CA1187273A - Method of splicing ends of optical fibers - Google Patents

Abstract

METHOD OF SPLICING ENDS OF OPTICAL FIBERS
by Joseph Zucker and Arthur H. Fitch Abstract of Disclosure A small amount of light that is transmitted in one of a pair of optical fibers having cleaved ends thereof loosely brought into butt contact is converted to leaky modes in the other fiber. Leaky mode light that is radiated out of the perimeter of the other fiber is collected in an integrating enclosure located proximate its one end and extending over a limited length or the other fiber. The light in the enclosure is detected for producing a measure of the degree of alignment of the adjacent ends of the fibers. After the cleaved ends of the fibers are aligned with micromanipulators so as to null the intensity of detected leaky mode radiation, an electrical arc is created across them for permanently joining the fiber ends together in a splice. The integrity of the resultant splice is determined by producing a measure of the splice loss 10 log (l-PR/Po), where PR is a measure of light scattered from the splice and/or radiated out of the perimeter of the leaky mode section of the other fiber for light of a radiant power PO in the one fiber and incident on the splice.

Description

~ 87273 D-23,526 1 Eac~ground of Invention

2 This invention relates to fornin~ splices in optical fibers and

3 more particularly to a ~lethod of alignlng ad~acent ends of opt~cal ~ibers,

4 prior to ~oining the~ in a splice, so as to reduce the amount of light that ls lost as a result of the splice.
6 It is desirable that ~ini~l~ loss occur as a result of a splice 7 between ad~acen~ one ends or ~irst a~d second optical fibers. Yarious 8 methods and structures ~or supporting and alignins adJacent ends of 9 optical riber~ so as to ~aximize t~e light tt~nst.litted throuyh the fibers prior to ~or~ing a splice therebetween are discl~sed in literature such 11 as: "Fusion Junctions for Glass-Fibre Waveguides" by R. B. Dyott, et al., 12 Electronic Letters, June 1, 1972, Vol. 8-11, pp. 290-292; "Low-Loss 13 Splices in Optical Fibers" by R. M. Derosier, et al.~ Bell Systerl 14 Technical Journal, Vol. 52~ No. 7, Septe~ber, 1973~ pp. 1229-1235;
"Optical Fiber Vacuum Chuc~;" by W. ~. Benson, et al~ Applied Optics, 16 April, 1975, Vol. 14, No. 4, pp. ~16-~17; "Hot Spl~ces of Optical 17 ~aveguide Fibers" by Y. Kohan~adeh, Applied Optics, ~larch, 1976, Vol. 15, 18 No. 3, pp. 793-795; "Splicing Silic~ Fibers With an Electrical Arc" by D.
19 L. Bisbee, Applied Optics, Vol. 15, No. 3, ~iarc~ 1976, pp. 796-79~;
'~echnique ~or Joinins S~all-Core Optical Fibres" by J. H. Stewart, et 21 al., Electronic Letters, October 14, 1976, Vol.l2~ No. 21, page 570 and 22 'tGompen ating Fibre Splice Technique" by M. K. Dakss, et ~1., Electronic 23 Letters, April 20, 1977, Vol. 13, No. 9, pp. 257-25~. In a eonventicnal 24 method of ~or~in~ a fusion splice, for example, the axes o~ ad~acent one ends of a pair o~ ~ibers are visually aligned in the y and z directions.
26 m e ~nds o~ the fibers are then aligned ~or obta~Nins a maximu~ value of 27 li~ht trans~itted ln the two ~ibers and deteeted at the output end o~ the 28 seeond ~.iber. After the ane ends o~ the ~ibers are brcught li~htly lnto 29 bu~t eontaet, an electrical arc is produced the~e for ~uslns the~
together. This teehnique is disadvantageous in ~ield applications 31 ineluding long distsnce com~unieation channels havins opposite ends of tl~e 32 seeond ~iber s~aeed mQny kila~eters apart sinee it nor~ally rsquires a 7~
D-23,526 hu~n operator at both ends Q~ the second fiber. An object of this invention is the provision o~ the improved method of for~ing a splice bet~reen adjacent ends Q~ optical fibers. Another object is the provision of an ~mproved method o~ ali~lin~ ends of fibers ti-at are to be joined in a splice.
S~ ary of Invention In accordance wi-th this invention, the method of splicing adJacent one ends o~ first and second optical fibers together comprises the steps of: passing light in the first fiber in the direction of tlle one end thereof prior to forming the splice; detecting lealcy mode light radiated out Qf the perimeter of the second fiber in a length thereof that is proximate its one end; and aligning the one ends Q~ the fibers for nulling the detected signal prior to operatin~ on them for effectuating a splice therebetween.
Description of Dra~,rir~
This invention will be ~ore fully understood frcm the following detailed d2scription of preferred methods embodying it, together with the drawing in which parts are not drawn to scale. In the dra~ing, FIG. 1 is a schematic representation of apparatus for practicing a fiber splicirg method embodying this invention, a plan view of means 15 providing relative movemellt o~ adjacent ends o~ a pair of fibers and an integrating cylinder 17 of split blocl; const~lction that encloses the output fiber 12 being sho~n here;
FIG. 2 is a sec-tion vie~ o~ the apparatus talcen alor~ the section line 2 - 2 in FIG. l;
FIG. 3 is an enlarged side view o~ a portion of the integrating cylinder 17 prior to clampil~ tl~æ two halves thereQf together, and talcen along section line 3--3 in FIG. l;
FIG. 4 is a section view, similar to FIG. 2, of other apparatus useful in practicing a method embodying ~n alternate fo m of this invention;

~3L87~ ~23,526 FIG. 5 is a side view af an alternate embodiment Qf the detector in FIG. 4; and FIG. 6 is a curve that graphicall~r illustrates alignment af adjacent ends of the two fibers ~or nullir~ lealiy mode light radiated by the output fiber, and more particularly is a plot Qf the po~er ratio PR/Po (i.e.3 lea~cy mode light PR radiated ~rom the output ~iber normaliz~d by light in the input fiber that is incident an the edge Qf the one end thereof) as a functiQn o~ the fiber Qffset ratio d~dC (i.e., the fiber Qffset d nor~alized by the diameter dc of the fiber cores).
Description of Pre~erred E~bodiments Referring now to FIG. 1, apparatus for practicing this invention comprises an input fiber 11 that is connected to a li~ht source 21, an output fiber 12 that may be connected to a load 22, fusion splicer means 15, an integrating cylinder 17 Qf split block constructiQn, and radiameter means 19. m e fusion splicer 15 includes apparatus for axially aligning the adjacent orle ends of the two fibers and apparatus ~or operating on the adjacent one ends Qf the fibers ~or joining them together in a splice 13.
Apparatus for per~or~ing these functions is co~mercially available ar~d is described in the open literature. m e fusion splicer means 15 may, by way v of example, be a model ~J301 Fusion ~plicer o~ Oriorics in Albuquerque, New Mexico. This splicer apparatus may include a microscope ~or visually aligning the one ends Q~ the ~ibers.
m e splicer ~eans in FIG. 1 is shown as comprising vacuum chucks 31 and 32 havir$ associated V-grooves 31A and 32A therein receivirg one ends o~ ~ibers 11 and 12, respectively. m e chuck 32 is rigidly mounted Qn a support plate 35. The chucl; 31~ however, is mounted on an x-y-z micromanipulator means 33 that is attached to the plate. m e micro~anipulator means 33 is caused by a drive means 34, which may comprise a plurality of mechanical micrometers, to adjust the relative positions o~ the adjacent ends of the ~ibers. The ore ends o~ the input and output ~ibers are laid in associated V-grooves and held there by vacuum. Alterratively, the ~ibers ~ay be held in the V-grooves by ~ D-23,526 magnetic or spring-loaded strips (not sho~nn). ~1 practice, the chucks 31 and 32 are located nluch closer together than is sho~n in Fl~. 1 for holding the fibers nearer to the adjacent or;e ends thereo~. Also, the thicl~ness of the stationary chuc~ 32 in the Y-direction in FlG. 1 is pre~erably as small as practicable.
The fusion splicer 15 also comprises a pair o~ electrodes 38 and 39 (see FIG. 2) that are electrically cormected between a DC power supply 41 and a ground reference potential. m e electrodes are held by support means (not sha~n) ~Yith their axes aligned in a plane that is orthogonal to the axes of the fibers at the one ends thereo~. The free ends (e.g.
end 39A) of the electrodes are located proximate the adjacent edge sur~aces of -the fibers and on opposite sides o~ the axes thereof (see FIG.
2). l~lhen the one ends of the fibers are in satisfactory align~ent and light~r butted together, the switch 43 is pressed for causing an electrical arc to be created across the junction of the fibers for fusing them together.
The integrating cylinder 17 is an enclosure that converts input light into diffuse li~ht in the interior thereof. Integrating enclosures are manufactured by Labsphere c~ New London, New Hampshire. T~le integrating cylinder 17 is split into halves 17A and 17B by a cutting plane that is parallel to the plane ot' the paper. Flanges 45A and 46A
extend over the ler~tll c~ the cylinder ad~acent the open edges of the top 17A of the cylinder. Associated flanges 45B and 46B (not shown) extend over the length of t~e cylinder adjacent the open edges o~ the bottom of the cylinder. A hinge 4~ i3 attached to the ~lary~es 45 to facilitate openiII~ and closin~ the cylinder. Alignment holes arx1 pins (not shown) may be located along the flanges ~or providin~ precision alignment oe the interior sur~aces Qf the cylinder parts. The ~wo halves of the integrating cylinder are secured to~ether with clamps 50 on the flanges to rorrS a light-tight enclosure. The top 17A of the cylinder may contain an input port 52 comprisil~g a socl;et receivin~ a fiber connector that is adapted for releasably holding the one end of the input fiber 11 prior to ~7~3 D-23,526 1 for~ing a splice and its being located in the vacuu~ chucl; 31, as is 2 descr~bed mDre flully hereina~ter. m e top Qf the cylinder also contains 3 an output port 54 comprisins a so~;et that is dimensioned ~or receiving a 4 ferrule that is attached to Qne end of a fiber bundle 56 that has its other end connected to the radiometer me~ns. The sockets in the input and 6 cutput ports are oriented so that a li~ht ray e~anatlng into the cyllnder 7 frnm a fiber in the input port or radiated ~rom the perimeter cf the 8 output ~iber will not be directly incident on the end o~ a bundle ~iber g inside the cyllnder.
Each of the cylinder parts includes axially-aligped spa oe d-apart 11 semi-cir¢ular openings that extend thrcu~h ~è ends thereo~ and which are 12 coaxial with the axis of the cylinder. m e se~icircular openings, e.g.
i3 openings~ 60A and 60B in FIG. 3, are made to fo m a circular opening that 14 is larger than the dia~eter o~ the fibers when the cylinder parts are clamped together. Se~icircular chal~nels, such as the channels 62A and 62B
16 in FIG. 3, are also fabricated on the ends of the cylinder coaxial with 17 the axis thereof and thus associated ones of the circular open~ngs.
18 Associated channels also ~ate Hhen the cylinder parts are clacped together.
19 The se~icircular channels 6~A and 62B, for exa~ple, are filled ~tith inserts 64A and 64B of resilient dielectric ~aterial such as a flexible 21 polyester polyurethane rOam that extends above the ed~es o~ the cyllnder 22 parts when it is open, see FIG. 3. Shallow trou hs 66 are cut into the 23 facin~ surfaces Qt' the fQam inserts to facllitate locatin~ the optical 24 fiber 12 alc~g the cylinder axis when it is open. m e cylinder ls pre~erably secu~ely attached to tlle fixea chuck 32 by scre~s 68 in flanges 69, 26 see ~IG. 2, with the axis of the cylinder spaced slightly above tlle botto~
27 c~ the V~roove 32A. In practicinæ this invention~ the cylinder is opened 28 so that the ~utput ~iber 12 can ~e looated in a groove 66 of an insert.
29 m e cylinder is then closed fcr firmly sand~tichin~ the output ~iber between the ~oam inserts ~hich securely hold it in place without introducing 31 compresslon modes in lt. I~e sides o~ the inserts that fa oe into the -7;~73 D-23,526 cylinder are preferably coated with a li~t re~lective paint, as is the interior of the sphere.
It has been discovered that the output one c~ a pair Q~ optical fibers connected in a poor splice, as well as tlle output ~iber o~ a pair o~ misc~ligned fibers that are brought toge~her for beinæ joined in a ~splice, supports lea~;y mode radiation of a signi~icant~neasurable level over a length of approximately one foot do~rnstream of (i.e.~ ~ovinæ awa~
from) the splice. That is, in addition to light in the input fiber being scattered by the junction of the edges of the ~ibers (i.e., the splice), some of the input light is converted into lea~y modes in the core and cladding of the output fiber. Tllis leaky r.ode radiation escapes through the circumference of the output fiber, being radiated generally trarsversely away from this fiber. It has been determined empirically tha~ when l~isaligned fibers are brought together for being joined in a splice, the a~ount of le~;y nlode light radiated by the output fiber downstream of the one end thereof r~y be greater than that scattered fran the immediate vicinity of ~he adjacent one ends Q~ the f_bers and the splice.
In accordance with this inventioll~ the protective pl~stic coating is removed fr~ a short length Q~ in~ut fiber and approxirnately 1.5 feet c~f output fiber adjacent t~le one ends thereo~. The ends of the fibers are then cleaved for providing edges thereof that are subs-tantially orthogonal to the fiber axes. The exposed output fiber is laid along the groove 66 in the o~en cylinder 17 and in the groove of the stationary chuck 32 with its one end Oenerally c~ligned with the c~Yes of the electrodes 3~ and 39. m e caltput fiber is held in this positian by a vacu~un that is generated in the chuclc 32. In a similar manner, the input fiber is laid in the groove o~ the other c}luclc 31 with its one end juxtaposed with and sp~ced slightly fror~ the c)ne end of the output fiber.
The input fiber is also held in this position by producinO a vacuurn in the chuclc 31. m is placement of the fibers locates the axes tllereo~ in geIleral aliO~nnent. The cylinder 17 preferably extends over a substantial portion of ~le length, e.g. five inches of output fiber, extending 3L~IL87273 D-23, 526 downstrea~ of tne one ends of the output fiber, and is securely closed prior to energizing the light source 21 for illuminatincr the one ends the fibers and producing leaky rnode radiation in the output ~iber. The diarneter c~ -the cylinder is pre~erably srall, e.g., one inch. Light that is scattered frora the adjacent edges of the ~ibers is lost. Light frorn the input fiber that is converted to lea~ rnode light in the output fiber c~nd radiated f`rcm the lel~;th thereo~ witnin the cylinder is converted to di~fuse light there. The operation of the cylinder integr ates or surns the radiated light in it. r~e radiol~aeter rreans produces c~ indication P~ of light radiated by the output fiber.
The drive rneans 34 ls r;anually operated, for exc~nple, ~lhile viewing the indication provided by the radicl:leter for raoving the one end of the input fiber transversely in the y and z directions for nulling the intensit~r of the detected light. That is, the a~ial position of tne one end of the ir-put fiber is rroved first in the ~ directions and then in the +z directions for producing rninir~m signal level indications on tlle radiorneter frora s~lhich tlle value increases on either side c~ the null point in both the y and z directions, the x and y directions being in the plane of the paper in FICT. 1. Stated differentl~, tiae one end o~ t~le input fiber is raoved transversely for adjusting the indication ~n the radi~eter to be a ~inim-un or los~ point on a saddle, ~lhich point corresponds to the lowest c~no~mt c~ variation reaclled on a control ~mcticn between two higller Vall.:leS. This iS illustrated graphically in FICT. 6 where the indication PI~ provided by the radi~neter is Ix~rmalized by the power Po o~ light in the input fiber that is incident cn the one ends c~ the Iibers, and the ~fset d ol the fiber a~es is normalized by the cornrnon dic~eter dC OI the ~iber cores. T`he indication Po rnay be obtained by locating tl~ o~ end oE the input ~iber in the socl;et 52 on the enclosure and taking tl~e readi~ rom the radiorleter prior to placing this fiber in c~luck 31. The cur~re here was plotted with the aid c~ an integrating sphere enclosing output fi~?r spaced 6 to 9 inclles dos~mstrearn c~ the splice point.

~L8~
D-23,526 ~ fter the ends o~ the fibers are satisfactorily aliO~ned, as indicated by y and z direction rllll points on the radiometer, the drive means is caused to move tlle input riber sliohtl~ in the +x direction in FIG. 1 so that the ends o~ the fibers are lightly in butt contact. The switch 43 is then actuated for producing an electrical arc bet~Yeen the electrodes for heating the one ends of the fibers and fusing them toget'her in a splice 13. After the splice is completed, the integrity or quality of the splice ~n be rreasured by again ill~ atinO the splice with the lig'ilt of intensity Po in the fiber 11 and rronitoring the light PR
radiated by thR length o~ output fiber in the integrating cylinder. A
good neasure o~ the splice loss is obtained fro~ the relationship 10 log (l-PR/Po) (1) As indicated above, sor~e of the li~lt transmitted in ~iber Il is scattered by the splice itself and sor~e o~ it is radiated fro~m the ad~acent length of da~nstream output fiber that is approxirnately one foot long. Analysis of a rumber of splices has shown that the intensity of leaky mode lio~lt radiated by t~le output fiber ~ay, in some instances, be greater than that o~ the light scattered fr~m ~hR splice itself. mus, the optin~u~ value of splice loss is obtained with a value of PR produced by integrating both thR light scattered by tl~R spli oe and thR light radiated out o~ the perirrRter of the ~ItpUt fiber. Since it is only necessary that adJacent ends o~ M'R fibers be precisely ali~ned for providing maximum transr~ission o~ ligllt in them, however, light scattered from the adjacent e~lds Or the fibers or light radiated fra~ any length of output fiber e~hibiting substantial radiation i~ lealcy mlode light provides an indication Oe the alig~nent of tlle two fibers. Additionally~ it has been detet~ined en~irically tl~at a g~od indicatioIl of the quality of a splice is obtai}led by integrating only scattered light in a length of output fiber e.~tending ~ror~ three inches to twelve inches downstream of the splice. Test results alSo Sh~l that light radiated from shorter lengtlls of output ~iber ri~y be employed satisfactorily for indicating the quality o~ a splice and aliOn~ent ~ fihers.
--8~

~ ~3 D~3,526 1 In t~o emhodiments that were built and operated for practicing the2 method of this invention, the ~nte~rating enclosure 17 was an 3 integrating sphere having an inner diameter of three inches, and a c~linder4 with an inner diameter of 3/4 lnch and a length o~ 1-3/4 inches. In these S apparatus, the thickness o~ the corresp~lding output chuc~ 32 caused the 6 sphere to integrate light in a length o~ output fiber extending ~ro~ three 7 inches to six inches do~nstream o~ the one ends of the ~lbers in the case 8 ~ the sphere and rrom 3 to 4-3/4 inches downstream cf the one ends of the 9 ~lbers in the case Q~ the cylinder. The enclosures were also sequentially advanced along the output fiber in incre~ents o~ their lengths for 11 obtainin~ indications PR of light nadiated from successive lengths c~
12 output fiber exhibiting lea~ mode radiation as a result of the spacing 13 between the one ends of the ~ibers and/or the splice. Lea~y mode 14 radiation at points along the output fiber was dete m ined to be of a significant level ~hen its power level was readily measureable and of a 16 magnitude having a real effect on the overall-integrated value of PR for 17 light emitted by the splice and t~le adjacent one-foot length ~f output 18 fiber. A value for P~ corresponding to the inte~ral o~ ht e~itted b~
19 ~he splice and the ad~acent ane foot length of o~ltpUt fiber is obtained with such a three inch sphere by su~Trllg values Or PR obtained from 21 successive three inc1 increments of output ~lber in which the splice is 22 located ~us~ inside the sphere for one of the measurements. By way cr 23 exa~ple, the leaky mode radiation is n~ lonser of a significant value when 24 ik decreases by an order Or magnitude fro~ the highest measureable ualue therec~ in the dcwn~trea~ len~th Or output riber. In analyæing a number 26 c~ spliced ribers, it was fc~nd that lealcy ~ode n~diaticn falls to a 27 relatively lcw level at a distan oe c~ approxinately one ~oot away frc~ the28 location of a splice. m e leak~ mode radiaticn rell to a level that was 2g at least an order of ma~nitude less than a previous high value thereof ror po~nts on an output riber within a rirteen inch length thereof downstrea~
31 ar the location ar a splice.

_9~

~8~3 D-23,526 Apparatus for practicing an alternate method embodying this invention is illustrated in FIG. 4 which is a section view of apparatus similar to that in FIG. 1 and ta~;en along line 2 - ~ there. The electrodes 38' and 39' in FIG. Ll are axially aligned in the vertical direction with the free ends thereof Qn opposite sides Q~ the ed~e surfaces of the fibers. A photodetector 71 and reflector 72 are located on opposite sides Qf the fibers at the location Qf the splice. The detector 71 is connected throu~ a switch 76 to meter means 78 for providing an indication ot light scattered from the i~mediate vicinity of adjacent edge surfaces Qf the fibers during alignment Qf the Qne ends thereo~. The detector 71 and reflector 72 are mounted in tracks 73 and 74 on the chuck 32 for moving them away fra~ the fibers prior to forming a splice. The switch 76 is also opened prior to producing an electrical arc for fusing the fibers together in order to protect the meter 78. The indication Qf scattered light provided by tlle meter 78 may be used alone or in conjunction with the indication pr~videà by the radiameter for identifyin~ null points and determining optimum ali~nment Qf the fibers. Alternatively, a semi-cylindrical photodetector means 81 m~y extend over t~le edges af ~e one ends Qf the fibers and adjacent short seg~ents thereof. The full breadth Qf the lnterior surface o~ the cylinder is ccated with a photo~sensiti~e ~aterial for detecting the maxi~um amount of light scattered frQn the edge surfaces Qf the fibers. A mounting plate 83 on the photodetector means is connected to a traclc 73' for moving it away from the area o~ the ~ibers prior to ~ cing a splice. The width S of the slot in the detector means 81 is greater than the diameter c~ the fibers.
Altho~ t~is inventiQn is described in relatiQn to pre~erred embodi~ents thereQ~, variations alld modi~ications will occur to those sl;illed in the art. BVV way Qf example, the n~vel ~lethod is applicable to radiant energy and li~ht in bot~l the visible and invisible electrQ~agnetic spectrwm in the high and low ends Q~ the ~requency spectrum including both ultraviolet and in~rared radi~tion. Also, the integrating enclosure may be Qf any other convenient shape, although it preferably has a regular D-23,526 shape. Further, the enclosure does not ~lave to ~e split into parts ~f the same size and a photodetector of the radiomRter means may be located directly in an oper~r~ of -thR OlltpUt port 54 on the integrating enclosure rather than coupling diffuse light to it over a fiber b~ldle or single ~iber. And i~ the intensity of di~fuse li,~lt co~lpled to the radiometer r.eans is lnsufficient to obtain a clear and definite reading~ the li,ght source n~ay be pulsed or the output thereof meciha~icc~lly chopped at a fixed repetition f~equency for producing a varying electrical current in the radiometer m,ea~s ~or increasing the sensitivity of the detector in a manner that is well Xnown in the art. Additior~ally, the enclosure 17 may be replaced with a photodetector n or 81 located adjacent the leal~y mode section of output fiber. Or a PIN or avalanche photodiode co~prising a light-pipe or bundle of optical fibers couplin~ radiated leal~y mode light frorn the perimRter of the ~ItpUt fiber to a light sensitive surface m~y be employed in place of -~le integratin~ enclosure. I~e diameter of such a light pipe is approximately 10 mils3 whereas t'le diameter of the ~Itput fiber is in the order c~ 1~0 microns, which is approximately 5 mils.
Also, other types of appratus may be employed ~or holdLng and adjusting the ends of fibers and producir~ other types of junctions joinin~ the ends o~ fibers together. Additionally, the axes Q~ the fibers nay be tilted with respect to each other for improving the transmission of light between adjacent ends thereof. The scope Qf this invention is therefore defined by the appended claims I~ther th~l the aforementioned detailed descriptions c~ preferred em~odimRnts tllereo~.

Claims (15)

What is claimed is:

1. A method of splicing adjacent one ends of first and second optical fibers together comprising the steps of:
passing light in the first fiber in the direction of the one end thereof, detecting light radiated from the perimeter of the second fiber in a length thereof that is proximate its one end and that supports substantial leaky mode light waves, adjusting the relative position of the one ends of the fibers for nulling the detected signal prior to operating on them for effectuating a splice therebetween, and splicing the one ends of the fibers together.

2. The method according to claim 1 wherein said adjusting step comprises adjusting the relative position of the one ends of the fibers in primarily planes orthogonal to the axes of the fibers which axes are maintained generally parallel to each other.

3. The method according to claim 2 wherein said detecting step comprises producing a measure of radiated light that is passed out of the circumference of this second fiber over at least a segment of the length thereof exhibiting substantial leaky mode radiation.

4. The method according to claim 3 wherein said detecting step comprises producing a measure of the average value of radiated light.

5. The method according to claim 3 wherein said adjusting step further comprises holding the fibers proximate the one ends thereof, said radiating segment of the length of second fiber extending downstream from points at which the one end of the second fiber is held.

6. The method according to claim 5 wherein said radiating segment of the length of the second fiber extends at least five inches downstream of the holding point on the second fiber.

7. The method according to claim 1 wherein said detecting step comprises integrating radiated light passed out of the perimeter of the second fiber over a portion of the length thereof supporting substantial leaky mode radiation.

8. The method according to claim 7 wherein said detecting step further comprises locating said portion of the length of second fiber inside an integrating light enclosure whereby light radiated through the circumference of said second fiber produces diffuse light in said enclosure, and detecting diffuse light in said integrating enclosure for producing the measure of radiated light.

9. The method according to claim 1 including the additional step of detecting light scattered from the immediate area o the adjacent one ends of the fibers; said adjusting step comprising adjusting the relative positions of the one ends of the fibers for minimizing the detected scattered light and the detected radiated light.

10. The method of splicing one ends of first and second fibers together comprising the steps of supporting the fibers proximate the one ends thereof for locating the one ends adjacent each other with the fiber axes in the area of their one ends being generally coaxial, transmitting light in the first fiber in the direction of the one end thereof so that it is propagated into the second fiber, detecting light radiated from the perimeter of the second fiber in a length thereof that is proximate its one end and which supports substantial leaky mode radiation of light, adjusting the relative positions of the one ends of the fibers for nulling the detected signal, and operating on the fibers for effectuating a splice between the one ends thereof.

11. the method according to claim 10 wherein said detecting step comprises producing a measure of radiated light passed out of the circumference of the second fiber over at least a segment of the length thereof exhibiting substantial leaky mode radiation.

12. The method according to claim 11 wherein said radiating segment of the length of second fiber extends at least five inches downstream from points at which the one end of the second fiber is held,

13. The method according to claim 12 wherein said detecting step comprises producing a measure of the average value of radiated light.

14. The method according to claim 10 wherein said detecting step comprises integrating radiated light passed out of the perimeter of the second fiber over a segment thereof exhibiting substantial leaky mode radiation.

15. The method according to claim 10 wherein said operating step comprises providing relative movement of the fibers in their axial directions so as to move the edge surfaces of the one ends thereof lightly into physical contact prior to completing the fabrication of a splice.