JPS6127721B

PURPOSE:To produce an optical fiber having a main quartz core as a center, a partial core layer formed coaxially with the main core, a quartz clad layer formed thereon and a pure quartz supporting layer formed thereon under uniformity and mass productivity by utilizing a tube rodding process. CONSTITUTION:Silicon compound gas and refractive index reducing additive gas are fed into the hollow portion of a pure quartz tube 3 to thereby form a first doped quartz layer to become a clad layer 2 in a gaseous phase reaction. Then, silicon compound gas and refractive index controlling additive gas is fed into the hollow portion to thereby so form a second doped quartz layer to become a partial core layer 11 in a gaseous phase reaction in a manner that the refractive index in this layer is lower than that in pure quartz and gradually increases from the exterior toward the core. Then, a pure quartz rod to become a main core 1 is inserted into the thus formed hollow portion, and heated to eliminate residual air gap between the tube and the rod in closely molten adherence as a mother material.