Mandrel for producing quartz glass and production method for optical fiber mother material, optical fiber and quartz glass body using the same

Abstract

A mandrel for producing quartz glass, comprising at least two columnar or cylindrical, carbon fiberreinforced carbon composite material made members joined in series by screw thread parts. The mandrel is carbonimpregnated and/or carbon-coated on the screw thread parts, and, in addition, may be provided with reinforcing members on the outer sides of the screw thread parts. Quartz glass fine particles obtained by flame-hydrolyzing a volatile silicon compound are deposited, using this mandrel, on the surface of a heat-resisting substratum or on a starting rod at the end of the mandrel to easily form a large porous quartz glass mother material, the porous quartz glass mother material is dehydrated and transparently vitrified to produce a large optical fiber mother material, and further the optical fiber mother material is drawn to produce a low-cost, high-precision optical fiber. In addition, a columnar or cylindrical mandrel for producing quartz glass is disposed at the center of a heat-resisting mold, is filled with silicon dioxide power, and melt in a heating furnace for vitrifying, thereby producing a large, high precision quartz glass body at low costs.

1 . A process for producing a large optical fiber mother material, comprising forming a mandrel used for producing a quartz glass body by joining at least two columnar or cylindrical, carbon fiber reinforced carbon composite material made members in series by screw thread parts, depositing quartz glass fine particles obtained by flame-hydrolysis of a volatile silicon compound on the surface of the mandrel to form a porous quartz glass mother material; and then dehydrating and transparently vitrifying the mother material.  
   
   
       2 . A process for producing a large optical fiber mother material comprising forming a mandrel used for producing a quartz glass body by joining at least two columnar or cylindrical, carbon fiber reinforced carbon composite material made members in series by screw thread parts, using the mandrel inserted after withdrawal of a heat resisting substratum of a porous quartz glass mother material.  
   
   
       3 . A process for producing a large optical fiber mother material, comprising forming a mandrel used for producing a quartz glass body by joining at least two columnar or cylindrical, carbon fiber reinforced carbon composite material made members in series by screw thread parts, depositing quartz glass fine particles obtained by flame-hydrolysis of a volatile silicon compound in the axial direction of a quartz glass starting rod placed at the end of the mandrel for producing quartz glass to form a porous quartz glass mother material and then dehydrating and transparently vitrifying the mother material.  
   
   
       4 . A process for producing an optical fiber comprising forming a mandrel used for producing a quartz glass body by joining at least two columnar or cylindrical, carbon fiber reinforced carbon composite material made members in series by screw thread parts, producing a rod for heat-stretching an optical fiber mother material and/or in a drawing step of drawing said rod suspending the optical fiber mother material and/or the rod from the mandrel for producing quartz glass.  
   
   
       5 . A process for producing a large quartz glass body comprising forming a mandrel used for producing a quartz glass body by joining at least two columnar or cylindrical, carbon fiber reinforced carbon composite material made members in series by screw thread parts, disposing the mandrel in the center of a heat resisting mold; filling a silicon dioxide powder in the mold; and then melt-vitrifying the powder in a heating furnace.  
   
   
       6 . The process for producing a large quartz glass body according to  claim 5 , comprising providing a graphite intermediate material between the mandrel for producing quartz glass and a silicon dioxide powder, and/or between a heat resisting mold and a silicon dioxide powder.