FIELD OF THE INVENTION 
   The present invention relates to an optical fiber coupler and manufacturing apparatus and method thereof, and particularly to an 1×4 optical fiber coupler structure and improvements on a loading fixture, a clamping device, a packaging device and a conveying mechanism for the manufacturing apparatus and method thereof. 
   BACKGROUND OF THE INVENTION 
   Optical communication technology has made great progress in recent years. In the past, optical fiber communication technology and optical fiber communication elements mainly were used on backbone networks. These days they are widely used in metropolitan optical communication networks. The vision of Fiber-To-The-Home (FTTH) is achievable in the near future. 
   The optical fiber coupler, also called optical fiber splitter, is an essential element to implement FTTH. The optical fiber coupler usually is fabricated through a fused biconical tapered fiber coupling technique. The optical fiber passive device thus made costs less and has excellent optical characteristics. It is suitable for mass production. Hence it is widely used in the industry. In the earlier days, the technology mainly focuses on 1×2 optical fiber coupler. With the rapid advance of optical communication technology, now 1×4 optical fiber couplers have gradually become the mainstream. Hence to provide a new and desired apparatus and method to manufacture optical fiber couplers, such as a clamping device, a packaging device and the like is important. 
   Moreover, fabrication of the optical fiber couplers at present mostly is semi-automatic. In general, the manufacturing process of the optical fiber couplers includes at least two main stages: one is stretching optical fibers, another is packaging the stretched optical fibers. As a clamping device, the optical fiber fusion splice device and packaging device have to be moved during fabrication. Conveying mechanisms are needed to do transportation. In conventional techniques, individual device such as a clamping device, optical fiber fusion splice device, packaging device and the like are moved by individual and independent conveying mechanisms. This is more expensive and the equipment cannot be made as compact as desired. 
   SUMMARY OF THE INVENTION 
   In view of the aforesaid problems occurring to the conventional techniques of fabricating optical fiber couplers, such as lacking suitable 1×4 clamping devices, and packaging device and conveying mechanisms being too complicated and too bulky, one of the objects of the present invention is to provide a loading fixture for manufacturing optical fiber couplers that has a groove on the top surface to hold a fourth optical fiber among a first optical fiber, a second optical fiber and a third optical fiber in a close contact manner. The connection lines between the center of the fourth optical fiber and the centers of the first optical fiber, second optical fiber and third optical fiber form three included angles, in which two are ranged from 90 to 120 degrees. 
   Based on the loading fixture set forth above, the invention further provides an optical fiber coupler to split the optical signal of the fourth optical fiber to the first, second and third optical fibers. It has the same characteristics as previously discussed. Namely the first, second and third optical fibers are located on the periphery of the fourth optical fiber, and the connection lines between the center of the fourth optical fiber and the centers of the first optical fiber, second optical fiber and third optical fiber form three included angles in which two are ranged from 90 to 120 degrees. 
   By means of the loading fixture set forth above, the invention further provides a method for manufacturing optical fiber couplers that includes steps of: providing a loading fixture which has the aforesaid characteristics, and placing a first optical fiber, a second optical fiber, a third optical fiber and a fourth optical fiber in a groove of the loading fixture, in arrangement as previously discussed. 
   In one aspect, the invention further provides a clamping device for manufacturing optical fiber couplers that mainly includes a holding stage, a loading fixture and a clamping member. The loading fixture is located on the top surface of the holding stage and has the characteristics mentioned above. The clamping member comprises a plurality of clamping arms pivotally coupled on one side of the top surface of the holding stage that the clamping arms may be turned to cover and press the optical fibers and the top surface of the loading fixture when the optical fibers are placed on the loading fixture. 
   In another aspect, the invention provides a packaging device for manufacturing optical fiber couplers that mainly includes a pedestal, a screw bar and a pair of carriers. The screw bar has two sections that have opposite screw threads formed respectively on the peripheral surface, and run horizontally through the base. The two carriers have screw holes with opposite screw threads to couple with the screw bar, and jointly hold a packaging substrate the top to package an optical fiber coupler. When the screw bar rotates, the two carriers are moved to reduce or increase the interval there between. 
   In yet another aspect, the invention provides an apparatus for manufacturing optical fiber couplers that includes a base, a pair of clamping devices, an optical fiber fusion splice device, a packaging device and a plurality of conveying units. The clamping device aims to clamp a plurality of optical fibers. The optical fiber fusing device aims to heat a bare portion of the optical fibers. The packaging device holds a packaging substrate to package the bare portion of the optical fibers. The conveying units are mounted onto the base to hold and transport the clamping device, optical fiber fusion splice device and packaging station during stretching and packaging processes of the optical fibers. The packaging station and the optical fiber fusion splice device are connected through a linkage bar. The conveying units drive the packaging station and the optical fiber fusion splice device to move synchronously. When the front end of the optical fiber fusion splice device is moved above an optical fiber stretching axis, the packaging station is moved away from the optical fiber stretching axis. When the packaging station is moved below the optical fiber stretching axis, the optical fiber fusion splice device is moved away from the optical fiber stretching axis. 
   Through the apparatus for manufacturing optical fiber couplers set forth above, the invention further provides a method for manufacturing optical fiber couplers. The method includes: coupling the packaging station and the optical fiber fusion splice device through the linkage bar; moving the packaging station and the optical fiber fusion splice device synchronously through the conveying units; moving the packaging station away from the optical fiber stretching axis when the front end of the optical fiber fusion splice device is moved above the optical fiber stretching axis, and moving the optical fiber fusion splice device away from the optical fiber stretching axis when the packaging station is moved below the optical fiber stretching axis. 
   Finally, the invention further provides an optical fiber coupler according to the apparatus and method for manufacturing optical fiber couplers set forth above. The optical fiber coupler includes a first optical fiber, a second optical fiber, and a third optical fiber surrounding the periphery of a fourth optical fiber. The connection lines between the center of the fourth optical fiber and the centers of the first optical fiber, second optical fiber and third optical fiber form three included angles in which two are ranged from 90 to 120 degrees. 
   In short, the invention mainly aims to provide a loading fixture, a clamping device and a packaging station in the manufacturing process for fabricating 1×4, 2×4 or 4×4 optical fiber couplers. It also improves the driving mechanism and operation of the manufacturing apparatus of the optical fiber couplers. The size of the apparatus is greatly reduced, and the building costs are lower. The reliability and production yield of the manufacturing system of the optical fiber coupler also is enhanced. 
   The foregoing, as well as additional objects, features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic view of a first embodiment of the clamping device of the invention; 
       FIG. 2  is a sectional view of the first embodiment of the clamping device of the invention; 
       FIG. 3  is an enlarged schematic view of the packaging section and the anchoring section of the loading fixture of the first embodiment; 
       FIG. 4  is a schematic view of the arrangement of the loading fixture trough and optical fibers of the first embodiment; 
       FIG. 5  is a schematic view of the arrangement of the loading fixture trough and optical fibers of a second embodiment; 
       FIGS. 6 and 7  are schematic views of the packaging station and an operating condition of a third embodiment of the invention; and 
       FIG. 8  is a schematic view of a fourth embodiment of the apparatus for manufacturing optical fiber couplers of the invention and an operating condition. 
   


   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention mainly aims to provide a 1×4, 2×4 or 4×4 optical fiber coupler, and an apparatus and method for manufacturing the optical fiber coupler. The apparatus includes a loading fixture, a clamping device, a packaging station and a driving mechanism. Details will be elaborated as follows. It is to be noted that the apparatus is not limited to manufacturing the 1×4, 2×4 or 4×4 optical fiber coupler. By changing different loading fixtures, it can also be used to fabricate 1×2, WDM (Wavelength Division Multiplexer) and WBC (Wide-Band Couplers) optical fiber couplers that function differently. 
   Refer to  FIGS. 1 through 5  for a first embodiment of the clamping device for fabricating the optical fiber coupler according to the invention. In general, two symmetrical clamping devices are to be used in a cooperative manner. The following discussion is based on one clamping device  100 . 
   Referring to  FIG. 1 , the clamping device  100  includes a holding stage  110 , a loading fixture  120 , a clamping member  130  and a push rod  140 . 
   Referring to  FIGS. 1 and 2 , the holding stage  110  is made of metal and has a vertical trench  111 . On a corner adjacent to the top surface of one side, there is a guiding slot  112  and an orienting slot  113  formed on one side. The top surface of the holding stage  110  further has pivot seats  114 ,  115 ,  116  and  117  to pivotally couple with the clamping member  130 . 
   Referring to  FIGS. 1 through 4 , the loading fixture  120  is located on the top surface of the holding stage  110  opposing the trench  111 . They may be integrally formed, or as shown in this embodiment, include a packaging section  121 , an anchoring section  122  and a plane deck  123  extended from an outer end of the anchoring section  122 . The packaging section  121  is pivotally coupled on the holding stage  110  as shown in  FIG. 2 , and is turning between a horizontal position and a vertical position in the trench  111 . It has a magnet  128  on the bottom. When the packaging section  121  is positioned vertically, the magnet  128  attracts one side of the holding stage  110  through the magnetic force. The packaging section  121  further has a recess  1210  as shown in  FIG. 3  that is sunk from the top surface of the packaging section  121  to form a selected area. It has one side abutting the anchoring section  122 . The recess  1210  aims to facilitate peeling of the shell (not shown in the drawings) of the optical fibers. Referring to  FIG. 1 , the anchoring section  122  is fastened to the holding stage  110 . The plane deck  123  aims to aid holding, and has a linear notch  129  on the top surface. 
   The top surfaces of the anchoring section  122  and the packaging section  121  have a groove  124  to hold four optical fibers (referring to  FIGS. 1 ,  3  and  4 ). The notch  129  of the plane deck  123  is abutting the groove  124  on the outer end of the anchoring section  122 . The groove  124  has a first bottom surface  125 , a second bottom surface  126  and a third bottom surface  127 . The first bottom surface  125  is deeper than the second and third bottom surfaces  126  and  127 , and they are formed in a stepwise manner. In  FIG. 4 , the sidewalls of the groove  124  are inclined. In practice, the sidewalls of the groove  124  may be in any shape desired, as long as they can hold the optical fibers.  FIG. 5  shows a second embodiment in which the sidewalls are vertical. The bottom surfaces also may be formed in any shape desired, such as concave surfaces. 
   Referring to  FIG. 4 , for holding the optical fibers. Place a first optical fiber  151  on the first bottom surface  125 , a second optical fiber  152  on the second bottom surface  126 , and a third optical fiber  153  on the third bottom surface  127 . Then place a fourth optical fiber  154  among and abutting the first optical fiber  151 , second optical fiber  152  and third optical fiber  153 . After the arrangement is finished, the top sides of the second, third and fourth optical fibers  152 ,  153  and  154  substantially coincide with the top surface of the anchoring section  122  or the packaging section  121 . 
   The design of the groove of the loading fixture aims to form three included angles by connecting the centers of all optical fibers and with two of the included angles in the range of 90 and 120 degrees (in this embodiment, two are 90 degrees, while another is 180 degrees). The desired layout has a Y-shape or T-shape. A 1×4, 2×4 or 4×4 optical fiber coupler thus formed can split the optical signal evenly to all optical fibers. Besides the two stepwise groove previously discussed, the groove of other shapes may also be used, such as a V-shape groove coupled with a clamping arm that can hold the first, second, third and fourth optical fibers  151 ,  152 ,  153  and  154  in a T-shape or Y-shape. 
   In short, in the optical fiber coupler provided by the invention, the first optical fiber  151 , second optical fiber  152  and third optical fiber  153  are located on the periphery of the fourth optical fiber  154 . Moreover, the connection lines between the center of the centers of the fourth optical fiber  154  and the centers of the first optical fiber  151 , second optical fiber  152 , and third optical fiber  153  form three included angles in which two are ranged from 90 to 120 degrees. 
   Based on the loading fixture previously discussed, the invention provides a method for manufacturing optical fiber couplers. The method includes the following steps: (1) providing a loading fixture which has a groove; and (2) placing a first optical fiber, a second optical fiber, a third optical fiber and a fourth optical fiber in the groove with the fourth optical fiber located among and abutting the first optical fiber, second optical fiber and third optical fiber; and the connection lines of the centers of the fibers form three included angles in which two are ranged from 90 to 120 degrees. There is no limitation on the shape of the groove. 
   Referring to  FIGS. 1 and 2 , the clamping member  130  is pivotally coupled on one side of the top surface of the holding stage  110 . It includes three clamping arms  131 ,  132  and  133  that are vertical to the longitudinal axis of the loading fixture  120 . In practice, there is no limitation on the number of clamping arms. When the optical fibers, previously discussed, are held by the loading fixture  120 , the clamping arms may be turned to cover and press the top surface of the loading fixture  120  to compress and anchor the arranged optical fibers in the groove  124 . 
   In order to anchor the optical fibers securely, the clamping arms  131 ,  132  and  133  have respectively a compressing portion  134  on the bottom surface, corresponding to the loading fixture  120 . The compressing portion  134  may be made from an elastic material such as rubber or the like. Another method to adjust the anchoring strength is through a handgrip  135  located on the top surface of a distal end of the clamping arm  131  as shown in  FIG. 1 . The handgrip  135  has a stem  136  running through the clamping arm  131  and exposing outside the bottom surface of the clamping arm  131 . There is an elastic element  138  between the handgrip  135  and the stem  136 . When the clamping arm  131  is turned downwards, the stem  136  slides in the guiding slot  112  of the holding stage  110  to be anchored (with the clamping arm  131  covering the packaging section  121  in a horizontal manner). The stem  136  may have a jutting tenon  137 . When the clamping arm  131  reaches the compression position, turn the handgrip  135  to drive the stem  136 , the jutting tenon  137  may be wedged in the orienting slot  113  of the holding stage  110 . The elastic element  138  provides a selected extension force to maintain a selected compression force when the clamping arm  131  reaches the anchor position. 
   Referring to  FIGS. 1 and 2 , the push rod  140  is located beneath the loading fixture  120 , and runs though the holding stage  110  horizontally. The push rod  140  has a front end to hold the packaging section  121  on a horizontal position as shown in  FIG. 2  (with the packaging section  121  indicated by solid lines). When the push rod  140  is pulled away from the packaging section  121 , the packaging section  121  may be turned from horizontal position to vertical position, and attracted by the magnet  128  to lean on an inner wall of the holding stage  110 , as shown in  FIG. 2  (with the packaging section  121  indicated by broken lines). 
   To limit the moving distance of the push rod  140 , the push rod  140  has a head  141  on one end formed in a larger diameter, and a handle  142  on the other end formed in a greater diameter. The holding stage  110  has a retaining member  118  to house the push rod that has an inner diameter smaller than the outer diameter of the head  141  or the handle  142 . In addition, the head  141  has an arched corner on the top surface, to facilitate turning of the packaging section  121  from vertical position to horizontal position. 
   Refer to  FIGS. 6 and 7  for a third embodiment of the packaging station  200  for fabricating optical fiber couplers. It includes a pedestal  210 , a screw bar  220 , carriers  230  and  240 , and guiding rods  250  and  260 . 
   The pedestal  210  is substantially formed in U-shape. The screw bar  220  runs through the pedestal  210  horizontally and has two ends extended outside the pedestal  210 . The two distal ends of the screw bar  220  are coupled respectively with a rotary bar  221  and  222  of a larger diameter to be grasped for turning. 
   The carriers  230  and  240  are substantially vertical posts and have screw holes  231  and  241  of opposite screw threads to couple on the screw threads (not shown in the drawings) of the screw bar  220 . The surface of the screw bar  220  has a left area and a right area with screw threads of opposite directions formed thereon. The guiding rods  250  and  260  run transversely through the pedestal  210  and anchor thereon in parallel with the screw bar  220 . The carriers  230  and  240  have corresponding apertures  232 ,  233 ,  242  and  243  to allow the guiding rods  250  and  260  to pass through. 
   When the screw bar  220  is turned, the carriers  230  and  240  are moved horizontally relative to each other and reduce the distance between the carriers  230  and  240 . Hence by coupling with a packaging baseboard of a selected length, the bare portion of the optical fibers may be packaged. 
   The carriers  230  and  240  have respectively an arched trough  234  and  244  on the top end to jointly hold a quartz tube (not shown in the drawings) which has a notch to serve as the “packaging substrate” for packaging the optical fibers. 
   Moreover, the carriers  230  and  240  have respectively through holes  235  and  245  running through the arched troughs  234  and  244  that have a bottom opening (not shown in the drawings) to couple respectively with a vacuum connector  236  and  246 , to link to a vacuum machine (not shown in the drawings). Thereby, the arched troughs  234  and  244  can provide a vacuum suction force to hold the packaging substrate (quartz tube) securely in the arched troughs,  234  and  244 , during the packaging process. 
   In addition, the carriers,  230  and  240 , have respectively a ceramic heater,  237  and  247 , on two sides of the top end to generate heat in the packaging process. The carriers,  230  and  240 , have respectively a side trough,  238  and  248 , on another side of the top end to hold a thermal sensor (not shown in the drawings) to control the heating temperature of the heating coils. In a desired condition, the packaging center of the optical finer coupler and the center of the thermal sensor are on the same concentric circle. The concentric circle has the center coinciding with the centers of the ceramic heaters,  237  and  247 , so that temperature variation may be measured accurately. 
   Refer to  FIG. 8  for the entire structure of the apparatus  300  for manufacturing optical fiber couplers of the invention. It includes a base  310 , clamping devices,  320  and  330 , an optical fiber fusion splice device  340 , a packaging station  350  and a plurality of conveying units that include a longitudinal conveying unit  360 , a vertical conveying unit  370  and a clamping device conveying unit  380 , to hold and transport the clamping devices,  320  and  330 , optical fiber fusion splice device  340 , and packaging station  350 . 
   The optical fiber fusion splice device  340  provides high temperature to heat the bare portion of the optical fibers so that they may be stretched and allow the optical signal to be evenly split or coupled. The clamping devices,  320  and  330 , are mounted onto a sliding track  381  of the clamping device conveying unit  380 , and are movable in opposite directions relative to each other on an optical fiber stretching axis  390  (the broken line in the drawings) to stretch the bare portion of the optical fibers. 
   The base  310  holds the vertical conveying unit  370  and the clamping device conveying unit  380 . It has a opening slot  311  to house a movable U-shape linkage bar  361 . The linkage bar  361  has two ends connecting respectively to the packaging station  350  and the optical fiber fusion splice device  340 . The optical fiber fusion splice device  340  and the linkage bar  361  are mounted onto a sliding track  362  of the longitudinal conveying unit  360  so that the optical fiber fusion splice device  340 , linkage bar  361  and packaging station  350  are moved synchronously and horizontally. The longitudinal conveying unit  360  is mounted onto a sliding track  371  of the vertical conveying unit  370  so that the optical fiber fusion splice device  340 , linkage bar  361 , and packaging station  350  are driven by the longitudinal conveying unit  360 , to move vertically. In this embodiment, two sets of conveying units are used, so that the optical fiber fusion splice device  340 , linkage bar  361 , and packaging station  350  may be moved in two dimensions. Similarly, another set of transverse conveying units (not shown in the drawings) may be added to increase the moving range and form a transmission system moving in three dimensions. 
   The objective of the aforesaid design is to move the packaging station  350  and optical fiber fusion splice device  340  synchronously, so that, while the optical fibers are stretched through the optical fiber fusion splice device  340 , the packaging process performed by the packaging station  350  is done consecutively in a front side and rear side manner. Through such a design, when the front end of the optical fiber fusion splice device  340  is moved above the stretching axis  390  of the optical fibers, the optical fiber fusion splice device  340  is heating the optical fibers, and the packaging station  350  is moved away from the stretching axis  390 . When the packaging process is proceeding, the packaging station  350  is moved beneath the stretching axis  390  of the optical fibers, and the optical fiber fusion splice device  340  is moved away from the stretching axis  390 . By means of the synchronous design of the packaging station  30  and the optical fiber fusion splice device  340 , their operations do not interfere with each other. Moreover, through the linkage bar  361 , only one set of conveying units is required. The structure is simpler than the conventional techniques that require two independent conveying units. 
   In practice, the packaging station and the optical fiber fusion splice device are driven synchronously through a linkage bar and a conveying unit. Alterations may be made based on this design. For instance, connecting the packaging station and the optical fiber fusion splice device is not limited to the linkage bar. The connecting positions, or number, degree of freedom, shape of the conveying units, and driving method between the conveying units may also have varying choices. 
   Based on the optical fiber coupler previously discussed, the invention also provides a method for manufacturing optical fiber couplers. It includes the following step: (1) connecting the packaging station and the optical fiber fusion splice device through a linkage bar; and (2) moving the packaging station and the optical fiber fusion splice device synchronously through a conveying unit. When the front end of the optical fiber fusion splice device is moved above the optical fiber stretching axis, the packaging station is moved away from the optical fiber stretching axis. When the packaging station is moved below the optical fiber stretching axis, the optical fiber fusion splice device is moved away from the optical fiber stretching axis. The embodiments set forth above employ a conveying method that includes a vertical conveying unit and a longitudinal conveying unit to transport the packaging station and the optical fiber fusion splice device in vertical direction and horizontal direction. Or a transverse conveying unit may be added to couple with the vertical conveying unit and longitudinal conveying unit to move the packaging station and the optical fiber fusion splice device in three dimensions. 
   While the preferred embodiments of the invention have been set forth for the purpose of disclosure, modifications of the disclosed embodiments of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments, which do not depart from the spirit and scope of the invention.
An optical fiber coupler and manufacturing apparatus and method thereof aim to provide a loading fixture and a clamping device to fabricate 1x4, 2x4 and 4x4 optical fiber couplers, and also improve driving mechanisms and operation of the packaging station and the entire manufacturing equipment. The 1x4 optical fiber coupler fabricated by means of the invention can split an optical signal more evenly and has a higher production yield. The total size of the equipment is smaller and the structure is less complicated, and the construction cost is lower.