Method for controlling diameter of grin lens fiber and fiber drawing equipment

Abstract

When a GRIN lens fiber is drawn from a preform, control of a fiber diameter is improved in order to increase a production yield of the GRIN lens fiber having a fiber diameter within a desired range. The problem is solved by controlling the drawing speed using a fiber diameter c, which is obtained by correcting a fiber diameter a using the fiber diameter b and a fiber diameter α. The fiber diameter a is measured using a diameter measuring instrument A that measures an outer diameter of the GRIN lens fiber, which is being elongated inside a heating furnace, the fiber diameter b is measured using a diameter measuring instrument B that measures an outer diameter of the GRIN lens fiber outside the heating furnace, and the fiber diameter α is a value of the fiber diameter a measured a specified period of time T earlier.

1 - 5 . (canceled) 
     
     
         6 . An apparatus for drawing a GRIN lens fiber, said apparatus comprising:
 a diameter measuring instrument A for measuring an outer diameter of a GRIN lens fiber, the GRIN lens fiber being elongated inside a heating furnace;   a diameter measuring instrument B for measuring the outer diameter of the GRIN lens fiber outside the heating furnace; and   a control device for controlling a drawing speed on the basis of a fiber diameter a measured using the diameter measuring instrument A and a fiber diameter b measured using the diameter measuring instrument B.   
     
     
         7 . The apparatus for drawing a GRIN lens fiber according to  claim 6 , further comprising an automatic controller and a correction device, wherein the correction device transmits a fiber diameter c to the automatic controller, the fiber diameter c being obtained by correcting the fiber diameter α using the fiber diameter b and a fiber diameter a, the fiber diameter α being a value of the fiber diameter a measured a specified period of time T earlier, the automatic controller controlling the drawing speed on the basis of the fiber diameter c. 
     
     
         8 . The apparatus for drawing a GRIN lens fiber according to  claim 7 , wherein the fiber diameter c is given by the following expression: fiber diameter a+fiber diameter b−fiber diameter a. 
     
     
         9 . The apparatus for drawing a GRIN lens fiber according to  claim 7 , wherein, when a distance in a GRIN lens fiber path between a measurement position of the diameter measuring instrument A and a measurement position of the diameter measuring instrument B is d mm, and the drawing speed in is V mm/second, the specified period of time T seconds falls within the following range:
   ( d− 20)/V≦ T≦ ( d+ 20)/ V.  
   
     
     
         10 . The apparatus for drawing a GRIN lens fiber according to  claim 7 , wherein the automatic controller includes a PID controller, the PID controller controlling the drawing speed using PI control or PID control. 
     
     
         11 . The apparatus for drawing a GRIN lens fiber according to  claim 8 , wherein, when a distance in a GRIN lens fiber path between a measurement position of the diameter measuring instrument A and a measurement position of the diameter measuring instrument B is d mm, and the drawing speed in is V mm/second, the specified period of time T seconds falls within the following range:
   ( d− 20)/ V≦T≦ ( d+ 20)/ V.      
     
     
         12 . The apparatus for drawing a GRIN lens fiber according to  claim 8 , wherein the automatic controller includes a PID controller, the PID controller controlling the drawing speed using PI control or PID control. 
     
     
         13 . The apparatus for drawing a GRIN lens fiber according to  claim 9 , wherein the automatic controller includes a PID controller, the PID controller controlling the drawing speed using PI control or PID control. 
     
     
         14 . A method for controlling a diameter of a GRIN lens fiber, said method comprising:
 controlling an outer diameter of the GRIN lens fiber so as to, when the GRIN lens fiber is drawn from a preform, make the outer diameter match a specified diameter;   controlling a drawing speed on the basis of:
 a fiber diameter a that is measured using a diameter measuring instrument A that measures the outer diameter of the GRIN lens fiber, the GRIN lens fiber being elongated in a heating furnace, 
 a fiber diameter b that is measured using a diameter measuring instrument B that measures the outer diameter of the GRIN lens fiber outside the heating furnace; 
   wherein the drawing speed is further controlled on the basis of a fiber diameter c, the fiber diameter c being obtained by correcting the fiber diameter a using the fiber diameter b and a fiber diameter α, the fiber diameter α being a value of the fiber diameter a measured a specified period of time T earlier, and   wherein the fiber diameter c is given by the following expression: fiber diameter a+fiber diameter b−fiber diameter α, wherein, when a distance in a GRIN lens path between a measurement position of the diameter measuring instrument A and a measurement position of the diameter measuring instrument B is d mm, and the drawing speed is V mm/second, the specified period of time T seconds falls within the following range:
   ( d− 20)/ V≦T≦ ( d+ 20)/ V.