Apparatus for recoating spliced lengths of coated optical fibers

Abstract: Spliced end portions (30-30) of two optical fibers are recoated in a manner which results in the cross section of the spliced length of fiber transverse to a longitudinal axis thereof being substantially constant. This is accomplished without compromising the adhesion of a curable recoating material (51) to an adjacent original coating material (38). In order to provide such a recoated portion, original coating material which is removed to permit splicing is removed in such a manner as to leave a tapered portion (52) remaining on the end portion of each optical fiber. As a result, the interface between the recoating material and the original coating material is increased sufficiently to avoid having to overlap some of the recoating material with original coating material on adjacent portions of the fibers being spliced. Further, the spliced, recoated end portions are positioned at the focal point of a parabolic reflective surface (75) so that a portion of the radiation which is emitted toward the spliced end portions to cure the recoating material is reflected to engage non-exposed peripheral portions of the recoating material to insure uniformity of cure.

Description: Technical Field This invention relates to an apparatus for recoating end portions of lengths of coated optical fibers as set forth in the preamble of claim 1 Background of the Invention The introduction of optical fiber applications to evermore hostile environments, such as in underwater cable, has required that more stringent requirements be imposed on physical properties of the fiber, such as strength. For these more demanding applications as well as for other less demanding ones, it has become increasingly more common to splice optical fibers which have broken, either accidentally, or during appropriate proof testing. Additionally, extremely long lengths of fiber may be obtained by splicing a plurality of lengths which are obtained using current manufacturing techniques. For these and other applications, splicing in which the coating material is removed from end portions of two fibers which are then fused together end to end provides a suitable means for joining the ends of two glass fibers with an acceptable loss. However, the recoating of bared spliced fiber end portions continues as a problem to be overcome, especially while maintaining stringent requirements on dimensional and strength parameters associated with the coated fiber. A method of recoating spliced end portions of optical fibers is disclosed in U.S. Pat. No. 4,410,561. The method involves placing the spliced fiber end portions from which the original coating material has been removed and adjacent portions within a cavity in the form of a groove in a split mold. The effective diameter of the groove is somewhat greater than that of the remaining coated portion of each fiber. The fibers are positioned so that only portions of the coated portions of the fibers touch the surface which defines the groove, while the vulnerable, uncoated spliced end portions of the fibers remain suspended and do not contact the groove surface. Then, the mold is covered to enclose the groove and a suitable curable coating material is injected into the groove to recoat the bared, spliced fiber end portions. The recoating material contacts the adjacent originally coated portions of the spliced fibers along substantially radial planes exposed when the original coating material was removed from the end portions and along overlapping portions of the outer surface of the original coating material adjacent to the radial planes. The coating material is then cured to yield a recoated splice section with a transverse cross section which is larger than that of the optical fiber having the original coating material thereon. This molding process provides a recoated splice; however, steps must be taken to avoid an undesirable number of residual bubbles in the recoating material. The existence of bubbles may lead to stress concentrations when the fiber is handled subsequently. This is particularly undesirable in underwater cables where splices are inaccessible and under stress for many years. It appears that there are three sources of bubbles. These are air already present in the recoating material, air entrained during the molding process, and bubbles formed during the shrinkage of the recoating material during its cure. The bubbles due to shrinkage tend to be concentrated at the interface between the coating on the unbared fiber portions and the recoating material. This is caused by the pulling away of the recoating material from the coating material on the unbared fiber portions during curing. US-PS 4410561 discloses an apparatus for recoating bared end portions of optical fibers which have been spliced together. This apparatus is adapted to avoid the formation of bubbles in the coating material.Therefore the spliced portions of the fibers are positioned in a groove of a mold base plate and enclosed with a cover. An UV-energy source is used to cure the recoating material encapsulating the bared end portion of optical fibers. As the UV radiation is directed past the recoated spliced end portions it is reflected by means of a plane base plate. The reflected radiation can not be directed to the underside of the recoating material which causes an uneven curing of the recoating material. Seemingly, a recoated splice having the same transverse cross section as that of the unspliced fiber has not been attained by the use of prior art methods and apparatus. The transverse cross section of the recoated portion had to be larger to provide overlap of the recoating material with portions of the original coating material adjacent to the recoated end portions, otherwise the necessary adhesion to the original coating material would not be achieved only along the radial planes exposed by the baring of the end portions. When the recoated portion is made larger in a transverse cross section than that of the original coating material, a portion of the recoating material becomes adhered to peripheral portions of the original coated fiber lengths which are adjacent to the beginning of the recoated end portions of the optical fibers and supplements the adhesion along the radial planes. It is an object of the present invention to provide an apparatus which produces relatively long length of recoated optical fibers having improved strength of splice. Also, the sought after apparatus which are to be used to recoat spliced end portions of optical fibers preferably are such that the formation of bubbles is avoided substantially. Summary of the Invention The foregoing problems of recoated prior art splices have been overcome as set forth in claim 1. In a method of recoating spliced portions of lengths of coated optical fibers, the coating material on end portions of the lengths of each of two coated optical fibers is removed to leave a bared portion and a portion on which the coating material is conically shaped. The prepared end portions which have been spliced together are positioned in a passageway of a fixture with original coated portions of the lengths adjacent to the end portions being held in opposed vacuum chucks at opposite ends of the fixture. An injection port communicates a supply of a curable recoating material with the passageway. The passageway is formed in a mold block of material which is transparent to radiation used to cure the recoating material. The mold block of material is supported on a metallic pedestal. Along an upper surface of the pedestal is provided a trough which is in alignment with the passageway and spaced therefrom and which includes a polished reflective surface. The apparatus of this invention ensure that the recoating material which covers the spliced portions of the lengths of coated optical fibers are cured uniformly. After a curable recoating material has been injected through the port into the passageway and caused to encapsulate the bared and tapered portions of the end portions, it is cured by exposing it to suitable radiation. The trough in the metallic pedestal has a transverse cross section which is parabolic. Advantageously, the passageway is positioned at the focal point of the parabolic cross section of the trough so that radiation extending past the coated optical fiber is reflected by the wall of the trough and caused to engage the peripheral portion of the coated optical fiber which is not exposed directly to the radiation. As a result, the entire periphery of the recoated optical fiber portions in the passageway is cured uniformly. Brief Description of the Drawing FIG. 1 is a perspective view of an apparatus for recoating spliced end portions of two lengths of optical fibers; FIG. 2 is a perspective view of a fixture of the apparatus of FIG. 1 which may be used to support spliced end portions of lengths of optical fibers for recoating in accordance with this invention; FIG. 3 is a perspective view of a prior art fixture for supporting spliced end portions of optical fibers to be recoated; FIG. 4 is a perspective view of spliced end portions of two lengths of optical fibers which have been prepared in accordance with this invention to receive a recoating material. Detailed Description Referring now to FIG. 1 there is shown an apparatus designated generally by the numeral 60 for recoating the spliced together ends of the lengths of coated optical fibers 32-33. The coated optical fibers 32-33 are well known and each includes an optical fiber 36 having a coating material 38 applied thereon (see FIG. 4). As is well known, the optical fiber 36 includes a core and a cladding. An outer diameter of the coated optical fiber is on the order of 250 microns. The bared end portions 30-30 from which the coating material 38 has been removed at least partially have been spliced together by a technique such as fusion bonding which is disclosed in an article entitled "Optical Fiber Joining Technique" which was authored by D. L. Bisbee and which appeared beginning at page 3153 of Vol. 50 No. 10 of the December 1971 issue of the Bell System Technical Journal. Each end portion 30 has a length of about 1,27 cm (0,5 inch). The spliced end portions 30-30 are recoated in accordance with the apparatus of this invention. The apparatus 60 includes a base 62 which includes two ways 64 and 66 spaced along a longitudinal axis of the base. Mounted in each of the ways 64 and 66 is a vacuum chuck 68. Each chuck 68 includes a groove 71 which extends generally parallel to the longitudinal axis of the base. Each of the grooves 71-71 has a transverse cross section such that it is capable of holding a length of coated optical fiber. Further, the wall of each of the grooves 71-71 is connected to a source of vacuum (not shown) to hold a coated optical fiber in the groove during the recoating process. As further can be seen in FIG. 1 (see also FIG. 2), a center portion 73 of the base 60 is raised somewhat over adjacent portions. The center portion 73 includes a longitudinally extending trough 75 which in transverse cross section has a parabolic configuration. This trough 75 is referred to as a reflective chamber and typically is milled in a base which is made of aluminium. The surface of the trough 75 is polished. Supported on the center portion 73 is a mold block 80 (see FIGS. 1 and 2). The mold block 80 includes a longitudinal extending groove 82 which is adapted to hold the spliced end portions of two lengths of coatedoptical fibers. Projecting upwardly from two corners of the mold block 80 are two alignment pins 84-84. The alignment pins 84-84 are used to align a top mold block 90 with the mold block 80. The mold blocks are made from a material which is transparent to ultraviolet (UV) radiation such as Plexiglas UV transparent material or equivalent resin material or quartz, for example. The top mold block 90 also includes a longitudinally extending groove 92 which is adapted to cooperate with the groove 82 in the mold block 80 to provide a passageway 93 to enclose the spliced end portions of the two lengths of coated optical fibers. Further, the top mold block 90 is secured to the mold block 80 to provide a close fitting groove for those end portions by four bolts 94-94, or other suitable clamping means. When the top mold block 90 is secured to the bottom mold block 80, passageway 93 communicates with an injection nozzle 96 (see FIG. 1). The injection nozzle 96 is connected to a supply of recoating material which preferably is the same material which was used to coat the drawn fiber. Such a material may be a UV curable acrylate material, for example. Portions of the spliced lengths 32 and 33 of the coated optical fibers adjacent to the end portions 30-30 are caused to be received in the grooves 71-71 in the chucks 68-68. Vacuum is applied to hold those portions during the recoating step. With the portions of the lengths of coated optical fibers held in the vacuum chucks 68-68, the lengths of the coated optical fiber which are spliced together are disposed in the passageway 93 formed by the cooperating grooves in the top mold block 90 and the mold block 80. Also, it should be observed that the passageway 93 formed by the grooves in the top mold 90 and in the mold 80 is aligned with the reflective chamber 75. The spatial relationship of the passageway 93 and the reflective chamber 75 is such that the passageway is disposed at the focal point of the parabolic configuration of the reflective chamber. As a result of this arrangement, the curing of the recoating material by exposure to UV radiation from a source (not shown) is enhanced substantially. This will become apparent by comparing FIGS. 2 and 3. In FIG. 3, there is depicted a prior art apparatus 100 for curing the recoating applied over spliced end portions. As the UV radiation is directed past the spliced end portions, it engages a metallic base plate 99 and is reflected. It is unlikely that the reflected radiation will be directed to the underside of the recoating material. Hence, the recoating material may not be cured uniformly. On the other hand, the arrangement of this invention which is shown in FIG. 2 assures substantially uniformity of cure in the recoating material. The UV energy radiating past the optical fiber end portions 30-30 and contacting the parabolic surface is reflected. Because the recoated portions are disposed at the focal point of the parabolic reflecting surface, the reflected radiation contacts those portions of the periphery- of the recoating material which are not exposed directly to the emitted radiation, thereby ensuring the uniformity of cure. The resulting product is a relatively long length of recoated optical fiber which has a substantially constant cross section transverse to the longitudinal axis of the optical fiber as well as an improved strength of the spliced portions. The recoating technique of this invention also helps to avoid the occurrence of bubbles adjacent to the interface. Bubbles tend to become entrapped at the interface between the original coating material and the recoating material. Also, when the recoating material is applied, it contracts and tends to pull bubbles outwardly from the original coating material into the interface. The existence of bubbles is unwanted, particularly at the interface, because of possible adverse affects on the adhesion level across the interface. It has been found that because of the lengthened interface provided by the apparatus of this invention, any bubbles tend to be moved outwardly toward the outer surface of the coated optical fiber and are not residual in the recoated splice portions.

Claims: An apparatus for recoating end portions (30) of lengths of coated optical fiber (32, 33) which have been spliced together, said apparatus including: chuck means (68) for holding portions (30) of lengths of fibers (32, 33) adjacent to the end portions thereof which are spliced together; mold means (80, 90) providing a passageway (93) in which are received the end portions (30) which are spliced together; injection means (96) for introducing a curable recoating material into said passageway (93) to recoat the end portions (30) ; radiation means for emitting energy toward engagement with the recoated portions of the optical fibers to cure the recoating material; and reflective means (75) for reflecting energy directed past the recoated end portions (30), characterized in that said reflective means (75) comprise a parabolically curved surface which is effective to cause the reflected radiant energy to engage portions of the recoated end portions (30) not directly engaged by energy from said radiation means, wherein said curved surface is in alignment with the passageway (93) and spaced therefrom. The apparatus according to claim 1, wherein said passageway (93) and said parabolically curved surface are positioned relative to each other such that the passageway (93) is disposed at the focal point of the parabolically curved surface. The apparatus according to claims 1 or 2, wherein said mold means comprising a first mold block (80) and a second mold block (90) aligned to each other, each mold block (80, 90) including a longitudinally extending groove (82; 92) forming said passageway (93). The apparatus according to anyone of claims 1-3, wherein said mold means (80, 90) are transparent to ultraviolet radiation and said recoating material is an UV curable material. The apparatus according to anyone of claims 1-4, wherein said mold means (80, 90) further receive portions of the optical fibers (32, 33) between those portions held in said chuck means (68) and the end portions (30). The apparatus according to anyone of claims 1-5, wherein said chuck means (68) are a vacuum chuck means.

Inventors: DARSEY RALPH JOEL, HURD WILLIAM JOSEPH, DARSEY, RALPH JOEL, HURD, WILLIAM JOSEPH
Applicants: AT & T CORP, AT&T CORP.
Application year: 1988
Main classification: G02B6
IPC codes: G02B6