METHOD FOR CONTROLLING REFRACTIVE INDEX OF OPTICAL FIBER PREFORM IN MODIFIED CHEMICAL VAPOR DEPOSITION AND OPTICAL FIBER MANUFACTURED BY THE METHOD

摘要

PURPOSE: Provided are a method for controlling a refractive index of optical fiber preform in modified chemical vapor deposition(MCVD), which regulates the amount of oxygen and helium in conformity with flow rates of reaction gases injected into quartz tube and thus controls flow rates and internal temperatures of the reaction gases, so as to minimize a fluctuation of refractive index of the optical fiber in the longitudinal direction. CONSTITUTION: The method for manufacturing a basic material of optical fiber having constant refractive index in the longitudinal direction by using MCVD, comprises regulating amounts of oxygen and helium injected into quartz tube(10). The q/Q value(q: total flow rate of reaction gas, Q: flow rate of oxygen gas) expressing the ratio of total reaction gas and oxygen rates in the quartz tube(10) is 1.2-1.4. The flow rate of oxygen is 1000-4000 sccm. The Q/a value(Q: flow rate of oxygen gas, a: thermal diffusivity of the reaction gas) is 4.0-6.0.