Patent Publication Number: US-2004050115-A1

Title: Optical fiber drawing apparatus for decreasing an optical fiber break and impressing a spin to an optical fiber

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to an optical fiber drawing apparatus for decreasing an optical fiber break by adjusting a curvature radius and impressing a spin to an optical fiber, and in particular to an optical fiber drawing apparatus which it is possible to decrease an optical fiber break by continuously installing at least one or more moving rollers after a fixed roller and adjusting a curvature radius of an optical fiber and to provide a spin to an optical fiber by vertically reciprocating at least one roller among a plurality of moving rollers with respect to an optical fiber drawing surface.  
       [0003] 2. Description of the Background Art  
       [0004] A process for fabricating a piece of an optical fiber is formed of an optical fiber mother material fabrication process, and a drawing process for drawing an optical fiber from the fabricated mother material.  
       [0005] In more detail, the optical fiber is fabricated by an optical fiber mother fabrication method such as a Modified Chemical Vapor Deposition (MCVD), an Outside Vapor Deposition (OVD) or a Vapor Axial Deposition (VAD).  
       [0006] The fabricated mother material is processed through the drawing process of FIG. 1. As shown in FIG. 1, the optical fiber is processed through a heating furnace  2 , a diameter measuring unit  3 , a cooling apparatus  4 , a coating apparatus  5 , an infrared ray hardening apparatus  6 , and a fixing roller unit  7  which are sequentially vertically installed in an optical fiber drawing direction.  
       [0007] The heating furnace  2  adapted as a heat source may be formed of one of an electric resistance furnace, a high frequency induction furnace or a carbon dioxide laser. The heating furnace  2  is movable upward or downward. The optical fiber mother material melted to a desired temperature by the heating furnace  2  is drawn to one piece of an optical fiber. At this time, the inner portions of the heating furnace maintain clean so that the surface of the optical fiber  1  is not polluted by a certain impurity, and that the strength of the same is not decreased.  
       [0008] The diameter measuring device  3  like a laser micro measuring unit is directed to continuously measuring the diameter during the drawing operation, and a capstan(not shown) controlled at a certain speed controls the measured diameter for thereby producing an optical fiber having a desired diameter.  
       [0009] The optical fiber is processed through the cooling apparatus  4  for thereby implementing a certain temperature proper for a coating process. The optical fiber is processed through the cooling apparatus  4  and is coated by the coating apparatus  5 . The above coating process is performed for protecting the optical fiber  1  from a moisture, friction, etc. Here, the coating material is a Kynar, an epoxy, a silicon RTV, an ultraviolet ray setting resin, etc.  
       [0010] Passing through the violet ray hardening apparatus  6  after being coated, the optical fiber is hardened. The optical fiber is passed through a capstan(not shown) adapted to apply a certain tensile force so that the optical fiber is drawn with a particular diameter after the optical fiber is passed through the violet ray hardening apparatus  6 . Thereafter, the optical fiber is wound onto a spool (not shown) or a take-up reel (not shown).  
       [0011] The fabricated optical fibers are tested by a prove-test for checking whether they satisfy a minimum tension standard. The above test is performed while the optical fibers are being wound after being coated or the test is independently performed after the drawing process.  
       [0012]FIG. 2 is a view illustrating a fixing roller unit of a conventional optical fiber drawing apparatus. As shown in FIG. 2, the fixing roller unit  7  includes a fixing roller  7 - 1  for changing the direction of the optical fiber  1 , and a plurality of vertical drawing rollers  7 - 2  for implementing a smooth drawing operation of the optical fiber  1 . In the conventional optical fiber drawing apparatus which has only a fixing roller unit  7  of FIG. 2, a roller having a smaller radius is used for obtaining a certain installation space because the space is limited. In this case, the direction is hastily changed, so that a tension force and bending stress (applied by a certain rotating member having a certain radius like a roller) are generated.  
       [0013] A micro particle  1 - 1  or a crack  1 - 2  may occur by a local bending and a torsion stress which are applied between the vertical drawing rollers  7 - 2  while the optical fiber is processed through the vertical drawing rollers  7 - 2 . If the micro particle  1 - 1  or the crack  12  occurs before the optical fiber passes through the fixing roller  7 - 1 , while the optical fiber passes through the fixing roller  7 - 1  the stress is concentrated at the portion where the micro particle  1 - 1  or the crack  1 - 2  occurs.  
       [0014] The bending stress due to the roller and the stress concentrations due to the micro particle  1 - 1  and the crack  1 - 2  are known as a major factor which causes a break during an optical fiber drawing process.  
       [0015] The inventors of the present invention disclosed that a safety factor by the stress applied to the optical fiber  1  is generally more than 10 by a pure torsion force and a bending stress as a result of the tests. But the inventors disclosed that the safety factor can be decreased to less than 1 by a certain external environment like the micro particle  1 - 1 , the crack  1 - 2  or other factors such as a vibration, so that a break may occur.  
       [0016] For example, assuming that the diameter of the optical fiber  1  is 125 μm, and the axial force (applied by the torsion force in the axial direction) is 0.3 kgf, the safety factor is about 18.86 because the fracture stress is 651.4 ksi without consideration of the safety factor crack, and the axial stress is 34.53 ksi(2.40×10 8  Pa) calculated by ρ q =F/A=0.3×9.81/[(π/4)×( 125 × 10   −6 ) 2 ].  
       [0017] In addition, the safety factor determined by both the axial stress and the bending stress applied due to the roller is about 11 because the fracture stress is 651.4 ksi without consideration of the safety factor crack, the bending stress is 23.2 ksi(1.61×10 8  Pa) calculated by ρ b =Ey/R=3×70×10 9 ×125×10 −6 /(2×0.082).  
       [0018] As described above, in the case that the stress concentration is not applied by the crack in the optical fiber, the safety factor by the axial stress and the bending stress applied to the optical fiber is above 10.  
       [0019] However, when the stress concentration by the crack is considered, the concentration stress based on the coefficient by the size and shape of the crack is 341 ksi as ρ c =YK{square root}{square root over (C)}, if crack is 1 μm, the shape coefficient Y is 3, and the fracture toughness K is 0.79×10 6 .  
       [0020] Therefore, when the stresses due to the torsion, bending and crack which occur by one roller are combined, the safety factor may be decreased to 1.6 by the size and shape of the crack and the concentration of the stress. In addition, the safety factor may be decreased to less than 1 based on the size and number of the rollers, so that a break may occur.  
       [0021] Even though the break does not occur during the drawing process, when the optical fiber receives a big stress in a state that the optical fiber is not fully hardened while the optical fiber passes through the violet ray hardening apparatus  6 , the optical fiber  1  may have a large damage.  
       [0022] The optical fiber drawing apparatus having only the fixing roller unit  7  directly transfers the vibration of the fixing roller unit  7  to an optical fiber and a drawing tower during the optical fiber drawing process, so the quality of the optical fiber may be degraded.  
       [0023] A preferred single mode optical fiber in a symmetrical circular shape is adapted to transfer light to two independent orthogonal polarizing modes. However, when an asymmetrical lateral stress which affects a desired circular symmetrical shape is applied to the single mode optical fiber, the above two independent orthogonal polarizing modes are transferred at different phase rates, so that a birefringence occurs. A undesired birefringence may cause a dispersion of an optical signal transferred through the optical fiber, namely, a polarization mode dispersion (PMD), so that an accuracy of a signal is decreased. Therefore, it is needed to decrease the polarization mode dispersion in the optical fiber. It is known that it is possible to decrease the polarization mode dispersion by impressing a spin to the optical fiber. In order to decrease the polarization mode dispersion phenomenon, the techniques for impressing a spin to the optical fiber are disclosed in the U.S. Pat. No. 5,298,047 and the U.S. Pat. No. 6,076,376.  
       SUMMARY OF THE INVENTION  
       [0024] Accordingly, it is an object of the present invention to overcome the problems encountered in the conventional art.  
       [0025] It is another object of the present invention to provide an optical fiber drawing apparatus which is capable of minimizing a break of an optical fiber by adjusting a curvature radius of an optical fiber using at least one or more moving rollers and releasing a bending stress and stress concentration and is capable of decreasing a break of an optical fiber by adjusting an optical fiber curvature radius.  
       [0026] It is further another object of the present invention to provide an optical fiber drawing apparatus which is capable of impressing a spin to an optical fiber by reciprocating one among at least one or more moving rollers in a vertical direction with respect to a drawing surface of an optical fiber.  
       [0027] To achieve the above objects, the present invention provides an optical fiber drawing apparatus comprising a heating furnace adapted to melt an optical fiber mother material and to draw an optical fiber, an optical fiber standard value controller unit adapted to control standard values of the optical fiber drawn, a fixing roller adapted to change a drawing direction of the optical fiber, at least one or more moving rollers which are movable on a drawing surface for adjusting a curvature radius of the optical fiber which has a changed drawing direction, and a winding apparatus adapted to wind the optical fiber which has an adjusted curvature radius. Also, the present invention provides an optical fiber drawing apparatus impressing a spin to an optical fiber by reciprocating one among at least one or more moving rollers in a vertical direction with respect to a drawing surface of an optical fiber. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0028] The present invention will be better understood with reference to the accompanying drawings.  
     [0029]FIG. 1 is a schematic view illustrating a conventional optical fiber drawing apparatus;  
     [0030]FIG. 2 is a schematic view illustrating a fixing roller unit of a conventional optical fiber drawing apparatus;  
     [0031]FIG. 3 is a schematic view illustrating an optical fiber drawing apparatus according to a first embodiment of the present invention;  
     [0032]FIG. 4A is a front schematic view illustrating a bracket of an optical fiber drawing apparatus according to a first embodiment of the present invention;  
     [0033]FIG. 4B is a lateral schematic view illustrating a bracket of an optical fiber drawing apparatus according to a first embodiment of the present invention;  
     [0034]FIG. 5 is a schematic view illustrating an optical fiber drawing apparatus according to a second embodiment of the present invention;  
     [0035]FIG. 6A is a front schematic view illustrating a bracket of an optical fiber drawing apparatus according to a second embodiment of the present invention; and  
     [0036]FIG. 6B is a lateral schematic view illustrating a bracket of an optical fiber drawing apparatus according to a second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0037] The optical fiber drawing apparatus for decreasing an optical fiber break and impressing a spin to an optical fiber according to the present invention will be described with reference to the accompanying drawings.  
     [0038]FIG. 3 is a schematic view illustrating an optical fiber drawing apparatus according to a first embodiment of the present invention.  
     [0039] In the optical fiber drawing apparatus for decreasing an optical fiber break and impressing a spin to an optical fiber according to the present invention, the fixing roller  17  and the moving rollers  18  and  19  may be installed by one of the following installation procedures.  
     [0040] In the optical fiber drawing apparatus according to the present invention, there are sequentially provided a heating furnace for melting an optical fiber mother material and drawing an optical fiber, a diameter measuring device for measuring a diameter of an optical fiber drawn from the heating furnace and controlling the same, a cooling apparatus for cooling an optical fiber which is heated by the heating furnace and has a high temperature, and a coating apparatus for coating the optical fiber after the optical fiber is cooled. At least one fixing roller is installed for changing a drawing direction of the optical fiber, and at least one or more moving rollers are installed after the fixing roller. And then there are provided a violet ray hardening apparatus for hardening an optical fiber, a capstan for adjusting the diameter measured by the diameter measuring device to a particular diameter, and a spool for winding the finished optical fiber.  
     [0041] As shown in FIG. 3, the optical fiber drawing apparatus according to the present invention comprises a heating furnace  12  for melting an optical fiber mother material and drawing an optical fiber  11 , a diameter measuring device  13  for measuring and controlling the diameter of the optical fiber  11  drawn from the heating furnace, a cooling apparatus  14  for cooling the optical fiber which is heated by the heating furnace  12  and has a high temperature, a coating apparatus  15  for coating the optical fiber  11  after the optical fiber  11  is cooled, and a violet ray hardening apparatus  16  for hardening the optical fiber  11 . At least one fixing roller  17  is provided for changing the direction of the optical fiber  11 . At least one or more moving rollers  18  and  19  are continuously installed after the fixing roller  17 . And then there are provided a capstan(not shown) for controlling the diameter measured by the diameter measuring device  13  to a particular diameter, and a spool (not shown) for winding the finished optical fiber.  
     [0042] Finally, in the optical fiber drawing apparatus according to the present invention, there are sequentially provided a heating furnace for melting an optical fiber mother material and drawing an optical fiber, a diameter measuring device for measuring and controlling a diameter of an optical fiber drawn from the heating furnace, a cooling apparatus for cooling the optical fiber which is heated by the heating furnace and has a high temperature, a coating apparatus for coating the optical fiber after the optical fiber is cooled, a UV hardening apparatus for hardening the optical fiber, and a capstan for controlling the diameter measured by the diameter measuring unit to a certain diameter. At least one fixing roller is installed for changing the direction of the optical fiber. At least one or more moving rollers are sequentially installed after the fixing roller. And then a spool is provided for winding the finished optical fiber.  
     [0043] As shown in FIG. 3, in the optical fiber drawing apparatus according to the above second installation procedure among the above three installation procedures, the adjusted curvature radius R 2  according to the present invention is larger than the curvature radius R 1  in which only the fixing roller is installed. Since the bending stress is in inverse proportion to the size of the radius R like σ b =Ey/R, in the optical fiber drawing apparatus of the present invention, it is possible to decrease the bending stress applied to the optical fiber by increasing the curvature radius R 2  which is adjusted using the fixing roller  17  and the moving roller  18  and  19 .  
     [0044]FIG. 4A is a front schematic view illustrating a bracket of an optical fiber drawing apparatus according to a first embodiment of the present invention.  
     [0045] As shown in FIG. 4A, there is provided a bracket  10  connected with the moving rollers  18  and  19  for moving the moving rollers  18  and  19  in the vertical and horizontal directions. The bracket  10  includes a vertical direction guide  21  installed in a longitudinal direction of the bracket  10 , and a pivot joint  22  formed in one side of the bracket  10 .  
     [0046] A shaft  12  of each of the moving rollers is installed along the vertical direction guide  21 . A ball bearing (not shown) is installed between the shaft  12  of the moving roller and the moving roller for rotating the moving roller with respect to the shaft. As the roller shaft  12  is moved along the vertical direction guide  21 , the moving rollers  18  and  19  of the present invention are reciprocated for thereby controlling the curvature radius of the optical fiber  11 .  
     [0047] The pivot joint  22  is installed in one side of the bracket  10  for rotating the bracket  10  in a horizontal direction on a reciprocating movement. Therefore, the moving rollers  18  and  19  of the present invention control the curvature radius during the direction change of the optical fiber  11  based on the movement of the bracket  10  which is rotated with respect to the pivot joint  22 .  
     [0048] Here, it is possible to measure the average strength value of the optical fiber  11  based on an experiment. In the present invention, it is possible to control the curvature radius of the optical fiber  11  during the direction change when the optical fiber  11  is drawn in such a manner that the moving rollers  18  and  19  are moved in the vertical and horizontal directions in order to prevent the bending force from being applied to the optical fiber  11 .  
     [0049]FIG. 4B is a lateral schematic view illustrating the bracket of the optical fiber drawing apparatus according to a first embodiment of the present invention.  
     [0050] As shown in FIG. 4B, one side of the bracket  10  of the optical fiber drawing apparatus according to the present invention is connected with the tower body  20  by the pivot joint  22 . The pivot joint  22  is engaged in such a manner that the bracket  10  is rotated with respect to the pivot joint.  
     [0051] Since the tower body  20  supports the optical fiber drawing apparatus, as the vibration of the tower body  20  is increased, a larger amount of vibrations are transferred to the optical fiber in the optical fiber drawing process, so that it is impossible to fabricate a circular symmetrical optical fiber. As shown in FIG. 4B, a spacer  23  is installed between the bracket  10  and the tower body  20  in such a manner that the vibrations occurring in the bracket  10  are not transferred to the tower body  20 . The spacer  23  is formed of a material which is capable of decreasing a mechanical vibration.  
     [0052]FIGS. 5 through 6B are views illustrating an optical fiber drawing apparatus according to a second embodiment of the present invention. The optical fiber drawing apparatus according to the second embodiment of the present invention further comprises an optical fiber spin impressing apparatus in the optical fiber drawing apparatus compared to the optical fiber drawing apparatus of the first embodiment of the present invention.  
     [0053]FIG. 5 is a schematic view illustrating the optical fiber drawing apparatus according to the second embodiment of the present invention.  
     [0054] As shown therein, an apparatus is installed in one moving roller  18  among the moving rollers  18  and  19  according to the preferred embodiments of the present invention for impressing a spin to the optical fiber. The moving roller  18  reciprocates in the vertical direction with reference to a drawing surface of the optical fiber. Therefore, the optical fiber is formed in a certain wave shape having a certain amplitude and wavelength in the direction vertical to the drawing surface. As a result, the moving roller  18  applies a certain spin to the optical fiber during the drawing procedure of the optical fiber.  
     [0055]FIG. 6A is a front schematic view illustrating a bracket of the optical fiber drawing apparatus according to a second embodiment of the present invention.  
     [0056] An apparatus adapted for impressing a spin to the optical fiber is connected with the pivot joint  22  of FIG. 6A, so that the spin impressing apparatus is driven in the direction vertical to the drawing surface of the optical fiber. Namely, in the case that the optical fiber spin impressing apparatus is connected with the pivot joint  22 , the connection portion of the spin impressing apparatus connected with the pivot joint  22  is not affected by the rotation of the bracket by the pivot joint  22 . Therefore, the spin impressing apparatus may be driven in only the direction vertical to the drawing surface of the optical fiber.  
     [0057]FIG. 6B is a lateral schematic view illustrating a bracket of the optical fiber drawing apparatus according to a second embodiment of the present invention.  
     [0058] The optical fiber drawing apparatus according to the second embodiment of the present invention includes one moving roller  18  which capable of impressing a spin to the optical fiber among a plurality of moving rollers  18  and  19 . The apparatus for impressing a spin to the optical fiber  11  according to the second embodiment of the present invention is a CAM driving apparatus  31 . As known to persons who are skilled in the art, the CAM driving apparatus  31  is capable of converting a rotational movement into a linear movement. Namely, the CAM driving apparatus rotates and is capable of reciprocating linearly the apparatus connected with the CAM driving apparatus.  
     [0059] As shown in FIG. 6B, the CAM driving apparatus  31  includes a first link line  31   c , a second link line  31   d , a first link  31   a , and a second link  31   b  for transferring a movement of the CAM driving apparatus. The first link  31   a  is adapted to connect the rotation movement portion of the CAM driving apparatus to the first link line  31   c , and the second link  31   b  is adapted to connect the first link line  31   c  to the second link line  31   d.    
     [0060] An elastic unit  33  is installed between the tower body  20  and the bracket  10  in order for the CAM driving apparatus  31  to move the bracket  10 . Also, the elastic unit  33  prevents a transfer of a vibration occurring in the bracket  10 . Preferably, a spring  34  having a certain recovering force is installed between the tower body  20  and the elastic unit  33 . The spring  34  supports the recovering operation of the CAM apparatus. The diameter of the hole of the tower body  20  is larger than the diameter of the CAM guide  35  for thereby implementing a smooth operation of the CAM guide  35 .  
     [0061] The CAM driving apparatus  31  according to the second embodiment of the present invention is adapted to rotate the first link  31   a . The rotation of the first link  31   a  is transferred to the second link  31   b  through the first link line  31   c  and is continuously transferred to the second link line  31   d . Therefore, the second link line  31   d  reciprocates, so that the bracket  10  reciprocates. The CAM driving apparatus  31  drives the moving roller  18  in a direction vertical to the drawing surface of the optical fiber based on the reciprocating movement of the bracket  10  during the drawing procedure of the optical fiber, so that a spin is periodically applied to the optical fiber  11 . The spin applied to the optical fiber may be controlled by changing the driving rate of the CAM driving apparatus  31  according to the present invention.  
     [0062] In another preferred embodiment of the present invention, a certain number n(n=1, 3, 4, 5, 6 . . . ) of the brackets  10  adapted to reciprocate the moving rollers may be continuously provided after the fixing roller.  
     [0063] As described above, it is possible to decrease a bending stress and stress concentration which occur during the drawing process by increasing the curvature radius on the drawing surface of the optical fiber and to decrease the stress concentration due to a micro particle or crack for thereby decreasing the break of the optical fiber. In addition, it is possible to decrease the polarization mode dispersion (PMD) which may occur during the transfer of the signal in the optical fiber by impressing a spin to the optical fiber. In addition, it is possible to enhance a safety with respect to the vibration in such a manner that moving rollers are additionally provided compared to the case that only fixing roller is provided for a high speed drawing process.  
     [0064] As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described examples are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the meets and bounds of the claims, or equivalences of such meets and bounds are therefore intended to be embraced by the appended claims.