Patent Publication Number: US-2005115277-A1

Title: Method and apparatus for manufacturing optical fiber preform

Description:
CLAIM OF PRIORITY  
      This application claims priority to an application entitled “Method and apparatus for manufacturing optical fiber perform,” filed in the Korean Intellectual Property Office on Nov. 27, 2003 and assigned Serial No. 2003-85071, the contents of which are hereby incorporated by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a method and an apparatus for manufacturing an optical fiber preform. More particularly, the present invention relates to a method and an apparatus for manufacturing an optical fiber preform by a modified chemical vapor deposition process.  
      2. Description of the Related Art  
      In a conventional process for manufacturing an optical fiber, there are four basic steps: a preform manufacturing step, a drawing step, a sheath coating step, and a winding step. Particularly, the preform manufacturing step is for forming a basic preform in order to draw an optical fiber. The basic preform can be manufactured according to various methods including a vapor-phase deposition method, an outer chemical vapor-phase deposition method, a plasma chemical vapor deposition method, and a modified chemical vapor deposition method.  
      In particular, according to the modified chemical vapor deposition method, raw material gas and oxygen gas are injected into a hollow tube in order to form an optical fiber preform. In this state, the hollow tube containing the raw material gas and oxygen gas is heated, so that a thermal oxidation reaction is created in the hollow tube, thereby depositing a transparent glass layer on an inside wall of the hollow tube.  
       FIG. 1  is illustrates an apparatus for manufacturing an optical fiber preform through a modified chemical vapor deposition method. Referring to  FIG. 1 , a conventional apparatus for manufacturing the optical fiber preform includes a quartz reaction tube  140  that is rotated at a constant speed during a portion of the manufacturing process, and a pair of chucks  130   a  and  130   b  that rotatably support both ends of the quartz reaction tube  140 . A table  110  permits support of the chucks  130   a  and  130   b  at respective sidewalls  112   a  and  112   b , and a sliding member  123 , which slidably moves in left and right directions along a base surface of the table  110 . A burner  150  arranged on the sliding member heats an outer wall of the quartz reaction tube  140  while moving in left and right directions along a longitudinal axis of the quartz reaction tube  140 . A feed screw  121  passes through the sliding member  123 , and formed with the feed screw is a motor  122  that transfers driving force to the feed screw  121 . A nitrogen tube  160  injects a nitride gas into the quartz reaction tube  140  in such a manner that raw material gas and soot smoothly flow in the quartz reaction tube  140 .  
      The quartz reaction tube  140  is rotated by the chucks  130   a  and  130   b  as the raw material gas and oxygen gas, such as SiCl 4  and GeCl 4 , are injected into the quartz reaction tube  140 .  
      The burner  150  is moved in both left and right directions along the longitudinal axis of the quartz reaction tube  14  so as to heat an outer wall of the quartz reaction tube  140  during the time that raw material gas is also being injected into the quartz reaction tube  140 .  
      As the inside of the quartz reaction tube  140  is maintained at a high temperature by the burner  150 , the raw material gas and oxygen gas injected into the quartz reaction tube  140  are subject to an oxidization reaction due to an increase of an internal temperature of the quartz reaction tube  140 . Accordingly, soot, such as SiCl 4  and GeCl 4 , formed by the oxidization reaction may be deposited at an inside wall of the quartz reaction tube  140 .  
      However, soot, which is a kind of oxide formed in the quartz reaction tube  140 , is deposited at the inside wall of the quartz reaction tube  140  with a low depositing efficiency, so only about 40 to 50 percent of soot is deposited along the inside wall of the quartz reaction tube  140 . The remaining soot stays in the apparatus during the manufacture of the optical fiber preform, thereby interrupting the optical fiber manufacturing process or causing defects in the optical fiber preform.  
      In order to discharge the soot that has not been deposited at the inside wall of the quartz reaction tube  140 , a ventilating pipe is connected to one end of the quartz reaction tube and vents the soot to an exterior of the optical fiber perform. A nitride gas is injected into the quartz reaction tube so as to more easily discharge soot remaining in the quartz reaction tube through the ventilating pipe.  
      In other words, the nitrogen tube  160  injects nitride gas into the quartz reaction tube  140 , so that a swirl flow is artificially formed in the inside of the quartz reaction tube  140 . The swirl flow formed in the inside of the quartz reaction tube  140  exhausts excessive soot and the remaining raw material gas to the exterior of the quartz reaction tube  140 .  
      However, the inventors of the present invention have discovered that one problem with the above conventional method for injecting nitride gas into the quartz reaction tube to reduce soot is that the nitride gas is injected into the quartz reaction tube in a reverse direction relative to an injection direction of the raw material gas. The reverse direction of the nitride gas causes problems because the swirl flow formed by the nitride gas flows in reverse direction to the injection direction of raw material gas, impeding a significant portion of the soot from being easily exhausted to the exterior.  
     SUMMARY OF THE INVENTION  
      Accordingly, the present invention has been made in part to solve at least some of the above-mentioned problems. A first aspect of the present invention is to provide a method for manufacturing an optical fiber perform, said method being adapted for the easy exhaust of excess soot formed in the quartz reaction tube to an exterior of the quartz reaction tube.  
      In order to accomplish the above and other aspects of the present invention, there is provided a method for manufacturing an optical fiber preform by depositing soot created through a chemical reaction on an inside wall of a quartz reaction tube, the method comprising the steps of electrically charging created soot with a first predetermined charge, adhering the soot that is not deposited on the inside wall of the quartz tube to an electrified body charged with a second predetermined charge that is opposite to the first predetermined charge, moving the electrified body having the soot adhered thereto to an exterior of the quartz reaction tube, and exhausting soot adhering to the electrified body by charging the electrified body with a charge identical to the first predetermined charge of soot to exhaust the soot to an exterior of the quartz reaction tube. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other aspects, 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:  
       FIG. 1  is a view showing a conventional apparatus for manufacturing an optical fiber preform; and  
       FIG. 2  is a view showing an apparatus for manufacturing an optical fiber preform according to a first aspect of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Hereinafter, preferred aspects of the present invention will be described with reference to the accompanying drawings. In the following description and drawings, the same reference numerals are used to designate the same or similar components, and so repetition of the description of the same or similar components will be omitted so as not to obscure the invention with unnecessary detail.  
      According to a method of manufacturing an optical fiber perform, a first portion of the soot formed through a chemical vapor deposition process is deposited to an inside wall of a quartz reaction tube. A second portion of the soot that comprises a remaining portion that has not been deposited at the inside wall of the quartz reaction tube. The remaining portion of the soot is charged with a positive charge. Subsequent to the charging of the soot with the positive charge, some of the soot adheres to a metal rod having a negative pole. In another variation of the invention, all of the soot can be charged with a positive charge.  
      Once the metal rod has soot accumulated thereon, the rod is then moved to an exterior of the quartz reaction tube so as to allow the rod to be charged with a positive pole in order to cause the soot adhering to the rod to be discharged to the exterior.  
       FIG. 2  is a view showing an apparatus for manufacturing an optical fiber preform according to an aspect of the present invention. Referring to  FIG. 2 , an apparatus for manufacturing the optical fiber preform according to the present invention may include a soot exhausting device  260  having an electrified body  263 , a table  210  having a guiding groove which is formed at a bottom surface of the table  210 , a burner  250 , a sliding member  223 , and a pair of chucks  230   a  and  230   b.    
      Accordingly, the apparatus for manufacturing the optical fiber preform of the present invention can also includes a quartz reaction tube  240  in order to form optical fiber preform while the reaction tube is being heated, so that an inside of the quartz reaction tube  240  reaches a high temperature. In addition, raw material gas, (such as SiCl 4  and GeCl 4 , and O 2 ), is injected into the quartz reaction tube  240  during the high state of temperature, so that soot is formed in the quartz reaction tube  240  through a chemical reaction. There is a portion of the soot that is deposited at an inside wall of the quartz reaction tube by a thermophoresis phenomenon, so as to form the optical fiber preform.  
      The chucks  230   a  and  230   b  passes through respective sidewalls  212   a  and  212   b  of the table  210  so as to rotatably fix the quartz reaction tube  240  to the table  210 .  
      The table  210  supports the chucks  230   a  and  230   b  passing through the respective sidewalls  212   a  and  212   b  of the table  210 , and a guiding groove  211   a  is formed at a bottom surface  211  of the table  210  so as to allow the sliding member  223  reciprocal movement in the left and right directions along a major axis of the quartz reaction tube  240 .  
      The burner  250  is arranged on one side of the sliding member  223  in such a manner that the burner  250  can heat the outer surface of the quartz reaction tube while moving in left and right directions along the major axis of the quartz reaction tube  240 .  
      The sliding member  223  is located on the guiding groove  211   a  of the table  210 , and a threaded feed screw  221  passes through a center portion of the sliding member  223 . The sliding member  223  reciprocates in the left and right directions along the major axis of the quartz reaction tube  240  by rotation of the feed screw  221 , the rotation being supplied by a motor  222 .  
      The sliding member  223  is provided on an upper surface thereof with the burner  250  and the electrified body  263 , so that the burner  250  and the electrified body  263  are reciprocal in left and right directions along the major axis of the quartz reaction tube  240 .  
      The soot exhausting device  260  includes the electrified body  263  for charging excessive soot formed in the quartz reaction tube  240  with a positive charge, a second electrified body  261  inserted into or at least partially ejected from the inside of the quartz reaction tube  240 , and a controller  262  for controlling a polarity and a position of the second electrified body  261 .  
      According to the present invention, the excessive soot formed in the quartz reaction tube  240  is first charged with a positive charge by means of the first electrified body  263 .  
      The second electrified body  261  repeatedly then moves with respect to the quartz reaction tube  240  under the control of the controller  262 . In other words, the polarity of the second electrified body  261  is changed to a negative pole by the controller  262  when the second electrified body  261  is inserted into the quartz reaction tube  240 , so that the second electrified body  261  absorbs soot charged with a positive charge. Also, the second electrified body  261  absorbing soot is moved to an exterior of the quartz reaction tube  240 . At the same time, the polarity of the second electrified body  261  is changed to a positive pole, so that soot adhering to the second electrified body  261 , which is also positively charged, is exhausted at the exterior of the quartz reaction tube  240 . The second electrified body  261  includes a metallic rod.  
      The soot that has not been deposited at the inside wall of the quartz reaction tube  240  is therefore exhausted to the exterior of the quartz reaction tube  240  by the soot exhausting device  260 .  
      The apparatus for manufacturing the optical fiber preform according to the present invention exhausts excessive soot formed in the quartz reaction tube by using the metal rod having a negative pole, after charging soot with a positive charge. Accordingly, excessive soot is easily exhausted, and a defect in manufacturing of the optical fiber preform caused by excessive soot can be reduced or almost eliminated.  
      Although preferred aspects of the present invention have 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.  
      For example, instead of removing soot from the electrified body by exposing same to a charge that matches the polarity of the soot to repel the soot from the body, it is also possible to use a cleaner body (not shown) having a predetermined charge (or being charged) that is equal in polarity to the second predetermined charge and greater in magnitude sufficient to attract the soot from the electrified body to the cleaner body, and wherein the electrified body is moved next to a cleaner body causing the soot to leave the electric body and attach to the cleaner body because of the greater magnitude of charge. It should also be understood while the aspects of the invention show a positively charged soot and a negatively charged electric body, it is well within the spirit of the invention and the scope of the appended claims that the polarities could be reversed, particularly if compounds are used to create the soot have a different magnetic attraction than those disclosed in the above examples. Also, although the term quartz tube is used, any tube that is able to withstand the heating process and can be used for a fiber optic perform can be used. Further, the electrified body may comprise electro magnets, solenoids, a charge corona, etc.