PRODUCTION OF PERFORM FOR DISPERSED SHIFT FIBER

摘要

PURPOSE:To produce a preform for dispersed shift fiber having a stepwise refractive index profile by forming a center core and a side core by a concentric burner and to obtain a preform for dispersed shift fiber capable of readily controlling structure parameters of center core and side core. CONSTITUTION:A center core 1 is formed by a concentric burner 30 and successively a side core 4 is made by a concentric burner 40 to produce a preform for shift fiber having a stepwide refractive index profile. The concentric burner 30 for forming the center core consists of a raw material gas discharge nozzle 31 and an oxyhydrogen flame-forming gas discharge nozzle 32, which is divided into an inner layer 33 of a hydrogen gas flow, an intermediate layer 34 of an inert gas flow and an outer layer 35 of an oxygen gas flow and the flow rate of the oxygen gas discharging from the outer layer 35 is made >=2.7 times the flow rate of the hydrogen flow sent from the inner layer.