Abstract:
The present invention relates to a method for mid-span branching of optical fiber cable which makes the mid-span branching possible without excess length of the optical fiber cable by forming main branching part and sub branching part for branched cores to be taken out from an existing main cable. It is an object of the present invention to provide a method for mid-span branching that provides marginal length of the existing main cable from which the branch cable branches off without the excess length of cables. To accomplish the above object of the present invention, there is provided a method for mid-span branching of optical fiber cable, comprising the steps of: setting an existing main cable and a branch cable; unsheathing main branched part and sub branched part of the main cable with preserved part; choosing and cutting branched cores with preserved cores remaining uncut; connecting the first branched cores to first branching cores to make temporary connection; pulling out the temporary connection to the sub branched part through the preserved part; and splicing the first branched cores and the first branching cores at the sub branched part, and splicing the second branched cores and second branching cores at the main branching part, second branching cores in the branch cable.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method for. mid-span branching of optical fiber cable network and more specifically to a method for mid-span branching of optical fiber cable which makes the mid-span branching possible without excess length of the optical fiber cable. 
     DESCRIPTION OF THE PRIOR ART 
     In general, optical fiber cables are installed in the networks of loop distribution, star distribution, or other distribution in consideration of economy and reliability of installation, and flexibility to quantitative change of and diversification of service. 
     By the loop distribution, as shown in FIG. 1A, the excess length of cables for mid-span branching is ensured beforehand in the manholes or on the poles  1 ,  2 ,  3 ,  4 ,  5 ,  6  which are, when the cables are initially installed, the anticipated points for branching. When the demand for the cores arises in the middle of service, branch cable is installed from the point of demand for the cores to the point of the loop distribution network for branching. Also, the branched cores of existing main cable in the network are spliced with the branching cores of the branch cable. Thus the network is of the loop-shape. 
     By the star distribution, as shown in FIG. 1B, the excess length of cables for mid-span branching is ensured beforehand in the manholes or on the poles  1 ,  2 ,  3 ,  4  which are, when the cables are initially installed, the anticipated points for branching. When the demand for the cores arises in the middle of service, branch cable is installed from the point of demand for the cores to the point of the star distribution network for branching. Also, the branched cores of existing main cable in the network are spliced with the branching cores of the branch cable. Thus the network is of the star-shape. 
     In branching of the optical fiber network described above, there have been provided methods for access-point branching by which branch cable is branched from the network at the point of access to the point of demand for the cores, and for mid-span branching by which branch cable is branched from the network, not at the point of access but at the mid-point of the network cable, to the point of demand for the cores. 
     In the method for mid-span branching, to avoid tension on the branching part, the excess length of the cables must be ensured for the minimum length of core of the optical fiber cable for the distance from the branching part to branching device, response to demand for re-access in the case of access-failure, malfunction, operational needs, and etc. 
     Because the prior arts need the excess length of cables as mentioned above, as shown in FIG. 2A, existing main cable  20  is pulled out from the conduit line  10  in the manhole  1  that is the position of mid-span branching, supported by supporter  30 , and the slack loop of cable is assumed. Thus the excess length of the cables is ensured. The cores of the existing main cable  20  and the branch cable  40  are placed in the manhole  1 . 
     As shown in FIG. 2B, the excess length of cables is fastened on the prop  31 . Branching part  100  is formed by unsheathing predetermined portions of the loop for the cores of the cable to be taken out. Splice closure is installed at the unsheathed part. 
     In the case where the excess length of cables either can&#39;t be or isn&#39;t ensured in the manhole that is supposed to be the position of mid-span branching, as shown in FIG. 3, branch cable  40  is installed in the manhole  2  adjacent to the manhole  1  which is supposed to be the position of mid-span branching. The splice closure  50  is disjointed and the branch cable  40  is branched from the existing main cable  20 , which is the access point branching method. Herein, for the mid-span branching to be completed, at most 500 meters of the branch cable is necessary. 
     Due to the long excess length of the cable for mid-span branching of prior arts described above, however, there are several problems listed below on usability, workability, and economy in efficient installation of the network. 
     Firstly, the excess length of cables is generally endured excessively because workers cannot decide exact points of branching when initial installation of the cables. Also, there are the cases when extra branch cables are installed to the access point of the loop/star distribution network because of the lack of the excess length of cables at the points of mid-span branching. Thus, the cost of installation or branching is excessively high. 
     Secondly, in the case of decision of the incorrect points for branching, ensured excess length of cables must be pulled to the points of mid-span branching or extra branch cables are installed to the points where the excess length of cables has been already endured. Thus the cost for extra installation occurs. 
     Thirdly, the ensured excess length of cables is of such length that preserved cores are accommodated in the splice closure, which may reduce workability. 
     Fourthly, unsheathing the slack loop of excess length of the cables takes long time. 
     Fifthly, the splice closure must have the room for, at least, the allowable radius of curvature of unit of cores with hardened Polybutadien Terephthalate (PBTP), unit of cores having preserved cores. So it is hard to put the unit of cores in order in the splice closure, which reduces reliability of cores of the preserved unit having the cores in operation. 
     Sixthly, the cables in the manhole cannot be put in order due to the ensured excess length of cables, which may reduce workability. The ensured excess length of cables on the poles also reduces the reliability and a fine view. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a method for mid-span branching that provides marginal length of the existing main cable from which the branch cable branches off without the excess length of cables that forms a slack loop. 
     To accomplish the above object of the present invention, there is provided a method for mid-span branching of optical fiber cable without excess length of cables, comprising the steps of: setting an existing main cable and a branch cable; unsheathing main branched part and sub branched part of the main cable with preserved part formed between the main branched part and the sub branched part; choosing and cutting branched cores with preserved cores remaining uncut at the main branched part, the branched cores having first branched cores and second branched cores; connecting the first branched cores to first branching cores to make temporary connection, first branching cores in the branch cable; pulling out the temporary connection to the sub branched part through the preserved part; and splicing the first branched cores and the first branching cores at the sub branched part, and splicing the second branched cores and second branching cores at the main branching part, second branching cores in the branch cable. 
     In accordance with another aspect of the present invention, there is provided a method for mid-span branching of optical fiber cable, comprising the steps of: setting an existing main cable and a branch cable; unsheathing main branched part and sub branched part of the main cable with preserved part formed between the main branched part and the sub branched part; choosing and cutting branched cores with preserved cores remaining uncut at the main branched part, the branched cores having first branched cores and second branched cores; pulling out the first branched cores to the sub branched part through the preserved part; setting hollow member above the preserved part; pulling out first branching cores to the sub branched part through the hollow member, first branching cores in the branch cable; and splicing the first branched cores and the first branching cores at the sub branched part and splicing the second branched cores and second branching cores at the main branched part, second branching cores in the branch cable. 
     Also, in accordance with another aspect of the present invention, there is provided a method for mid-span branching of optical fiber cable, comprising the steps of: setting an existing main cable and a branch cable; unsheathing main branched part and sub branched part of the main cable, preserved part formed between the main branched part and the sub branched part; choosing and cutting branched cores with preserved cores remaining uncut at the main branched part, the branched cores having first branched cores and second branched cores; pulling out the first branched cores to the sub branched part through the preserved part; aligning end of the branch cable with end of the sub branched part; unsheathing main branching part and sub branching part of the branch cable with second preserved part formed between the main branching part and the sub branching part, main branching part and sub branching part of the branch cable corresponding respectively to the main branched part and the sub branched part of the main cable; pulling out second branching cores to the main branching part through the second preserved part, second branching cores in the branch cable; and splicing the first branched cores and first branching cores at the sub branched part and splicing the second branched cores and the second branching cores at the main branched part, first branching cores in the branch cable. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The object, features and advantages of the present invention are understood within the context of the description of the preferred embodiments as set forth below. The description of the preferred embodiments is understood within the context of accompanying drawing. Which form a material part of this disclosure, wherein: 
     FIGS. 1A and 1B show general distribution of optical fiber cables; 
     FIGS. 2A and 2B show the mid-span branching method in accordance with prior art; 
     FIG. 3 shows in the access point branching method, branch cable installed in the manhole adjacent to the manhole that is supposed to be the position of mid-span branching; 
     FIG. 4 shows the position of mid-span branching according to present invention; 
     FIG. 5 shows points representing the portion to be unsheathed for the branched parts; 
     FIGS. 6A to  6 I show first embodiment according to present invention; 
     FIG. 7 shows the main and branch cable after applying the first embodiment of present invention FIGS. 8A to  8 G show second embodiment according to present invention; 
     FIG. 9 shows the main and branch cable after applying the second embodiment of present invention; 
     FIGS. 10A to  10 G show third embodiment according to present invention; and 
     FIG. 11 shows the main and branch cable after applying the third embodiment of present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Preferred embodiments of the present invention will be described in detail referring to the accompanying drawings. 
     Referring to FIG.  4  and FIG. 5, main cable  20  coming out from the conduit line  10  in the manhole  1  that is the position of mid-span branching is fastened of the prop  31  of supporter  30 . 
     Kept straight in shape, the main cable  20  is unsheathed with the length corresponding to that of main splice closure, forming main branched part  100  at the mid-point of main cable  20 . 
     The main cable  20  is also unsheathed with the length corresponding to that of sub splice closure, forming sub branched part  200  adjacent to the main branched part  100 . The main branched part  100  and the sub branched part  200  are separated by preserved part  300 . 
     The length of the main branched part  100  and the sub branched part  200  is no longer than that of the main splice closure and the sub splice closure that accommodates the main branched part  100  and the sub branched part  200  respectively. 
     The length of preserved part  300  of the main cable is also restricted by space of the manhole  1 . 
     Preferably the length of the main branched part  100  is about 50 cm to 60 cm long, the sub branched part  200  about 25 cm to 30 cm long, and the preserved part  300  about 25 cm to 30 cm long. 
     The unsheathing step of the main cable  20  and forming step of preserved part  300  and main and sub branched part  100 ,  200  described above are included in all the embodiments described below. 
     In first embodiment of the present invention, a method for mid-span branching of loop distribution, the branching cores of the branch cable  40  is pulled out from the main branched part  100  to the sub branched part  200  of the main cable  20  through the preserved part  300 . 
     Referring to FIG. 6A, as described above, kept straight in shape, the main cable  20  is unsheathed with the length corresponding to that of main splice closure, forming main branched part  100  at the mid-point of main cable  20 . 
     The main cable  20  is also unsheathed with the length corresponding to that of sub splice closure, forming sub branched part  200  adjacent to the main branched part  100 . The main branched part  100  and the sub branched part  200  are separated by preserved part  300 . 
     Preferably the length of the main branched part  100  is about 50 cm to 60 cm long, the sub branched part  200  about 25 cm to 30 cm long, and the preserved part  300  about 25 cm to 30 cm long. 
     Also, some portion of the unit of branched cores  21  of the main branched part  100  are selected and cut, thus the unit of branched cores  21  consists of branched cores  60  that are the portion cut and preserved cores  70  that remains uncut. Also, the branched cores  60  consist of the first branched cores  61  and the second branched cores  62 . 
     Referring to FIG. 6B, with end of the branch cable  40  aligned with the main branched part  100 , the branching cores which consist of the first branching cores  41  and the second branching cores  42  are pulled out from the branch cable  40 . 
     After that, connecting the first branched cores  61  and the first branching cores  41  makes temporary connection. 
     Referring to FIG.  6 C and FIG. 6D, the temporary connection is disconnected after the temporary connection is pulled out from the main branched part  100  to the sub branched part  200  through the preserved part  300 , thus the first branching cores  41  and the first branched cores  61  are placed in the sub branched part  200 . 
     Referring to FIG.  6 E,the preserved cores  70  in the main branched part  100  and sub branched part  200  are covered by unit spiral  80  for protection. 
     Referring to FIG. 6F, after trays  11  and  12  for protecting and supporting cores are set to the main branched part  100  and sub branched part  200  respectively, the first branched cores  61  and the first branching cores  41  are convolved and arranged on the tray  12  set to the sub branched part  200 , and the second branched cores  62  and the second branching cores  42  on the tray  11  set to the main branched part  100 . 
     Referring to FIG. 6G, main splice closure  13  and sub splice closure  14  are set so that the main branched part  100  and the sub branched part  200  including the trays  11 ,  12  are accommodated in the main slice closure  13  and sub splice closure  14  respectively, which makes it possible that the method for mid-span branching is operated without excess length of cables. 
     Referring to FIG.  6 H and FIG. 6I, in the case of branch of whole cores of a unit in the cable, there is not unit spiral for protection of preserved cores because there are not preserved cores in the main branched part  100  and the sub branched part  200 . 
     In this case, the step of making temporary connection, pulling out the temporary connection from the main branched part  100  to the sub branched part  200  through the preserved part  300 , setting trays and convolving and arranging the cores are same as described above except that there is not the step of protecting the preserved cores with the unit spiral. 
     Referring to FIG. 7, after applying the first embodiment of present invention that is the method for mid-span branching with utilization of the branched cores unit  21 , both the main splice closure  13  for mid-span branching and the sub splice closure  14  are in line with the main cable  20  in the manhole  1 , which also can be installed on the pole. The main splice closure  13  accommodates branch cable  40 . 
     In second embodiment of the present invention that can be applied to the case where the branching cores are difficult to pull out from the main branched part to the sub branched part through the preserved part by the branched cores, the branching cores are easy to place on the main branched part and sub branched part by the extra empty pipe cable. 
     Referring to FIG. 8A, kept straight in shape, the main cable  20  is unsheathed with the length corresponding to that of main splice closure, forming main branched part  100  at the mid-point of main cable  20 . 
     The main cable  20  is also unsheathed with the length corresponding to that of sub splice closure, forming sub branched part  200  adjacent to the main branched part  100 . The main branched part  100  and the sub branched part  200  are separated by preserved part  300 . 
     Preferably the length of the main branched part  100  is about 50 cm to 60 cm long, the sub branched part  200  about 25 cm to 30 cm long, and the preserved part  300  about 25 cm to 30 cm long. 
     Also, some portion of the unit of branched cores  21  of the main branched part  100  are selected and cut, thus the unit of branched cores  21  consists of branched cores  60  that are the portion cut and preserved cores  70  that remains uncut. Also, the branched cores  60  consist of the first branched cores  61  and the second branched cores  62 . 
     Referring to FIG. 8B, the branch cable with the first branching cores  41  and the second branching cores  42  is aligned with the end of the main branched part  100 . Also, empty pipe cable  15  is placed above the preserved part  300 . 
     Referring to FIG. 8C, the first branched cores  61  are pulled out from the main branched part  100  to the sub branched part  200  through the preserved part  300 , thus the first branched cores  61  are placed in the sub branched part  200 . 
     The first branching cores  41  are also pulled out to the sub branched part  200  through the empty pipe cable  15 , thus the first branching cores  41  are placed in the sub branched part  200 . 
     Also, the first branching cores  41  exposed between the empty pipe cable  15  and the branch cable  40  and the preserved cores  70  exposed in the main branched part  100  and the sub branched part  200  are covered with the unit spiral  80  for protection. 
     Protecting tube  10  also protects the second branching cores  42 . 
     Referring to FIG. 8D, after trays  11  and  12  for protecting and supporting cores are set to the main branched part  100  and sub branched part  200  respectively, the first branched cores  61  and the first branching cores  41  are convolved and arranged on the tray  12  set to the sub branched part  200 , and the second branched cores  62  and the second branching cores  42  on the tray  11  set to the main branched part  100 . 
     Referring to FIG. 8E, main splice closure  13  and sub splice closure  14  are set so that the main branched part  100  and the sub branched part  200  including the trays  11 ,  12  are accommodated in the main slice closure  13  and sub splice closure  14  respectively, which makes it possible that the method for mid-span branching is operated without excess length of cables. 
     Referring to FIG. 8F, and FIG. 8G, in the case of branch of whole cores of a unit in the cable, there is not unit spiral for protection of preserved cores because there are not preserved cores in the main branched part  100  and the sub branched part  200 . 
     In this case, the step of setting the empty pipe cable  15 , pulling out the first branched cores  61  from the main branched part  100  to the sub branched part  200  through the preserved part  300 , pulling out the first branching cores  41  to the sub branched part  200  through the empty pipe cable  15 , setting trays and convolving and arranging the cores are same as described above except that there is not the step of protecting the preserved cores by the-unit spiral. 
     Referring to FIG. 9, after applying the second embodiment of present invention that is the method for mid-span branching with utilization of the empty pipe cable  15 , both the main splice closure  13  for mid-span branching and the sub splice closure  14  are in line with the main cable  20  in the manhole  1 , which also can be installed on the pole. The main splice closure  13  accommodates branch cable  40 . 
     The main cable  20  and the empty pipe cable  15  connect the main splice closures  13  for mid-span branching and the sub splice closure  14 . 
     In third embodiment of the present invention that can be applied to the case where the branching cores are difficult to pull out from the main branched part to the sub branched part through the preserved part by the branched cores, the branching cores are easy to place on the main branched part and sub branched part by the branch cable itself. 
     The difference between the second embodiment and the third embodiment is that predetermined portions of branch cable corresponding respectively to the main branched part and the sub branched part of the main cable are unsheathed, the unsheathed portions of the branch cable forming second preserved part, main branching part and sub branching part of the branch cable, which the third embodiment does not need extra empty pipe cable. 
     Referring to FIG. 10A, kept straight in shape, the main cable  20  is unsheathed with the length corresponding to that of main splice closure, forming main branched part  100  at the mid-point of main cable  20 . 
     The main cable  20  is also unsheathed with the length corresponding to that of sub splice closure, forming sub branched part  200  adjacent to the main branched part  100 . The main branched part  100  and the sub branched part  200  are separated by preserved part  300 . 
     Preferably the length of the main branched part  100  is about 50 cm to 60 cm long, the sub branched part  200  about 25 cm to 30 cm long, and the preserved part  300  about 25 cm to 30 cm long. 
     Also, some portion of the unit of branched cores  21  of the main branched part  100  are selected and cut, thus the unit of branched cores  21  consists of branched cores  60  that are the portion cut and preserved cores  70  that remains uncut. Also, the branched cores  60  consist of the first branched cores  61  and the second branched cores  62 . 
     The end of the branch cable  40  is placed on the sub branched part  200 , and the branch cable  40  is unsheathed with the length corresponding to that of main splice closure, forming main branching part  400  at the mid-point of the branch cable  40 . 
     The branch cable  40  is also unsheathed with the length corresponding to that of sub splice closure, forming sub branching part  500  adjacent to the main branching part  400 . The main branching part  400  and the sub branching part  500  are separated by second preserved part  600 . 
     The position of the main branching part  400 , the sub branching part  500  and the second preserved part  600  correspond to the main branched part  100 , the sub branched part  200  and the preserved part  300  respectively. 
     Therefore the first branching cores  41  and the second branching cores  42  in the sub branching part  500  are placed on the side of the sub branched part  200 . 
     Referring to FIG. 10B, the second branching cores  42  are pulled out from the sub branching part  200  to the main branching part  400  through the second preserved part  600 . 
     Therefore the first branching cores  41  in the sub branching part  500  are placed on the side of the sub branched part  200  and the second branching cores  42  in the main branching part  400  are placed on the side of the main branched part  100 . 
     Referring to FIG. 10C, the first branching cores  41  exposed in the main branching part  400 , the preserved cores  70  exposed in the main branched part  100  and the sub branched part  200  are covered with the unit spiral  80  for protection. 
     Protecting tube  10  also protects the second branching cores  42  in the main branching part  400 . 
     Referring to FIG. 10D, after trays  11  and  12  for protecting and supporting cores are set to the main branched part  100  and sub branched part  200  respectively, the first branched cores  61  and the first branching cores  41  are convolved and arranged on the tray  12  set to the sub branched part  200 , and the second branched cores  62  and the second branching cores  42  on the tray  11  set to the main branched part  100 . 
     Referring to FIG. 10E, main splice closure  13  and sub splice closure  14  are set so that the main branched part  100  and the sub branched part  200  including the trays  11 ,  12  are accommodated in the main slice closure  13  and sub splice closure  14  respectively, which makes it possible that the method for mid-span branching is operated without excess length of cables. 
     Referring to FIG.  10 F and FIG. 10G, in the case of branch of whole cores of a unit in the cable, there is not unit spiral for protection of preserved cores because there are not preserved cores in the main branched part  100  and the sub branched part  200 . 
     In this case, the step of forming the main branching part  400 , the sub branching part  500  and the second preserved part  600 , pulling out the first branched cores  61  from the main branched part  100  to the sub branched part  200  through the preserved part  300 , pulling out the second branching cores  42  from the sub branching part  500  to the main branching part  400  through the second preserved part  600 , setting trays and convolving and arranging the cores are same as described above except that there is not the step of protecting the preserved cores by the unit spiral. 
     Referring to FIG. 11, after applying the third embodiment of present invention that is the method for mid-span branching with utilization of the branch cable  40 , both the main splice closure  13  for mid-span branching and the sub splice closure  14  are in line with the main cable  20  in the manhole  1 , which also can be installed on the pole. The main splice closure  13  accommodates branch cable  40 . 
     The main cable  20  and the branch cable  40  connect the main splice closures  13  for mid-span branching and the sub splice closure  14 . 
     Accordingly, when the methods in accordance with the present invention is applied to the networks of loop distribution, star distribution, or other distribution, the branching cores in the branch cable can be connected to the main cable with ease without excess length of cable. Also, the main and the branch cable are easily arranged after connection. When additional demand for cores arises, the mid-span branching is operated efficiently by opening the main and sub splice closure, pulling out the branched cores from the main cable, and splicing the branched cores of the main cable and the branching cores of the branch cable. 
     Therefore, by the methods in accordance with the present invention, planning of cable distribution of the networks is established without difficulty because there is no need for predicting the position of mid-span branching for future service demand. 
     The cost for setting excess length of cable does not occur due to the absence of the excess length of cable, which reduces cost for network-installation and mid-span branching. 
     The reliability of the optical fiber cores increases also due to the absence of the excess length of cable that needs the room for, at least, the allowable radius of curvature of unit of cores in the prior arts. 
     The efficiency of maintenance and workability of network-installation and mid-span branching can increase due to easy acceptance of additional demand for cores by the methods in accordance with the present invention. 
     Although the preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.