Redundant length handling mechanism for optical fiber at terminal of optical cable

Abstract: A redundant length treatment mechanism for an optical fiber (2) which is stored in an optical cable (5) and has one end connected to an optical connector (6), includes a storage case (1) in which a redundant part of the optical fiber exposed from the optical cable is stored while wound up in a loop form (L), a bent form or an S-shape form, the storage case having a draw-out portion (1a) through which one end portion of the looped optical fiber (2) is drawn out, and curvature restricting means comprising a pair of stoppers (3, 4) secured to the optical fiber for restricting radius of curvature of the optical fiber sotred in a loop form in the storage case.

Description: The present invention relates to a redundant length handling mechanism for an optical fiber which is stored in an optical cable and has one end connected to an optical connector, including a storage case in which the optical fiber exposed from the optical cable is stored and from which one end portion of the S-shaped optical fiber is drawn out. In GB-A-2 074 544 there is described an apparatus for terminating an optical fiber. This apparatus includes a storage box for storing a surplus length of optical fiber left at the termination point for subsequent use on reterminations. The box consists of a flat pack that includes a disc member which is fixedly installed with screws and cannot be moved within the storage box. A connector is connected on a side plate. Further, in DE-U-9 105 942 there is described a storage box for a particular fiber. The optical fiber contains a reel that is guided in vertical guidance grooves in dependence of the amount of optical fiber drawn out of the storage box. Here, it is not possible to pull the reel independently of the optical fiber or to connect two different optical fibers using optical connectors. To the contrary, in a case where plural optical fibers enclosed in two optical cables located so as to be confronted to each other are required to be connected to one another through optical connectors, the connection between the optical fibers in the optical cables would be impossible if the length of each optical fiber between the end of the optical cable and the end of the optical fiber core is extremely short, and this obstructs a connection work of the respective optical fiber cores of the two optical cables. In order to avoid this obstruction, the optical fiber is designed to be superfluously extended or exposed from the end of the optical cable to the outside, and this redundant part of the optical fiber is beforehand wound around an external reel. That is, the optical fiber core is designed so as to have a redundant length and assure the minimum bend radius thereof. However, a conventional technique requires additional work for winding around an external reel the redundant part of the optical fiber which is superfluously extended or exposed from the optical cable enclosing the optical fiber to the outside, and thus the working efficiency of the conventional technique has been low. Summary of the Invention An object of this invention is to provide a redundant length handling mechanism for an optical fiber in which the optical fiber is drawn out or fed out from the end of an optical cable by a desired amount by freely adjusting the redundant length with minimum width and length of the redundant length handling mechanism in directions perpendicular to the plane where the optical fiber is stored. In order to achieve this object, according to this invention, a redundant length handling mechanism of the type outlined above further comprises fiber bending means for bending back the optical fiber so as to be stored in a substantially S-shaped form substantially in a single plane plane in said storage case; and a bend-back length adjusting portion including a recessed curved surface in the storage case for contacting with a length of a bent portion of the S-shaped optical fiber when the optical fiber is retracted into the storage case to its maximum extent. According to the invention it is possible to connect optical fibers in an easy way with one another so that the working efficiency is improved. Also, a plurality of optical fibers can be connected to each other by using, e.g., a laminated structure. Further, the optical fiber is supported in a bent state in a single plane in the storage case so that the radius of curvature of the optical fiber stored in the bent state is reduced when the optical fiber is drawn out and increased when the optical fiber is slackened. In addition, optical fibers can be arranged in a single plane without intersecting with one another so that the width and length in directions perpendicular to the plane can be reduced to their minimum values. Overall, the optical fiber exposed from the optical cable is stored while bent in a substantially S-shaped and its end portion is drawn out from the storage case. A bent portion of the S-shaped part of the optical fiber is freely movable in the bend-back length adjusting means inside the storage case so that the redundant length of the optical fiber is freely adjustable in accordance with displacement of the bent portion of the bend-back length adjusting portion which is carried out in accordance with the draw-out and retracting operation of the optical fiber from and into the storage case. The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention. Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the scope of the invention will become apparent to those skilled in the art from this detailed description. Brief Description of the Drawings Figs. 1A-1C are schematics diagram of a basic aspect underlying the redundant length handling mechanism for an optical fiber according to this invention; Figs. 2A and 2B show an embodiment of an optical connector; Figs. 3A and 3B are schematic diagrams showing further aspects of the redundant length handling mechanism underlying the invention; Fig. 4 is a longitudinal-sectional view of a cable coupling structure, which is taken along a plane on which a movable reel is moved, the redundant length handling mechanism being applied to the cable coupling structure; Fig. 5 is a flowchart for a connection work of the optical connector with the cable coupling structure to which this invention is applied; Figs. 6A-6G are diagrams for a series of processes for the connection work of the optical connector with the cable coupling structure according to this invention; Fig. 7 is a diagram showing a state where a pivot housing supporting the optical connector is stored in the first cable connecting adaptor in the connection work of the optical connector using the cable coupling structure to which this invention is applied; Figs. 8A-8C show a main embodiment of the redundant length handling mechanism according to this invention; and Figs. 9A and 9B show a modified embodiment of the redundant length handling mechanism according to this invention. Description of the Preferred Embodiment An embodiment according to this invention will be described hereunder with reference to the accompanying drawings. In the following embodiments, the same elements are represented by the same reference numerals, and the repetitive description on the same elements is eliminated. Figs. 1A-1C and 2A-2B show a principle of the redundant length handling mechanism of an optical fiber underlying this invention. Fig. 1A is a longitudinal-sectional view of the redundant length handling mechanism in which the optical fiber is stored at its maximum length in the storage case, and Fig. 1B is a longitudinal-sectional view of the redundant length handling mechanism in which the optical fiber is drawn or fed out at its maximum length from the storage case. The redundant length handling mechanism includes a storage case 1 and stoppers 3 and 4 which are fixedly secured to an optical fiber unit 2 at two positions. The optical fiber unit 2 is constructed by plural ribbon fibers laminated in an assembled-state, for example. The optical fiber unit 2 is drawn or fed out from the optical cable 5 comprising a slot-type of high-density ribbon cable. The optical fiber unit 2 exposed from the optical cable 5 is guided to the storage case 1, and spirally wound up in the storage case, so that a loop L having arcuate portions is formed in the storage case 1. After the loop L is formed, the end portion of the optical fiber unit 2 is inserted into a draw-out port la of the storage case 1 and guided therethrough to the outside. The end portion of the optical fiber unit 2 which is drawn out to the outside is connected to an optical connector 6. Figs. 2A-2B show a lateral-arrangement type of optical connector in which 40 cores are laterally arranged on a row and which can be used. Fig. 2A is a front view of the optical connector which is viewed from an incidence/emission end surface of the optical connector, and Fig. 2B is a side view of the optical connector. The optical connector includes ribbon fibers 6a each comprising eight cores which are laterally connected to one another on a row, and guide pin insertion holes 6b formed at both sides thereof. Since the optical fiber unit 2 is fed out from the optical cable 5 while plural ribbon fibers are laminated, it has sufficient rigidity and a substantially circular or substantially elliptical loop L is formed in the storage case 1. Therefore, the optical fiber unit 2 is prevented from being twisted or hitched in the storage case 1, and it can be smoothly drawn out or retracted into the storage case 1. The stoppers 3 and 4 serving as curvature restricting means for setting or restricting the radius of curvature of the loop-shaped optical fiber unit 2 are secured to the two positions of the optical fiber unit 2 at the front and rear sides of the draw-out port la (inside and outside of the storage case 1). Each of the stoppers 3 and 4 is formed of a member having a larger size than the profile of the draw-out port la, so that each of the stoppers 3 and 4 is inhibited from being passed through the draw-out port la to the outside and the inside of the storage case 1, respectively. Therefore, the optical fiber unit 2 is provided with a redundant part whose length (redundant length) is variable in a range corresponding to a distance between the stoppers 3 and 4. The stopper 3 is secured to the optical fiber unit 2 at such a position that when the optical fiber unit 2 is drawn out from the storage case 1 at its maximum length (as shown in Fig. 1B), the optical fiber unit 2 is prevented from being damaged due to excessive reduction of the radius of the loop L of the optical fiber unit 2 in the storage case 1 which is caused by excessively drawing out the optical fiber unit 2 from the storage case 1, that is, at such a position that the permissible minimum radius of curvature is assured for the optical fiber unit 2. On the other hand, the stopper 4 is secured to the optical fiber unit 2 at such a position that when the optical fiber unit 2 is retracted into the storage case 1 at its maximum length (as shown in Fig. 1A), the optical fiber unit 2 is prevented from being damaged due to excessive increase of radius of the loop L of the optical fiber unit 2 in the storage case 1, that is, at such a position that the permissible maximum radius of curvature is assured for the optical fiber unit 2. These securing positions of the stoppers 3 and 4 can be easily calculated on the basis of the permissible minimum bend radius of the used optical fiber unit 2 and the length of the storage case 1. According the redundant length handling mechanism as described above, the optical fiber unit 2 can be simply drawn out from the storage case by a desired length for the connection work of the optical connector, and the redundant part of the optical fiber unit 2 can be simply retracted into the storage case 1 when the connection work is completed. Next, further aspects of the redundant length handling mechanism underlying this invention will be described with reference to Figs. 3A and 3B. The redundant length handling mechanism differs from the one shown in Fig. 1 in the point that a movable reel 7 is used as curvature restricting means for setting or restricting the radius of curvature of the optical fiber unit 2 stored in the storage case 1. The movable reel 7 comprises a circular reel having a larger radius than the permissible minimum radius of curvature of the optical fiber unit 2 at which the optical fiber unit 2 is not damaged, and it is provided in the storage case 1 so as to be movable in the storage case 1. The end portion of the movable reel 7 is connected through plural pulleys to a redundant length adjusting string 8 with which the movable reel 7 is moved in such a direction that the radius of curvature of the loop of the optical fiber unit 2 is increased. According to the redundant length handling mechanism as described above, when the optical fiber unit 2 in a state where it is drawn out from the storage case 1 at its maximum length (Fig. 3B) is required to be retracted into the storage case 1, the optical fiber unit 2 can be retracted into the storage case 1 for a short time by merely drawing out the redundant length adjusting string 8. Next, a cable coupling structure to which the redundant length handling mechanism is applied concretely, will be explained in reference with Fig. 4. The cable coupling structure includes a redundant length adjusting portion T and aconnector securing portion F. Five sets of redundant length adjusting mechanisms as described above are installed into the redundant adjusting portion T. Therefore, the connection work for 200 (40 X 5) optical fibers at maximum can be subjected to the redundant length adjustment. The connector securing portion F includes a connector securing case 9 to which the optical connector 6 is secured, and is contained in a pulling eye 10. In addition, a tube 11 having screw members at both ends thereof is screwed between the optical cable 5 and the pulling eye 10, and the redundant length adjusting portion T is fixedly secured in the tube 11. The storage case 11 of the redundant length handling mechanism is fixed at such a position that the draw-out port la is located at the upper portion of the tube 11. The optical fiber unit 2 is drawn out through the draw-out port la from the storage case 1, and is secured to the connector fixing case 9 located at the lower portion of the pulling eye 10. Therefore, the alignment direction of the optical fibers in the optical fiber unit 2 can be naturally changed without applying an enforced force to the optical fiber unit 2. Here, the five ribbon fibers are laminated inside of the optical cable 5 and the storage case 1 in the arrangement structure of 8-core rows in the lateral direction and 5-core columns in the vertical direction. Therefore, the above core arrangement can be changed to a 40-core row arrangement in the lateral direction (See Figs. 2A and 2B) which is connectable to the optical connector 6 by displacing the cores in a direction perpendicular to the ribbon surface. The connection work of the optical connectors using the coupling member as described above will be next described with reference to Figs. 5, 6A-6G and 7. First, the pulling eye 10 is removed from the coupling structure with the end in traction (Fig. 6A), which is connected to the optical cable 5, the tube 11 and the pulling eye 10 (Step 101). When the pulling eye 10 is removed, the connector securing case fixed inside of the coupling structure is exposed to the outside as shown in Fig. 6B. Thereafter, the optical connector 6 is separated from the connector securing case 9 to remove the connector securing case 9 (Step 102). The optical connector 6 is allowed to be freely movable as shown in Fig. 6C. Thereafter, the tube 11 is inserted in an adaptor hold ring 12, and the coupling thus mounted in the adaptor hold ring 12 is confronted to another coupling structure in the same state. Subsequently, a first cable connecting adaptor 13 is secured to both of the coupling members (Step 102). This connection state is shown in Fig. 6D with a part cross-sectional view of the first cable connecting adaptor 13. Thereafter, the optical connectors 6 are connected to each other, and stored into a pivot housing 14 as shown in Fig. 6E. In addition, the redundant part of each optical fiber unit 2 is stored into the storage case of the redundant length handling mechanism (Step 4). The optical fiber unit 2 which is connected to another optical connector 6 at the right side) is omitted from the figures 6 and 7. A pair of optical connectors which are drawn out from the respective optical cables 5 and connected to each other are stored in each pivot housing 14. Here, five optical fiber units 2 are supplied from each optical connector 6 at maximum, and the pivot housing 14 are stored into the cable connecting adaptor 13 while laminated on one another as shown in Fig. 6F. After the connection work for all optical connectors 6 is completed, a second cable connecting adaptor 15 is secured to the first cable connecting adaptor 13, and the adaptor hold rings 12 are slid so that the adaptor hold rings 12 are secured to the first cable connecting adaptor 13 and the second cable connecting adaptor 15 (Step 105). According to this redundant length handling mechanism, the optical connectors can be easily connected to each other, and thus the working efficiency is improved. As described above, the optical fiber unit comprising laminated ribbon-shaped optical fibers is used for the optical fibers, however, this mechanism is not limited to the above example in the number, the alignment direction, the size and the structure of optical fibers. Further, in the above mechanism, the optical fiber is looped once in the storage case, and guided to the draw-out port. However, the number of loops of the optical fiber in the storage case is not limited to 1. The embodiment of this invention will be next described with reference to Figs. 8A-8C and 9A and 9B. The redundant length handling mechanism of this embodiment is equipped with a storage case 22, and the storage case 22 comprises a base plate 23 having a guide groove for bending the optical fiber unit 2 in an S-shape and side plates 25 disposed at both sides of the base plate 23. The base plate 23 has a predetermined board thickness, and by cutting out this board thickness portion, an inlet 26 and an outlet 27 for the optical fiber unit 2 are formed at both end sides of the base plate in the longitudinal direction, respectively. In the base plate 23, the guide groove 24 for bending the optical fiber unit 2 in the S-shape is formed between the inlet 26 and the outlet 27, and a length adjusting portion 28 for adjusting a bend-back length of the optical fiber unit 2 which is bent in the S-shape is formed at a bent portion of the S-shape between the inlet 26 and the outlet 27. The S-shaped guide groove 24 is formed by both of projected curved surfaces 29a and 30a of arcuate first and second guide projections 29 and 30. The bend-back length adjusting portion 28 is formed between the projected curved surface 30a of the second guide projection 30 and a recessed curved surface 31 formed on the inner wall of the storage case 22 which is located so as to confront the projected curved surface 30a. According to the redundant length handling mechanism of this embodiment, when the optical fiber unit 2 is retracted into the storage case 22 at maximum, the bent-back portion 2a is moved so as to be contacted with the recessed curved surface 31 of the bend-back length adjusting portion 28, and the radius of curvature of the optical fiber unit 2 is restricted by the curvature of the recessed curved surface 31, so that the optical fiber unit 2 is prevented from being bent such that the bent radius of the optical fiber unit 2 is decreased over its permissible minimum bend radius. For the connection work of the optical connector, the optical fiber unit 2 can be drawn out through the outlet 27 from the storage case 22 by a desired length. When the optical fiber unit 2 is drawn out from the storage case 22 at maximum, the bend-back length adjusting portion 28 is moved to such a position that it is contacted with the projected curved surface 30a of the second guide projection 30, and the radius of curvature of the optical fiber unit 2 is also restricted by the curvature of the projected curved surface 30a, so that the optical fiber unit 2 is prevented from being bent such that its bend radius is decreased below its permissible minimum radius. The modified embodiment of the invention shown in Fig.9 differs from the embodiment described above in that plural sets of optical fiber units 2 are stored in one storage case 22a, and a redundant part of each of the optical fiber units 2 is individually adjustable in length. In this modified embodiment, three sets of optical fiber units 2 are stored in a bundle in the storage case 22, and thus the S-shaped guide groove is formed wider. In addition, a bend-back length adjusting portion 28 which is formed between the projected curved surface 30a of the second guide projections 30 and the recessed curved surface 31 on the inner wall of the storage case 22 is partitioned by arcuate partition frames 32 and 33, whereby first, second and third partition portions 28a, 28b and 28c are formed in the bend-back length adjusting portion 28. Each of the arcuate partition frame 32 (33) is formed with a projected curved surfaces 32a (33a) and a recessed curved surface 32b (33b) at both side surfaces thereof. The three sets of optical fiber units 2 are separated from one another after passing over the S-shaped guide groove 24, and individually guided to the first partition portion 28a, the second partition portion 28b and the third partition part 28c respectively. The optical fiber units 2 are bent back in the respective partition portions, and then guided through the respective outlets 27 to the outside. Therefore, in this modified embodiment,the three sets of optical fiber units can be individually drawn out or retracted in through the corresponding outlets 27. In this case, the bent-back portions 2a of the respective optical fiber units 2 are moved in the first to third partition portions 28a, 28b and 28c respectively to perform the redundant length adjustment of the respective optical fiber units 2. When the bent-back portions 2a of the respective optical fiber units 2 are moved in the first to third partition portions 28a , 28b and 28c respectively, the radius of curvature of each optical fiber unit 2 is restricted by the projected curved surface portions 32a and 33a and the recessed curved surface portions 32b and 33b, and thus each optical fiber unit 2 is prevented from being bent to the extent that the radius of curvature thereof is less than its permissible radius of curvature. In this embodiment, the redundant parts of the three sets of optical fiber units 2 are individually subjected to the redundant length adjustment, however, the number of the sets of optical fiber units is not limited to the above embodiment. As described above, the redundant length handling mechanism of this embodiment is so designed that the optical fiber is retracted into the storage case in an S-shaped form, so that the draw-out or retraction of the optical fiber unit can be freely carried out, and thus the working efficiency of the connection work of the optical connectors can be improved. From the invention thus described, it will be obvious that the invention may be varied in many ways. Such variations are not to be regarded as a departure from the scope of the invention.

Claims: A redundant length handling mechanism for an optical fiber (2) which is stored in an optical cable and has one end connected to an optical connector (6), including: a storage case (22) in which the optical fiber (2) exposed from the optical cable is stored while wound up and from which one end portion of the optical fiber is drawn out; characterized by fiber bending means (29a, 30a) for bending back the optical fiber (2) so as to be stored in a substantially S-shaped form substantially in a single plane between side plates (25) of said storage case (22); and a bend-back length adjusting portion (28) including a recessed curved surface (31) in the storage case (22) for contacting with a length of a bent portion of the S-shaped optical fiber (2) when the optical fiber is retracted into the storage case (22) to its maximum extent. The redundant length handling mechanism as claimed in claim 1, wherein said fiber bending means includes an S-shaped guide groove (24) comprising first and second guide projections (29, 30) each having an arcuate curved surface (29a,30a) at the outer periphery thereof, and said bendback length adjusting portion (28) is formed between the projected curved surface (30a) of said second guide projection (30) at the outer periphery thereof and wherein said recessed curved surface (31) is formed in said storage case (22) so as to be opposed to said projected curved surface (30a). A redundant length handling mechanism for optical fiber as claimed in claim 2, wherein said guide groove is formed in an S-shape with radius of curvature larger than at least said minimum radius of curvature of said optical fiber (2). A redundant length handling mechanism for optical fiber as claimed in claim 2, wherein said projected curved surfaces (29a, 30a) and said recessed curved surface (31) are formed with radius of curvature larger than said minimum radius of curvature of said optical fiber (2). The redundant length handling mechanism as claimed in claim 2, wherein said guide groove has a groove width such that plural sets of optical fibers (2) are insertable, and said bend-back length adjusting portion (28) includes plural partitioned portions (28a,28b,28c) into which the plural sets of optical fibers (2) are individually insertable to perform an individual length adjustment for each of the optical fibers (2) stored in each of said partition portions (28a,28b,28c).

Inventors: HAIBARA TADASHI, ISHIDA HIDETOSHI, KAKII TOSHIAKI, MARUYAMA KYOJI, TOMITA SHIGERU, UEDA TOMOHIKO, HAIBARA, TADASHI, ISHIDA, HIDETOSHI, KAKII, TOSHIAKI, MARUYAMA, KYOJI, TOMITA, SHIGERU, UEDA, TOMOHIKO, ISHIDA, HIDETOSHI, C/O YOKOHAMA WORKS OF, KAKII, TOSHIAKI, C/O YOKOHAMA WORKS OF, Maruyama, Kyoji, c/o Yokohama Works of, UEDA, TOMOHIKO, C/O YOKOHAMA WORKS OF
Applicants: NIPPON TELEGRAPH & TELEPHONE, SUMITOMO ELECTRIC INDUSTRIES, NIPPON TELEGRAPH AND TELEPHONE CORPORATION, SUMITOMO ELECTRIC INDUSTRIES, LIMITED
Application year: 1992
Main classification: G02B6
IPC codes: G02B6