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welcome to lecture 3 have the FOA lecture series on fiber optics this time we're going to talk

about optical fiber.

Within the scope a fiber optic components, the fiber transmits a signal as light. The cable

protection fibers, splices join two fibers permanentl, an! connectors join fibers to connect toactive !evices so the can be !isconnecte! for rerouting, testing, an! the like. An! then this

har!ware which hol!s everthing together for this chapter we're going to focus optical fiber.

Within the optical fiber, the light is transmitte! the core, is trappe! in the core an! optical

cla!!ing that surroun!s it. On top of that, there's a buffer or primar coating, ma!e out usuall

an! curl plastic that protects the fiber from moisture !amage. This is what we strip off, we'll

prepare the fiber for termination or splicing. "ost fibers are all glass, some fibers have a glass

core, an! plastic cla!!ing, an! some are all plastic the ones we calle! #OF.

The secret of optical fiber works is total internal reflection. $ou seen this ourself when ou

stick that step !own in water an! ou see it banne! that cause! b the !ifferent in!e% of

refraction between water an air. Well the core of the fiber an! a clanging have !ifferent in!ices

of refraction an! that use to reflect light at certain angles to totall trappe! them in the fiber.

The angle which the're trappe! is calling numerical aperture.

We !ivi!e fibers in the two tpes& multi mo!e an! single mo!e. "ultimo!e fiber has a large

core, that supports multiple raise we call the mo!es a light. Where a single mo!e fiber has a

ver small core an! it supports onl one mo!e or ras of light. ecause the !ifferent mo!es

supporte! in multimo!e fiber, it ten!s to have higher continuation in lower ban!with thensingle mo!e fiber. "ultimo!e fibers tpicall use! in premises applications or local area

networks !ata links securit sstems. Where single mo!e fiber is use! for all high spee!,

long(!istance outsi!e plant applications.

"ultimo!e fiber comes in two tpes& step in!e% has a corner that's all the same material so

the light or the mo!es travel in straight lines basicall bouncing from one si!e for the court to

the other. )ra!e! in!e% fiber has a core with varing in!e% of refraction, that gui!es them out.

The light is traveling in the outsi!e of the core is in a lower in!e%ing refraction material an!

actuall travels faster. *o it tries to keep all the mo!es an! snchroni+ation throughout the

entire fin!er.

There are !ifferent si+es of optical fiber, but the majorit of fiber is glass fiber with the -

micron cla!!ing !iameter. That's about /// inch, there are several !ifferent multimo!e si+es

with !ifferent core !iameters / micron an! 0-. micron being the most popular. Although in

the past we've ha! 1 an! // micron course. #lastic optical fibers ver large fiber bottom

millimeter in !iameter with a ver thin cla!!ing an! 2*4#* fiber has a glass core plastic

cla!!ing, with the corner about -// microns in a cla!!ing about -/ micron.

The attenuation the optical fiber is cause! b two factors& scattering an! absorption.*cattering is a inverse function of the wavelenght. 5n fact the fourth power the wavelength so

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its got a longer wavelengths when a scattering goes !own. 5s also observe! shit specific

wavelengths tpicall cause! b the /.1 ra!ical which is sort of like water. That is left in the

fiber, in fact we make a low water peak fiber that re!uces the absorption at those peaks to

allow the wavelengths to be use! for wavelength !ivision multiple%ing

ecause the attenuation the optical fiber is less at longer wavelengths, that's where we ten!

to use them for transmission. Those longer wavelengths a car infrare! light an! it's mostl

invisible to the human ees. *ince the light in the optical fiber is invisible to our ee is

problem, if it is large enough in power to be harmful to our ees, ou can't see it. ut ou can

check the power level with a power meter, where !igital camera. There's an FOA $ouTube

vi!eo showing ou how to use a !igital camera to !etermine if there's light in the fiber

$ou can see the !ifference in attenuation in the optical fiber at !ifferent wavelengths b

looking at tpical fiber specs. "ultimo!e fiber for e%ample, as a loss in 1/ nanometers which

is just above the visible a 3 !b per kilometer, well 3// nanometers, it's !own ! per

kilometer. 5nstea! of losing half the power per kilometer / nanometers loses about -/

percent per km at 3// nanomter. $ou can see the same specification changes occurre! with

single(mo!e fiber an! these are tpical specs, the actual stan!ar! sometimes have much

higher losses just to make sure that all fibers can meet the minimum specifications. Those are

not tpical specs.

Fiber has e%tremel goo! ban! with but not infinite. Within multimo!e fiber we have two

factors& "o!al !ispersion an! chromatic !ispersion. "o!al !ispersion is actuall cause! b

the !ifferent times it takes, each !ifferent mo!e of light of travel !own the fiber, an! step in!e%fibers the have much lower ban!wi!th because it lacks the compensation provi!e! b the

gra!e! in!e% score upgra!e! multi mo!e fiber.

oth single(mo!e an! multimo!e fiber suffer from chromatic !ispersion, that cause! b the

fact that !ifferent colors are wavelengths of light have !ifferent spee!s through the glass core

the fiber an! actualit the re! light travels through the fiber faster than the blue light. *o as

source that has a ver broa! spectral with are lots of colors in its spectrum like an 678 suffers

much more chromatic !ispersion an! as a source with a ver narrow wavelength like a laser

an! that's one of the reasons for e%ample even in multimo!e fiber that pi%els transmit light

much further an! faster in 678s.

6ong single(mo!e fibers, the're use! tpicall for long(!istance telecommunications have

other factors that affect the !ispersion, for e%ample polari+ation. #olari+ation means that the

light waves are traveling in !ifferent planes in the fiber. 5t's actuall cause! b stress on the

fiber, where the fact that the core the fiber is it perfectl roun!. #olari+ation mo!e !ispersion

is ver pick, it can var with temperature were even when stresse! on an aerial cable. 5t's a

ver small effect but it's ver important for long fiber operating at 9-(// gigabits per secon!

or more.

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"ultimo!e fiber comes in several !ifferent varieties, !epen!ing on its ban!wi!th, when use!

with 1/ nanometer pi%el laser sources their tpical high(spee! sstems use! to premises

cabling. *ingle mo!e fiber has lot a !ifferent variations too, accor!ing to what !istance it's

going to go, what wavelength it's going to be use! at, an! how it might be use! for

wavelength !ivision multiple%ing. That is a ver comple% subject beon! the scope of thissimple lecture.

When the things people often want to know is, how fibers ma!e. Well it's ma!e from a

preform. $ou take a glass tube or a ro!, ou !eposit material aroun! it an! heat it up to shrink

it into a soli! glass ro!. The si+e as the one ou see in the top picture. From a preform like

this, ou can pull as much as / kilometers optical fiber.

The preform is place in a pulling tower, it:s heate! on the en! an! the fiber is pull is a then

strain from that giant preform. The fibers is pull carefull to control rate an! monitore! for

!iameter an! teste! for strength. As it cools !own a half is covere! with that primar buffer

coating we talke! about usuall a ;< cure! acolte. The fibers is then spoole! up an! full

teste! to make sure it meets all its specifications. Then those spoole! are set to cable who

built it into cable, which is going to be the topic a ver ne%t chapter.

where the fiber optic Association professional societ fiber optics we're happ to have ou join

us for this lecture series on optical fiber an! hope ou enjo all the lectures and videos on

our YouTube channel