Fiber Fabrication 2

7/23/2019 Fiber Fabrication 2

1/7

FIBER FABRICATION

Two basic techniques in fabrication of all glass optical waveguides

! "apor!phase o#idation process ! $irect %elt %ethods

$irect &elt &ethods

!Optical fibers are %ade directl' fro% the %olten state of purified co%ponents ofsilica glasses

"apor (phase O#idation )rocess

!*ighl' pure vapors of %etal halides react with O+ to for% white powder of ,iO+

particles

!The particles are then collected on the surface of a bul- glass and are sintered

to for% a glass rod

!This rod or tube is called a prefor%

!T'picall' ./!+0%% dia and 1/!.+/c% long

!Fibers are %ade fro% prefor% using the following equip%ent


2/7

Outside "apor (phase o#idation

!2oss less than +/dB3-%

!A la'er of ,iO+ particles called ,OOT is deposited fro% a burner onto a rotating

graphite

!The glass ,OOT adheres to this bait rod and la'er and la'er4 a c'lindrical porous

glass prefor% is build up

!B' controlling the constituents of the %etal halide vapor strea% during thedeposition process4 the glass di%ensions desired for the core and cladding can be

incorporated into the prefor%

!5hen the deposition process is co%pleted the %andral is re%oved and porous

tube is then virtified in a dr' at%osphere at high te%perature to a clear glass

prefor%

!This prefor% is %ounted in a fiber drawing tower and %ade into a fiber


3/7

"apor!phase A#ial $eposition

! ,iO+ particles are for%ed in the sa%e wa'

!These particles e%erge fro% the torches the' are deposited onto the end surface

of a silica glass rod which acts as a seed

!A porous prefor% is grown in the a#ial direction b' %oving the rod upward

!The rod is also continuousl' rotated to %aintain c'lindrical s'%%etr' of the

particle deposition

!As the porous prefor% %oves upward4 it is transfor%ed into a solid4 transparentrod prefor% b' %elting with the carbon ring heater

&odified Che%ical "apor $eposition

!)ioneered at Bell laboratories

!2ow loss graded inde# fibers

!The glass vapor particles 4 arising fro% the reaction of %etal halide gases and

o#'gen flow through inside of silica tube

!As the ,iO+ are deposited4 the' are sintered to clear glass la'er which travel bac-

and forth along the tube


4/7

!5hen the desired thic-ness of glass rod have been deposited4 the vapor flow is

shut off and tube is heated strongl' to cause it to collapse into solid rod prefor%

!The fiber is drawn fro% this prefor% rod 4 core consists of vapor deposited

%aterial and cladding consists of original silica tube

)las%a Activated Che%ical "apor $eposition6

!)hilips research invented

!,i%ilar to &C")

!A non isother%al %icrowave plas%a operating at low pressure initiates the

che%ical reaction

!5ith the silica tube 4 a %oving %icrowave resonator operating at +708*9

generates a plas%a inside the tube to activate the che%ical reaction

!This process deposits clear glass %aterial directl' on the tube wall

!No ,OOT for%ation 4 no sintering is required

!5hen desired glass thic-ness is deposited 4 the tube is collapsed into a prefor%


5/7

$ouble Crucible &ethod6

!,ilica4 Chalgenide and halide glass fibers can be %ade

!8lass rods for the core and cladding %aterials are first %ade separatel' b'

%elting %i#tures of purified powders!These rods are used as feedstoc- for each of two concentric crucibles

!The inner crucible contains the %olten core glass and outer contains cladding

glass

!The fibers are drawn fro% the %olten state through orifices in the botto% of the

two concentric crucibles in a continuous production process

!Attention %ust be paid to avoid conta%inants arise fro% furnace environ%ent and

fro% the crucible


6/7

&EC*ANICA2 )RO)ERTIE, OF O)TICA2 FIBER

Fiber strength and durabilit'

!Optical fibers e#clusivel' fabricated fro% silica or co%pound of glass

!&aterials are brittle and e#hibit perfect elasticit' until their brea-ing point is

reached

!Bul- %aterial strength of flawless glass is quite high and esti%ated for individual

%aterials using the relationship

,t: ;


7/7

!This theor' assu%es that surface flaws are narrow crac-s with s%all radii of

curvature at their tips

!It postulates that the stress is concentrated at the tip of the crac- which leads to

crac- growth

!,tress intensit' factor

?i:,>C.3+@@@@@@@@@@.

,: %acroscopic stress on the fiber

>: constant

C: depth of the crac-

!Critical stress intensit' factor where fracture occurs

?ic:;+E

Fiber Fabrication 2

Documents

Transcript of Fiber Fabrication 2