PREPARATION OF PARENT MATERIAL FOR OPTICAL FIBER

PURPOSE:To reduce lot-to-lot variability of band characteristics, by controlling transfer of a torch holder in such a way that it has the same speed that of growth of a parent material for optical fiber which is set arbitrarily by a growth speed setting device, a growth speed detector and the torch holder movable backward and forward, and to right and left. CONSTITUTION:The titled method is related to preparation of the parent material 4 for optical fiber by vapor phase axial deposition. The position of the torch holder 14 is maintained in such a way that signal inputted to the growth speed setting device 11 by the growth speed setting device 11 for the porous glass parent material 4, the growth speed detector 10, and the torch holder 14 movable backward and forward, and right and left is identical with a signal outputted from the growth speed detector 10. The crossing point and angle of the central axis of the flame stream 2 and the central axis of the porous parent material 4 are regulated so that they are constant.