a bifurcatorbifurcator from … from …Infra-RedA form of light having a longer wavelengththan ordinary constituents of white light.Invisible to the human eye.

LASERA source of exceptionally pure light which canconsist of single wavelengths concentratedinto a straight beam. Used to transmit infra-red along an optical fibre; employed when highdata-rate performanceis required.

LED(Light emitting diode). An electricalcomponent which produces light whenstimulated by electricity. The cheapest andmost common means of transmitting infra-redalong an optical fibre.

Loose TubeRefers to a type of cable in which one or moreoptical fibres is/are laid loosely within a tube.

ModeThe path taken by a light ray as it travels alonga fibre.

Moisture BarrierA layer of protection built into a cable to keepwater out.

Multimode FibreAn optical fibre which allows the signal-carrying light to travel along more than onepath.

Optical AmplifiersDevices which boost the optical signal levelwithout converting it to an electrical signal asan intermediate stage.

PhotdetectorA device at the receiving end of an opticalfibre link which converts light to electricalpower.

Primary CoatingA thin plastic coating applied to the outercladding of an optical fibre. Essential inprotecting the fibre from contamination andabrasion.

Refractive Index ProfileA description of how the optical density of anoptical fibre alters across its diameter.


RegeneratorsDevices placed at regular intervals along atransmission line to detect weak signals andre-transmit them – seldom required in a fibreoptics system. (Often wrongly referred to as‘repeaters’).

SheathThe outer finish of a cable. Usually anextruded layer of either PVC or polyethylene.

Silica GlassExceptionally pure glass used to make anoptical fibre.

Single Mode FibreAn optical fibre so constructed that lighttravelling along the core can follow only onepath. (Also called ‘monomode’).

Step Index(More precisely, step index profile). Adescription of how the refractive index ofglass used in this type of optical fibregraduates, in a clearly defined step, from thehighest density to the lowest. The shift fromone level of density to another causes the lightto bounce as it travels.

Strain MemberPart of an optical fibre cable which removesany strain on the fibres. Commonly usedmaterials include steel, glass and syntheticyarns.

Tight BufferedA type of cable in which the optical fibres areencapsulated in a plastic material.

Time MultiplexingInterleaving digital signals to increase datarates.

WavelengthA measurement of the length of anyelectromagnetic wave. The shorter thewavelength, the higher the frequency. SeeFrequency.

Wavelength MultiplexingUsing more than one wavelength of light in thesame fibre to allow greater rates ofinformation transmission.

A useful glossary of terms

… a strain member… a strain member

The original content of "UFOs Explained" has been suppliedcourtesy of Brand-Rex Ltd, www.brand-rex.com, and copyright

remains with Brand-Rex Ltd. This FIA publication may bereproduced in whole or part for non-profit making educational activities.

It may not be copied in whole or part or used for any commercial activity.

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