Method, apparatus and burner for fabricating an optical fiber preform

An optical fiber preform fabrication method comprising the steps of:

• using a burner having a central raw material supply orifice for supplying a glass raw material and a plurality of flame forming orifices disposed around said raw material supply orifice sequentially for forming a plurality of flames, respectively, the number of flames being at least equal to k+1;
• determining and controlling the flame speed V.sub.k of a kth flame, the flame speed V.sub.k+1 of a (k+1)th flame outwardly surrounding said kth flame and the flow speed Vm of the glass raw material supplied through the center of the burner in such a way that the following relations are satisfied:
• 0.1V.sub.k+1 .ltoreq.Vk.ltoreq.2.5V.sub.k+1,
• Vm.ltoreq.V.sub.k+1 and
• Vm.ltoreq.V.sub.k ;
• positioning said kth flame axially rearwardly of said (k+1)th flame outwardly surrounding said kth flame in such a way that the downstream end of said kth flame is substantially continuous to the upstream end of said (k+1)th flame;
• supplying combustion gases to said flame forming orifices and combusting to provide said flames;
• supplying said glass raw material to the multiflame produced by said burner to synthesize fine glass particles;
• depositing said fine glass particles on a seed rod to form a porous preform;
• and
• consolidating said porous preform into a transparent optical fiber preform.