Abstract:
An optical fiber preform fabricating apparatus capable of simultaneously mounting and fabricating a plurality of preforms and adaptable according to the length of performs is provided. The apparatus heats a plurality of quartz tubes using at least one burner to deposit chemical reactants on the outer walls of the quartz tubes. To this end, the apparatus includes a chamber housing extending longitudinally and a variable-length structure mounted within the chamber housing in a longitudinal direction, wherein the variable-length structure is adjustable in accordance with the length of the quartz tubes and horizontally moves back and forth in the longitudinal direction.

Description:
CLAIM OF PRIORITY  
       [0001]     This application claims priority to an application entitled “Optical Fiber Preform Fabricating Apparatus,” filed with the Korean Intellectual Property Office on Nov. 24, 2004 and assigned Serial No. 2004-96759, the contents of which are hereby incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an optical fiber preform fabricating apparatus that is capable of simultaneously mounting and fabricating a plurality of preforms and adapting to different lengths of preforms.  
         [0004]     2. Description of the Related Art  
         [0005]     An optical communication medium using light over an optical fiber can transmit larger volumes of information than a coaxial cables transmission medium can.  
         [0006]     In general, the fabrication of optical fibers involves a production of an optical fiber preform. There are several methods of preparing preforms which include outside vapor deposition (OVD), vapor-phase axial deposition (VAD) and modified chemical vapor deposition (MCVD). In the OVD, a rotating target rod (an alumina mandrel) is heated using a burner, which burner feeds chemicals to be deposited on the outside of the target rod by thermophoresis. The OVD method is characterized by the layer-by-layer deposition of chemicals to form a core layer on the outside of the target rod and a cladding layer on the core layer. The MCVD differs from the OVD in that the deposition occurs inside a quartz tube instead of on the outside. While the quartz tube is being heated by a burner, chemicals are fed into the tube to form a cladding layer on the internal wall of the tube and then a core layer inside the internal wall of the cladding layer is formed by thermophoresis. In the VAD, two different burners (an upper burner and a lower burner) are used to simultaneously deposit a core layer and a cladding layer on a target rod in the upright position.  
         [0007]      FIG. 1  shows an apparatus used to perform the OVD process. Briefly, in a chamber  1  and a hood  2 , a pair of chucks  3  is provided on a horizontal lathe to face each other and support a quartz tube  4  in such a manner that the quartz tube  4  can rotate about its longitudinal axis. Also, a burner  6  movable along a rail  5  is provided below the quartz tube  4 . While moving along the rail  5 , the burner  6  traverses back and forth along the length of the rotating quartz tube  4  to heat the tube  4 . SiCl and other chemical reactants  100  entrained in oxygen gas are fed in the form of a gaseous mixture into the quartz tube  4  to form soot particles that will be deposited on the quartz tube  4 .  
         [0008]     Various approaches have been suggested to improve productivity in the MCVD process. In the OVD process, a large-size preform fabricating apparatus has been developed to fabricate multiple and larger performs. Accordingly, it is possible to fabricate larger sized preforms to a certain extent using the initially designed apparatus, without the need for enlarging or reforming the apparatus. Fabricating longer performs increases the cost for production facility. In addition, the linear reciprocating rail generally has a complicated burner structure. Changes in the burner structure and the gas lines may cause serious problems in achieving a uniform flow of gas which results in vortex of gas flow and deteriorates the quality of the resulting preform. Further, the rail placed at a relatively lower temperature area may improperly operate due to condensation of corrosive gas and load of undeposited soot particles. Ultimately, the corrosion frequently leads to reduced durability in the preform fabricating apparatus.  
       SUMMARY OF THE INVENTION  
       [0009]     Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art and provides additional advantages, by providing an optical fiber preform fabricating apparatus that is capable of simultaneously mounting and fabricating a plurality of preforms and adapting to different lengths of preform.  
         [0010]     One aspect of the present invention is to provide an optical fiber preform fabricating apparatus having means for a horizontal reciprocating motion of a plurality of preforms at the upper part thereof, thereby preventing corrosion due to the drop of undeposited soot and chemical reactants and enhancing durability.  
         [0011]     Another aspect of the present invention is to provide an optical fiber preform fabricating apparatus capable of discharging undeposited soot and chemical reactants entrained in oxygen gas in the form of a gaseous mixture, thereby preventing the generation of vortex and providing uniform and stable deposition conditions.  
         [0012]     Still another aspect of the present invention is to provide an optical fiber preform fabricating apparatus for heating a plurality of quartz tubes using at least one burner to deposit chemical reactants on the outer walls of the quartz tubes, which comprises: a chamber housing extending longitudinally and having a plurality of hoods on top thereof; a pair of moving means provided within the housing in a longitudinal direction; first and second stocks mounted on the moving means in a plane perpendicular to the longitudinal direction to rotatably hold the plurality of quartz tubes and perform a horizontal reciprocating motion in the longitudinal direction; a pair of bed module arrays, each comprising at least one module and mounted between the first and second stocks to be extendable in the longitudinal direction to adjust the distance between the first and second stocks in accordance with the length of the quartz tubes; and a power transfer means for transferring power to make the first and second stocks horizontally move back and forth. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The above features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0014]      FIG. 1  is a schematic view of a conventional optical fiber preform fabricating apparatus using outside vapor deposition (OVD);  
         [0015]      FIG. 2  is a front cut-away view of the structure of an optical fiber preform fabricating apparatus according to the present invention;  
         [0016]      FIG. 3  is an enlarged front view of part A in  FIG. 2 ;  
         [0017]      FIG. 4  is a cross-sectional side view of an optical fiber preform fabricating apparatus according to the present invention;  
         [0018]      FIG. 5  is a perspective view of an optical fiber preform fabricating apparatus according to the present invention;  
         [0019]      FIG. 6  is an enlarged perspective view of part B in  FIG. 5 ;  
         [0020]      FIG. 7  is an enlarged perspective view of part C in  FIG. 5 ;  
         [0021]      FIG. 8  is an enlarged perspective view of part D in  FIG. 5 ;  
         [0022]      FIG. 9  is an enlarged perspective view of part E in  FIG. 5 ;  
         [0023]      FIG. 10  is a perspective view of the assembled state of an optical fiber preform fabricating apparatus according to the present invention;  
         [0024]      FIG. 11  is a perspective view of the operational state of an optical fiber preform fabricating apparatus according to the present invention;  
         [0025]      FIG. 12  is a side view of the operational state of an optical fiber preform fabricating apparatus according to the present invention;  
         [0026]      FIG. 13  is an enlarged perspective view of part F in  FIG. 12 ; and  
         [0027]      FIG. 14  is a cross-sectional view showing the mounting of a permanent magnet of an optical fiber preform fabricating apparatus according to the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0028]     Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. For the purposes of clarity and simplicity, a detailed description of known functions and configurations incorporated herein will be omitted as it may make the subject matter of the present invention unclear.  
         [0029]     Referring to  FIG. 2 , an optical fiber preform fabricating apparatus  10  according to the present invention includes a chamber housing  20 , a pair of moving means  30 , first and second stocks  40  and  50 , a pair of bed module arrays  60 , and a power transfer means  70 . As shown in  FIGS. 2 and 3 , a plurality of hoods  21  is provided on top of the chamber housing  20  to discharge undeposited soot  100  and chemical reactants entrained in oxygen gas in the form of a gaseous mixture  100 .  
         [0030]     Referring to  FIG. 4 , the pair of moving means  30  is provided within the chamber housing  20  in a longitudinal direction for enabling a horizontal reciprocating motion of the first and second stocks  40  and  50  in the same longitudinal direction.  
         [0031]     Referring to  FIG. 5 , the first and second stocks  40  and  50  are mounted on the moving means  30  in a plane perpendicular to the longitudinal direction in order to rotatably hold a plurality of quartz tubes and perform a horizontal reciprocating motion in the longitudinal direction. The bed module arrays  60  mounted between the first and second stocks  40  and  50  are extendable in the longitudinal direction to adjust the distance between the first and second stocks in accordance with the length L 1  of the quartz tubes. The power transfer means  70  provided on the lateral side within the chamber housing  20  transfers power to make the first and second stocks  40  and  50  horizontally move back and forth.  
         [0032]     Referring to  FIGS. 2 and 3 , the hood  21  on top of the chamber housing  20  includes an inner hood  21   a  and an outer hood  21   b  to discharge undeposited soot  100  and chemical reactants entrained in oxygen gas in the form of a gaseous mixture  100 . A pair of hood adapters  22  provided at both top ends of the chamber housing  20  is used to connect and fix the hood  21  to the chamber housing  20 . Gas outlets  23  formed adjacent to the hood adapters  22  discharge the gaseous mixture  100  of undeposited soot and chemical reactants entrained in oxygen gas through the hood  21 . In addition, at least one support rib  24  for supporting the chamber housing  20  is provided at both sides of the chamber housing  20 .  
         [0033]     Referring to  FIGS. 5 and 6 , the moving means  30  consists of a pair of moving rails  31  and at least one roller  32 . The moving rails  31  are mounted on the inner wall of the upper part of the chamber housing  20  in a longitudinal direction. The roller  32  is mounted in the moving rails  31  to be horizontally movable in the longitudinal direction along the moving rails  31 .  
         [0034]     Referring to  FIGS. 5 and 12 , the first stock  40 , which comprises a head stock, has a housing  45  containing at least one rotating means  42  and at least one link  43 . The housing  45  is connected to the roller  32  by means of a head connection member  41  provided on top thereof. The rotating means  42  for rotating the quartz tube  4  is received in the housing  45  under the head connection member  41 . The link  43  in the housing  45  fixes the rotating means  42  to the head connection member  41 .  
         [0035]     Referring to  FIG. 6 , the head connection member  41  has a projection  41   a  formed in the longitudinal direction of the chamber housing  20  to be fitted into a recess  62  formed on a bed module of the bed module array  60 .  
         [0036]     Referring to  FIG. 12 , the rotating means  42  consists of a rotating motor  42   a , a reduction module  42   b , a rotating shaft  42   c , and a rotating chuck  42   d . The rotating shaft  42   c  is connected to the reduction module  42   b  to transfer a turning force generated from the rotating motor  42   a  to the rotating chuck  42   d . The rotating chuck  42   d  provided at one end of the rotating shaft  42   c  serves to hold one end of a quartz tube  4  and rotates with the rotation of the rotating shaft  42   c.    
         [0037]     The link  43  has one end connected to the bottom surface of the head connection member  41  and the other end connected to the top surface of the reduction module  42   b , thereby connecting the reduction module  42   b  to the head connection member  41 .  
         [0038]     Referring to  FIG. 12 , a load cell  44  is provided between the head connection member  41  and the reduction module  42   b  to measure in real time the weight of the quartz tube  4  which changes with the deposition of chemical reactants during the rotation of the quartz tube  4 .  
         [0039]     Referring to  FIGS. 5 and 8 , the second stock  50  comprising at least one tail stock  50  has a tail connection member  51  to be connected to the roller  32 . The tail stock  50  has a recess  52  into which a projection  63  of the last bed module of the bed module array  60  can be inserted. Thus, it is possible to interlock as many bed modules as needed to adjust the distance between the head stock  40  and the tail stock  50  in accordance with the length L 1  of the quartz tube  4 . Also, at least one tail chuck  53  is provided at the lower part of the tail stock  50  at the position opposite to the rotating chuck  42   d . The tail chuck  53  is rotatably connected to the other end of the quartz tube  4 .  
         [0040]     Referring to  FIG. 8 , the tail chuck  53  has a V block in which a pair of bearings  53   a  is provided to enable the quartz tube  4  to rotate therebetween.  
         [0041]     Referring to  FIG. 13 , the tail stock  50  has a support bracket  54  for supporting the tail chuck  53 .  
         [0042]     Referring to  FIG. 9 , each bed module of bed module array  60  consists of a body  61 , a recess  62  formed on one end of the body  61 , and a projection  63  formed on the other end of the body  61 . The overall length of the bed module arrays  60  can be increased by interlocking additional bed modules in such a manner that the projection  63  of one bed module is fitted into the recess  62  of another, thereby adjusting the distance between the head stock  40  and the tail stock  50  in accordance with the length L 1  of the quartz tube  4 .  
         [0043]     Referring to  FIGS. 7 and 10 , the power transfer means  70  includes a driving motor  71 , a gear  72 , and a power transfer belt  73 . The driving motor  71  is provided at one side of the chamber housing  20  to transfer a driving force to the gear  72 . The gear  72  provided along the length of one bed module array  60  converts a rotary motion from the motor  71  into a horizontal reciprocating motion. The power transfer belt  73  is held securely in place over a belt pulley  71  a of the driving motor  71  and a belt pulley  72   c  of the gear  72 .  
         [0044]     Referring to  FIG. 7 , the gear  72  consists of a rack gear  72   a  and a pinion gear  72   b . When the pinion gear  72   b  rotates with the rotation of the driving motor  71 , the rack gear  72   a  connected to the outer lateral side of the bed module array  60  horizontally moves the bed module array  60  back and forth in the longitudinal direction. When the pinion gear  72   b  in mesh with the rack gear  72   a  turns with the rotation of the driving motor  71 , it causes the rack gear  72   a  to linearly move back and forth.  
         [0045]     Referring to  FIG. 9 , the two bed module arrays  60  are provided at both inner sides of the chamber housing  20  in the longitudinal direction. The bed module array  60  at one side is coupled to the gear  72 , while the bed module array  60  at the other side is coupled to a guide rib  80  that guides the horizontal reciprocating motion of the bed module array  60 .  
         [0046]     Referring to  FIG. 14 , at least one permanent magnet  81  is provided within the guide rib  80  to guide a horizontal reciprocating motion of the bed module array  60  using a repulsive force of the magnet  81 .  
         [0047]     Referring to  FIGS. 10 and 11 , at least one burner  6  is placed below the quartz tube  4  in a plane perpendicular to the length of the chamber housing  20 .  
         [0048]     Hereinafter, the operation of the optical fiber preform fabricating apparatus according to the present invention will be explained in detail with reference to FIGS.  2  through  14 .  
         [0049]     When at least one quartz tube  4  is mounted within the longitudinally extending chamber housing  20  as shown in  FIGS. 2 and 3 , the distance between at least one head stock  40  and at least one tail stock  50  is adjusted in accordance with the length L 1  of the quartz tube  4 .  
         [0050]     Referring to  FIG. 12 , the bed module arrays  60  and the tail stock  50  can be separated from each other by pulling out the projection  63  of the last bed module  60  from the recess  52  formed on the tail stock  50 .  
         [0051]     The separated tail stock  50  can be moved along the rails  31  provided on the inner wall of the chamber housing  20 .  
         [0052]     Since the tail connection member  51  formed on top of the tail stock  50  is connected to the roller  32 , the tail stock  50  is guided by the roller  32  mounted on the moving rails  31 .  
         [0053]     Referring to  FIG. 9 , each bed module of the separated bed module arrays  60  has a projection  63  and a recess  62 .  
         [0054]     The overall length of the bed module arrays  60  can be adjusted in accordance with the length L 1  of the quartz tube  4 . When the length L 1  of the quartz tube  4  is increased, the overall length of the bed module arrays  60  can also be increased by interlocking additional bed modules in such a manner to fit the projection  63  of one bed module into the recess  62  of another.  
         [0055]     The projection  63  of the last bed module  60  is then fitted into the recess  52  formed on the tail stock  50 .  
         [0056]     Referring to  FIGS. 4 and 5 , the tail stock  50  faces the head stock  40 . Both ends of the quartz tube  4  are held respectively by the rotating chuck  42   d  of the head stock  40  and the counterpart chuck  53  of the tail stock  50 .  
         [0057]     Under this condition, as shown in  FIGS. 10 and 11 , the quartz tube  4  horizontally moves back and forth along the moving rails  31  provided in the longitudinal direction of the chamber housing  20 .  
         [0058]     Referring to  FIG. 12 , at least one burner  6  provided below the quartz tube  4  heats the tube  4 .  
         [0059]     Referring to  FIGS. 7 and 11 , the rack gear  72   a  provided along the lateral side of one bed module array  60  in the longitudinal direction changes the rotary motion from the driving motor  71  into a linear reciprocating motion. When the driving force generated from the driving motor  71  rotates the pinion gear  72   b , the rack gear  72   a  in mesh with the pinion gear  72   b  horizontally moves in the longitudinal direction.  
         [0060]     With the horizontal movement of the rack gear  72   a , the head stock  40  and the tail stock  50  also move and cause the quartz tube  4  to move simultaneously.  
         [0061]     The other bed module array  60  is coupled to the guide rib  80  that guides the horizontal reciprocating motion of the head stock  40 , tail stock  50 , and the quartz tube  4 .  
         [0062]     Referring to  FIG. 14 , at least one permanent magnet  81  is provided within the guide rib  80  to guide the horizontal reciprocating motion using a repulsive force of the magnet  81 .  
         [0063]     Referring to  FIG. 12 , the head connection member  41  connected to the roller  32  is provided on top of the head stock  40 . Also, at least one rotating means  42  for rotating the quartz tube  4  is provided under the head connection member  41 .  
         [0064]     The rotating means  42  includes the rotating chuck  42   d  that holds one end of the quartz tube  4 . The rotating chuck  42   d  is connected to the rotating shaft  42   c  which is connected to the rotating motor  42   a.    
         [0065]     When the rotating motor  42   a  operates and generates a turning force, the rotating shaft  42   c  transfers the turning force to the rotating chuck  42   d.    
         [0066]     The burner  6  heats the rotating quartz tube  4  and deposits chemicals on the quartz tube  4  to produce an optical fiber preform.  
         [0067]     With the deposition of chemical reactants, the quartz tube  4  becomes heavier. As shown in  FIG. 12 , the load cell  44  provided in the head stock  40  measures the weight of the quartz tube  4  in realtime. The measured weight can tell the progress of the fabrication of the optical fiber preform from the quartz tube  4 .  
         [0068]     Referring back to  FIGS. 2 and 3 , a pair of hood adapters  22  is provided at both top ends of the chamber housing  20  to connect and fix the hood  21  consisting of the inner hood  21   a  and the outer hood  21   b  to the top of the chamber housing  20 .  
         [0069]     Referring back to  FIG. 3 , the gas outlets  23  formed adjacent to the hood adapters  22  discharge undeposited soot  100  and a gaseous mixture  100  of chemical reactants entrained in oxygen gas through the hood  21 . Undeposited soot  100  and gas  100  remaining at the bottom of the chamber housing  20  pass through the gas outlets  23  and enter the inner hood  21   a  and the outer hood  21   b  to be discharged.  
         [0070]     As explained above, the length of the bed module arrays and the distance between the head stock and the tail stock can be adjusted in accordance with the length of the quartz tube when fabricating a preform. Accordingly, it is possible to fabricate preforms of various sizes without the need for enlarging or reforming the optical fiber preform fabricating apparatus which in turn saves any additional expenses in the production facility and reduces the manufacturing cost. In addition, the gas outlets provided on the chamber housing rapidly discharge undeposited soot and chemical reactants, thereby preventing corrosion and enhancing the durability of the preform fabricating apparatus.  
         [0071]     Although an embodiment of the present invention has been described 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, including the full scope of the equivalents thereof.