Method of encasing fusion spliced optical fibers in a casting

Abstract: In a method of preventing twisting of a fusion-spliced optical fiber in the process of encasing the optical fiber in a casing, one (16₂) of a pair of optical fibers (16₁, 16₂) is wound N turns in one direction to form a first coil. Another (16₁) of the pair of optical fibers is wound N turns in another direction opposite to the direction to form a second coil. Ends of remainder portions of the optical fibers which are not wound are fusion-spliced to each other to form a fusion-spliced portion (48). The fusion-spliced portion is fixed within a casing (14). The remainder portions of the optical fibers are pushed into the casing to expand the first and second coils.

Description: The present invention relates to a method of preventing twisting of a fusion-spliced, tube-removed fiber portion in the process of encasing the fiber portion, in a coil form, in a casing. In a conventional process of fusion-splicing a pair of optical fiber cords, first, the protective tubes of the fiber cords are removed over a predetermined length, generally, 1 meter, from the ends of the fibers, which are to be fusion-spliced. Next, the coating layers of the fibers are stripped off over a predetermined length from the ends of the fibers, which are fusion-spliced. Thereafter, the coating layer stripped fiber portions are disposed on a pair of supporting members of a fusion-splicing apparatus, with the fiber ends facing to one another. Thereafter, the fibers are moved to contact each other, while applied with arc discharge to the fiber ends, so that the fibers are fusion-spliced. However, there is a case where the cores of the fibers are in misalignment. In another case, the fusion-spliced portion does not have sufficient mechanical strength. In such cases, the operator removes the fibers from the supporting members and cuts off the tip portions of the fibers by a predetermined length, generally, 35 mm, from the fusion-spliced portion. The fibers are again subjected to the above processes. This sequence is repeated until a good fusion-splicing is obtained. Taking into consideration a case where such a defective fusion-splicing may occur several times, the length of the portion of each of the fibers where the protective tube is removed is generally set to about 1 meter. This portion of the fiber is referred to as "tube-removed fiber portion". When a good fusion-splicing is once obtained, the fusion-spliced fiber comprising the tube-removed fiber portions 16₁ and 16₂ is removed from the fusion-splicing apparatus, and put into a casing 14 to be held therein, as shown in Fig. 1A. Specifically, referring to Fig. 1A, the fusion-spliced portion 12 of the fusion-spliced fiber is fixed in a casing 14 as shown in Fig. 1A. Thereafter, the tube-removed fiber portions 16₁ and 16₂ of the fusion-spliced fiber are coiled as illustrated in Figs. 1A and 1B. Next, a cover (not shown) of the casing 14 is closed to seal therein the fiber portion 16₁ and 16₂. It is observed that coiling confronts subsequent twisting, and that the degree of twisting grows as the number of turns increases. As shown in Fig. 1A, the initial turn of coiling entails twisting with the upper fiber portion, for example, 16₁ at an intersection of the fiber portions 16₁ and 16₂, and further twisting emerge with every other turn of even numbers. It is likewise observed that the initial turn of coiling does not give rise to twisting with the lower fiber portion, for example, 16₂ but subsequent turns of the odd numbers after the third bring about twisting each. The tube-removed fiber portions 16₁ and 16₂ are each generally coiled in the form of a 3-turn. In such a case, the twisting occurring is as intensive as not negligible with regard to optical characteristics, thereby inflicting the fibers some loss of optical transmission. It must also be noted that the optical fiber interfere with deformation of the cable due to twisting whereby resulting in causing ease for the coiled optical fiber to spring up, getting out of the casing, with safe workability to encase a coiled optical fiber and close a casing cover subsequently thus lessened. DE-A-2914217 discloses a method of placing a splice and its associated fibres in a casing in which the fibres are apparently held under tension in a coiled configuration whilst the fibre ends are spliced. In respect of the above-mentioned circumstances, the present invention was devised to provide a method of preventing twisting the fusion-spliced, stripped fiber portions in the process of encasing the fiber portion, in a coilform, in a casing, whereby the fiber portions may be encased without undergoing twisting, springing up, and getting out of the casing, and workability of encasing the fiber portions may be improved. According to the present invention, there is provided a method of preventing twisting of a fusion-spliced optical fiber in the process of encasing the optical fiber in a casing as disclosed in claim 1. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Figs. 1A and 1B each show a fusion-spliced optical fiber contained in a casing; Fig. 2 is a graph showing a relationship between length of a tube-removed fiber portion and the number of turns; Fig. 3 shows a coil forming jig; Figs. 4A-4H show a sequence of encasing an optical fiber in a casing; Figs. 5A-5G show another sequence of encasing an optical fiber in a casing; Fig. 6 shows another coil forming jig; Fig. 7A shows a top plan view of a further coil forming jig; and Fig. 7B shows a cross sectional view of the further coil forming jig shown in Fig. 7A. A casing commonly used at present can accommodate a coil whose diameter is 210 through 370 mm long. In case a good fusion-spliced portion were obtained in one attempt of fusion-splicing process, cutting-off of the fiber ends is not required to remove a defective fusion-spliced portion, and the length of each of the tube-removed fiber portions remains unchanged as being 1 m. In this case, it is necessary that each of the tube-removed fiber portions be wound in a three-turn coil so that the coil may be encased. It is accordingly required to wind each tube-removed fiber portion around a fiber winding receiver member to form the three-turn coil. Meanwhile, where a defective fusion-spliced portion is produced, the tube-removed fiber portions must suffer cutting to a length of 35 mm from each end of the fusion-spliced portion, resulting in shortening. Therefore, if the tube-removed fiber portions experience 10 successive attempts of fusion-splicing, with each resulting in producing a defective fusion-spliced portion, the total cut-off length would amount to 350 mm, and the resultant length of each tube-removed fiber portion would be 650 mm. With such tube-removed fiber portion, it is necessary to provide a three-turn coil with each turn measuring a length of 216 mm or a two-turn coil, with each turn measuring 325 mm. Referring to the graph presented in Fig. 2, how is the relationship between the total length of tube-removed fiber portions and the number of turns is appreciated. The abscissa of the graph represents the total length of the tube-removed fiber portions while the ordinate denotes the number of turns. Where there are provided a plurality of triangles which are defined according to the total length of the tube-removed fiber portions, any one of the triangles may be selected to define the number of turns. By reference to the drawings provided for this specification, the methods disclosed in preferred embodiments of the present invention to prevent twisting a fusion-spliced, tube-removed fiber portions, in the process of encasing the fiber portion, in a coilform, in a casing are described hereunder. First, referring to Fig. 3, a description is made here of a coil forming jig 22 around which a fusion-spliced, tube-removed fiber portion is wound, and which is disclosed in the embodiment of the present invention. The coil forming jig 22 comprises an ellipsoidal base 24, a cylindrical support 26 extending upward from the central part of the base 24, a lower winding core 28 inserted into the support 26, a center partition comprising elliptic disc 30, an upper winding core 32, an elliptic top disc 34, and a knob member 36 provided at the top of the support 26 to lock the above members through its thread engagement with the support 26. To make a coil, a fusion-spliced tube-removed fiber portion is wound around the coil forming jig 22, wherein around the lower winding core 28, one fiber portion is first wound N turns in one direction and then, a fiber holder (not shown) is pressure-inserted in between the center partition disc 30 and the ellipsoidal base 24 thereby to lock an optical fiber coil to the lower winding core 28. Successively, around the upper winding core 32, another fiber portion is wound N turns in the direction opposite the above, followed by pressure-inserting a fiber holder (not shown) in between the center partition elliplic disc 30 and the elliptic top disc 34 whereby to another fiber coil to the upper winding core 32. As shown in Fig. 4A, a pair of optical fiber cables 42₁ and 42₂ are clamped by means of a pair of engaging clamp means 44₁ and 44₂ which are provided, respectively at the left and right corners on a side S1 of the rectangular casing 14. The tube-removed fiber portions 16₁ and 16₂ extend from the fiber cables 42₁ and 42₂ generally by 1 meter, respectively. As shown in Fig. 4B, around the lower winding core 28 situated between the ellipsoidal base 24 and the center partition elliptic disc 30 of the coil forming jig 22 mounted at the center part of the casing 14, the tube-removed fiber portion 16₁ extending from the left fiber cable 42₁ is wound N turns in the counterclockwise direction (N = 3 in case the tube-removed fiber portion measures 1 m). Then, the optical fiber coil is thrust against the lower winding core 28 with a fiber coil holder member 46₁ pressure-inserted in between the ellipsoidal base 24 and the center partition elliptic disc 30. As shown in Fig. 4C, around the upper winding core 32 situated between the center partition elliptic disc 30 and the elliptic top disc 34, the tube-removed fiber portion 16₂ extending from fiber cable 42₂ is wound (N + 1) turns in the clockwise direction (when N = 3, (N + 1) = 4). Thereafter, the optical fiber coil is thrust against the upper winding core 32 with a fiber coil holder member 46₂ pressure-inserted in between the center partition disc 30 the elliptic top disc 34. Next, as shown in Fig. 4D, ends of the tube-removed fiber portions 16₁ and 16₂ are fusion-spliced by a known conventional method. The process of fusion-splicing itself is not essential to the present invention, and thus the description thereof is omitted. As shown in Fig. 4E, the fusion-spliced, tube-removed fiber portion is given half a turn in the counterclockwise direction while holding the fusion-spliced portion 48. Namely, the fiber portion is turned 180°. This half a turn results in lapping the fiber portion 16₂ over the fiber portion 16₁, with the former thus intersecting the latter, whereby a ring R is formed. Then, as shown in Fig. 4F, with the fusion-spliced portion 48 held in the hand, the ring R is turned upside down over the casing 14 so that the ring R will come to get situated on a S2 side opposite the S1 side of the casing 14 whereby the fusion-spliced portion 48 is pressure-inserted into a coil retaining clip 50 provided in proximity of the S2 side of the casing 14 to hold the fusion-spliced portion 48 therein. The turning of the ring R upside down produces a small twisted ring r either with the tube-removed fiber portion 16₁ or 16₂. Therefore, the operator involved is required to turn the ring R upside down as shown in Fig. 4F so that the small twisted ring r may come into existence with either of the tube-removed fiber portions, whichever is greater in the number of turns, namely with the fiber portion 16₂ with (N + 1) turns in this embodiment of the present invention. Next, as shown in Fig. 4G, the fiber coil holder member 46₁ for the fiber portion 16₁ is removed to release the fiber coil which has thus far been thrust against the lower winding core 28. Under this condition, the fiber portion 16₁ lying outside the casing 14 is fed inside the casing so as to expand the size of the fiber coil. Thereafter, as shown in Fig. 4H, the coil holder member 46₂ provided for the tube-removed fiber portion 16₂ is removed thereby to release the fiber coil held thrust against the upper winding core 32, and one turn of the coil is taken off not only to make equal the number of turns with the N turns of the fiber coil 16₁ but also to make the small twisted ring r disappear. In this condition, the tube-removed fiber portion 16₂ outside the casing 14 is fed into the casing thereby to enlarge the size of the coil. After feeding the fiber portion 16₂ into the casing 14, the coil forming jig 22 is removed from the casing 14, and a cover (not shown) is set in position. Following the method referred to above, the tube-removed fiber portions 16₁ and 16₂ are wound around the lower and upper winding cores 28 and 32 without ring twisted since the ends of the tube-removed fiber portions are free when these fiber portions are wound around the winding cores, and a twist generated in a winding process undergoes offsetting in the subsequent winding process, thereby disappearing, whereby a twist-free ring is finally obtained. In the above embodiment, the step of taking off one turn of the fiber coil of the tube-removed fiber portion 16₂ is performed after the step of turning the ring R of the tube-removed fiber portion upside down is performed. However, these steps can be reversed. Specifically, after the step of turning the tube-removed fiber portion half a turn to form the ring R, the coil holder member 46₂ is removed to release the fiber coil of the tube-removed fiber portion 16₂ thrust against the upper winding core 32, and one turn of the fiber coil is taken off to make equal the number of turns with the N turns of the fiber coil of the tube-removed fiber portion 16₁. Thereafter, with the fusion-spliced portion 48 held in the hand, the ring R is turned upside down over the casing 14 so that the ring R will come to get situated on a S2 side opposite the S1 side of the casing 14 whereby the fusion-spliced portion 48 is pressure-inserted into a coil retaining clip 50. Next, the fiber coil holder member 46₁ for the fiber portion 16₁ is removed to release the fiber coil thrust against the lower winding core 28. Next, by reference to either Fig. 5A to Fig. 5G, another embodiment of the present invention is described. As shown in Fig. 5A, using the engaging clamp means 44₁ and 44₂ arranged at the left and right corners of a side S1 of the rectangular casing 14, a pair of optical fiber cables 42₁ and 42₂ are fixed in their places. The tube-removed fiber portions 16₁ and 16₂ extend from the optical fiber cables 42₁ and 42₂ respectively. Thereafter, the tube-removed fiber portion 16₂ is wound N turns in the counterclockwise direction (in case the length of the tube-removed fiber portion is 1 meter, 3 turns) around the lower winding core 28 between the ellipsoidal base 24 and the center partition elliptic disc 30 of the coil forming jig removably mounted at the central part of the contain case 14. Then, the optical fiber coil at the lower winding core 28 is thrust against the lower winding core 28 by pressure-inserting the coil holder member 46₂ in between the ellipsoidal base and the center partition elliptic disc. The remainder of the tube-removed fiber portion 16₂ is extended to the side S2 opposite the side S1 of the casing 14. Next, as shown in Fig. 5B, the tube-removed fiber portion 16₁ is wound about the upper winding core 32 between the center partition elliptic disc 30 and the elliptic top disc 34 of the coil forming jig 22 the same number of turns as with the tube-removed fiber portion 16₂ in the clockwise direction. Then, the optical fiber coil at the upper winding core 32 is thrust against the upper winding core 32 by pressure inserting the coil holder member 46₁ in between the center partition elliptic disc and the elliptic top disc. The remainder of the tube-removed fiber portion 16₁ is extended to the side S₂ of the casing 14. Next to the above, as illustrated in Fig. 5C, the ends of the tube-removed fiber portions 16₁ and 16₂ are fusion-spliced according to a known conventional method. To prepare for this fusion-splicing, the coating layers of the tip portions of the fiber portions 16₁ and 16₂ are removed, and the ends of the fiber portions are aligned in a line and fusion-spliced using arc discharge. The process of fusion-splicing is not within the scope of the present invention, and thus the detailed description thereof being omitted. Then, as shown in Fig. 5D, the fusion-spliced portion 48 is pressure-inserted into the coil holding clip 50 for fixing thereto which is provided in proximity to the side S₂ of the casing 14. Thereafter, as shown in Fig. 5E, the fiber coil holder member 46₂ for use with the optical fiber cable 16₂ is removed to release the optical fiber coil thus far held thrust against the lower winding core 28. Under this condition, the tube-removed fiber portion 16₂ staying outside the casing 14 is drawn into the casing to expand the size of the fiber coil. Following the steps above, as shown in Fig. 5F, the coil holder member 46₁ for use with the tube-removed fiber portion 16₁ is removed thereby to release the optical fiber coil, which has so far been kept thrust against the upper winding core 32. Under this condition, the tube-removed fiber portions 16₁ lying outside the casing 14 is drawn into the casing thereby to increase the size of the optical fiber coil. Expanding the size of the optical fiber coils results in separating the tube-removed fiber portions sufficiently from the coil forming jig 22 whereby it becomes practicable at this stage to take out the coil forming jig 22 from the casing 14, followed by placing the cover (not shown) in position to close the casing. Though in the above embodiments of the prevent invention, a wound-core type shown in Fig. 2 is employed for the coil forming jig, a coil spring type shown in Fig. 6 may be applied to substitute for the wound core type. The coil spring type coil forming jig is characterized by its outstanding simple construction. A coil spring 52 with a tight winding structure is favorable so that a tube-removed fiber portion may be wound spirally while being caught between each neighboring two of the turns 54. After winding the fiber portion to a predetermined number of turns, the coil thus formed is fixed temporarily to the coil spring 52, using an engaging clamp members such as a clip, and so forth or an adhesive tape. In Fig. 6, no other fiber portion than one is presented but, in actuality, two fiber portions experience similar winding with the coil spring 52 as described above, with the fiber coils thus formed being fixed temporarily to the coil spring 52. Thereafter, the ends of the remainder of the tube-removed fiber portions are fusion-spliced to each other, and the temporarily fixing members are removed from the coil spring 52 so as to take out the coils into which two fiber portions are wound, from the coil spring, followed by being encased in the casing 14. Shown in Figs. 7A and 7B is another example of the coil forming jig 22. These two figures give a plan view and a cross-sectional view of the another embodiment of the coil forming jig. The coil forming jig defined in this example is characterized in that the jig provides service with great ease of temporarily fixing the fiber coil to the jig as well as of releasing the fiber coil from the jig. Structurally precise with this coil forming jig, it comprises a base 62, a cylindrical optical fiber winding core 64 integrally formed with the base 62 and which extends upward from the center part of the base 62, and optical fiber holding levers 70₁ and 70₂, pivottaly mounted to the base with respective pins 68₁ and 68₂. The lower ends of the pins 68₁ and 68₂ are set in left and right notches 66₁ and 66₂ provided in the base 62. Into these notches 66₁ and 66₂, a pair of flexible tongues 72₁ and 72₂ extend respectively left and right outward in the radial direction from the lower end of the optical fiber winding core 64. The tongues 72₁ and 72₂ hold the lower ends of the optical fiber holding levers 70₁ and 70₂, respectively, thereby to maintain these optical fiber holding levers at their vertical positions. When the optical fiber holding levers 70₁ and 70₂ are brought down in the radial directions outwardly as shown by the arrows in resistance against the flexibility of the tongues 72₁ and 72₂, the tongues 72₁ and 72₂ come into contact with the outside peripheries of the optical fiber holding levers 70₁ and 70₂, whereby these optical fiber holding levers 70₁ and 70₂ are maintained horizontally. The tube-removed fiber portion is wound a predetermined number of turns around the optical fiber winding core of the coil forming jig. The fiber portion wound into a coil is pressed against the optical fiber winding core 64 by means of the optical fiber holding levers 70₁ and 70₂, whereby the fiber coil is held around the winding core. In this case, one tube-removed fiber portion is wound in one direction around the lower part of the winding core, while the other tube-removed fiber portion is wound in the opposing direction around the upper part of the winding core. Thereafter, the ends of the tube-removed fiber portions wound into coils are fusion-spliced to each other by a known conventional method. With a plurality of V-grooves 74₁ and another plurality of V-grooves 74₂ provided in the inside peripheries of the optical fiber holding levers 70₁ and 70₂, and which extend in the circumferential direction, it becomes feasible that a coil-formed fiber portions are held further positively around the optical fiber winding core. In case where the coil forming jig shown in Fig. 2 is used, it is permissible that a tube-removed fiber portion is wound around the winding core while securing the coil forming jig outside the casing 14 using certain means, and pressed against the winding core by the fiber core holder members 46₁ and 46₂. Under this condition, the coil forming jig is attached inside the casing 14. On the other hand, where the coil forming jig shown in each of Figs. 6, 7A and 7B is employed, it is allowed to wind either one tube-removed fiber portion 16₁ or 16₂ around one each coil forming jig. Alternatively, two tube-removed fiber portions 16₁ and 16₂ may be wound commonly around one coil forming jig. It is preferable to secure the coil forming jig shown respectively in Figs. 2, 6, 7A and 7B outside the casing 14 using some proper means to easily perform the respective steps of winding a tube-removed fiber portion around the fiber coil winding core, and encasing the coilformed fiber portion in the casing 14 under the condition that the coilformed fiber portion is fixed to the winding core, resulting in providing ease of encasing the coilformed fiber portion, compared with the case wherein fiber coil encasing is done with the coil forming jig set within the casing 14. The method of the present invention eliminates the need of altering a conventional casing and allows repetitive use of the coil forming jig around which the tube-removed fiber portion is wound, whereby the running cost required for embodying the present invention may be maintained small without raising the production cost of the casing. In addition, according to the method of the present invention, both optical fibers 16₁ and 16₂ can be wound around the coil forming jig without being subjected to twisting, whereby ease is provided for expanding the size of a coilformed fiber portion within the casing.

Claims: A method of preventing twisting of a fusion-spliced optical fiber in the process of encasing the optical fiber in a casing, the method comprising the steps of: a) disposing a coil forming member (22) at a central part of a casing (14), b) winding one (16₂) of a pair of optical fibers (16₁, 16₂) in one direction around a part of said coil forming member (22) a predetermined number of turns to form a first coil, c) restricting said first coil from expanding due to flexibility of the optical fiber, using a first holder member (46₂) for holding the first coil around said coil forming member (22), d) winding the other (16₁) of said pair of optical fibers said predetermined number of turns around another part of said coil forming member (22) in the direction opposite to said one direction to form a second coil, e) restricting said second coil from expanding due flexibility of the optical fiber, using a second holder member (46₁) for holding the second coil around said coil forming member, f) fusion splicing two ends of the remainder portions of said optical fibers which have not been wound into coils, for form a fusion-spliced portion (48), g) fixing said fusion-spliced portion within said casing (14) by use of an engaging clamp member (50), h) releasing said restricting of said first and second coils from expanding due to flexibility of the optical fibers by removing said first and second holder members (46) and i) pushing said remainder portions of said optical fibers into said casing (14) to expand said first and second coils. A method of preventing twisting of a fusion-spliced optical fiber in the process of encasing the optical fibers in a casing, according to claim 1, wherein, in step f) the fusion-spliced portion (48) is formed adjacent to and spaced from one side of the casing (14), and in step g) the fusion-spliced portion (48) is moved to a position inside the casing (14) adjacent to and spaced from said one side of the casing, where said engaging clamp member (50) is located. A method of preventing twisting of a fusion-spliced optical fiber in the process of encasing the optical fibers in a casing, according to claim 1 or 2, in which said coil forming member (22) comprises a base member (24), a cylindrical support (26) extending from substantially the center part of said base member, a lower winding core (28) on said support, a center partition member (30) on said support, an upper wind-ing core (34) on said support, and a top member (34) on said support. A method of preventing twisting of a fusion-spliced optical fiber in the process of encasing the optical fibers in a casing, according to claim 3, in which said base member (24), center partition member (30), and top member (34) are of substantially elliptical form. A method of preventing twisting of a fusion-spliced optical fiber in the process of encasing the optical fibers in a casing, according to claim 3, wherein, in step b) of winding one (16₂) of a pair of optical fibers, said one optical fiber is wound around said lower winding core (28), and in step d) of winding another (16₁) of said pair of optical fibers, said another optical fiber is wound around said upper Winding core (34). A method of preventing twisting of a fusion-spliced optical fiber in the process of encasing the optical fibers in a casing, according to claim 5, wherein, in step c) of restricting said first coil from expanding, said first holder member (46₂) is inserted between said base member (24) and said center partition member (30), and in step e) of restricting said second coil from expanding, said second holder member (46₁) is inserted between said center partition member (30) and said top member (34).

Inventors: OOBA MASAO, SETAISHI YUKIO, YOSHINUMA MIKIO, OOBA, MASAO, SETAISHI, YUKIO, YOSHINUMA, MIKIO
Applicants: FUJIKURA LTD, NIPPON TELEGRAPH & TELEPHONE, FUJIKURA LTD., NIPPON TELEGRAPH AND TELEPHONE CORPORATION
Application year: 1990
Main classification: G02B6
IPC codes: G02B6