METHOD FOR SYNTHESIZING POROUS PREFORM FOR OPTICAL FIBER AND APPARATUS THEREFOR

摘要

PURPOSE:To stably synthesize a porous glass preform for optical fiber with high quality. CONSTITUTION:Flame for forming core part ejected from a core burner 4 toward a soot body 2 is measured by a CCD camera 32 and pictured image data are changed to binary digit in an image treating device 30 and the position of the middle point P is obtained using a measuring window 40. An air flow rate controller 54 is operated so that this position is kept to a prescribed position to control air amount which is made to flow from the upper part of a bell jar 11 toward the flame 8. Further, an amount of air introduced from a control valve 60 into a discharge cylinder 13 is controlled so as to suppress fluctuation of the flame 8 in a specific range to control the pressure of the bell jar 11. The fluctuation of the flame 10 for forming a clad part from a clad burner 6 is suppressed similarly to position control of the flame 8 for forming the core part by controlling an amount of air which is made to flow toward flame 10 for forming clad part.