Transmission loss of optical fibers; achievements in half a century

Abstract

This paper reviews the evolutionary process that reduced the transmission loss of silica optical fibers from the report of 20 dB/km by Corning in 1970 to the current record-low loss. At an early stage, the main effort was to remove impurities especially hydroxy groups for fibers with GeO₂-SiO₂ core, resulting in the loss of 0.20 dB/km in 1980. In order to suppress Rayleigh scattering due to composition fluctuation, pure-silica-core fibers were developed, and the loss of 0.154 dB/km was achieved in 1986. As the residual main factor of the loss, Rayleigh scattering due to density fluctuation was actively investigated by utilizing IR and Raman spectroscopy in the 1990s and early 2000s. Now, ultra-low-loss fibers with the loss of 0.150 dB/km are commercially available in trans-oceanic submarine cable systems.