Optical connector and a method for assembling the same

Abstract: An optical connector comprising an optical fiber cable including a plastic-coated fiber (1), a tension member (2) thereon, and a sheath (3) covering the plastic-coated fiber (1) and the tension member (2), a ferrule (9) provided at the distal end of the optical fiber cable so as to be attached to the distal end of the plastic-coated fiber (1), and a holder (11) having a distal end restricted in position by the ferrule (9) when mounted on the plastic-coated fiber (1). The optical connector is constructed so that the holder (11) is mounted on the plastic-coated fiber (1) after attachment of the ferrule (9) to the distal end of the fiber (2). A method for assembling such an optical connector comprises forming the holder (11) of a split body and mounting the holder (11) on the plastic-coated fiber (1) after the ferrule (9) is mounted on the distal end of the fiber (1) and after a spring (8) is fitted at the rear of the ferrule (9).

Description: The present invention relates to an optical connector for optically connecting single-core optical fibers and a method for assembling the same. As shown in Fig. 16, an optical fiber cable includes a nylon-coated fiber 1 formed of an optical fiber 1a and a coating 1b of nylon or the like thereon, a tension member 2 formed of aramid fibers or the like arranged around the fiber 1, and a sheath 3 of polyvinyl chloride (PVC) or the like covering the fiber 1 and the tension member 2. An optical connector for optically connecting the nylon-coated fibers 1 is attached to an end of each fiber 1. This optical connector is assembled by putting a plurality of components together. In doing this, a rubber boot 4, ring 5, gripper 6, holder 7, and urging spring 8 are previously fitted onto the optical fiber cable in the order named, as shown in Fig. 17. Subsequently, the sheath 3 at the distal end portion of the optical fiber cable is removed, and a ferrule 9 is attached to the exposed distal end of the nylon-coated fiber 1. Then, the components 4 to 8 are successively moved forward or toward the ferrule 9 and fixed to one another. Thereafter, a plug frame 10 is fitted on these components, whereupon the optical connector is assembled. Conventionally, this assembling work is a manual one. In assembling the optical connector in this manner, the gripper 6 is gripped so that the tension member 2 is held between the gripper 6 and the holder 7, and at the same time, the distal end of the sheath 3 is held between the ring 5 and the gripper 6, as shown in Fig. 18. By doing this, the tensile strength of the connector mounting portion of the optical fiber cable is ensured. If the gripper 6 and the holder 7 are moved forward during the aforesaid assembly of the optical connector, however, the tension member 2 and the sheath 3 will be caught between the nylon-coated fiber 1 and the holder 7 and between the fiber 1 and the gripper 6, respectively, as shown in Fig. 19. In assembling the optical connector, therefore, the tension member 2 and the sheath 3 should be drawn out of the holder 7 and the gripper 6, respectively, before the gripper 6 is gripped. Since the sheath 3 has a wall thickness greater than that of the tension member 2, however, it cannot be easily drawn out of the gripper 6, and requires a very complicated drawing operation. Thus, the assembling work for the optical connector is troublesome, so that the productivity is low. The present invention has been contrived in consideration of these circumstances, and its object is to provide an optical connector capable of being assembled quickly and easily. In order to achieve the above object, an optical connector according to the present invention comprises an optical fiber cable including a plastic-coated fiber, a tension member layer thereon, and an outer sheath covering the plastic-coated fiber and the tension member layer; a ferrule fixed onto the distal end of the optical fiber cable that is attached to the distal end of the plastic-coated fiber; and a tubular holder mounted on the plastic-coated fiber, said tubular holder having a distal end positioned behind said ferrule and restricted in its forward movement by the ferrule; said tension member layer being held on the rear outer surface of the tubular holder by a tubular gripping member; characterized in that said tubular holder is formed with a slit extending parallel to the axis of the plastic-coated fiber or is in the form of a two-part, longitudinally split body, whereby, during assembly, the holder may be mounted on the plastic-coated fiber after attachment of the ferrule to the plastic-coated fiber. the gripper is formed of a split body mounted on the fiber after attachment of the ferrule. Preferably, furthermore, the optical connector further comprises an urging spring fitted on the plastic-coated fiber so as to be interposed between the ferrule and the holder and adapted to urge the ferrule forward, the urging spring being formed of a shape memory alloy wire and fitted on the plastic-coated fiber after attachment of the ferrule. A method according to the present invention is also provided for assembling an optical connector which comprises an optical fiber cable including a plastic-coated fiber, a tension member layer thereon, and an outer sheath covering the plastic-coated fiber and the tension member layer, a ferrule fixed onto the distal end of the optical fiber cable and, in particular, attached to the distal end of the plastic-coated fiber, a tubular holder mounted on the plastic-coated fiber, said tubular holder having a distal end positioned behind said ferrule and restricted in its forward movement by the ferrule, said tension member layer being held on the rear outer surface of tubular holder by a tubular gripping member, a spring encompassing the plastic-coated fiber interposed between the ferrule and the holder so as to urge the ferrule forwards, the assembling method being characterized by using a tubular holder which is formed with a slit extending parallel to the axis of the plastic-coated fiber, or is in the form of a two-part, longitudinally split body and mounting the holder on the plastic-coated fiber after the ferrule is mounted on the distal end of the fiber and after the spring is fitted at the rear of the ferrule. Preferably, the gripper is formed of a split body such that the gripper is mounted on the rear portion of the holder after attachment of the ferrule, spring and holder, whereby the distal end of the tension member is held between the gripper and the holder. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a front sectional view of an optical connector according to a first embodiment of the present invention; Fig. 2 is a perspective view of a holder used in the optical connector of Fig. 1; Fig. 3 is a front view for illustrating a method for assembling the optical connector shown in Fig. 1, in which a gripper and a spring are fitted on an optical fiber cable whose nylon-coated fiber is exposed; Fig. 4 is a front view showing a ferrule attached to the nylon-coated fiber of the optical fiber cable; Fig. 5 is a front view showing the way the holder is mounted on the optical fiber cable; Fig. 6 is a front view showing a state in which the holder of Fig. 5 is mounted in position; Fig. 7 is a front view showing a state in which the gripper is fitted on the holder; Fig. 8 is a front view of an optical connector according to a second embodiment of the present invention; Fig. 9 is a front view for illustrating a method for assembling the optical connector shown in Fig. 8, in which a ferrule is attached to the distal end of a nylon-coated fiber; Fig. 10 is a front view showing a state in which an urging spring is fitted on that portion of the nylon-coated fiber near the ferrule of Fig. 9; Fig. 11 is a front view showing a state in which a shape memory alloy wire to be formed into the urging spring is disposed beside that portion of the nylon-coated fiber near the ferrule of Fig. 9; Fig. 12 is a front view showing the way of mounting a holder; Fig. 13 is a front view showing the way of mounting a gripper; Fig. 14 is a front view showing the way of mounting a C-ring; Fig. 15 is a front view showing the way of mounting a heat-shrinkable tube; Fig. 16 is a front view of an optical fiber cable used in a conventional optical connector; Fig. 17 is an exploded front view of the conventional optical connector; Fig. 18 is a front sectional view showing a state in which a tension member and a sheath are held by means of a holder and a gripper; and Fig. 19 is a front sectional view showing a state in which the tension member and the sheath are caught in the holder and the gripper, respectively. DETAILED DESCRIPTION Preferred embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings. In the description of the individual embodiments to follow, like or same components as are used in the conventional optical connector mentioned before are designated by like reference numerals for simplicity. A first embodiment of the present invention will now be described in detail with reference to the drawings of Figs. 1 to 7. As shown in Fig. 1, an optical connector according to the first embodiment comprises a fiber 1 coated with nylon or other plastics and a ferrule 9 attached to the distal end thereof. A holder 11 is mounted so that a spring 8 is interposed between the holder 11 and the ferrule 9. The holder 11, whose distal end position is restricted by the ferrule 9, is a cylindrical metal member having a longitudinal slit 11a, as shown in Fig. 2. The holder 11 includes a large-diameter portion 11b on the front or ferrule side, a knurled nipping portion 11c having a crosshatch pattern on its surface, a tapered slope portion 11d, and a small-diameter portion 11e whose inside diameter is a little greater than the diameter of an optical fiber cable. The slit 11a has a width such that the nylon-coated fiber 1 can be passed through it. A gripper 12 is fitted on the holder 11 so as to cover the nipping portion 11c and the small-diameter portion 11e at the rear portion of the holder 11. Thus, a tension member 2 of the optical fiber cable and the distal end of a sheath 3 are held between the two members 11 and 12. A rubber boot 13 is fitted on the rear portion of the holder 11 so as to cover the gripper 12 and the optical fiber cable extending therefrom, thereby protecting the rear side of the optical connector. A plug frame (not shown) is fitted on the circumference of the front portion of the holder 11 which is not covered by the rubber boot 13. The following is a description of a method for assembling the optical connector constructed in this manner. First, the rubber boot (not shown), the gripper 12, and the spring 8 are previously fitted on the optical fiber cable, and a predetermined length of the sheath 3 at the distal end of the cable is removed to expose the distal end of the nylon-coated fiber 1 in advance, as shown in Fig. 3. Then, the ferrule 9 is attached to the distal end of the exposed nylon-coated fiber 1, as shown in Fig. 4. Subsequently, the spring 8 on the optical fiber cable is moved to the side of the ferrule 9, the sheath 3 at the distal end of the cable is cut into two branches, and the tension member 2 and the sheath 3 are moved rearward. Thereafter, the nylon-coated fiber 1 is passed through the slit 11a, and the holder 11 is mounted on the fiber 1, as shown in Fig. 6. Then, the gripper 12 previously mounted on the optical fiber cable is moved toward the ferrule 9, and is fitted onto the rear portion of the holder 11, as shown in Fig. 7. Then, the gripper 12 is gripped so that the tension member 2 and the distal end of the sheath 3 are held between the nipping portion 11c and the small-diameter portion 11e of the holder 11 and the gripper 12. Since the nipping portion 11c of the holder 11 is knurled and has a crosshatch pattern on its surface, it enjoys increased friction with the tension member 2, so that the gripper 12 can hold the member 2 with a great nipping force. Thereafter, the rubber boot is moved toward the ferrule 9 to cover the rear portion of the holder 11 and the gripper 12, and the plug frame (not shown) is fitted onto the front portion of the holder 11, whereupon assembling the optical connector is completed. In the optical connector assembled in this manner, the holder is formed with the slit, so that it can be mounted on the nylon-coated fiber by after-attachment without catching the tension member or the sheath therein. Thus, the optical connector can be mechanically assembled with ease in an automatic line, so that its productivity can be improved. Although the holder is made of metal in the embodiment described above, it may alternatively be formed of synthetic resin. When using a plastic holder, the tension member 2 and the sheath 3 are fixed between the holder and the gripper by means of an adhesive agent. In this case, moreover, the gripper may be formed with a slit, so that the assembling efficiency for the optical connector can be further improved. A second embodiment of the present invention will now be described in detail with reference to the drawings of Figs. 8 to 15. In an optical connector according to the present embodiment, as shown in Fig. 8, a holder 15 formed of half pieces 15a and 15b is mounted on the rear portion of a ferrule 9, which is attached to the distal end of a nylon-coated fiber, so that an urging spring (not shown) is interposed between the holder 15 and the ferrule 9. A gripper 16 formed of half pieces 16a and 16b is mounted on the rear portion of the holder 15 so that a tension member (not shown) is held between them. The half pieces 15a and 15b or 16a and 16b are divisions obtained by halving the holder 15 or the gripper 16 along a plane which passes through the axis of the members 15 or 16. In the optical connector, moreover, a sheath 3 is nipped by means of a C-ring 17 which is mounted on the rear portion of the gripper 16, and the ring 17 and the nipped portion of the sheath 3 are covered by means of a heat-shrinkable tube 18. The optical connector constructed in this manner is assembled by the following method. First, in a first process, a predetermined length of the sheath 3 at the distal end of the optical fiber cable is removed to expose the nylon-coated fiber 1 and the tension member 2, and the ferrule 9 is fixed to the distal end of the fiber 1, as shown in Fig. 9. Then, in a second process, the urging spring 19 is fitted on that portion of the nylon-coated fiber 1 near the ferrule 9, as shown in Fig. 10. The spring 19 is formed of a Ti-Ni-based shape memory alloy wire, which is previously stored with the shape of the spring 19. In fitting the urging spring 19 on the nylon-coated fiber 1, the shape memory alloy wire W M having a straight shape is located beside the fiber 1 and heat-treated. By doing this, the wire W M is transformed into the previously stored spring shape, and is fitted on the fiber 1. Alternatively, the shape memory alloy wire, stored with the shape of the urging spring 19, may be previously shaped like a coil having a diameter greater than that of the ferrule 9 so that it can be fitted on the nylon-coated fiber 1 from the outside. In this case, the coiled shape memory wire is transformed into the urging spring 19 having a previously stored predetermined diameter by being heat-treated. In a third process, the holder 15 formed of the pair of half pieces 15a and 15b is mounted on the rear portion of the ferrule 9 so that the urging spring 19 is interposed between them, as shown in Fig. 12. The holder 15 is halved with respect to its axial direction so that it can be fitted from the outside. In mounting the half pieces 15a and 15b, the distal end of the sheath 3 is cut into two branches, and the tension member 2 and the sheath 3 are bent rearward lest they be caught in the holder 15, as shown in Fig. 12. In this state, the pieces 15a and 15b are mounted from the outside, and are fixedly bonded to each other by means of an adhesive agent. Then, in a fourth process, the gripper 16 is mounted on the rear portion of the holder 15, as shown in Fig. 13. The gripper 16, like the holder 15, is formed of the half pieces 16a and 16b which are divided from each other with respect to the axial direction, as shown in Fig. 13. In mounting the gripper 16, the tension member 2 is moved forward along the holder 15, and the half pieces 16a and 16b are fixed by means of an adhesive agent in a manner such that the member 2 is held between the two members 15 and 16. In a fifth process, the C-ring 17 is attached to the rear portion of the gripper 16, as shown in Fig. 14. In doing this, the rearwardly bent distal end portion of the sheath 3 is moved toward the gripper 16, as shown in Fig. 14, and the C-ring 17 is fitted on the distal end portion. Then, the C-ring 17 is inwardly pressed to be gripped. Thus, the distal end of the sheath 3 is held between the members 16 and 17. Then, in a sixth process, the heat-shrinkable tube 18 is fitted on to the resulting structure from the side of the ferrule 9, and is heat-treated to cover the rear side of the ferrule 9. The tube 18 is used in placed of the rubber boot of the first embodiment. In the assembling method according to this second embodiment, the optical connector is assembled following the various processes described above. In this case, each of the holder 15 and the gripper 16 is a split body such that it can be mounted by after-attachment. It is unnecessary, therefore, to fit these members on the optical fiber cable beforehand and to move them toward the ferrule 9 with every process. Thus, the optical connector can be assembled very easily. According to this method, moreover, the optical connector can be assembled in an automatic assembly line, whereby the productivity can be further improved.

Claims: An optical connector comprising: an optical fiber cable including a plastic-coated fiber (1), a tension member layer (2) thereon, and an outer sheath (3) covering the plastic-coated fiber and the tension member layer; a ferrule (9) fixed onto the distal end of the optical fiber cable that is attached to the distal end of the plastic-coated fiber; and a tubular holder (11;15) mounted on the plastic-coated fiber, said tubular holder having a distal end positioned behind said ferrule and restricted in its forward movement by the ferrule; said tension member layer being held on the rear outer surface of the tubular holder by a tubular gripping member (12;16) ; characterized in that said tubular holder is formed with a slit (11a) extending parallel to the axis of the plastic-coated fiber or is in the form of a two-part, longitudinally split body, whereby, during assembly, the holder may be mounted on the plastic-coated fiber after attachment of the ferrule to the plastic-coated fiber. An optical connector according to claim 1, which said tubular gripping member is also in the form of a two-part longitudinally split body which can be mounted on the holder after attachment of the ferrule. An optical connector according to claim 1 or 2, which further comprises a spring (8;19) encompassing the plastic-coated fiber and interposed between the ferrule and the holder so as to urge the ferrule forwards, said spring being formed of a shape memory alloy wire and fitted on the plastic-coated fiber after attachment of the ferrule. A method of assembling an optical connector which comprises an optical fiber cable including a plastic-coated fiber (1), a tension member layer (2) thereon, and an outer sheath (3) covering the plastic-coated fiber and the tension member layer, a ferrule (9) fixed onto the distal end of the optical fiber cable and, in particular, attached to the distal end of the plastic-coated fiber, a tubular holder (11;15) mounted on the plastic-coated fiber, said tubular holder having a distal end positioned behind said ferrule and restricted in its forward movement by the ferrule, said tension member layer being held on the rear outer surface of the tubular holder by a tubular gripping member (12;16), a spring (8;19) encompassing the plastic-coated fiber interposed between the ferrule and the holder so as to urge the ferrule forwards, the assembling method being characterized by using a tubular holder which is formed with a slit (11a) extending parallel to the axis of the plastic-coated fiber, or is in the form of a two-part, longitudinally split body and mounting the holder on the plastic-coated fiber after the ferrule is mounted on the distal end of the fiber and after the spring is fitted at the rear of the ferrule. A method of assembling an optical connector according to claim 4, wherein said tubular gripping member is also in the form of a two-part, longitudinally split body which is mounted on the rear portion of the holder after attachment of the ferrule, the spring and the holder, whereby the distal end of the tension member layer is held between the gripping member and the holder.

Inventors: SHIBATA NOBUYUKI, SUZUKI KENJI, YUGUCHI REN-ICHI, SHIBATA, NOBUYUKI, SUZUKI, KENJI, YUGUCHI, REN-ICHI, SHIBATA, NOBUYUKI, THE FURUKAWA ELECTRIC CO. LTD., Suzuki, Kenji, c/o The Furukawa Electric Co. Ltd, YUGUCHI, REN-ICHI, THE FURUKAWA ELECTRIC CO. LTD
Applicants: FURUKAWA ELECTRIC CO LTD, THE FURUKAWA ELECTRIC CO., LTD.
Application year: 1991
Main classification: G02B6
IPC codes: G02B6