Yasuhiko Benino

Transparent nonlinear optical crystallized glass fibers with highly oriented Ba2TiGe2O8 crystals

Glass fibers with a diameter of 100–200μm are drawn by just pulling up melts of 30BaO–15TiO2–55GeO2 glass, and transparent crystallized glass fibers consisting of nonlinear optical Ba2TiGe2O8 crystals are fabricated by crystallization of glass fibers. It is clarified from linearly polarized micro-Raman scattering spectra that fibers show the surface crystallization and Ba2TiGe2O8 crystals grow from the surface to the interior, giving c-axis orientations. It is found that holes are formed frequently in the center of fully crystallized glass fibers, and transparent hollow crystallized glass fibers are fabricated through careful heat treatments, e.g., fibers with ϕ=200μm show hollows (capillary-type holes) with ϕ=40μm. By adding a small amount of Sb2O3 in glass fiber preparations, transparent crystallized glass fibers with no holes are developed and second harmonic generations (SHGs) are clearly observed from such fibers. The present study proposes that transparent crystallized glass fibers showing strong SH...

Novel Technique for Fabrication of Nanoparticle Structures in KNbO3–TeO2 Glass for Photonic Integrated Circuits

We succeeded in fabricating novel nanoparticle structures on KNbO3–TeO2 glass induced by ultraviolet (UV) laser irradiation and found that the size and size distribution could be controlled by the conditions of laser irradiation, such as fluence, pulse repetition rate, and the temperature of the glass specimen by heat assistance (HA). Nano-sized particles are an interesting new material, because they will be able to open the door to the invention of photonic circuits of extremely small size, which transfer optical signals through optical near-field energy operating by a completely different principle. The particle diameters may be controlled from approximately 200 nm up to 500 nm by modifications of UV laser fluence and the repetition rate of pulses. When using HA with a glass specimen during laser irradiation, it has been found that nanoparticle formation is activated and particle size increased as the temperature of the glass increased, and the uniformity of particle size is markedly improved by HA treatment. The standard deviation of particle size is 20 nm at 100 °C. A 60% improvement in the size variation of particles is possible in comparison with laser irradiation without HA. These results suggest that heat is involved in nanoparticle formation during UV laser irradiation, which means that the overall history of heating with pulsed laser irradiation is critically important to control the form of the particles. Furthermore, periodic structures with an 800 nm pitch constructed by lines of ordered nanoparticles with diameters of approximately 150–300 nm were successfully fabricated by laser irradiation through a phase mask. This is a significant advancement towards the realization of nanophotonic circuits.

Nano–Micrometer-Architectural Acidic Silica Prepared from Iron Oxide of Leptothrix ochracea Origin

We prepared nano-micrometer-architectural acidic silica from a natural amorphous iron oxide with structural silicon which is a product of the iron-oxidizing bacterium Leptothrix ochracea. The starting material was heat-treated at 500 °C in a H2 gas flow leading to segregation of α-Fe crystalline particles and then dissolved in 1 M hydrochloric acid to remove the α-Fe particles, giving a gray-colored precipitate. It was determined to be amorphous silica containing some amount of iron (Si/Fe = ~60). The amorphous silica maintains the nano-microstructure of the starting material-~1-μm-diameter micrometer-tubules consisting of inner globular and outer fibrillar structures several tens of nanometer in size-and has many large pores which are most probably formed as a result of segregation of the α-Fe particles on the micrometer-tubule wall. The smallest particle size of the amorphous silica is ~10 nm, and it has a large surface area of 550 m(2)/g with micropores (0.7 nm). By using pyridine vapor as a probe molecule to evaluate the active sites in the amorphous silica, we found that it has relatively strong Brønsted and Lewis acidic centers that do not desorb pyridine, even upon evacuation at 400 °C. The acidity of this new silica material was confirmed through representative two catalytic reactions: ring-opening reaction and Friedel-Crafts-type reaction, both of which are known to require acid catalysts.

Fabrication of Optical Waveguide in Glass by Laser-Induced Crystallization

Homogeneous crystal lines were fabricated at the surface of 8Sm2O3.37Bi2O3.55B2O3 glass by irradiations of cw Nd: YAG laser (λ=1064 nm) with laser powers of 0.7-0.9 W and laser scanning speeds of 3-5 μm/s. It was confirmed from micro-Raman scattering spectra that the lines consist of nonlinear optical SmxBi1-xBO3 crystals showing second harmonic generations. The curved crystal lines with bending angles of 0∼90° were successfully written by just changing laser scanning directions. The light (λ=632.8 nm) transmission was confirmed for a crystal line (length: 850 μm) with two bending angles of ±30o, where significant light scattering losses were not observed at the bending points. We propose that the curved crystal lines written by YAG laser irradiations have a high potential for applications in optical waveguides.

Nano-Crystallized Glass Fibers with Second-Order Optical Nonlinearity

Transparent nano-crystallized glass fibers with 300μm diameter were successfully fabricated in tellurite (TeO2) based glass systems. Structure of crystallized glass fibers and orientation of nano-size crystals were quantitatively investigated by microscopic Raman spectroscopy and X-ray diffraction. Second harmonic generation was measured in the nano-crystallized optical fibers.

Synchrotron X-ray Scattering Measurements of Disordered Materials

Abstract With the advent of third-generation synchrotron sources and the development of light source techniques, X-ray scattering techniques have become feasible, leading to new approaches for studying the structures of disordered materials in a quantitative manner. We introduce a dedicated diffractometer for high-energy total X-ray scattering measurement and a newly developed anomalous X-ray spectrometer at SPring-8. As advanced methodologies for the measurement of liquids, we now offer three state-of-art levitation instruments for aerodynamic levitation, electrostatic levitation, and acoustic levitation at the SPring-8 beamlines, covering a wide temperature range of −40–3000u202f℃. Furthermore, scientific investigations of glasses, liquids, and amorphous materials reported in the last five years at SPring-8 are reviewed.

Fabrication and characterization of Er3+-doped tellurite glass waveguide by Ag+-Na+ ion-exchange method

The planar waveguides of 12Na2O10NbO2.525WO353TeO2+1Er2O3 ([NbWEr]) glasses were prepared by Ag+-Na+ ion-exchange at 320-380°C for 5-30 h. The optical properties of the waveguides were characterized. Waveguiding property was successfully confirmed under all the ion-exchange conditions in this study. The thickness of the waveguides increased with increasing ion-exchange temperature and time. The minimum propagation loss of the waveguides was approximately 0.8 dB/cm at 632.8 nm. Hence, the [NbWEr] glass waveguides were considered to be promising for broadband optical amplifiers.

Phase separation of borosilicate glass containing phosphorus

Sodium borosilicate glasses containing P2O5 and Al2O3 were prepared, and the behavior of phosphorus associated with the phase separation and the effect of Al2O3 addition have been investigated. After the heat treatment, phase separation by spinodal decomposition was observed in the all samples. In the Al2O3-free glasses, phosphorus was preferentially distributed into B2O3-rich glass phase after the phase separation. With increasing Al2O3 content, the amount of phosphorus distributed into SiO2-rich glass phase increased. According to 31P MAS NMR measurements, in the Al2O3-containing glasses, Q4 units free from terminal oxygen atoms were formed. It was suggested that the distribution of phosphorus depend on the PO4 units.

Order/Disorder Hybrid Structures in Photonic Glass Materials

Investigations for space-selected structure ordering from nano-particles to single-crystal patterning in glasses will be described. Transparent crystallization in glass must be the best material solution to obtain novel functional glasses with a permanent second-order optical nonlinearity. We focus on the new functions created by structure ordering in glass by means of laser micro-fabrication for space-selected crystallization. Two topics in our recent experimental results of space-selected structure ordering in glass will be presented as follows: 1) Single crystalline patterning by atom heat laser processing in Sm-doped glasses for optical waveguides with second-order optical nonlinearity, 2) structure ordering of domains in crystallized glass fibers for possible photonic fiber-type devices with active signal processing.

Anomalous x-ray scattering studies of functional disordered materials

We have developed anomalous x-ray scattering (AXS) spectrometers, that employ intrinsic Ge detectors and crystal analyzers, at SPring-8. The use of LiF analyzer crystal provides us with an energy resolution of ~ 12 eV. Furthermore, it has been established that the use of AXS technique is essential to reveal the relationship between the atomic structure and its function of a fast phase-change material, Ge2Sb2Te5. We were able to address the issue of why the amorphous phase of fast phase change materials is stable at room temperature for a long time despite the fact that it can rapidly transform to the crystalline phase by using a combination of AXS and large scale density functional theory-based molecular dynamics simulations.