CA1323228C - Optical fiber feedthrough - Google Patents

Abstract

TITLE
OPTICAL FIBER FEEDTHROUGH
ABSTRACT
An optical fiber feedthrough comprising a glass seal for sealing the optical fiber within a metal sleeve. The fiber is held in a fixed position with respect to the sleeve while a glass solder, pre-ferably an annular preform, is heated to its glass transition temperature and then cooled to form a glass to metal seal.

Description

1 323228 ' Ca~e No; A23459 ~D-o3s7 WP No: 0307S

TITL~ !
~15~1~5 BACK ROU~D OF ~ INv~?aTI

~IEl.D 0~ T~ INv~ S ON
This i~ventlon relate~ to feedthrouqh o~
10 optical ~boc~ an~ in p~cticular but not ex~lu~lve~y to f eedth~ough in'co device pac~ages .
~ESCEIIPTSON 0~ T~ P~
Deviee packa~e~ that inco~poeat~ all opt~ Gal oc op~o-elect~onlo co~nponent hav~ ~ a~ertu~ ~or th~
lS f eedthcough o~ the opticDl f ~bera th~t conduct light to or ~ro~ the ~ackage~ St h~ ~e~rl u~u~l peaoti~e tO 6up~oct th~ Go~n~et~ng ~o~tlon o~ th~ ~ibar~ in a ~etal 61eev~ ar~d the~ ~o~ tho alae~lo to be ~ounte~
th~ a~ertu~o, the ~ibo~s bei~ h~ tha ~leeYe ~y 20 ~ metal ~ola~ or ~o~y re~
~ f ~ ~ber 1~ to be Boldel:e~ ~nto t~e ~lee~
~t 1~ naco~sa~y to ~tallize ~h~ ~ilbeL ~o that tt~
al ~oldor w~ll adl~e to e~ r ~r~d ~h~ ~a~-tiQn~l handling o~ ~h~ dol~aat~ Pll~er dur~g th~
25 ~etalliz~tion pro~s~ can cau~e d~n~g~ ~38pcc~ally tC~
~e en~ of t~e t~b~r Whi~h in ~o~e ~n~ta~c~ will -already h~ve be~n proY~ded W~th a l~n~. The lensir~g o~es~ canno~ be ~et~oe~e~ e~ly a~t~ ~e~alllzae~o b~?ci~u~e the ~roY~mitr ~ a ~et~l 8U~CI~ tend~ to 30 lllter~r~ with t!~e ar~ ch~eg~ t~ctlnlqu~ g~;~era~
e~10yed. A1~o, ~et~1 ~ol~r ~ ~ub~ to ~roe~ an~
thi~ ~an l~aa to 10~8 o~ a1ig~ t o t21a ~lbe~ t~ ~e o~tlcal OE op~o-~le~tron~c ~ . ar~d ove~ ell~ ~our~ :
o~ tl~e i~ ~aay e~en c~ u~e~cien~ co ~2U~O lo~
35 of l~ermetla 6ealln~ tweo~ lCb~ ~ib~r ~na ~lee~e.

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On ttle othe~ hand ~ epoxy ~esin i~ u~ed ~o hold ttle optic~l f ~bers in posltion there 1B a ~lo~
releage o~ gases ~ro~ tl~e ~e~in (even aft~r heat treatment ) ~nd the S~ e8 that are difi~harged ~an be 5 ha~ful to component~ within the pac~ags. A ~urthç~r problem ~ha~ i8 encountered wieh bo~h me~al ~older an~ epoxy re~n i~ tha~ the f lb~ ~ay not be concentric uith the sl~eve an~ ther~or~ ~he preci6e po~lt~on o~ the tibar may not ~e l~nown 80 that onae 10 the sleeve ha~ been allgned lt i~ nece~sary to ~er~orm compen6~t~nq ~d3~tmenta in order to en~ure allgr~ment o~ the o~t~cal ~e~ w~th the opto-electronlc o;
opelcal coa~ponent in t5~ cka~.
The pre~erlt inv~nt~o~ i~ directe~ tow~rd~
lS provi~ing a hermetic ~eal between an optl~al ~lber and ~eedthrou~h sleeve utilizing ~l~ss ~ol~er.
SUMMARY O~ T~ NSlON
~ o~dlnglr ~h~ p~ t inve~tion ~ ovide~ a~
opt~cal f lhoL ~eq~through co~prl~ng ~ ~etalli~
20 sleev~. an opt~ ~al 1~iber in tho ~lee~,re and a gl~8 ~eA1 b~t~een the opt~cal ~lbe~ an~a t~e ~le~e for~ln~
~ lber to ~la~ ~ea~in~ inter~a~o ~t l;he t~b~r au~face an-~ a qla~s eo ~tal ~aling int~rfaee at the i ~ne~ ~ur~ace o~ th~ ~le ~5 ~ a inve~tlon al~o pco~l~es ~ ~etho~ o~
~e~}in~ ept~al f~e~ ~n a g~ hrou~h ~o~nprl~ing thcea~insJ an opt~¢~l ~lber through ~ ~leeve, dl~posins a ~u~5cient ~uantity o~ glaRs ~ol~er with ~ lower ~low t~por~tura th~rl t2~e ~ber ~a ~t lea~t a po~tion 30 of ~he ~ ve an~ he~t1~ t.be ~la~ ~ol~e~ so ~at ie focD~ la3~ to ~bec ~e~ g interl~ce A!t the ~lbes ~ur~e~ ~nd gl~ to Det~l ~neer~a~ at the ~ur~ac~
o~ t~ 7 P~ bly th~ ql~ al ~empr~an 1I gl~
3s cag~llury et~s~d~ on to th~ ~b@r.

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BRlEF D~scaIpTIoN OF THE DRA~IN~S
The in~.rention i~ now de6cr1bed by way of exampl~ with re~rence to ehe accompar~ylng drawing~
in whic~ lgure l ~ a ecl~o~atic ~C0~8 ~c~ional 5 ~iew ehrou~h a f ~rst es~bodin~en~ Or ~he invent~on;
~ igure 2 iB a ~hem~tlc ¢EOS6 ~ect~onal view thcough a ~econd embo~iment of the ~nvenelol-:
Plgure 3 ~how~ a modif lca~on to th~ ambodi-ment o~ ~lgur~ 2, ~nd P`igu~d~ 4 ~nd 5 show r~p~c-lO tively, the e~bo~imen~ o Figuce 2 be~ore and du~ingheating.
~ lgure ~ showc an ~lt~rnate embodimerlt or ehorm~l con19uction oe~ber.
I)ETAlLED D~S~IP~ON OF THE I~V~NT10~
Referrln~ tO F~guYe 1, a ~eedthrouqh ~s~e~bly gGner~lly indlc~te;~ by reference characte~ 100 comprl~as an outer meta~l~c ~leevo 1 ehrou~h v~lc~ ~n op~lcal ~ er 2 o~ 0~ lic~ glaE~R 15 thr~aded . I~be lnr~er ~ur~ac~ o the oleeve 1 18 p~ovld~d wlt~ at 20 le~t on~ inw~r~ p~otrll~ion clo~a to ono end o~ ti~
~leeve wh~ ch con~tri~t~ the ~leeY~ and whlct~ can b~
~o~d conran~ontly by di~pl~ng tho 31e~ 1 lerosP. ~he outs~de by p~esaing a point ~nto the ~le~ wall to ~o~ ~ d~tosa~at~oll. In the dsa~i~g a pDlr o~ di~plo~
zs 3 ~r~ illu~tr~t~d ~ T~e f lber ~ i~ t~rea~e~ througb the ~lee~e l ~o th~S lts te~ at~on pcotcu~ a ~host a~ance beyo~a tl~e ~l~ple~ ena o~ ~h~ æl~vo, PP~
to lnsartion lnto tl e 31eev~ 1 th~ fi~ee Z l~ ~tr~pped o~ ally ~rote~tlve ~oaein~s ~na. ~lE appropr~e~, tP~
3Q ~nd ~ay b~ foe~od l~o a len~. ~h~ ~ilo~ e~en slld o~ e fl~E 2 ~o t~iat ~i ~ho~e leal~h o~ ~nna~
pro~es~tiY~ ~oat~ng~ ~OE ~Xillll~l2 ~bo~ 3~ xt~nd~i ineo the 0lee~e 1 A~t the ~n~ ot~ tro~ t2~is dl~leoi 3. t~l~eena~l~aly the sl~eve 1 laay ~ pl~aedl o~re~ tho 35 ti~er 2 ~ir~ n~ ~ilil away ~co~n th~ ea~ o~ ~hH

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f ~ber, the tlbQr ~hen being str~pped and ~ermln~3ted ~nd tlle ~10eVQ 1 slid ba~k to a~opt the Rosltion illu~trate~ ehe drawing.
A ~acer 4 con~stin~ of an ~nnul~r membee 5 of brass, ~liea ~la68 or other su~table ~aterlal i~
thre~ded on to the æt~lpped ~ber 2 and abu~6 ~he d~mple~ 3 for po~itlve loca~ioAJ and adjacent to ~he ~pa~er 4 a pre~or~ 5 o~ gla~s solder i~ al~o 10cated on th~ tibor 2. I~u~ins a sub~equent l~eat t~eat~asnt 10 the gla~s ~olâer ~0 heated to le~ flow te~perature BO
th~ lt for~ a ~eal betwe~n the ~lbe ~ an~ t~e ve ~. In the poxition~ ustraeed ~n ~e draw~n~
the glas~ ~older ~111 also 6eal to t~e ~pae~r 4, ot at lea3t tra~ ~he l;pa~er. However, ~t ~ ~ al30 15 pos~lble to ~rm ~ ~al ~f~t~lOUt u~ng ~ spa~er or ~ith t~le position~ of the ~pacer an~ preferlD rever~d. In . th0 lat~r ~a~ the 6p;~CQ~ ma~ o~ ~ ma~e1al ehat i~ no~ e~e~ to by the g1aso so1d~r or 1~ it 1~
coat~ lth gr~plllt~. for ex~nple, ther: the ~acer ~2n 20 b~ rerqo~re~ after t~l~ heat treatm~nt:. When the peeorm 5 1~ po~1t10n~d next to th~ d1PRp1e~ 3 the dimp106 ~a~c to 10cate the pre~oe~ 5 an~ BO te,~d ~o r~ta~n the g1as~ so1d~r to the end reg1 on of th~ elqeve 1 wnen ~t ~lo~ ~u~nq he~t~ng. ~t ~hould be un~erse~od ehæt 25 Wtl1l2 in ~ e ~mbodi~nen~ o~ ~1gure 1 ~he di~ple~ 3 are u~ed to 10a~t~ the ~pacel ~oc th~ preform) a1t~r~ate arranS~en~ ~ay be u~ea tD lo~ate ~he~ meh~rs. U~e o~ ~ ~pa~r ~ en~ure~ that the ~ber ~ i8 retair~od i~
~ ~1xad ~paeial ~rrange~ent w1thiD. the ~laev~ 1 ~uElng 30 t~e ~lo~ 3ta~e o~ t~ glaç:~ ~old~r. That 1~ to ~a~, ~h~ ~p~er 4 ~er~e~ to ~d1a11y ce4t~r t~e rib~r 2 th ~s~e~ to th~ ~nn~r ~a~e~er of the 3~ee~0 1 during tn~ ~low ~aqe o~ t~'le ~o1d~r~ ID thl~ rega4rd lt ~8 t~ ~o~itio~ o~ ~ho e~d of th~ er ~h~t ~B
35 most l~pol~e~ na the~ef o~e to h~ hc ~co~

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~mr4~diat~ly ad jacent ~tle ~lbe~ end ~ay be advar~-tageou~. Al~e~nati~rsly, or ~n addltlon, ~n ~x~arnal ~her~al conductlon ~aelober 1~ ~Figure 5~ ~ay bo u~ad a~ ds~crlbea l~t~r her~in.
S ~ar~ou~ types of ~1~188 ~ay be chos~rl fo~ tl~e gla$l3 solder. t;enerally lt i~ de~ red to achlev~ ~lo~
a~ one o~ ~e low~t teu~pe~atu~eR po~ibl~ to aYoid ~ib~r e~nb~ittlement and becau~ thers ace sth~r ~omponent~ (lqcl~ding ac~yli~ co~ting~ ~urther alon~
~he ~ r ~ eh~t cannot w~thstand high te~ratu~e~ .
In oxder to minl~ ze heat ~r~n~fsr alon~ b~ ~n~
~laev~ ~he ~leeve ~8 ere~e~bly held i~ ~ont,act wleh heat sinl~. A glas~ ~older pre~o~RI wit~ ~ Xlow telDperatUr~ r~.e.. gl~l88 t~an~tioll te~eratulre l~a) 15 ~n the r~n~e of ~00C to 480-C 1~ prR~er~ed ~or u~e in th0 ln~ nt~on. Flo~ ~ay be ~ ie~d a~ lo~re~
ter~4rstU~es wlt~ ~oloe ~1~BB~ bUt th~ tl~ ~ake~ ~or ou~r~lont f lo~r beco~e~ lorlge~ .
q~ho ho~ tr~at~ t tor tho glas~ aol~
20 pr~f~r~bly conslst~ o~ heat~ th~ Bleey~ 1 hel~ ~a an up~ ht po3~tion untll t~a ~la~ ~ol~e~ flow~ i~eo se~lln~ cont~ct wlttl th~ ~ber ~d ~ ve. Tt~ s1e~ve n~ ot be ll~ld up~ght, bUt t~ gen~r~l1y pre~rre~ 1~ order to o-~ a~ n ~ e i ~
25 en~l~asle~ tl~at gl~ old~r ~ould be ~ntrs~u~ed to tlle ~leeYe in ~ f~r~ oth~r th~ refor~k. e~psalallr when an ~nto~n~l 2~ac~r ~ use~ ~ t~iB al~o ~or~ a n th~ ~u~e.
tl~ ~ pa~t~ ~uldrly ~r~ge~r~ mbodl~9~t o~
3d t~ v~ntion tl~ 6pa~er ~ placefi by an ~x~ern~l ~en~erin~ o and th~ e~ ~ 18 ~o~if ~ed to l1~a~0 ~e~tion~ o~ f~rlng dlaoet~r8 aE~ own ln 11~1~ur~
~n~l 3. A de~ail~ al~ #Oo~ly ~roc~u~e o~
~e~theous~h ut~alzlng a~ e~Xt~!E~al ~ent4Pr r~ow ~e~rlb~a ~ re~on~ o F~gu~ to 5 S

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Figuce~ 2 and 3 ~howin~ Co~pletea se~ nd ~lgur~ ~
and 5 ~tlowin~ t~e ~tlU~:i;UC~ beo~e and ducl~g h~at~ng.
A len~th o ~n~le o~ ~ult~-~nod~ ~b~ 2 to be U~e~ ~or th~ ~ee~th~ougll 1~ proce~sed throtl~b S ~ev0r~1 ~tep~ erior to ~oc~l~g the deslred ~e~ he Siber Z ~ny be ~ol^ ~xample a ~9~1;!5~' ~lngl~ ~o~
~ber r the 19H ~eprese~t~n~ th~ diamete~ cro-~ete~, o~ t~e puce gla~s core tor t~ans~tt~g ll~t and the U125" repr~eent~tlg the d~a~Qeter. al~o ia 10 ~iCI:omet~. o~ an ~d~acel3e cla~dlng for r~flect~ng t~he 1~ qh~ wh~ tr~ ttad thcou~h tb~ cor~
type o~ ~lbe~ al~o tlas ~n In~er bu~er o ~ on~ o~
~ylate over th~ ~la~ y~r WhiCh ~ u~n coat~d wlth an ou~er b~ffer o~ nylon or ~yt~l lS (q`radaM~rlt) poly~t~r ~ to~er . 'rhe ~ rsc pro~e~
~op 1~ to ~t~ip tho oUtetr: al~l lnner bu~e~ laysr8 ~o expoBo A bace opt~aal ie~be~ tb, 1~t8 r~loctl~ra cla~ lng.
This baren opt~al ~ib~r lls ~lean~
~richloroethylene and ~hen placed In ~n 019~:tr~1c d~chac~8 ar~ and pull~d i~l ~ oorl~.roll~d fa~!hlon to fOr~ ~n lnteg~al len~d enl~. T~e lens~a oll?t~c~l ~gber f ~ ttl0~ ~lednod w~tb meth~aol ~ low~d to d~
t~l8 ~?~ A~ ol3lph~
~he ~t~l ~lo~vo 1 1~ ~or~d ~it~ two ln~
di~to~cs~ ~ lar~s diaDe~o~ e~a 9 eh~e i~ g~ anol-gh to ~ e ov~r ttle ~utor ~ur~ o~ the o~tl~al ~b~r 2 a~d ~ 3ma}1e~ ~ns~de ~a~otos ~s~d lO t3~at ~ ~o~d 'Co w~t~ tw~cr-8lYo ~l~ro~etoc~ of th~ ou~s~de dla~n~to~ o~ ehe p1e~a~0tlll 5, ~hlc?a 1~ e~atlally ~ ~ .
~hol:t l~t~geh o~ pl al:y. T~o ~e~ V~ 1 ha~ a ~n~ulu~, ol: 8~ve~ o~lt~d ~ 3 ~tay~ally ~o~e~ o~ tl~ ~n~d~ o~ eh~ ~otor ~ostlo~ o~
th~ sl~v~ Ol~ ~o wh~c~ ono O~a o~ gl~ a~la~y 35, ~p3æ~ i lo~aS~. l?r~o~ to ~ae~tion o~ t~a . I ond ~ras~o~ th~ 810~ ol~n~ t~lc~loco~e~yl~n~

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or 6ev~ra~1 ~inuteB. ulte~Boniaally cleane~ ~ n Boapy w~eer a~ 37C foe two mln~lte~, eln~ed in âeioni2~d watet, ~ h cleane~ in ~nechanol and ~lown dry with nlt~ogen .
The gla~ preko~sA capillary 5 ~ ~ade f co~
lead bo~ate ~olde~ gla~s. Th~ ~n~i~e dlame~e~ of ~he capill~y i6 ~ocmed to wiSh~ n twenty~ re ~laro~eter~
o~ the ba~ o~tic~l ~lber oU~siae ~iamet~r. ~S~e cap~llacy ~ polL~hed to remove para~in, ~ ~esid~
10 contam~na~t that iB depo~ted on the aap~llary~ durtng the gla~s ~w~g operat~ on ~ml?loyed ~o eut l:hO
aapillar~ e,o t21e desi~ leng~h and 1~ tho-~ cl~n2d with ~Q~ch~nol ~nd blown ~ry w~th.r~tcogen.
The absence o~ fore~gn cDnta~inants ~
15 lmpo~tant ~n maklrlg the ~eal, If tbe~ are Any oeganlc tllat~L~ Y p~o~ent Whic~ could go throu~h a phas~ cllan~ at eleYated ~eN~et~tu~ uri~ s~al~n~, euC~ ao the ;Ioee~entloned ~a~a~n, th~ lead ~or~sent ~n the ~ n cap~l~a~y Blat~ aoula b~ r~ od a~a 20 aAu~ed to pr0cip~tate ~nd l?~event a~ aa~eptabl~ B~
f ~ go~
Th~ l~n~ nd o~ tho b~r~ o~e~c~ h~
~nse~ted i~to th~ lar~e ~ aeteY en~ g o~ tho oll~eal sl~ til the lena p~ot~ade~ 0.0~0 lnah~ ~ro~
2S tho ~ll di~net~r end lO o~ the ~ vo. 'P~e la~g~
aia~et~ as~ o t~e ~leeVe i~s then ~4sA~d a~ 13 to the outer buf~er o~ the opt~cal lEib~r by ~e~o~ln~ ~he sle~ve in a c~cu~ cen~ial fashion. T3~ 1x~ t~e ax~al r~lationæh~ o~ tha ~tal ~ee~re 1 and the ~ar~
30 ~p~ iber Z.
Next th~ a~ ry 5 ~ sli~pe~ over tt~ opt~al gibe~ len~ ~n~ ~nto t~e s~tal ~l~o~re 1 U~til i~ coDie~ to r~e on tt~ 10~ 3.
~oc to ~aa~ng ~n axially ~xeen~
35 ~o~1tlo~1ng coll~r ~ac ~ t p~e~ion 22 o~ a ~h~r~al ..
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cond~ction me~ber 1~ n~er~ed o~e~ ~he ~educed dlametsr end 10 of the ~iber ieeathrough a~e~bly 100. A8 wlll be developed her~n the ther~
conductlon m~ber 14 6er~e~ to ~ov~de unl~ocm he~tl~g o~ ~he glasc pre~oE~ S~ In ad~itio~, a~ m~y be 8een ~o~ Flgure 5, the ~hermal conduction member 14 ~ay be Qrme~ with a ~losed end 24 ~e~eon. The ~nn~
sur~e 2~ ~f c~e c103~d end 24 may b~ p~o~ded w~
~ center~ng r~ce~s 28 whlch ~ ~ds~te~ to rec~Ye the ~o~e~t~ng len~e~ end o~ the i~ber 2. An annula~ llng 30 pro~ect~ axlally fro~ th6 lnner ~ur~e o~ th~ 26 o~ the clos~ end ~4 o ~;he ~0mbe~
r~e r i ng 30 eng~ges the ~n~e~ ~ur~a~e o~ the ~duced dis~eter en~ 10 of the ~l~e~ 1 w~ the 15 gkirt por~on 2Z ~urrounas the outer fiurfa~ o tha~
~a~n~ end o~ ~ho Bleey~ 1. Sh~ ther~nal aond~3ctiozl ma7llbeL 14 car~ ~er~e to ra~lly C~nte~ tll~ ~ib~ ~rlth eespect to the ~nr~ai ~iameeer o~ thfl ~Qtal ~1e~re 1.
It ~ho~ld be un~r~tood hoYevel: l;hat ~ r~ag 30 ~y 20 b~ o~ltted. iA ~hleh e~rent t~e ~ rt poreiosl 2Z, enga~ed agalnst tt~e outer sur~ac~ o~ tho ~lee~ 1 8~r~r~B to odnter the ~lbe~ ~ wltl:l re~p~ct to th~
outer suri~ea.
Figu~e S illu~trate~ ~h~ optt~al ~lbe~ ~aed~
th~ough assfl~b~y ~00 ~ ~t ~ould loo~ au~lng tho gl~s ~aællla~y ~eatin~ oQe~at~on. Th~ rec~ 2~ Of th~
alo~2d end o~ th~ m~e~ 1~ m~y be lu~rlc~eed with a ~et graphite ~lYture 15 tD pr~Yen~ the so~ten~d gla~
c~p~lla~y ~rom wettl~ to le ~urin~ the heati~g cyele.
It ~s ~hen ~are~ully ~ p~ ovar tha len~ an~ o~ ~o th~ ~tal ~le~ ora~r S0 aent0~ e~o l~ns r~latlvo eo tho ~nt~ xi~ o~ ~9tal ~lee~ 1, the cen~ec~ng ~ead r~a~ng in th~ looa~lo~ until : Sh~ gla6~ c~illary Aa~ ~oled a~d h~r~ene~ a~t~r 35 h~atin~ ~t~

1 32322~ ' Ttl~ center~ng bead ~8 made of Kovar, ~l~ich ha~ a r~latl~r~ly low thermal ~oe~'~clen~ of expan~lon, and wt~n t~le op~i~al f ~ber ~eedthrougll a~elably l~
tleated, the ~lee~re expand~ ~nore ~han the Ko~ar head 5 and re~ules ~t~ a snug glt between the ~leeve ~n~ th2 be~d. Thit~ bene~lt~ the centerlng upera~on by red~lcing the e~fect o ol~rance betwe~n the ¢erl~e~Lng bea~ ~nd ~etal ~leuve.
T4~ oVe~ 1~ ma~ f rom a cera~ic tlub~ 16 an~
14 t~as ~n ele~tr~aal heat~ng ele~es~t 17 i~ the ~o~ of NICHP~OMEO ~oai~tænce ~rir~.
T~e l?~lDary ~unct~og~ of the ~her~al con~
tlon ~e~ber 1~ to tr~n~mlt he~t unito~ly ~io~ the heatlng el@n~nt into ehe raau~ed d~aMe~r e~ o~
l'i th~ as6embly 100. Tll~ mlni~lze~ thsrraal ~ra~i~nt~
~ithln t~ r~or~ S occa~oned by coill~l~ o~ tn~ Wir~
and m~ oc ~ore ef~lc~ent heatln~ o~ ~he pr~or~ 5.
Figur~ 6 illu~ te~ an alteena~ bodi~nt o~ t~a th0r~al con~u~t~on ~el~bec 1.~ ~h ldlll~h tba 20 clol3e~ an~ poetion 1~ o~itted. The ~3~1rt portloa 22 aue~ound8 th~ outer ~u~ace o~ tlle ~l~eve 1, a~
dl~usse~ o~rli~. Tt 3ho~ be r~adily und~r~tood ~hat wtlen ~3lng this e~bodim~nt of the ~h~r21!al con~llctl~n ~ber 14 t~ aent~r1n~ o~ the ~1bec 14 25 ~ith Jc~pe~t to t~ae 81eeY~ 1 ~UBt ~a ~oYIe u~g th~
8~a~a~ au~e~ e~r11~r.
Pre~rably the ~e~bly ~ h~ted to a t~pecatllr~ a~ox~Qate1y ~O~C abov~ the ~lasa tean~lt~oll t~ e~ature o~ tl~ ¢~Qe~ or S~ur 30 rd~nut8~ a~ld t~ a11~s~e~ to eoo1.
3~f~e~n~ ~la~ 801~i~ES ~l~y r~gulre ai~re~
hea~in~ aon~t10ns, but ~n g~3n~ra1 ~h~ af~691~ly 1I~ alO~:
~ub)~a~d So te~ rature~ ~ n e~cc~ o~ 600"~ be~au~
&h~ l~n%~d tlp o~ the o~ti~a1 ~b~r t~nd~ l:o ~r~elt or 35 ~realc o~ tluo ~o ~lb~r eRI~c~elt1eaen~.

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The ICovaL centerins bead i6 ther~ rer30tted ana cleaned ~o~ r*use, dnd anr re~idual graphite l~t on lihe lenses end o tbe ~eedthrough i~ reroo~ed wltl s~e tha no 1 .
S The f eedthrough i~ the~ te~ted ~or ~erme~ialty u~inq ha~ lu~. A ~eal i~ con~ldeced h~emetlc lt the dQtect~d lealc rate do~ not ~xc~ed 10 ~ atmoa~her~ ~ub~c centimeter6/~econd Helium, MIL ~P~C 883. The feedthrou~h as showrl in Fl~ure 2 10 i~ n~ cott~pl~te. An altern~te embodi~ent o~ th~8 feedthrou~h, ~ure 3, ~oul~ ~ to bdçk-flll the ~mpty ~pac~ in~d~ the me~al ~l~eve u81n~ arl epo3cy ees~n lB.
Thi~ re~ could be inje~te~ into the ~et~ eve ~er ~ealin~ d he~tic~cy ~e~t~ng u~n~ ~ slDall 15 acae~ hol~ 19. ~he pur~oBe of addl~s t,hia ~t~lal uould b~ tO ~truct~rally ~upport that portlo~ P~ tlle ba~e optiaal ~ib~r ~rom the ctr~ppea end o~ th3 ~nn~r and outer bu~er to th~ qlafi~ oapilla~r 69al.
The l~aterlal~ 0t ~or ~h~ tal ~ n~
20 the ~la~ aap~ llary are ~elected such th~t the ther~al p ope~ie~, ~uch a~ thel~ coeY~icient~ o~
t~er~a~, oxp~n~lo~ ~nd their ~l~en~ion, ar~ oolaated su~h th~t, the O~tre~1~8e3 ln Sho gla~s sa~llls~y ~r~ largely ~onlpre~ive. A th~ocatic~ anal~ 8 ~y 25 be us~t to evaluate several ~tecial cand~date~ ~o~
the ~ Ve ~n~ the capillary at ~ gllran ~et o ~o~etrlc pa~a~cter~ an~ tho reBult~ u~ed to ind~ cate lC2~oB2 eo~lnat~on~ e~timatea eo haYe ten~il0 r~ther th~rl eom~res~ e ~tre~s~. Such an an~ la ~ S~lY~A
30 b~lGw. It ~ noted that tho~e ar~ t;o~ ~pprox1-~a~lon~ t~ Qalc~ tl~e analy~ ou~del~n~ n~F
tha~ e~actO
Th~ ~e~l c4nsl~ o~ th~e co~x~al cylilaa~r~
wl~SI d~erlng pso~ert~ . The b~r~ opti~l i~ec d~lg~ata~ ~B~ re571Orl 1, th~ EI$ ~plllary 8 ` ~ ' :` ' ~' `
;
, . . . . ..
` ; :. ` - . ~ ~ ~ , : ' leg~on 2, ~nd ~he D~etal ~lee~e ce~on ~; ~he outer radiu~ of the optical ~ber ~aken as e~luAl to the Lnner r~dlu0 of the gla~ capillary 6e~13 rl, the~
outer rsdius o~ ~he glas~ capil~sry ~e~l (t~lteZI a~
S egud~ to the lnner ~ad~u~ o the ~et~ eY~ r;~, an~ el~e ou~er ~adiu~ of ~he ~eeal ~leeve ~3, E:a~h reglon hag it~ O~dR ~e~ og phy~
~roperties: t~odulu~ o~ elasti~lty ~ PO1B~O~B r~lo o, ~nd coe~lcient of th~al expans~ on ~L. {ba~tl 10 r~gion al~o ha3 i&fi own ~et o phys~ca~ d~nslon~.
The dl~en~lon~ sel~ted are ty~lcal ~or th~ ~nt~n~ed app~l~nt~on oî 'che ~dth~o~lgh.
TA~31,12 I: P~OPE~TtE38 US~:D I~ CAl rlJLAT~S
~rl,62.5 ~icro~oter~: r j~n200 m~cro~ete~s~; r3-~300 ~ro~et~
~5 ,~ ~ ~
COlSFF. B~1.157 at!a~ ( l . E-7~:) P~ P81 ) T,~
1. OPTICAL PIB15~
~SLIeA . 5 .16 1. 0 ;20 2 aLI'.~S CAPI~L~RY
~o~ a 1015 QLAS8 ~ 2 1. O ~0~
"~CIIOT~ 471 ~LA~S106 .22 1.0 ~32 "Ot " ~P-lOO aLAS5 11~ . 22 1. 0 305 !~ nOI" PP-200 al,~ss 1~S .~a l.o 2~0 3. 74~TAL S~
~S l~O~AE~ ~LLOY M~TAL 52 . Z . 30 2 . o 52~ LSOY 97.2 .30 ~.
10~0 ~EI. 151. 0 . 30 2 . 9 304L STAI2~L~S8 ST15~ a . o . 30 2 l 8 E~P. COEPF. ~ L~e~ the~al ~xp~na~o coe~ ~ la l~S
Pa Pol~son~ ~a~clo ~ lu~
3~ ~s~l~aeadl~
1~ ~ Younsl~s ~o~ul~ nl~ 6t~ o~a3 T~ r~ tlo~ o~p~r~tur~
~0~ ~ P~o~u~ vall~bl~ ~Co113 ~w~n~- I l l lno~ e .
"SCHOTT~ ott Gla~werk~ r~g O F~tl .
-,: . : .

1 32322~

~z KOVAP~ ~ T~adem~tk o~ We~tlnghQu~2 E19CtL~C c~rpO a;a alloyed ~etal havin~ 17~ ~obalt, 29t n~kel.
0.2~ oa~ 0.3~ ~ang~n~e.
O. 2~ carbon. re~ainder ~ICo~
l'52-ALLOY" = a ~etal alloy o~ 5a~ nlcls~
S 49~ ico~
u lo10 ~ ca r bon ~ teel "3V4L", ~ weldable stainle~s ~te~l, 19 chro~ , 10~ nlckel, rem~lnder l~on The ~wo-lalfe~ comp~slte ayl~nder Wdl3 analy~ed by G.E. Red~ton ana J.X. Stanwo~th, ~,~. So~.
Gla~s Ta~hnol. . 2~ ~132~ 48-7~, 1945) ana t~e g~ner~llzed multllayer oyl~n~r w~s ~cU~& by ~.
~ar~hr~eya, ~"Te~ati~ o~ ~a~c~le 8ci~nce éln~
'reahnology, Vol. 22, ~ 5~ }lI"~ pp. 2ql 306, ~a~. M.
TolQozawa a~d a.ll. Dore~nus, ~ca c Pre~s. NY 9 ~h~ ~olutlcn 1B ob~alned aq ~!ollo~:
Th~ con~titutlve oquAclo~s rolat~n~ ~Be~s~
to str~ln ~oc ~1~ ela~tl~ oaterl~l, in pvla~ ~oor~l-naeea. S~ T1~o~henko an~ J.N. aoo~ oosy o~
131a~tio~ty, page ~44, 3~ l~d. MoGraw-Hlll ~ook ~0. . NY, 1970 ), ar~ :

~ ~ Cf ~ E ~ la~ 3)1 zs ~e ~ ~ ~ ~ lae~ ~ ~, t~r ~ ~æ1 1 ~2~ :

~z ~ C~ aE ~ o5)l ~3 whoro ~ , a ~re th~ ra~
c~r~u~fe~ent~l (or ~oop~, ~n~ ~xlal ~c~ s: c~, z ~ee St~9 ~e~pect~ r~ss~
Young'~ ao~llu~ o~ n'~ ~at40 i~ t~ 13t~n.

35 C~ n 11 ~T (4 .

,~. . ~ , ..
,, :` ` ~ ` ' ' ~ ., : .' : ' . :: ` . , : : , :

..

where a i~ the linear thermal expansion coefflcient and ~T i8 the temperaturs change ~nega~lv~ when coolin5~ he ~tr~n0 ~ra d~lned ~n ter~6 o~ th2 radlfll diapla~ement. u, e~
s c~ ~ dU/d~ ( S ) c~ r ( 6 ) wheee r 1% the radial coordinat~ ng ~qUa~iO~B
10 (1) - (6) it can be shown that the ~tre~s distribut~on in ~ cyl~rAder h~ the for~:
a~n ~ P~n ~ 2 ~ Pn + ~ 2 ~
15 tJz~ ~ Cn t93 wh~ An~ Bn~ ~nd C~ on~ant~l. A
~t~erent ~et dppl~e toc O~C~I ~r~vloualy ~le~ine~
re~ion: u a~ n~ 3- Tbe f~trl@s~e~ ~uot ~e 20 ~inite at r ~ o ~quat~on~ (7) ~nd t~) lmply Cll~t ~1 mu~t ~e Zero. ~rhls 12ave~ hlC eon~tant3 to ~o deterr4~ned usln~ the followi~ boundaey condltlon~
1~ The di~pla~e~ntB ~U~ atch ~t eA~
~oundarle~ e ~egion~ (~he lay~r~ do ltOt ~e~ar~te 25 OL lnterpenet~ate~. 8Q

UL(C~ ) ~ U2(r~ ) U~r2~ ~ U3~r2) . ~11) 30 2) Th~ ~adial sSrea~e~ IRU~t ~:a~ch ~e the ~ound~rlez of ths ~egion~ to ~?r~ee~re ~qulll~iu~a o~
~or~

ael (r~ e2 (r 35 ~sa(rZ) ~ 3(1~2) ~L3 i ~ :

.
,:
~ , :

.

1 32322~

1~
3~ Th~ce c~n be no net ~orae ove~ the end of the ~yl~nd~r, slllce a net ~orce woul~ u~e ~c~eleratll~n ~3 ~zl d~ . o ~14 ) o 4) s~loilael3r, the~e ca~ be llo net ~oroe 10 norR~l to khe l~t~a~ ~u~AC~

~r3~C3) 9' ~15) 5,1 Th~ axi~l ~t~a~ ns IDuat ~atata, ~nc~ t2~e 15 reglon~ Ot, s~ld~ ~2~t one llnoth~3r C2~ 22 ( 1~ ) e5~2 ~3 ~ ) 20 Th~se condltion~ pro~ o~ht ~quation~ that f 15 th~
valu~ o~ t~o olght oon~ta~e~ ~n~ . and CD~' T4e ~ iitlon~ b~ ~cpr~ d ~13 s~ht tlill~Ult31n20U8 .' l~n~ar ~q~latlo~, Wtllcb a~eor ~el~3elti~ no~
~or ~, Vll and e~ e~ b~ ~01Y~ ~UIaO~iCaa1Y
25 u~insl ~a ao~ut~c.
naly~l~ as~u~ he ~eor~al~ ar~
elan~ or~ tho ~ot ~ cap~ rg 18 S~OtUa11r . v~,scola~tla, tt~ hr~roL. a~axation~ S ~nd Co~po~t~;o~, Job~ y ~ ~on~ 98~). T~ere~o~
30 th~a~o r~ule~ ~houl~ not ~o e~r~a a~ ce~, ~u~ a~
t~ ti~B [an~l a~ ~u~h ~r~ ~?robably ~o~Qr~r~t~ ro~
w~ ow~ t~r ~ h~
b~ sre~ b~ o~ tlh~ ~hy~5~al dl~en~on~ ~o~
,~ the~ ~bOE~ a~ ~arîil~ æot ~or~h.

1~

,. .: . .
; . . . ..

,.
: . . , :

Tabla lI ~nOws the ~t~e~e~ at the ~be~-gla~ interfa~e fo~ ~vaciou~ cap~ cy and ~le~
~at~r 14111 .

S T~ CALCUL~T~ S~ES~S ~1 at 103P~I 3 AT FlBe~-~LP~S C~PtL~RY ~r~TEaPACE

~, ae2 ~g 2 ~L ~ ~ E ~
OI E~G 1015 KO~ 10 . 7Z5 . 6 13 . 0 5~ A~t~OY -ZO . 71~ . 7 1010 -35 ~ 5 -3 . 9 -2 30~1. S~AIN-L~ T~EL -~3 . 2 -1~ . O -~2 .1 ~O~T ~tOVAR - 8 . 7 2 ~ . 9 17 . ~
5~ ~LLOY -16.3 19.8 3,5 ~LO10 -27.~ $.~ -15,~
304 6~AEN _3~ 26 .0 OI PP- 100 I~C VAEI - ll . l 2 9 . 5 1a . 5 52 ALS.OY-l.~l ~ B ~ .S . 9 1~10 -~S.O 9.2 -11.1 3041. ~ASN-Ll~ S'rE6L-30 . 7 2 . 4 -20 01 PP-200 I~O/AYI _13 ~ 31 2 20 3 2g ~,010 -~3.4 12,4 -7.5 30~t. 8T~
t.~t55 ~ L-2a . g 5 . 9 -16 . 6 POSI~ ~I.UeS 1~D',CCATI5 Tl~SI~
U13GP~TIV~ C~SeR~SS10N, ~1 x 1O3PSI
O~ co~binatlon~ 1~sted ~bo~ th~
o~ pr~or~ ~n~ e ~or1~ u11 ~tcuatur~ Wll~ch all thre~ e~tc~ o~onen~c~ ac~
com~ ion, Y~ Ol ESG 1015 ~1as~ GaE~S llac~
1010 ~ e; ~) OI ~G 1015 ql~ and ~ea~Lnl~
35 ~t~l s1e0~: ana 3 ) Saho~t g~ a~ in1e~ e ; . .
'' ' ~ : :

~ee~e. The ~econd of the thcee above 116ted ~o~$-n~t~on~ i~ tlle pce~ecred comb1nation o~ ~tecials ~r the physical dlmen~ionz ~et out ~n TABt~E ~..
S~:~lnles~ ~teal 18 prell~er~d ~or the ea~e o S weldability th~t ~ t impart~ eo the ~CU~;ure o~ ~e ~eedthrough a~s~ly.
It should be noted ~roDI foce~Joing ~h~ a suitable ~ealing i~ter~ace ~y be de~ ed ~et~ees~ th~
~leeîre and the p~efor~ wl ether or not ~he material 10 u~ed to for~ the ~leeve is wett~ble by the 5~1a~B o~
the p~Q~orm. The lOlo slQeVe ~B wet~able by the ~la~. Tho ~tainle~ ~teel sle~vs i~ not. ~By ~ealing lnter~a~e~ 1t i8 ~earl~; that a hec~tic ~eal ~8 def l~e~ bet~een ~w~ ~ember~ haYing a ~ ty 15 le~k cat~ ot le~6 than lo 8 ~t~o~phe~es ~u~1 ce~ ters~second Hel~u~.
The Rqua~ionB ~erQ gur~b~er ~l~ed to d3S4r~a~ne the ~lnl~u~ guide1i~o va1ue of thoc~al ~paAelon coQ~c~ t ~or the ~tal 01e~Ye at t~e l~t~
20 di~en~lonn eo yi~l~ a c~pr~lvo h~o~ 6tro~ ~lth OI
e~G 1015. and th~ re~ult va~ 1. 30 sc 10-5~C. q~hl~
thQ~ma~ expansion co~f$clQnt ln~llcate~ &abllity o~ ~any coppor alloy~ ~ W~11 as ~eYera1~ta~nle~
~te~l co~pol~itions.
A11 of t40 ~oregolng, it 1~ empha~ized, llolds on1y ~or the P~r~ca~ ai~en~ions above d~cus~d. The analy~6 ~1~o Rhow~ that va~ae~o~ in ehe di~ion of the ~eta1 f?~ 2VI~ nay r~sult ~1~ a given ao~blna~30n o~ ~lee-re ar~ a88 ca~lllary 3~ exh1blt~nq th~ de~ired ~om~r~sive 6t e~e~. F~r e~asup~, T~ble~ III an~ IV ~11u~eeat~ ~h~ r~lt~ for a ~ta1nlfl~s ~teel ~10~e ~n~ PP~100 gl~s whe~ ~he inner ra~lus r;~ anD t~æ outer ra~lu~ r3 o~ th~
81e~ Q ~ i ed ,.

, : ` , :
: . ` ' `: :

'f ~, Gla~8 PP-100 Me~al ~leev~ ~;tain~.~38 Steel rl ~ 6Z . 5 ~lcromet~r~; r3 ~ 300 ! ~icromete e2 a~ ~l3 az crQ~et~r~) 125 -36 . 1 -3 . 5 -2fi .
150 -3~ . 3 -:L . 7 -24 . 6 17~ -32 . 6 . 3 2~ . 9 200 -~0. 7 2 . ~ -~0 . ~ :
az5 ~28.5 5.0 -18.0 2~0 -25 . 7 ~ . 3 - 3 PO8~'rIVE VALUES YNDI~ TEN8ION, NE~:ATI~ 113fi~;IO~103 PSI) l~E I~
6~.5 al~ro~t~c-; r3 Rl 400 ~lcro~ot~

~2 ~r` '~e 58 ~mic~o~ete2s) 1~5 -37 . 2 -5 . 0 -2? . 2 lS0 -36 . O -3 . ~i -26 .
a6 175 -34 . 9 -~.4 -25. ~
200 -33 .~ -1.a -2~.5 22~ -3Z . a . ~ . 4 a50 -3~ . 5 -2~ . 0 PO~IT~ ALU~S It~ICAT~ ~ENSIO~, N~CA~ C0~ E8SIO~o ~lx~03 P8I) e~n ~ola TA{~l.t J,II ~y ~ is~g ~2 f ro!ll ~;!00 I~l~CI:O~ t~rR ~;0 175 Pl~C~o~Ot~ e t~
hoo~ ~t~ a~ do~r~a~ t~ros ~400 ~a ~o 300 3~!i P~;I)o ~ns ~e~le o~ th1~ ~ t~ogol~: 1) T~ ile .. ~ .
. .

` `, .

1 32322~

1~
~eresses whlch in~luence increa6~ the ~usce~eibllity o~ tl~ qla~ capilldry to the ~or~Ation and qubsequent ~rvpagat~on o cr4ck~ are ~ign~fiaantly ~limin~e~; ~) The E~roc~ss ~e~peratUre ~90C plu~
5 ~1la88 tran~ on ter~p~ratu~e TG) iq ~edu~ed ~co~
49~PC ~or 1~ L015 glas~ ~0 395~ or PP100 (~ee rABLE I) whic~ reduces ~e tende~c~r o~ ~1be~
e~4bciteleanen~ a~ elevated tem~ratUre~ ~u~3 ~o 'c~e appcoximatlons ~ch ~uake tlle analys~ a guldeline 10 ~aSher Sh~n exAc~ u~ed her~i~ the ~erm N largQ3,y coolp~o~ e" w~en rel~t~ng to r~idual ~tre8~e~
~houl~ b~ conæt~ue~a to ~n~ e tho~e ~tre~o~ that Appa~r in th~ Table~ ~18 ~ htly ten~le.
~x~le a~ ay be ~e~ ~rith re~erenc~ to ~ABLE I~I
15 for L2 equ~l to 175 ~lcco~tsLs ~3 ~ htly ten~ile ~300 P~l 8tce~) yet a~
a~e~cabl~ ~al ~ s produ~d . ~ur~h~c . a~ ~a~
with r~eence tO ~ABL~ IV when l~2 ~ualo ~25 ~icro~t~r~ ~0 i8 ~hown a~ ly ten~llo 20 tlOO P~I 8tr~s~) yot an accs~t~blo ~ nay b-produceA. ~s ~ ~e~u~t, l~ acCoc~ance Wlt~ the pre~eqt ~n~ention a ~eal 1~ ~ro~rided 1~ whlc~ ~Q
~u~optlb~lity o~ cLa~k propagatlon i~ lt~d. ~rle hyail~d~ e~han~ '18 bQl rl~ o al~o pcevent 25 th~ for~lon ~ ccacl~a. It i~ l~oee~ that th~
~o~enc~ o2 ~ol~ t~ he~ tal ~lee~e ~y htly lncr~as~ proces~ 2ratu~
The ~a30r be~ef~ o~ ha~r~n~ the ~la~s ca~llla~y totnl1y 1D~ co~l?~e~lon is t4at the~ tor~t~on 30 of ~l qra~ks ~ue to te~sl1e ~tre~aes iL~ ~ n3 ~ ze~ .
Thl~ ,naees th~ nee~ to ~on~or~ onlesel~ wlt~
p~d~tlng the ~ropa~at~o~ r~t~ of ~las~ c2aq~1e~ .
re~a~dla~ o~ ~hseber th~y ~re ~x~Al~ c~LrcuD~er~nti~l o~ ca~ial, ~n th~s ~ e o2 applio~ion. Th0 r~sult 3S 1~ ~n o~tical ~lbo~ ~o~eh~ou~l~ 0~ riq~ eo~ ru~ ~on ~Y~ng exoellent long te~ h~rRs~ele ~rop~tles.

.

. `

Claims (55)

1. An optical fibre feedthrough for feeding a fibre through a wall of a package, the feedthrough comprising a metallic sleeve, an optical fibre in the sleeve and a glass seal between the optical fibre and the sleeve forming a fibre to glass sealing interface at the fibre surface and a glass to metal sealing interface at the inner surface of the sleeve, the sleeve and the fibre each having an end, the end of the fibre protruding past the end of the sleeve, the exterior of the sleeve being able to be mounted to a wall of a package such that the sleeve and the fibre pass therethrough.

2. An optical fibre feedthrough according to claim 1 in which the glass seal comprises a glass capillary member having a bore through which the optical fibre is threaded.

3. An optical fibre feedthrough for feeding a fibre through a wall of a package, the feedthrough comprising a metallic sleeve, an optical fibre in the sleeve and a glass seal between the optical fibre and the sleeve forming a fibre to glass sealing interface at the fibre surface and a glass to metal sealing interface at the inner surface of the sleeve, the sleeve and the fibre each having an end, the end of the fibre protruding past the end of the sleeve, the exterior of the sleeve being bale to be mounted to a wall of a package such that the sleeve and the fibre pass therethrough, and wherein the glass seal comprises a glass capillary member having a bore through which the optical fibre is threaded and wherein the materials and the dimensions of the glass capillary and metallic sleeve are selected to have predetermined thermal expansion properties such that after heating the assembly to a predetermined temperature and then cooling to form the sealing interfaces any residual stresses in the glass capillary member in the radial, circumferential and axial directions are largely compressive, thereby to limit the susceptibility of the glass capillary to the propagation of cracks.

4. An optical fibre feedthrough according to Claim 1 incorporating an internal spacer for maintaining a fixed spatial relationship between the fibre and the sleeve.

5. An optical fibre feedthrough according to Claim 2 incorporating an internal spacer for maintaining a fixed spatial relationship between the fibre and the sleeve.

6. An optical fibre feedthrough according to Claim 3 incorporating an internal spacer for maintaining a fixed spatial relationship between the fibre and the sleeve.

7. An optical fibre feedthrough according to Claim 1 in which the fibre has a lensed end and is concentrically disposed within the metallic sleeve.

8. An optical fibre feedthrough according to Claim 2 in which the fibre has a lensed end and is concentrically disposed within the metallic sleeve.

9. An optical fibre feedthrough according to Claim 3 in which the fibre has a lensed end and is concentrically disposed within the metallic sleeve.

10. An optical fibre feedthrough according to Claim 4 in which the fibre has a lensed end and is concentrically disposed within the metallic sleeve.

11. An optical fibre feedthrough according to Claim 5 in which the fibre has a lensed end and is concentrically disposed within the metallic sleeve.

12. An optical fibre feedthrough according to Claim 6 in which the fibre has a lensed end and is concentrically disposed within the metallic sleeve.

13. An optical fibre feedthrough according to Claim 1 in which the metal sleeve has a coefficient of thermal expansion of at least 12 x 10-6 per °C.

14. An optical fibre feedthrough according to Claim 2 in which the metal sleeve has a coefficient of thermal expansion of at least 12 x 10-6 per °C.

15. An optical fibre feedthrough according to Claim 3 in which the metal sleeve has a coefficient of thermal expansion of at least 12 x 10-6 per °C.

16. An optical fibre feedthrough according to Claim 7 in which the metal sleeve has a coefficient of thermal expansion of at least 12 x 10-6 per °C.

17. An optical fibre feedthrough according to Claim 8 in which the metal sleeve has a coefficient of thermal expansion of at least 12 x 10-6 per °C.

18. An optical fibre feedthrough according to Claim 9 in which the metal sleeve has a coefficient of thermal expansion of at least 12 x 10-6 per °C.

19. An optical fibre feedthrough according to Claim 4 in which the metal sleeve has a coefficient of thermal expansion of at least 12 x 10-6 per °C.

20. An optical fibre feedthrough according to Claim 5 in which the metal sleeve has a coefficient of thermal expansion of at least 12 x 10-6 per °C.

21. An optical fibre feedthrough according to Claim 6 in which the metal sleeve has a coefficient of thermal expansion of at least 12 x 10-6 per °C.

22. An optical fibre feedthrough according to Claim 10 in which the metal sleeve has a coefficient of thermal expansion of at least 12 x 10-6 per °C.

23. An optical fibre feedthrough according to Claim 11 in which the metal sleeve has a coefficient of thermal expansion of at least 12 x 10-6 per °C.

24. An optical fibre feedthrough according to Claim 12 in which the metal sleeve has a coefficient of thermal expansion of at least 12 x 10-6 per °C.

25. A method of sealing optical fibres in a feedthrough comprising threading an optical fibre through a sleeve, disposing a sufficient quantity of glass solder with a lower glass transition temperature than the fibre in at least a portion of the sleeve and heating the glass solder so that it forms a glass to fibre sealing interface at the fibre surface and a glass to metal interface at the surface of the sleeve.

26. A method according to Claim 25 including the step of locating the fibre on a spacer to maintain a fixed spatial relationship between the fibre and the sleeve as the seal is formed.

27. A method according to Claim 26 in which the spacer comprises member threaded on the fibre.

28. A method according to Claim 25 including the step of locating the fibre end in a centering jig and locating the end of the sleeve proximate the end within an annulus on the jig that has a lower coefficient of thermal expansion than the sleeve so that during heating the sleeve expands sufficiently to reduce circumferential clearance between the sleeve and the annulus and any eccentricity between the annulus and sleeve is minimized by permitting radial movement of the sleeve within the annulus.

29. A method according to Claim 26 including the step of locating the fibre end in a centering jig and locating the end of the sleeve proximate the end within an annulus on the jig that has a lower coefficient of thermal expansion than the sleeve so that during heating the sleeve expands sufficiently to reduce circumferential clearance between the sleeve and the annulus and any eccentricity between the annulus and sleeve is minimized by permitting radial movement of the sleeve within the annulus.

30. A method according to Claim 27 including the step of locating the fibre end in a centering jig and locating the end of the sleeve proximate the end within an annulus on the jig that has a lower coefficient of thermal expansion than the sleeve so that during heating the sleeve expands sufficiently to reduce circumferential clearance between the sleeve and the annulus and any eccentricity between the annulus and sleeve is minimized by permitting radial movement of the sleeve within the annulus.

31. A method of forming a hermetically sealed optical fibre feedthrough assembly that is resistant to the propagation of cracks comprising:
a) taking an optical fibre with an inner and outer buffer layer and stripping a predetermining length of the inner and outer buffer layer from the optical fibre to form a stripped and a buffered portion thereon;
b) positioning a glass capillary member around the fibre and within the sleeve so that the glass capillary rests against a constriction in the sleeve and the end of the fibre protrudes a predetermined distance beyond the end of the sleeve;
c) coating a central depression formed in a centering bead with a lubricant, the centering bead having a positioning collar thereon;
d) placing the centering bead over the protruding end of the fibre such that the positioning collar extends down and over the metal sleeve; and e) heating the assembly formed by the preceding steps a) through d) to a temperature above the glass transition temperature of the glass capillary member without exceeding 600°C for approximately four minutes and thereafter cooling the assembly.

32. The method of Claim 31 wherein the assembly is heated to a temperature approximately ninety degrees above the glass transition temperature.

33. An optical fibre feedthrough comprising an optical fibre threaded through a sleeve, with a sufficient quantity of glass solder with a lower glass transition temperature than the fibre in at least a portion of the sleeve, said glass solder forming a glass to fibre sealing interface at the fibre surface and a glass to metal interface at the surface of the sleeve.

34. An optical fibre feedthrough according to Claim 33 wherein the fibre is located on a spacer to maintain a fixed spatial relationship between the fibre and the sleeve.

35. An optical fibre feedthrough according to Claim 34 wherein the spacer comprises a member threaded on the fibre.

36. An optical fibre feedthrough according to Claim 33 wherein the fibre end is centered by a centering jig and the end of the sleeve is located proximate the end within an annulus on the jig that has a lower coefficient of thermal expansion than the sleeve so that when the sleeve is heated the sleeve may expand sufficiently to reduce circumferential clearance between the sleeve and the annulus and any eccentricity between the annulus and sleeve may be minimized by permitting radial movement of the sleeve within the annulus.

37. A hermetically sealed optical fibre feedthrough assembly, that is resistant to the propagation of cracks, having:
a) an optical fibres with an inner and outer buffer layer, said inner and outer buffer layer being stripped a predetermined length, thus forming a stripped and a buffered portion thereon;

b) a sleeve;
c) a glass capillary member positioned around the fibre and within the sleeve so that the glass capillary rests against a constriction in the sleeve and the end of the fibre protrudes a predetermined distance beyond the end of the sleeve;
d) a central depression formed in a centering bead, coated with a lubricant, the centering bead having a positioning collar thereon; and e) the centering bead being placed over the protruding end of the fibre such that the positioning collar extends down and over the metal sleeve.

38. An optical fibre feedthrough according to Claim 37 wherein the assembly has been heated to a temperature above the glass transition temperature of the glass capillary member without exceeding 600°C for approximately four minutes and then cooled.

39. An optical fibre feedthrough according to Claim 37 or Claim 38 wherein the assembly has been heated to a temperature approximately ninety degrees above the glass transition temperature of the glass capillary member.

40. An optical fibre feedthrough according to Claim 34 wherein the fibre end is centered by a centering jig and the end of the sleeve is located proximate the end within an annulus on the jig that has a lower coefficient of thermal expansion than the sleeve so that when the sleeve is heated, the sleeve may expand sufficiently to reduce circumferential clearance between the sleeve and the annulus and any eccentricity between the annulus and sleeve may be minimized by permitting radial movement of the sleeve within the annulus.

41. An optical fibre feedthrough according to Claim 35 wherein the fibre end is centered by a centering jig and the end of the sleeve is located proximate the end within an annulus on the jig that has a lower coefficient of thermal expansion than the sleeve so that when the sleeve is heated, the sleeve may expand sufficiently to reduce circumferential clearance between the sleeve and the annulus and any eccentricity between the annulus and sleeve may be minimized by permitting radial movement of the sleeve within the annulus.

42. An optical fibre feedthrough according to any one of Claims 1 to 3 in which the fibre comprises silica.

43. An optical fibre feedthrough according to any one of Claims 4,5 or 6 in which the fibre comprises silica.

44. An optical fibre feedthrough according to any one of Claims 7, 8 or 9 in which the fibre comprises silica.

45. An optical fibre feedthrough according to any one of Claims 10, 11 or 12 in which the fibre comprises silica.

46. An optical fibre feedthrough according to any one of Claims 13, 14 and 15 in which the fibre comprises silica.

47. An optical fibre feedthrough according to any one of Claims 16, 17, 18, 19, 20, 21, 22, 23 or 24 in which the fibre comprises silica.

48. An optical fibre feedthrough according to any one of Claims 33, 34, 35, 36, 37, 38 or 39 in which the fibre comprises silica.

49. An optical fibre feedthrough according to any one of Claims 40 or 41 in which the fibre comprises silica.

50. An optical fibre feedthrough according to any one of Claims 1 to 3 in which the fibre comprises fluoride.

51. An optical fibre feedthrough according to any one of Claims 4, 5, 6, 7, 8, 9, 10, 11 or 12 in which the fibre comprises fluoride.

52. An optical fibre feedthrough according to any one of Claims 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23 or 24 in which the fibre comprises fluoride.

53. An optical fibre feedthrough according to any one of Claims 33, 34, 35, 36 or 37 in which the fibre comprises fluoride.

54. An optical fibre feedthrough according to any one of Claims 38, 39, 40 or 41 in which the fibre comprises fluoride.

55. A method of forming a hermetically sealed optical fibre feedthrough assembly that is resistant to the propagation of cracks comprising:
a) taking an optical fibre with an inner and outer buffer layer and stripping a predetermined length of the inner and outer buffer layer from an optical fibre;
b) inserting the fibre into a metal sleeve and centering the fibre with respect thereto;
c) positioning a glass capillary member around the fibre and within the sleeve so that the end of the fibre protrudes a predetermined distance beyond the and of the sleeve;
d) heating the assembly formed by the preceding steps a), b) and c) to a temperature above the glass transition temperature of the glass capillary member without exceeding 500 degrees C
for four minutes.