Optical Fiber Manufacturing

7/24/2019 Optical Fiber Manufacturing

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Made How Volume 1 Optical Fiber

Optical Fiber

Background

An optical ber is a single! hair"ne lament drawn #rom molten silica glass. $hese

bers are replacing metal wire as the transmission medium in high"speed! high"

capacit% communications s%stems that con&ert in#ormation into light! which is then

transmitted &ia ber optic cable. 'urrentl%! American telephone companies

represent the largest users o# ber optic cables! but the technolog% is also used #or

power lines! local access computer networks! and &ideo transmission.

Ale(ander )raham Bell! the American in&entor best known #or de&eloping the

telephone! rst attempted to communicate using light around 1**+. Howe&er! light

wa&e communication did not become #easible until the mid"twentieth centur%! when

ad&anced technolog% pro&ided a transmission source! the laser! and an e,cient

medium! the optical ber. $he laser was in&ented in 1-+ and! si( %ears later!

researchers in /ngland disco&ered that silica glass bers would carr% light wa&es

without signicant attenuation! or loss o# signal. 0n 1-+! a new t%pe o# laser was

de&eloped! and the rst optical bers were produced commerciall%.

0n a ber optic communications s%stem! cables made o# optical bers connectdatalinks that contain lasers and light detectors. $o transmit in#ormation! a datalink

con&erts an analog electronic signal2a telephone con&ersation or the output o# a

&ideo camera2into digital pulses o# laser light. $hese tra&el through the optical

ber to another datalink! where a light detector recon&erts them into an electronic

signal.



3aw Materials

Optical bers are composed primaril% o# silicon dio(ide 4SiO 5 6! though minute

amounts o# other chemicals are o#ten added. Highl% puried silica powder was used

in the now"outmoded crucible manu#acturing method! while li7uid silicon

tetrachloride 4Si'l 8 6 in a gaseous stream o# pure o(%gen 4+56 is the principal

source o# silicon #or the &apor deposition method currentl% in widespread use. Otherchemical compounds such as germanium tetrachloride 4)e'l 8 6 and phosphorus

o(%chloride 4PO'1 9 6 can be used to produce core bers and outer shells! or

claddings! with #unction"specic optical properties.

Because the purit% and chemical composition o# the glass used in optical bers

determine the most important characteristic o# a ber2degree o# attenuation2

research now #ocuses on de&eloping glasses with the highest possible purit%.

)lasses with a high :uoride content hold the most promise #or impro&ing optical

ber per#ormance because the% are transparent to almost the entire range o# &isible

light #re7uencies. $his makes them especiall% &aluable #or multimode optical bers!which can transmit hundreds o# discrete light wa&e signals concurrentl%.

;esign

0n a ber optic cable! man% indi&idual optical bers are bound together around a

central steel cable or high"strength plastic carrier #or support. $his core is then

co&ered with protecti&e la%ers o# materials such as aluminum! <e&lar! and

pol%eth%lene 4the cladding6. Because the core and the cladding are constructed o#

slightl% di=ering materials! light

$o make an optical ber! la%ers o# silicon dio(ide are rst deposited on the inside

sur#ace o# a hollow substrate rod. $his is done using Modied 'hemical Vapor

;eposition! in which a gaseous stream o# pure o(%gen combined with &arious

chemical &apors is applied to the rod. As the gas contacts the hot sur#ace o# the rod!

a glass% soot se&eral la%ers thick #orms inside the rod. A#ter the soot is built up to

the desired thickness! the substrate rod is mo&ed through other heating steps to

dri&e out an% moisture and bubbles trapped in the soot la%ers. ;uring heating! the

substrate rod and internal soot la%ers solidi#% to #orm the boule or pre#orm o# highl%

pure silicon dio(ide.

$o make an optical ber! la%ers o# silicon dio(ide are rst deposited on the insidesur#ace o# a hollow substrate rod. $his is done using Modied 'hemical Vapor

;eposition! in which a gaseous stream o# pure o(%gen combined with &arious

chemical &apors is applied to the rod. As the gas contacts the hot sur#ace o# the rod!

a glass% soot se&eral la%ers thick #orms inside the rod.

A#ter the soot is built up to the desired thickness! the substrate rod is mo&ed

through other heating steps to dri&e out an% moisture and bubbles trapped in the



soot la%ers. ;uring heating! the substrate rod and internal soot la%ers solidi#% to

#orm the boule or pre#orm o# highl% pure silicon dio(ide.

tra&els through them at di=erent speeds. As a light wa&e tra&eling in the ber core

reaches the boundar% between the core and cladding! these compositional

di=erences between the two cause the light wa&e to bend back into the core. $hus!

as a pulse o# light tra&els through an optical ber! it is constantl% bouncing awa%#rom the cladding. A pulse mo&es through the optical ber at the speed o# light2

1*!5-+ miles per second 45--!98+ kilometers per second6 in a &acuum! somewhat

slower in practice2losing energ% onl% because o# impurities in the glass and

because o# energ% absorption b% irregularities in the glass structure.

/nerg% losses 4attenuation6 in an optical ber are measured in terms o# loss 4in

decibels! a unit o# energ%6 per distance o# ber. $%picall%! an optical ber has losses

as low as +.5 decibels per kilometer! meaning that a#ter a certain distance the

signal becomes weak and must be strengthened! or repeated. >ith current datalink

technolog%! laser signal repeaters are necessar% about e&er% 9+ kilometers 41*.?

miles6 in a long"distance cable. Howe&er! on"going research in optical material

purit% is aimed at e(tending the distance between repeaters o# an optical ber up to

1++ kilometers 45 miles6.

$here are two t%pes o# optical bers. 0n a single"mode ber! the core is smaller!

t%picall% 1+ micrometers 4a micrometer is one"millionth o# a meter6 in diameter! and

the cladding is 1++ micrometers in diameter. A single"mode ber is used to carr%

@ust one light wa&e o&er &er% long distances. Bundles o# single"mode optical bers

are used in long"distance telephone lines and undersea cables. Multimode optical

bers! which ha&e a core diameter o# ?+ micrometers and a cladding diameter o#

15? micrometers! can carr% hundreds o# separate light wa&e signals o&er shorter

distances. $his t%pe o# ber is used in urban s%stems where man% signals must be

carried to central switching stations #or distribution.

A#ter the solid glass pre#orm is prepared! it is trans#erred to a &ertical drawing

s%stem. 0n this s%stem! the pre#orm is rst heated. As it does so! a gob o# molten

glass #orms at its end and then #alls awa%! allowing the single optical ber inside to

be drawn out. $he ber then proceeds through the machine! where its diameter is

checked! a protecti&e coating is applied! and it is cured b% heat. Finall%! it is wound

on a spool.

A#ter the solid glass pre#orm is prepared! it is trans#erred to a &ertical drawings%stem. 0n this s%stem! the pre#orm is rst heated. As it does so! a gob o# molten

glass #orms at its end and then #alls awa%! allowing the single optical ber inside to

be drawn out.

$he ber then proceeds through the machine! where its diameter is checked! a

protecti&e coating is applied! and it is cured b% heat. Finall%! it is wound on a spool.

$he Manu#acturing



Process

Both the core and the cladding o# an optical ber are made o# highl% puried silica

glass. An optical ber is manu#actured #rom silicon dio(ide b% either o# two

methods. $he rst! the crucible method! in which powdered silica is melted!

produces #atter! multimode bers suitable #or short"distance transmission o# man%

light wa&e signals. $he second! the &apor deposition process! creates a solidc%linder o# core and cladding material that is then heated and drawn into a thinner!

single"mode ber #or long"distance communication.

$here are three t%pes o# &apor deposition techni7ues Outer Vapor Phase

;eposition! Vapor Phase A(ial ;eposition! and Modied 'hemical Vapor ;eposition

4M'V;6. $his section will #ocus on the M'V; process! the most common

manu#acturing techni7ue now in use. M'V; %ields a low"loss ber well"suited #or

long"distance cables.

Modied 'hemical Vapor

;eposition

1 First! a c%lindrical pre#orm is made b% depositing la%ers o# speciall% #ormulated

silicon dio(ide on the inside sur#ace o# a hollow substrate rod. $he la%ers are

deposited b% appl%ing a gaseous stream o# pure o(%gen to the substrate rod.

Various chemical &apors! such as silicon tetrachloride 4Si'l 8 6! germanium

tetrachloride 4)e'l 8 6! and phosphorous o(%chloride 4PO'1 9 6! are added to the

stream o# o(%gen. As the o(%gen contacts the hot sur#ace o# the rod2a :ame

underneath the rod keeps the walls o# the rod &er% hot2silicon dio(ide o# high

purit% is #ormed. $he result is a glass% soot! se&eral la%ers thick! deposited insidethe rod. $his soot will become the core. $he properties o# these la%ers o# soot can be

altered depending on the t%pes o# chemical &apors used.

5 A#ter the soot is built up to the desired thickness! the substrate rod is mo&ed

through other heating steps to dri&e out an% A t%pical optical ber cable usuall%

includes se&eral optical bers around a central steel cable. Various protecti&e la%ers

are applied! depending on the harshness o# the en&ironment where the cable will be

situated.

A t%pical optical ber cable usuall% includes se&eral optical bers around a central

steel cable. Various protecti&e la%ers are applied! depending on the harshness o#

the en&ironment where the cable will be situated.

moisture and bubbles trapped in the soot la%ers. ;uring heating! the substrate rod

and internal soot la%ers solidi#% to #orm the boule or pre#orm o# highl% pure silicon

dio(ide. A pre#orm usuall% measures 1+ to 5? millimeters 4.9- to .-* inch6 in

diameter and ++ to 1+++ millimeters 459. to 9-.9 inches6 in length.

;rawing the bers



9 $he solid pre#orm is then automaticall% trans#erred to a &ertical ber drawing

s%stem. $he machines that make up a t%pical &ertical drawing s%stem can be two

stories high and are able to produce continuous bers up to 9++ kilometers 41*

miles6 long. $his s%stem consists o# a #urnace to melt the end o# the pre#orm!

sensors to monitor the diameter o# the ber being pulled #rom the pre#orm! and

coating de&ices to appl% protecti&e la%ers o&er the outer cladding.

8 $he pre#orm rst passes through a #urnace! where it is heated to about 9++

degrees Fahrenheit 4about 5+++ degrees 'elsius6. e(t! a drop o# molten glass

called a CgobC #orms at the end o# the pre#orm! much like a droplet o# water that

collects at the bottom o# a leak% #aucet. $he gob then #alls awa%! and the single

optical ber inside is drawn out o# the pre#orm. As the optical ber is pulled #rom the

pre#orm! the material in the original substrate rod #orms the cladding! and the

silicon dio(ide deposited as soot #orms the core o# the optical ber.

? As the ber is drawn out! measuring de&ices monitor its diameter and its

concentricit%! while another de&ice applies a protecti&e coating. $he ber then

passes through a curing #urnace and another measuring de&ice that monitors

diameter! be#ore being wound on a spool.

Dualit% 'ontrol

Dualit% control begins with the suppliers o# the chemical compounds used as the

raw materials #or the substrate rods! chemical reactants! and ber coatings.

Specialt% chemical suppliers pro&ide detailed chemical anal%ses o# the constituent

compounds! and these anal%ses are constantl% checked b% computeriEed on"stream

anal%Eers connected to the process &essels.

Process engineers and highl% trained technicians closel% watch the sealed &esselsas pre#orms are being created and bers drawn. 'omputers operate the comple(

control schemes necessar% to manage the high temperatures and high pressures o#

the manu#acturing process. Precise measurement de&ices continuousl% monitor

ber diameter and pro&ide #eedback #or control o# the drawing process.

$he Future

Future optical bers will come #rom ongoing research into materials with impro&ed

optical properties. 'urrentl%! silica glasses with a high :uoride content hold the

most promise #or optical bers! with attenuation losses e&en lower than toda%s

highl% e,cient bers. /(perimental bers! drawn #rom glass containing ?+ to +percent Eirconium :uoride 4GrF 8 6! now show losses in the range o# +.++? to +.++*

decibels per kilometer! whereas earlier bers o#ten had losses o# +.5 decibels per

kilometer.

0n addition to utiliEing more rened materials! the producers o# ber optic cables are

e(perimenting with process impro&ement. Presentl%! the most sophisticated



manu#acturing processes use high"energ% lasers to melt the pre#orms #or the ber

draw. Fibers can be drawn #rom a pre#orm at the rate o# 1+ to 5+ meters 495.* to

?. #eet6 per second! and single"mode bers #rom 5 to 5? kilometers 41.5 to 1?.?

miles6 in length can be drawn #rom one pre#orm. At least one compan% has reported

creating bers o# 1+ kilometers 4-- miles6! and the #re7uenc% with which ber

optics companies are currentl% retooling2as o#ten as e&er% eighteen months2

suggests that still greater inno&ations lie ahead. $hese ad&ances will be dri&en in

part b% the growing use o# optical bers in computer networks! and also b% the

increasing demand #or the technolog% in burgeoning international markets such as

/astern /urope! South America! and the Far /ast.

>here $o earn More

Books

Ieh! 'hai. Handbook o# Fiber Optics. Academic Press! 1--+.

Periodicals

Jungbluth! /ugene ;. CHow ;o $he% Make $hose Mar&elous FibersKC aser Focus

>orld. March! 1--5! p. 1?.

<etron! isa A. CFiber Optics $he Lltimate 'ommunications Media.C 'eramic

Bulletin. Volume ! number 11! 1-*! p. 1?1.

Shu#ord! 3ichard S. CAn 0ntroduction to Fiber Optics!C B%te. ;ecember! 1-*8! p. 151.

So@a! $homas A. C>orldwide $elecom ;emand Spurs Fiber Optics Market.C aser

Focus >orld. ;ecember! 1--5! p. *9.

>ire Journal 0nternational. October! 1--5 4entire issue de&oted to ber optics6.

2 3obert '. Miller

Also read article about Optical Fiber #rom >ikipedia



Lser 'ontributions

1 asi#3eport this comment as inappropriateJul 59! 5++ 9+9 am

i want to learn about optical #ocer latest news and #eatures

5 kishor bansi3eport this comment as inappropriateSep 8! 5+11 5+5 am

Pls send me the Fiber cables shortl% in#ormation .

9 )Har% Stowell3eport this comment as inappropriateAug 1+! 5+15 1515 pm

DuestionN >hat is the raw9 material usede to make osK

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