AbstractWe experimentally studied the optical properties of multicomponent oxide glasses that contain metallic components, such as potassium and sodium, and their glass fibers. The Rayleigh scattering coefficients of glasses such as Na2O‐B2O3‐SiO2 (NBS), K2O‐MgO‐SiO2 (KMS), K2O‐Na2O‐MgO‐SiO2 (KNMS) are smaller than that of pure quartz glass. In particular, the Rayleigh scattering coefficient of KNMS glass was significantly lower at 38% of the value for pure quartz glass. This is believed to be the result of suppressing the composition fluctuations of KNMS glass by the mixed alkali effect. Furthermore, we studied the absorption properties of OH group impurities included in multicomponent oxide glasses. In particular, we fabricated NAS glass fibers that substituted the OH group impurity with an OD group (deuterium) by the double crucible method and verified a loss reduction of about 800 dB/km at the 1.55‐µm wavelength. Through these studies, we clearly showed that the absorption losses of the OH group that hydrogen bonds to nonbridging oxygen clearly affected the increase in the 1.55‐µm band loss in multicomponent oxide glass fibers. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(12): 21–35, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10128