Hoya Glass Works, Ltd.

Yoshito Nogami

Kenji Nakagawa

Susumu Horikawa

An optical fiber comprising a core glass and a cladding glass therearound, wherein at least the core glass contains GeO.sub.2 as an additive to increase the refractive index with respect to the cladding glass. The fiber glass is prepared by heat treating a starting glass to separate out a B.sub.2 O.sub.3 --Na.sub.2 O-rich phase for subsequent acid leaching, and by sintering a residual glass with low concentrations of light absorbing impurities. Ingredients of the starting glass in weight percent are as follows:

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Saitama, Japan

Yoshito Nogami