Array splice for ribbon-like multi-core optical fibers

Abstract: An array splice for ribbon-like multi-core optical fibers (4) comprises capillary tubes (8) of ultraviolet-transmitting glass each having an inner diameter slightly larger than the outer diameter of the clad (2) of an optical fiber. Each glass capillary tube (8) includes tapered portions (11) on the opposite ends thereof for insertion of optical fiber bodies, and a groove (7) formed in the middle upper surface region thereof for discharging bubbles and adhesive agent. A base (12) includes recesses (13) formed in the middle upper surface region thereof for receiving and supporting the lower portions of the tube walls of the glass capillary tubes (8), and a plurality of front-edged separators (14) each disposed at the opposite ends of the associated receiving and supporting recess. The separators (14) are disposed with approximately the same pitch as that for the capillary tubes (8). Defined between adjacent separators (14) are optical fiber insertion paths (15) having a width which increases with incresing distance from the opposite ends of each capillary tube.

Description: The present invention relates to a multifiber splice for optical fiber ribbons and particularly to a multifiber splice which uses an ultraviolet-curing adhesive agent. Splices for optical fibers having such features as low loss, long distance transmission, large-capacity transmission, no electromagnetic induction, small diameter, and explosion-proof property are used in large-capacity basic trunk lines for long distance including submarine cables, local inter-office trunk lines, inter-office and subscriber's transmission systems, power systems for communications only, monitor control circuits for railways and superhighways, and computer networks. An optical fiber 4, as shown in Fig. 6, has a construction in which a glass core 1 having a diameter of about 10 µm or about 50 µm and a glass cladding 2 having an outer diamter of about 125 µm and concentrically surrounding said core are covered with a silica glass jacket member 3 having an outer diameter of about 250 µm or about 900 µm, the refractive index of the core 1 being somewhat higher than that of the cladding 2 so as to provide a total reflection type optical path which prevents light from leaking through the core. This optical fiber can be left alone or integrated with a plurality of other identical optical fibers in an optical fiber ribbon. In connecting optical fibers 4 together, the axes of the cores are aligned with each other to minimize connection loss and in this condition the optical fibers are positioned and fixed on a splice and use is made of such bonding medium as an ultraviolet-curing adhesive agent. In the case of an optical fiber ribbon, a base 6 having a plurality of parallel V-shaped grooves 5 is used as a splice (see Fig. 7). In the case where the aforesaid base 6 having V-shaped grooves 5 is used, in order to decrease connection loss it is necessary that the optical fibers 4 be positioned and fixed on the base 6 so that the claddings of the optical fibers 4 having their jacket members 3 stripped are closely contacted with the bottoms of said V-shaped grooves 5. However, to correctly position and fix the individual optical fibers 4 in the V-shaped grooves 5, it is necessary to adjust the relative position of engagement between the individual optical fibers 4 and the V-shaped grooves 5 to ensure a uniform push-in pressure over the entire length of the optical fibers 4. However, since the optical fibers 4 have a small diameter, the positioning and fixing often tend to be unstable and the butted front ends of the optical fibers often tend to escape from the bottoms of the V-shaped grooves 5 to a space on the opposite side; thus, minimization of connection loss of optical fibers has been greatly limited. For the purpose of solving the aforesaid problem, the applicant of the present invention previously proposed, in European Patent Application No 0 381 766 (which constitutes a document pursuant to Article 54(3) EPc), the use of a glass capillary tube 8, with an adhesive agent discharging slot 7 formed in the lengthwise middle portion thereof, as a positioning and fixing jig or connecting member for optical fibers (see Figs. 8 and 9). The use of this capillary tube type splice makes it possible to secure the positioning and fixing conditions which substantially prevent occurrence of connection loss between two optical fibers 4. In the case of an optical fiber ribbon as shown in Fig. 10, however, smooth insertion of the optical fibers 4 has been very difficult since the diameter of the optical fiber insertion ports of the glass capillary tubes is small. According to the present invention, there is provided a multifiber splice for permanently connecting optical fiber ribbons, said multi-fiber splice comprising: a plurality of capillary tubes of ultraviolet transmitting glass extending adjacent to one another, each of said capillary tubes being capable of being filled with an ultraviolet curable adhesive agent, having an inner diameter slightly larger than the outer diameter of the optical cladding of the optical fibers of the ribbons to be permanently connected, and including a tapered portion at the opposite ends thereof and a transverse slot provided in a central portion of the wall thereof for discharging bubbles and some of the UV-curable adhesive agent to be contained in the tube; and an elongate base provided with an elongate recess in the central region thereof, each of said glass capillary tubes being longitudinally received and secured in said elongate recess by the side of its wall opposite to that provided with said transverse slot, said elongate base further including a plurality of wedge-shaped separators disposed at each end of said elongate recess with approximatively the same pitch as that of the capillary tubes, each of said wedge-shaped separators extending longitudinally from the ends of adjacent sides of two adjacent capillary tubes, whereby adjacent separators define optical fiber insertion paths therebetween, which have a width which increases with increasing distance from the ends of each capillary tube. In a preferred multifiber splice for an optical fiber ribbon, said elongate base has a H-shaped tranverse cross-section, with a groove transversly formed in the central portion of the two arms of the H which protrude from the side of the base having the elongate recess, said transverse groove serving as a guide for guiding a pressing jig against said glass capillary tubes when they are to be secured into said recess. When the cores and claddings of the optical fibers of an optical fiber ribbon are to be inserted into the glass capillary tubes, the lower portions of the glass capillary tubes are supported in the receiving and supporting recesses formed in the base. Therefore, the optical fibers to be connected smoothly slide into the tapered portions formed on the opposite ends of each associated glass capillary tubes through the insertion paths separated by the wedge-shaped separators and having a width gradually decreasing in the direction of advance of the optical fibers. Further, the formation of the cross section of the base in H shape prevents the warping or deformation of said base during formation of said base and ensures that when a transverse slot for discharging bubbles and adhesive agent is formed in the middle upper surface region of each of the glass capillary tubes adhesively fixed on the base, the depth of such slots is within a predetermined allowance. After the optical fibers have been inserted into the glass capillary tubes, the optical fibers, now positioned end to end, are joined together by an ultraviolet-curing adhesive agent. In this case, a pressing jig descends along the groove formed in the middle of the base to hold down the glass capillary tubes. Thereby, the floating of the glass capillary.tubes due to the ultraviolet-curing adhesive agent flowing out of said transeverse slot is prevented and the optical fibers are simultaneously connected together in concentric end-to-end relation. Fig. 1 is a plan view showing a multifiber splice according to an embodiment of the present invention; Fig. 2 is a front view partly in section; Fig. 3 is an enlarged plan view of the principal portion of the splice of the present invention; Fig. 4 is an enlarged front view; Fig. 5 is an enlarged side view. Fig. 6 is a perspective view of the principal portion of an optical fiber; Fig. 7 is a perspective view of a conventional array splice; Fig. 8 is a top view of a glass capillary tube; Fig. 9 is a longitudinal sectional view thereof; and Fig. 10 is a perspective view of the principal portion of an optical fiber ribbon. In the following description, the same structural parts as those found in Figs. 6 through 10 employed for explaining the prior art are denoted by the same reference numerals, and repetitive explanation will be omitted. An optical fiber ribbon 10 comprises four quartz glass optical fibers 4 having a diameter of 125 µm and a jacket member in which said fibers 4 are gathered together for integration in ribbon form. The cores 1 and claddings 2 which are to be connected are inserted into glass capillary tubes 8 after the portion of the jacket member covering them has been stripped. The capillary tubes 8 are made from an ultraviolet-transmitting glass material, for example, borosilicate glass, and in the case where the clads 2 of the optical fiber ribbons 10 have a diameter of 125 µm, the capillary tubes 8 have a slightly larger inner diameter, for example, of 126 µm. By immersing the respective opposite ends of the capillary tubes in a glass-etching solution for a predetermined time, tapered portions 11 for introducing optical fibers 4 are formed. Further, a transverse slot 7 for discharging bubbles and adhesive agent is formed in the middle upper surface region of each capillary tube 8 by using a cutter or drill. Before the glass capillary tubes 8 are fixed to an elongate base 12 to be later described, they are filled with an ultraviolet-curing adhesive agent whose refractive index matches with that of the cores 1 of the optical fibers 4 or a matching gel whose refractive index matches with that of the optical fibers. To prevent said ultraviolet-curing adhesive agent from curing prior to insertion of the optical fibers 4, the glass capillary tubes 8 filled with said ultraviolet-curing adhesive agent are wrapped with a light-tight packaging material and kept in the wrapped state until the optical fibers 4 are to be inserted. On the other hand, the base 12 is made from a material having a low linear expansion coefficient, such as silicone, ceramic or plastic material, to prevent warping or deformation during formation, and is in the form of an elongate plate member of H-shaped transverse cross section. It is formed in the middle upper surface region thereof with an elongate recess 13 for receiving and supporting the lower portions of the tube walls of said glass capillary tubes 8, while a plurality of wedge-shaped separators 14 having ends 14a and arranged with substantially the same predetermined pitch as that for the glass capillary tubes extend upward from and are fixed to the respective opposite ends of said receiving and supporting recess 13. The distance between two adjacent separators 14 is determined on the basis of the outer diameter of the cladding 2 of the optical fibers 4. In this connection, to facilitate insertion of the optical fibers 4 into the glass capillary tubes 8, the width of insertion paths 15 for optical fibers 4 defined between said wedge-shaped separators 14 is gradually increased as the distances from the respective opposite ends of the glass capillary tubes 8 increase. To prevent the optical fibers 4 from going out above said insertion paths 15 when they are inserted along the front-edged separators 14, the top surfaces 14b of the separators 14 are located above the level of the upper surfaces 8a of the glass capillary tubes 8 fixed on the base 12 (see Fig. 4). On the other hand, the middle region of the upper surface of the base 12 is provided with a transverse groove 16. This groove 16 functions as a guide for guiding a pressing jig (not shown) when the glass tubes 8 are fitted in the recess 13 formed in the upper surface of the base 12 and adhesively fixed therein. The floating of the glass capillary tubes 8 due to the adhesive agent is prevented by pressing the pressing jig; thus, the plurality of glass capillary tubes 8 are simultaneously positioned and fixed in place. The middle region of the upper surface of each glass capillary tube 8 is formed with a transverse slot 7 for discharging part of ultraviolet-curing adhesive agent and air bubbles contained therein. Such slots 7 may be formed either at the time when the glass tubes are drawn before the glass capillary tubes 8 are fixed in the receiving and supporting recess 13 formed in the base 12 or at the time when the adhesive fixing of the capillary tubes in the recess 13 has been completed. It is preferable that the depth of the slots 7 be not more than 1/2 of the inner diameter of the glass capillary tubes 8 in order to prevent the optical fibers 4 from escaping and to facilitate coaxial connection of the cores 1. Further, it is also desirable that the depth of said recess 13 be equal to or greater than the wall thickness of the glass capillary tubes in order to ensure smooth insertion of the optical fibers 4 into the glass capillary tubes 8. The angle of inclination of the insertion paths 15 is selected according to the depth of the recess 13. To ensure smooth advance of the front portions of the optical fibers 4 along the bottom surfaces of the insertion paths 15, the insertion paths 15 extending from the end of the base 12 toward the ends of the glass capillary tubes 8 are made in the form of somewhat upwardly sloping guide surfaces, having no sudden change in level, for the optical fibers 4. A description will now be given of the way the device of the present invention is used. As many glass capillary tubes 8 as there are optical fibers 4 which constitute an optical fiber ribbon 10 are prepared, and a suitable amount of ultraviolet-curing adhesive agent is injected into each glass capillary tube 8 by utilizing such injection means as a syringe. When optical fiber ribbons 10 are to be connected, the light-tight packaging material is removed. A suitable amount of adhesive agent (not shown) is applied to the outer peripheral surface of each glass capillary tube 8, whereupon the glass capillary tubes are orderly fitted in the receiving and supporting recess 13 formed in the middle region of the upper surface of the base 12. Subsequently, an unillustrated pressing jig is lowered with in the groove 16 serving as a guide until its lower surface depresses the upper surfaces of the glass capillary tubes 8, thereby positioning and fixing the glass capillary tubes 8 in the recess 13 with a predetermined pitch. Thereafter, the optical fibers 4 of the optical fiber ribbons 10 are inserted into the respective opposite ends of the glass capillary tubes 8 each having the transverse slot 7 for discharging the adhesive agent and air bubbles. In this state, ultraviolet rays are radiated from above the glass capillary tubes 8. The insertion of the optical fibers 4 causes the excessive ultraviolet-curihg adhesive agent to be discharged together with the air bubbles through the transverse slots 7, while the ultraviolet-curing adhesive agent remaining in the glass capillary tubes 8 is cured by irradiation with ultraviolet rays, whereby the optical fibers 4 are concentrically permanently connected end to end within the respective glass capillary tubes 8. According to the present invention, the individual optical fibers which constitute optical fiber ribbons are smoothly inserted into the glass capillary tubes 8 by using the wedge-shaped separators 14. As a result, an increase in connection loss due to off-centered connection which has been a problem in the prior art is effectively avoided. With the multifiber splice of the present invention used, the cores and claddings of optical fibers are connected with a connection loss of about 0.2 dB, so that even in a limited environment as in explosion-proof and narrow places, conditions for high precision permanent connection can be secured quickly and easily.

Claims: A multifiber splice for permanently connecting optical fiber ribbons (10), said multi-fiber splice comprising: a plurality of capillary tubes (8) of ultraviolet transmitting glass extending adjacent to one another, each of said capillary tubes being capable of being filled with an ultraviolet curable adhesive agent, having an inner diameter slightly larger than the outer diameter of the optical cladding (2) of the optical fibers (4) of the ribbons (10) to be permanently connected, and including a tapered portion (11) at the opposite ends thereof and a transverse slot (7) provided in a central portion of the wall thereof for discharging bubbles and some of the UV-curable adhesive agent to be contained in the tube; and an elongate base (12) provided with an elongate recess (13) in the central region thereof, each of said glass capillary tubes (8) being longitudinally received and secured in said elongate recess by the side of its wall opposite to that provided with said transverse slot (7), said elongate base further including a plurality of wedge-shaped separators (14) disposed at each end of said elongate recess with approximatively the same pitch as that of the capillary tubes, each of said wedge-shaped separators (14) extending longitudinally from the ends of adjacent sides of two adjacent capillary tubes, whereby adjacent separators define optical fiber insertion paths (15) therebetween, which have a width which increases with increasing distance from the ends of each capillary tube. A multifiber splice as set forth in claim 1, characterized in that said elongate base (12) has a H-shaped tranverse cross-section, with a groove (16) transversly formed in the central portion of the two arms of the H which protrude from the side of the base having the elongate recess (13), said transverse groove (16) serving as a guide for guiding a pressing jig against said glass capillary tubes when they are to be secured into said recess.

Inventors: FUJIKAWA JUNJI, TAMURA FUMIAKI, FUJIKAWA, JUNJI, TAMURA, FUMIAKI
Applicants: NIPPON ELECTRIC GLASS CO, NIPPON ELECTRIC GLASS COMPANY, LIMITED
Application year: 1990
Main classification: G02B6
IPC codes: G02B6