Significant suppression of Rayleigh scattering loss in silica glass formed by the compression of its melted phase

10^th International Conference and Exhibition on Lasers, Optics & Photonics

November 26-28, 2018 | Los Angeles, USA

Madoka Ono

AGC Research Center, Japan

Scientific Tracks Abstracts: J Laser Opt Photonics

Abstract :

Silica glass had long and intensively been studied due to its technological interest in manufacturing higher-performance optical fibers. Recently, silica glass formed at high temperature and pressure is attracting much attention due to its physical properties which cannot be obtained by compression at room temperature. For example, the intermediate-range order structure of silica glass which was hot-compressed at several GPa around the glass-transition temperature (Tg ~1400K) was reported to be more homogeneous and is completely different from that of silica glass compressed at room temperature, even though their densities were similar. The threshold pressure to trigger the change seemed to decrease with increasing temperature. We have previously reported that the Rayleigh scattering intensity in silica glass can be explained in terms of the voids in the glass behaving as scattering particles. Here, the expression of �??void�?� stands for sub-nanometer size structural empty space, not bubbles. The void size was observed to decrease as the fictive temperature, Tf (temperature at which the glass network structure is �??frozen�?�), decreased, by using positron annihilation lifetime spectroscopy. The decrease of the void size was found to suppress local density fluctuations which, in turn, led to less intense light scattering. Thus, a decrease of the Rayleigh scattering intensity was expected if a reduction of the void size can be achieved. For industrial usage, pressures of less than 200MPa is desirable since samples of up to one-meter size are obtainable in a ready-made hot isostatic pressure (HIP) machine. Therefore, we investigated the Rayleigh scattering intensity of hot-compressed silica glass using HIP under its melted phase. As a result, the optical transport properties of the silica glass was largely improved by the process. The lowest Rayleigh scattering loss was obtained for the glass held at 200MPa and 2073K for 4h. The observed loss corresponds to 0.07dB/ Km at 1.55μm, which is about half of the loss in conventional silica glass fiber. The decrease in the loss was well explained in terms of the decrease in the size of the sub-nanometer-sized structural voids. Due to the compressive stress, the refractive index increased simultaneously with the decrease in the void size and the scattering intensity. This is very favorable for fibercore media, where high transparency and strong confinement of light are desired. It is not possible to otherwise get such glass homogeneity (corresponding to such a low Tf) and reduce the Rayleigh loss simply by thermal engineering at standard atmospheric pressure.

Biography :

Madoka Ono has completed her PhD in the year 2004 from Tokyo University. Her PhD research was the study of optically excited states in low-dimensional Mott insulators by using linear and nonlinear optical measurements. She joined Asahi Glass Company in the year 2004. Her researches since then were; 1. Electronemission properties of Calcium Aluminate electride 2. Improvement of the transmittance and laser-durability of silica glass 3. Study of the glass structures by positron annihilation measurements and 4. Optimization of glass composition and structures to obtain stronger glass with various strengthening processes. She is now working as a senior researcher and a project leader in AGC. She also works as a part-time lecturer of Yokohama National University, teaching glass science and its applications. She is a board member of photonics division of Japanese Society of Applied Physics.

E-mail: madoka-ono@agc.com