US3830667A

US3830667A - Method of making flexible fiberoptic bundles

Info

Publication number: US3830667A
Application number: US00252866A
Authority: US
Inventors: G Carpenter
Original assignee: American Optical Corp
Current assignee: American Optical Corp; Warner Lambert Technologies Inc
Priority date: 1970-12-14
Filing date: 1972-05-12
Publication date: 1974-08-20
Anticipated expiration: 1991-08-20

Abstract

A flexible fiberoptic bundle of light-conducting multifibers wherein each multifiber comprises a plurality of fused together individually glass-clad glass monofilaments having overcladdings of glass along their respective lengths. The overcladdings are removed throughout at least intermediate portions of the lengths of each multifiber in the fused bundle to free corresponding portions of the glass-clad glass monofilaments whereby both the flexibility of the bundle and its resistance to fiber breakage are enhanced.

Description

TTfI hii-ed STQU "Car enter 145 20, 1974 1 METHOD OF MAKING FLEXIBLE 3,033,731 /1962 C616... /4 x FIBERQPTIC BUNDLES 3,554,721 1/1971 Gardner 65/4 7 3,567,549 3/1971 Hoffmeister et al 65/4 X 1 lnventorz' rg J- Carpenter, southbndge, 3,530,775 5/1971 Siegmund 65/4 1x Mass. 1 7 3,615,313 10/1971 P1166 61 65 4 3,624,816 11/1971 s1 k t 1.... 65/4x {73] Asmgnee: 0PM! P 3,669,772 6/1972 61221 65/4 SOulhbndge, Mass- 3,674,452 7 1972 Strack.... 65/4. 3,690,853 9/1972 Law l .m: 65/4- {21} APPL N01? 7 Primary Examiner-Stephen .l. Lechert, Jr.

Related us. 4 116611611 061 Division of Sen abandoned,

u. s. c1 156/155, 65/4, 156/167, 156/168, 156/173,156/174,156/175, 156/180, 156/296 161. c1 6326 31/00 Field 6: Search 156/180, 174, 296, 1-73, ,1. 156/155, 167,163, 65/4 References Cited UNITED STATES PATENTS 3,004,368 10/1961 Hicks 350/9613 Attorney, Agent, or Firm-William C. Nealon 57 ABSTRACT,

A flexible iiberoptic bundle-of light-conducting multifibers wherein each multifiber comprises a plurality of fused together individually glass-clad glass monofilaments having overcladdings of glass along their respective lengths. The overcladdings are removed throughout at least intermediate portions of the lengths of each multifiber in the fused bundle vto free corresponding portions of the glass-clad glass monofilaments whereby both the flexibility of the bundle and its resistance to fiber breakage are enhanced.-

6 Claims, 6 Drawing Figures I Pmmm samzm a' FIG. 5

INVENTOR. GEORGE ,d, CARPENTER ATTORNEY 3,830,667 1 l 2 METHOD OF MAKING FLEXIBLE FIBEROPII suitably flexible for the winding of endless ribbons is of BUNDLES exceptionally large cross-sectional size, e.g., greater I This is a division, of application Ser. No. 97,7 l9,tiled Dec. 14, 1970, now abandoned.

BACKGROUND oFrIIE INVENTION l, Field of the Invention 1 V Fiber optics with particular reference to flexible image-transmitting fiber bundles.

2.. Description of the Prior Art In dealing more particularly with the manufacture of flexible image-transmitting or coherent fiberoptic bundles, usually called fiberscopes," there is the longstanding need for easier and more economical fabrication procedures, improvement in coherency (i.e.,

image resolving capabilities of the finished bundle),

greater bundle strength and a reduction of the adverse effect of fiber breakage upon image definition.

The foregoing has, to some extent, been accomplished by US. Pat. No. 3,033,731, but not entirely without problems. g in seeking greater coherency through better fiber alignment and bundle packing fraction it is necessary to turn to the use oflarger fibers which may, of course,

be multifibers. The use of larger fibers, however, renders finished bundles less flexible and more susceptible to breakage. Adding to this, the breaking of a large fiber (multifiber), leaves a correspondingly large void or non-transmitting areain the bundle. Thus, as fiber size is increased, degradation of transmitted optical images resulting from fiber breakage increases by an order of magnitude corresponding to the increase in fiber size.

The present invention, in dealing with the manufacture of flexible fiberoptic bundles, particularly of large format, relates to matters of avoiding the aforementioned problems of bundlefragility and optical image degradation resulting from fiber breakage by minimizing both. Greater than usual fiber alignment and bundle packing fraction attended by improved bundlecohen ency and optical image resolution is achieved.

SUMMARY OF THE INVENTION The foregoing objectives are accomplished by utilizing, as much as possible, the flexible fiberoptic bundle manufacturing technique of US. Pat. No. 3,033,731 which obviates some of the earlier problems of fiber hand-packing and aligning operations. In this regard, a

than 60 microns in thickness, so as to offer the important advantage of easy and accurate side-by-side alignment of convolutions thereof in the winding operation as well as exceptional ease in handling of the ribbons in making the fiber bundle assembly as outlined hereinabove.

- The bundle, however, being relatively inflexible and fragile at this stage, is prepared for leaching. Its opposite endsare coated with an acid-resistant plastic, wax or the like and the remaining intermediate portion of the length of the bundle is exposed to a glass leaching medium, e.g., hydrochloric acid. The'leaching medium,

in being free to circulate in between and around the 'multifibers, readily effects removal of the overclad- .dings of the monofilaments of each multifiber. This I greatly increases the flexibility of the fiberoptic bundle Q and correspondingly reduces image degradation resulting from accidental breakage of individual loose fibers (monofilaments) of the bundle. Thus, large losses of image definition which would ordinarily result from individual multifiber fiber breakage are avoided.

.While leached fiberoptic bundles per se, are known (e.g., as shown in US. Pat. No. 3,004,368) the fiber aligning and packing techniques in such cases have not been entirely satisfactory, particularly when the resulting bundles are required to transport optical images. Furthermore, there has been a definite limitation as to the thickness or cross-sectional size of a bundle which can be properly and efficiently leached to free its fibers without effecting damage thereto. This has been overcome by the present invention wherein large format fiber bundles of individually flexible multifibers are leached to disconnect respective monofilament ele ments of each multifiber.

The invention will be more clearly understood by reference to theifollowing detailed description when taken in conjunctionwith the accompanyingdrawing. DESCRIPTION or THE DRAWINGS FIG. 1 diagrametically illustrates a proposed technique for making overclad glass-clad fiber from which multifiber may be produced according to the present invention; I

FIG. 2 diagrametically illustrates a technique for producing-an endless ribbon of a multifiber made up of a plurality of the aforementioned overclad glass-clad cal opposite endfaces of the resulting flexible fiberoptic bundle. I

in accordance with the'present invention, however, the multifiber used to form each of the aforementioned endless fiber ribbons is comprised of a preselected a ja glass fibers;

FIG. 3 diagrametically illustrates an assembly of the endless multifiber ribbons from which a flexible bundle may beformed;

FIG. 4 illustrates the type of flexible fiber bundleresulting from cutting transversely through the assembly of FIG. 3, opposite ends of the bundlein this case are shown as having protective coverings thereover;

FIG. 5 is a greatlyenlarged fragmentary, partially cross-sectioned elevational view of one end of the fiber bundle shown in FIG. 4; and

FIG. 6 is a similarly greatly enlarged elevational view 7 of the same bundle followingtreatment thereof to enhance the flexibility of the bundle and its resistance to breakage according to principles of the present inven tion.

DESCRIPIIQN OF PREFERRED EMBOD1MENTS Referring more particularly to FIGS. 1-3, the operat'ions illustrated therein represent a technique for forming a flexible bundle of optical fibers as follows:

A monofilament is formed of a rod and tube assembly 12 by the well-known practice of heating and drawing the assembly through a suitable heating element 14. ln the present case, assembly 12 is comprised of'a rod 16 of high refractive index core glass, an inner intermediate sleeve 18 of cladding glass having a relarnaterial having a coefficient of thermal expansion and melting temperature compatible with the core and

cladding materials

16 and 18. Exemplary leachable materials are borosilicate glass or aluminum which may be conducting core of high refractive index glass 16, a first cladding of relatively low refractive index glass 18 and, additionally, a unique overcladding 22 of the aforementioned weathering or leachable material 20. A plurality of sections 24 of monofilament 10 are cut or bro.- ken away from the monofilament and bundled together as a boule 26 (FIG. 2) from which a multifiber 28 is drawnthrough heating element 14. For purposes of illustration, boule 26 is shown as being three fiber diameters wide whereby the multifiber 28 comprises a fused together rectangular-array of nine monofilaments (sections 24). Any desired greater or lesser number of monofilaments (sections 24) may be used to form boule 26 and multifiber 28.

Fabrication of the'ultima-te flexible bundle ofoptical fibers is accomplished by winding multifiber 28 on a suitable former, e.g. drum 20, to produce endless ribbon 32 having a preselected number of tightly packed convolutions 34. These convolutions may be wound vertically, one over another, or horizontally, as shown. A plurality of similar ribbons are wound, removed from the winding drum and stacked together in accurately extent of the individual flexibility of each multifiber 28.

'- Each length of multifiber 28, being formed of a plurality of fused together monofilaments is, by compaiison to the size and flexibility of each monotilament.-rela- V tively rigid and similarly relatively fragile in bending.

- Thus, the present invention involves further processing tively low index of refraction and an outer tube of 'acid-leachable fweathering" glass or metallic casing 1 0' of bundle 42 wherewith, as an objective, the bundle is rendered considerably more flexible and, similarly, considerably less fragile. This isachieved by leaching overcladdings 22 of materials 20 of the individual monofilaments in the bundle away from the flexible intermediate sections of their respective lengths.

Since the connected together integrity of opposite ends 38 and 40 of bundle 42 must be preserved so that these ends may ultimately become light-receiving and I light-emitting opposite ends of the bundle,

coverings

44 and 46 of plastic, wax or other materials which are resistant to acid are applied to bundle 42 over these ends 38 and 40 (H0514 and 5). These coverings, being of a material selected for its insolubleness in acid or other leaching solutions may be applied by painting, dipping or taping of ends 38 and 40 of the bundle.

Referring more particularly 'to FIG. 5 which is a greatly enlarged fragmentary elevational view of one end of bundle 42, it can be seen that, prior to' leaching of the intermediate portion of the bundle, its multilibers 28 eachcomprise a plurality of fused together superimposed relationship with each other throughout a short portion .1 (FIG. v3:) of their corresponding lengths. These ribbons 32"are cemented, fused or otherwise secured together in portions .r thereof and sawn or otherwise cut, e.g., along line 36, to form opposite ends 38 and of flexible fiber bundle 42 (see H6. 4) which results from opening the assembly of ribbons after cutting. The ends 38 and 40 of bundle 42 are usu ally subsequently optically finished as light-receiving and light-emitting opposite faces respectively of the bundle. Those interested in greater details concerning the technique of 3 forming optical fiber imagetransrnitti'ng bundles of endless fiber ribbons, as briefly described hereinabove, may refer to US. Pat. No. 3,033,731.

Referring now to flexible fiber bundle 42 of FIG. 4, it should be understood that the term flexible" is used res'ervedly at this point in the process ofthe present ingether. Accordingly, the bundle is flexible only to the monofilarnents which are all fixedly secured together beneath covering 44, and likewise beneath covering 46 (FIG. 4). lntermediately of these coverings, however,

they are individually flexible but only to an extent lim-.

ited by their relatively large cross-sectional size.

Enhancing the flexibility of bundle 42 and correspondingly decreasing its fragility according to principles of this invention, the bundle, with coverings .44 and V 46, is immersed in a bath of a preselected leaching solution such as 5 percent (by volume) hydrochloric acid maintained at a temperature of approximately 65 C. This solution, of course, is only useful when the overcladdi'ngs 22 are formed of leachable glass. For overcladdings 22 of metal such as aluminum or its equivalent, sodium hydroxide may be used.

,The leaching solution would be placed in a tank, dish of. suitable receptacle, not shown, which is selected to be of a size sufficient to receive bundle 42.

tion of bundle 42 and spaced from each other or adapted to be so spaced by movement of bundle 42 in the leaching bath by vibration of the bath or bundle or both or by pumping of the leaching bath through these multifibers, relatively rapid and complete separation of all monofilaments '10 from each other by leaching of their overcladdings is effected. Thus, large format highly flexible bundlesof optical fibers can be readily produced according to the present invention concept. More particularly, building of the large bundle format can be achieved with exceptional accu'racyin fiber alignment and packing fractionjThis being the result of the now possible use of large fiber (multifiber) in the initial fabrication (before leaching) of the bundle.

, Comparing FIG. 6 with PK}. 5 wherein the same fragmentary end section of the bundle is shown in each case but with covering 44 removed and monofilament 10 released in FIG. 6,'the unique results of the invention can be seen. ln this respect, the initial secured to--' gether integrity of end portions of the bundle is maintained, ie with Connected together materials of the fiber overcladdings, while each and every rnonofilameat 10 throughout the intermediate portionof the bundle is disconnected from all other monofilaments and free to flex individually. in this way, bundle 42 is given a substantialincrease in its overall flexibility which corresponds to the decrease in cross-sectional size from mu'ltifiber 28 to monofilament 10. Also, the

bundle is given a corresponding decrease in its fragility and degradation of transmitted optical images occuring from fiber breakage. In the latter respect, the breaking of one monofilament in bundle-42 (FIG. 6) will obviously affect only a relatively very small portion of an overall image transmitted through the bundle while breakage of a larger fiber (e.g., the size of multifiber 28 in the FIG. 5) would affect a considerably larger portion of such an over-allima-ge intended to be transferred through the bundle. An intent and purpose of the invention is to avoid the latter.

l claim: w

l. The method of making a flexible bundle of lightconducting fibers having oppositely disposed lightreceiving and light-emitting end faces comprising:

assembling a plurality of lengths of monofilament in juxtaposed relationship with each other as a boule,

said lengths of monofilarnent in each case comprisifig a core of glass having a high refractive index,

said core being clad with a layer of glass of relatively low refractive index and an overcladding of fusible leachable material;

heating and drawing the boule into the form of a rriultifiber wherein said monofilament overcladdings' are fused together as a unit; winding said multifiber into the form of a plurality of short portions of said ribbons to form said convolutions of multifiber into a plurality of individual lengths of multifiber with corresponding opposite ends thereof constituting said end faces ofsaid bundle; and leaching at least the major portion of all of said over- 'claddings away from all monofilaments of all of said multifibers intermediately of said end faces of said bundle.

2. The method according to claim 1 wherein said ribbons are fused together throughout said corresponding relatively short portions of their respective extensions.

-3 The method according to claim 1 wherein said ribbons are cemented together throughout said corresponding relatively short portions of their respective extensions. I

4. The method according to claim 1 wherein said overcladding material is an acid-soluble glass.

5,. The method according to claim 4 wherein said glass is a silica-free composition.

6. The method according to claim 1 wherein said overcladdings are formed of a metallic material.

Claims

2. The method according to claim 1 wherein said ribbons are fused together throughout said corresponding relatively short portions of their respective extensions.
3. The method according to claim 1 wherein said ribbons are cemented together throughout said corresponding relatively short portions of their respective extensions.
4. The method according to claim 1 wherein said overcladding material is an acid-soluble glass.
5. The method according to claim 4 wherein said glass is a silica-free composition.
6. The method according to claim 1 wherein said overcladdings are formed of a metallic material.