PURPOSE: To obtain the title matrix of reduced transmission loss by surface treatment of a glass rod containing a glass to be an optical fiber core followed by accumulating clad glass thereon to suppress the contamination of foreign substances to a minimum.
CONSTITUTION: A shutter 3 is opened, and a starting glass rod 4 containing a glass to be an optical fiber core, formed at the tip of a dummy glass rod 41 is inserted into a heating furnace 2 and heated in a rotational state; and at the same time, both an etching gas (e.g. CF4) and a carrier gas are introduced thereinto to uniformly treat the surface of the glass rod 4. Thence, the resultant glass rod 4 is coaxially pulled upward and set up in a chamber 11, and the shutter 3 is closed and then glass fine particles to be a clad, formed in a flame from a burner 1 for glass fine particle accumulation is accumulated on the glass rod to obtain a glass fine particle-accumulated form 42, which is then returned to the heating furnace 2 where transparent vitrification is accomplished.
NISHIDE KENJI
HORIKOSHI MASAHIRO
