Patent ID: 7698908

Claim:
A method for manufacturing a glass base material which is a base material of an optical fiber, comprising: forming a clad around a core by accumulating glass particles on said core to form a porous-glass-base-material; sintering and dehydrating said porous-glass-base-material to form said glass base material; determining a rate of change in a diameter of said core of said glass base material; determining a rate of change in a relative-refractive-index-difference between said core and said clad of said glass base material using the equation: Δ n={ ( n 1 −n 2 )/ n 1 }×100% Δn being a relative-refractive-index-difference between said core and said clad, n 1 being a refractive index of said core and n 2 being a refractive index of said clad; and removing all portions of said glass base material defective for use as a base material of an optical fiber where said rate of change in a relative-refractive-index-difference of said removed portions of said glass base material is more than substantially 6% or said rate of change in a core diameter is more than substantially 7%, such that a part of the optical fiber subsequently drawn from said glass base material remaining after the defective portions are removed which has a transmission loss more than 0.1 dB is detectable by measuring the incidental light from only one end of said optical fiber using OTDR measurement.