Electric furnace extension method and extension apparatus for optical fiber glass preform

Abstract

An electric furnace extending method and apparatus for an optical fiber glass body alignment when connecting the extension use body and pulling member and making it possible to immediately start the extension after the fusing of the connection portion. A centering mechanism for centering the free end portion of the body and member on the furnace center side is provided between the furnace pipe of the electric furnace and grips of the extension use glass body and between the furnace pipe and the pulling member. The free end portion is centered by this centering mechanism, then the gripped sides of the body and member are fixed, the front ends of the two free end portions are abutted and fused and bonded at the highest temperature portion inside the electric furnace, then the highest temperature portion is moved to the extension portion of the glass body side and the extending of the glass body is commenced.

1 . A method for extending an optical fiber glass body using an electric furnace extension apparatus comprising an upper holder which holds an upper end of the extension optical fiber glass body to be extended; a lower holder, provided at a position coinciding with an axial center of said upper holder and facing said upper holder, which holds a lower end of a pull glass member and is pulled toward a lower portion; and an electric furnace provided between said upper holder and said lower holder, the extension method comprising the following steps:
 holding the upper end of the extension optical fiber glass body to be extended by using the upper holder;   aligning a lower end of the extension optical fiber glass body with an upper end of the pull glass member being held by the lower holder;   joining the lower end of the extension optical fiber glass body and the upper end of the pull glass member by subjecting the lower end of the extension optical fiber glass body and the upper end of the pull glass member to a heat-melt at a maximum temperature portion inside the electric furnace; and   moving the maximum temperature portion of the electric furnace to an extending portion and moving the lower holder toward a low position to pull the extension optical fiber glass body downwardly to extend the optical fiber glass body.   
   
   
       2 . The method according to  claim 1 , further comprising the step of joining the lower end of the extension optical fiber glass body with a dummy member before the step of aligning the lower end of the extension optical fiber glass body with the upper end of the pull glass member being held by the lower holder. 
   
   
       3 . The method according to  claim 2 , wherein the dummy member has a lower tip with a diameter that is smaller than a diameter of the upper end of the pulling glass member and has an upper tip with an upside down semi-conical shape, wherein the upper tip of the dummy member is substantially equal to a diameter of the extension optical fiber glass body. 
   
   
       4 . The method according to  claim 3 , wherein the lower tip of the dummy member has a diameter that is ½ to ⅓ the diameter of the pulling glass member.