This paper reviews the evolutionary process that reduced transmission loss of silica optical fibers from report 20dB/km by Corning in 1970 to current record-low loss. At an early stage, main effort was remove impurities especially hydroxy groups for with GeO2-SiO2 core, resulting 0.20dB/km 1980. In order suppress Rayleigh scattering due composition fluctuation, pure-silica-core were developed, ...
