Toward ultra-lucent optical fibers

From infrared absorption spectra, the present authors elucidated behaviors of the structural relaxation in silica glass doped with various elements, and claim that sub-relaxation process exists besides the main-relaxation given by the viscous flow. Light scattering measurement also suggested the existence of such an additional relaxation channel. The sub- and main-structural relaxations are in general greatly accelerated by a proper dopant. And, the sub-relaxation, which extends below the glass transition temperature, gives a breakthrough to bring silica glass to a more stable structure even below the glass transition temperature. The sub-relaxation then reduces the Rayleigh scattering, a predominant component of the optical loss in the glass. Fluorine and chlorine seem to greatly accelerate the relaxations in silica glass.