Multiple quasi-phase-matched device using continuous phase modulation of /spl chi//sup (2)/ grating and its application to variable wavelength conversion

We propose a new multiple quasi-phase-matched wavelength converter based on the continuous phase modulation of a /spl chi//sup (2)/ grating for use in variable wavelength conversion. A numerical study shows that the proposed device exhibits a high conversion efficiency, flexible design, and robust fabrication tolerance. A waveguide device fabricated by annealed proton exchange agrees well with the numerical design. Fine-tuning the device enabled us to demonstrate variable wavelength conversion between signals on the standard optical frequency grid. Using the device, we also demonstrated fast (<100 ps) wavelength switching of 4-channel 40-Gb/s signals. The obtained results clearly show that the proposed multiple quasi-phase-matched devices will be useful when constructing future flexible photonic networks.     

Hot-water treatment of sol–gel derived SiO2–TiO2 microparticles and application to electrophoretic deposition for thick films

SiO₂–TiO₂ spherical microparticles of about 0.7 μm in diameter were prepared by the sol–gel method. Anatase nanocrystals were formed in the microparticles and their specific surface area was increased after a hot-water treatment at 90 °C. From the changes in the concentration of I₂ photocatalytically generated from KI aqueous solution, the activity of the SiO₂–TiO₂ microparticles was found to increase with increasing the hot-water treatment time. Particulate, thick films were electrophoretically deposited on indium tin oxide (ITO)-coated glass substrates using the anatase nanocrystal-precipitated SiO₂–TiO₂ microparticles. The thickness of the electrophoretically deposited particulate film increased to be approximately 10 μm with an increase in applied voltage. The resultant thick film showed a high photocatalytic activity.     

Water permeation properties of SiO2-RSiO3/2 (R = methyl,vinyl, phenyl) thin films prepared by the sol-gel method on nylon-6 substrate

Nylon-6 substrates were coated with SiO₂-RSiO_3/2 (R = methyl, vinyl, phenyl) thin films by the sol-gel method, and their water permeability was evaluated Tetraethoxysilane (TEOS) and trifunctional alkoxides such as methyltriethoxysilane (MTES), vinyltriethoxysilane (VTES), and phenyltriethoxysilane (PhTES) were used as starting materials. Water permeability coefficients of the nylon-6 substrates coated with these SiO₂-RSiO_3/2 thin films were increased with an increase in the content of these trialkoxysilanes in the films. The water permeability coefficients of these coated nylon-6 substrates were smaller in the order of the systems TEOS-PhTES < TEOS-VTES < TEOS-MTES in the relatively low content of the trialkoxysilanes. © 1996 John Wiley & Sons, Inc.     

Template-assisted synthesis of PbTiO3 nanotubes

Nanotubes of ferroelectric lead titanate (PbTiO₃) have been made by a template-assisted method. An equimolar Pb–Ti sol was dropped onto porous alumina membranes and penetrated into the channels of the template. Single-phase PbTiO₃ perovskite nanotubes were obtained by annealing at 700 °C for 6 h. The nanotubes had diameters of 200–400 nm with a wall thickness of approximately 20 nm. Excess PbO or annealing in a Pb-containing atmosphere was not necessary in order to achieve single-phase PbTiO₃ nanotubes. The influence of the heating procedure and the sol concentration is discussed.     

Formation Process of Super-Water-Repellent Al2O3 Coating Films with High Transparency by the Sol–Gel Method

Alumina thin films with a roughness of 20 to 50 nm were formed by immersing porous alumina gel films prepared by the sol-gel method in boiling water. When hydrolyzed fluoroalkyltrimethoxysilane was coated on the alumina films, the contact angle for water was increased with an increase of immersion time, and immersion for 30 s was long enough to give super-water-repellency and high transparency; the contact angle for water of the film was 165° and the transmittance for the visible light was higher than 92%. It was found that the surface of the alumina gel films immersed in boiling water consisted of boehmite crystals. It was shown that the existence of air in the hydrophobic pores on the surface caused the super-water-repellency.     

Preparation of CdS-doped Glasses from Gels Containing Diethyldithiocarbamatocadmium

CdS-doped SiO₂ glasses were prepared via silica gels containing diethyldithiocarbamatocadmium Cd(S₂CN(C₂H₅)₂)₂. Heat treatment of the gels gave transparent yellow SiO₂glasses doped with hexagonal CdS crystals. In optical absorption and fluorescence spectra, the optical absorption edge and the emission peak clearly exhibited a blue shift, which was attributed to the quantum size effect of the carrier confinement, as the CdS content was decreased. In the fluorescence spectra of the CdS-doped silica glasses, the emission peak was observed only near 500 nm and not observed at longer wavelengths which were known to be present if there were sulfur vacancies.     

High-power mid-infrared wavelength generation using difference frequency generation in damage-resistant Zn:LiNb03 waveguide

High-power 3.4 mum difference frequency generation (DFG) using a quasi-phase-matched Zn:LiNbO₃ waveguide fabricated by direct bonding technology is presented. The high resistance of the waveguide to photorefractive damage allows high-power generation. A 65 mW mid-infrared output was obtained using a continuous-wave high- power fibre amplifier as pump source. The DFG source can access over 10 nm continuously simply by scanning the signal wavelength, and will be useful for real-time trace gas sensing.     

Super-Water-Repellent Al2O3 Coating Films with High Transparency

We have prepared transparent, super-water-repellent coating films of alumina on glass plates by a combination of geometric and chemical approaches. The contact angle for water in the films was 165° and the transmittance for visible light was higher than 92%. A roughness of 20 to 50 nm was obtained, which is too small to scatter visible light, while the degree of roughness was great enough to enhance the water-repellent properties together with the chemical effect of a fluorine-containing agent and gave a super-water-repellent surface. The coatings have great potential for practical applications such as eyeglasses, cover glasses for solar cells, windshields of automobiles, and so on.     

Microstructure and Dielectric Properties of YMnO3 Thin Films Prepared by Dip-Coating

YMnO₃ thin films with Y/Mn ratios from 1.00/1.05 to 1.00/0.90 were prepared by dip-coating from solution, in which starting materials were refluxed, and the effects of the Y/Mn ratio on the structure and dielectric properties of YMnO₃ thin films were investigated. XRD measurements indicated that the films with the Y/Mn ratios in this study were a single phase of polycrystalline YMnO₃. The lattice constants along the a -axis and c -axis lengthened with an increase in the Y/Mn ratio. FE-SEM micrographs of the films showed that the surface of the films became smoother and denser with an increase in the Y/Mn ratio. YMnO₃ thin films with good dielectric properties were obtained with an Y/Mn ratio of 1.00/0.90, which gave the smoothest and densest microstructure and the smallest leakage current.