Shigeki Sakaguchi

Refractive index and material dispersions of multi-component oxide glasses

Abstract Refractive index dispersion curves in the wavelength region of 0.40 to 5.03 μm are presented for multi-component oxide glass systems: borate, silicate, aluminate, germanate, tellurite, antimonate and heavy metal gallate. The material dispersion was determined using the refractive index data. Reflection spectra in the ultraviolet and infrared regions were measured to investigate the effects of electronic transitions and lattice vibrations on the material dispersion. Thallium tellurite, thallium antimonate and lead gallate glasses exhibit zero material dispersion wavelengths (ZMDWs) over 2.4 μm. The factors affecting the ZMDW are discussed.

Preparation of Elevated NA Fluoride Optical Fibers

Elevated NA fluoride optical fibers having minimum losses of less than 1 dB/km have been prepared using a dry processing technique. NA ranging from 0.19 to 0.24 has been obtained by substituting LiF and/or ZrF4 in basic core and cladding glasses consisting of ZrF4–BaF2–LaF3–YF3–AlF3–LiF by NaF and/or HfF4, respectively. It has been demonstrated by measuring critical cooling rates for glass-formation that glasses containing NaF applied to elevated NA fibers have high glass-forming ability, It is found that elevating NA enables low OH impurity absorption to be successfully reproduced in FEP coated fibers and that applying glasses containing NaF to elevated NA fibers effectively reduces extrinsic scattering.

Optical properties of GeO2 glass and optical fibers.

The optical properties of GeO(2) glass were investigated to clarify its potentiality as an optical fiber material. Glass samples were prepared by the flame hydrolysis and the melting techniques, and their Rayleigh scattering and infrared absorption properties were examined. Optical fibers composed of a pure GeO(2) core and an F-doped GeO(2) cladding were drawn to clarify the scattering loss characteristics. The Rayleigh-scattering intensity obtained from spectral loss measurements on the fibers agreed with that measured in bulk samples, and the intensity relative to that of SiO(2) glass was found to be approximately 3. These results suggest that a minimum loss of 0.15 dB/km is expected at a wavelength of 2 microm.

Viscosity of silica core optical fiber

Abstract Since we found that Rayleigh scattering of silica core optical fiber can be reduced by heat treatment, we studied the viscosities of the fiber to investigate this phenomenon from the viewpoint of viscous relaxation. To this end, the viscosity of silica core fiber was measured by the bending method in a temperature range of 1050–1200°C. We found that the viscosities were a few orders of magnitude less than those of silica glasses. This result is due to the larger fictive temperature of the fiber, which results from the drawing process, compared with those of silica glasses. We suggest that the relaxation process for Rayleigh scattering is related to the drawing conditions of the fiber.

Scattering characteristics of crystallites in fluoride optical fibers

This paper evaluates the scattering loss in ZrF(4)-based fluoride optical fibers that is caused by ZrF(4) and ZrO(2) crystallites. To determine this, efficiency factors of each of these crystals are calculated. We make clear that the presence of ZrO(2) crystals of the order of a submicron smaller than 0.2 microm in diameter effectively elevates the Rayleigh scattering factor as the particle number increases. Scattering loss characteristics in current fluoride fibers are also discussed. In addition, ZrO(2) microcrystals in fluoride fibers are identified for the first time using Raman microprobe analysis. It is concluded that ZrO(2) microcrystals cause serious extrinsic scattering loss in current ZrF(4)-based fluoride fibers.

Rayleigh scattering of silica core optical fiber after heat treatment

We investigated the Rayleigh scattering of silica core optical fibers, parts of which were heat treated at various temperatures, in relation to their fictive temperatures (T(f)). The scattering intensities from short fiber segments were clearly reduced by heat treatment compared with those of the unheated parts. The T(f) values of the heated parts of the fibers were determined by measuring the infrared reflection spectrum for cleaved end surfaces and were also reduced by controlling the heating temperature. The reduction in the scattering intensity correlates well with the reduction in T(f).

Relationship between Scattering Loss and Oxygen Content in Fluoride Optical Fibers

To clarify the cause of scattering loss in fluoride optical fibers, oxygen content in fibers having various loss values is analyzed by activation analysis using a cyclotron. It is found that fibers with higher loss contain a higher oxygen content. It is concluded that oxygen tends to cause scattering loss in fluoride optical fibers.

Rayleigh scattering in silica glass with heat treatment

Abstract We investigated Rayleigh scattering in silica glass with heat treatment under various conditions, including quenching and slow cooling, and its relation to fictive temperature. The Rayleigh scattering intensity varied according to the conditions of the heat treatment. The scattering intensity in slowly cooled samples is less than that in quenched samples after heating at the same temperature. We evaluated fictive temperatures based on measurements of infrared absorption and Raman scattering. The Rayleigh scattering intensity was related to the fictive temperature regardless of the heat treatment conditions, and a linear relation between them was obtained. In addition, we suggest that the decrease in scattering intensity in slowly cooled samples results from structural relaxation due to viscous flow during the cooling process.

Light Scattering Properties in Ternary Germanate Glasses

Ternary germanate glass systems of GeO2-P2O5-MFx ( MFx : CaF2, ZnF2, PbF2, AlF3, and GaF3) are developed to investigate their light scattering properties. Glass-forming regions for these ternary systems are determined, and the systems containing the divalent fluorides, such as CaF2 and ZnF2, are found to exhibit wide glass-forming regions. Light scattering (Rayleigh scattering) and related properties for the systems are examined by comparison with those of pure GeO2 glass which is prepared by flame hydrolysis techniques. It is clarified that some glasses containing fluorides such as CaF2, ZnF2 and GaF3 at specified compositions exhibit scattering intensities less than that of GeO2 glass. The scattering intensity as low as 0.43 that of GeO2 is obtained for the GeO2-P2O5-CaF2 system.

Study on the Nature of Extrinsic Scattering Centers in Fluoride Glass Optical Fibers

The origin and loss characteristics of extrinsic scattering centers in ZrF4-based fluoride optical fibers have been investigated. Scattering centers larger than about 1 µm have been found to be micro-crystallites, inclusions of impurity particles or bubbles. They can be reduced by improving the preform-preparation conditions. For scattering centers of submicron size, scattering loss has been estimated at wavelengths of 0.633 and 2.55 µm and has been indicated to exhibit wavelength dependence of λ-2. Loss factors for a fiber fabricated under improved preform-preparation conditions have been analyzed. A minimum loss of 3.0 dB/km at a wavelength of 2.55 µm was proved to arise from about 2 dB/km of scattering and about 1 dB/km of absorption.