Method of and apparatus for securing elongate members of generally cylindrical form in end-to-end relationship

Abstract: A method and apparatus for securing enlongate members (24, 28) of generally cylindrical form in end-to-end relationship, particularily for forming an optic fiber splice (30). Optic fibers are spliced by pressing a form, preferably an optic fiber of the same diameter as those to be spliced, into a deformable body (8) to create a groove for receiving the ends of the optic fibers in close alignment. To secure the optic fibers, an index matching adhesive is cured by UV irradiation through a glass cover (20) plate bonded to the deformable body.

Description: This invention relates to a method of and apparatus for securing generally cylindrical elongate members, particularly end portions of optical fibers, in end-to-end relationship. An optical fiber comprises a core of high index material surrounded by a cladding of low index material. The diameter of the core ranges from about 4-9 µm for single mode transmission to about 50-100 µm for multi mode transmission. The radial thickness of the cladding is generally about 125 or 140 µm, regardless of the diameter of the core. The fiber is provided with a plastic buffer coating to protect it from damage. Although optical fibers can, using known technology, be manufactured so as to have essentially uniform properties over essentially indefinite lengths, it is conventional for such fibers to be sold in lengths of, e.g., 1 km, and for two or more lengths of fiber to be spliced together, i.e., joined together end-to-end, in order to produce a fiber longer than 1 km. Moreover, even though a fiber of 1 km or more can readily be manufactured so that it is without significant defects, handling of the fiber during installation as part of a fiber optic link may result in damage to the fiber, rendering it necessary to remove the damaged portion of the fiber and splice the undamaged portions together. Accordingly, techniques for splicing optical fibers have been developed. Several techniques that are currently in use in installation of fiber optic links involve use of special splice units for receiving the ends of the fibers to be spliced and holding those ends in accurately determined alignment. It will be understood that any error in alignment of the ends of the fibers results in potential loss in transmission of optical energy through the splice. The splice units are, therefore, manufactured to high accuracy and they typically include several components. Consequently, such units are expensive. Splice units themselves remain permanently installed on the spliced fiber, and therefore cannot be used in making multiple splices. Several types of splices for optical fibers are described in Fiber Optics Technology and Applications by S. D. Personick, published by Plenum Press. An inexpensive technique for splicing optical fibers is described in U. S. Patent No. 4,594,121, issued June 10, 1986 (Mitch). A method of joining optical fibres in which two fibres are aligned in a groove is described in GB 2 046 466. In accordance with one aspect of the present invention, there is provided a method of splicing end portions of generally cylindrical elongate members by in end-to-end relationship, providing a splice unit having a groove formed in a plastically deformable body with a cover plate over the groove, and characterized by the step of using a deformable body which comprises a layer of deformable material covered by a layer of ductile material relatively harder than the deformable material so as to prevent shaving of the deformable material by the action of the end portions of the elongate members sliding along the groove. The method may be applied to splicing end portions of optic fibers. The groove may be formed by pressing a form corresponding in its external cross-section to the end portions of the elongate members into the body. The groove then is of equal diameter to the members to be secured, and the end portions thereof are aligned closely when placed in the channel. The members to be secured may be held in the groove by adhesive material and a cover plate. In accordance with another aspect of the present invention there is provided a splice unit for splicing end portions of optic fibers in end-to-end relationship, said unit having a groove formed in the surface of a plastically deformable body and a cover plate over the groove, and characterized in that the deformable body comprises a layer of deformable material covered by a layer of ductile material relatively harder than the deformable material so as to prevent shaving of the deformable material by the action of the end portions of the optic fibers sliding along the groove. For a better understanding of the invention, and to show how the same can be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which, FIGS. 1, 2, 3 and 4 are similar views of a component used in splicing two optical fibers together, at successive times during the process of fabricating the splice, FIG. 5 is a perspective view of a splice unit including the component illustrated in FIGS. 1-4, FIG. 6 is a view similar to FIG. 5 with the splice completed. The splice unit illustrated in FIGS. 1-6 comprises a substrate 4 of essentially rigid material, such as glass, quartz, and certain plastics and metals, and a plastically deformable body 8. The body 8 is secured to the substrate 4, and is formed with a groove 12 in its upper surface. The manner in which the groove 12 is formed is illustrated in FIGS. 1, 2, 3 and 4. As shown in FIG. 1, an optic fiber 16 is positioned on top of the body 8 so that it extends along the path to be followed by the fibers that are to be joined by the splice unit. A pressure plate 15 is placed above the optic fiber 16 and pressure is applied thereto, as indicated by arrows 17 in FIG. 2, forcing optic fiber 16 into body 8. When the fiber 16 has been forced into the body 8 to such an extent that the maximum depth of the groove 12 is at least as great as the diameter of the fiber 16, the fiber 16 is removed from the groove, see FIG. 3. The pressure used in forming the groove must be controlled so that the groove is sufficiently deep to receive the fiber yet the portions of the body 8 adjacent the groove are not significantly deformed. Groove 12 is thereby dimensioned to receive optic fibers 24 and 28 (FIG. 6) for splicing, each optic fiber having a diameter equal to that of fiber 16. In FIG. 4, a glass cover plate 20 is secured to body 8 so that it extends over groove 12 but leaves the two opposite ends of groove 12 exposed. The splice unit, as illustrated in FIG. 5, is now ready to receive optic fibers 24 and 28. Turning to FIG. 6, a small quantity of a UV curable index matching fluid is introduced into the groove 12 beneath the cover plate 20, and the optic fibers 24 and 28 are inserted into the groove by way of exposed ends respectively. The quality of the optical coupling between the fibers 24 and 28 is observed by local injection detection (LID) or by introducing light into one of the fibers by way of the end remote from the splice unit and observing the light emitted from that end of the other fiber which is remote from the splice unit, and when the desired degree of coupling is achieved the adhesive is cured by irradiation through the cover plate with ultraviolet light to form a butt joint 30. To relieve strain on butt joint 30, a bonding agent 32 is used to affix fibers 24 and 28 to substrate 4. Before fitting fibers 24 and 28 in the groove 12, fibers 24 and 28 are cleaved in order to provide them with flat end faces which are perpendicular to the central axes of the fibers respectively. The cleaving tends to result in the fiber ends having very sharp edges. If deformable body 8 is a unitary body of soft material, the sharp edges may be capable of cutting into the soft material and forming a shaving as the fibers are advanced towards each other in groove 12. This shaving can prevent the ends of the fiber from being brought into close, optically-coupled relationship. To overcome this problem, body 8 comprises a soft foil 21, such as lead, and a protective layer 19 of relatively harder ductile material laminated upon the upper surface of foil 21. The protective layer 19 must be capable of conforming to the shape of fiber 16 as fiber 16 is forced into body 8 yet hard enough to resist shaving by the cleaved fiber sections. Suitable materials for protective layer 19 include some metals, and organic materials such as mylar, a polyimide such as is sold under the trademark Kapton, or a PTFE such as that sold under the trademark Teflon. In the completed assembly of the splice unit, the index matching material serves not only to displace air from between the confronting end faces of the fiber and thereby reduce discontinuities in refractive index but also to secure the fibers to the deformable body and the cover plate. Also, use of an optic fiber to form the groove insures that the size of the groove formed in the body will conform closely to the size required for accommodating ends of the fibers to be joined. This serves to minimize need for clearance to accommodate variations in the size of the fiber and therefore insures that the fibers can be accurately aligned. It will be appreciated that the present invention is not restricted to the particular methods and devices that have been described with reference to the drawings, and that variations may be made therein without departing from the scope of the invention as defined in the appended claims and equivalents thereof. For example, the invention is not limited to the use of an optical fiber to form the groove in the body, and a wire of suitable size may be used instead. Multiple grooves may be formed in a single deformable body in order to allow splicing of multiple fibers. Nor is the present invention restricted to use of lead as the deformable material. Other suitable materials include clays, putties, and settable organic materials.

Claims: A method of splicing end portions of generally cylindrical elongate members (24, 28) in end-to-end relationship, by providing a splice unit having a groove (12) formed in a plastically deformable body (8) with a cover plate (20) over the groove, and characterized by the step of using a deformable body which comprises a layer of deformable material (21) covered by a layer of ductile material (19) relatively harder than the deformable material so as to prevent shaving of the deformable material by the action of the end portions of the elongate members sliding along the groove. A method according to claim 1 wherein the elongate members are optic fibres. A method as recited in claim 2 further comprising the steps of: bonding the cover to the deformable body prior to placing the end portions of the optic fiber in the groove; and bonding the end portions of the optic fibers together after being placed in the groove. A method as recited in any one of claims 1 to 3 wherein the ductile material is selected from the group consisting of metal and organic materials. A method as recited in claim 4 wherein the organic materials are selected from the group consisting of mylar, a polyimide and PTFE. A method according to any one of the preceding claims including the step of forming the groove (12) by pressing a form corresponding in its external cross-section to the end portions of the elongate members into the body. A splice unit for splicing end portions of optic fibers (24, 28) in end-to-end relationship, said unit having a groove (12) formed in the surface of a plastically deformable body (8), and a cover plate (20) over the groove, and characterized in that the deformable body comprises a layer of deformable material (21) covered by a layer of ductile material (19) relatively harder than the deformable material so as to prevent shaving of the deformable material by the action of the end portions of the optic fibers sliding along the groove. A splice according to claim 7 wherein the ductile material is selected from the group consisting of metal and organic materials. A splice according to claim 8 wherein the organic materials are selected from the group consisting of mylar, a polyimide and PFTE.

Inventors: MITCH JOHN H, MITCH, JOHN H.
Applicants: TEKTRONIX INC, TEKTRONIX, INC.
Application year: 1988
Main classification: G02B6
IPC codes: G02B6, B29C51, B65H69