Mitsuhiro Kawazu

Hybrid electro-optic polymer and selectively buried sol-gel waveguides

An approach to utilizing electro-optically (EO) active polymers in hybrid waveguide structures is described and demonstrated. Buried sol-gel waveguides provide a robust basis for planar integrated circuitry, suitable for coupling with optical fibers. By selectively exposing the core of a buried channel guide, overcoating with an EO polymer, and using appropriately tapered transition zones, a guided mode can be made to undergo adiabatic transitions from sol-gel waveguide up into the EO polymer and back. Such a single-mode device was constructed. These transitions were proven via modulation of the emerging wave’s polarization ellipse by application of voltage to the EO polymer.

Polarization-insensitive transition between sol-gel waveguide and electrooptic polymer and intensity modulation for all-optical networks

An intensity modulation using a hybrid electrooptic (EO) polymer/sol-gel straight channel waveguide, useful in the 1550-nm wavelength regime is demonstrated without using Mach-Zehnder interferometric waveguide. The sol-gel waveguide is selectively buried so that a vertical transition into and out of an EO polymer coated on the sol-gel waveguide is arranged. The throughput ratio for transverse electric (TE) and transverse magnetic (TM) modes of the light coupled out of the hybrid waveguide is improved up to 0.9 dB with the help of reduced birefringence of the EO polymer after corona poling. We show that the fabrication process of such hybrid-type waveguides enables production of a phase modulator operating at 1550-nm wavelength. The fabricated straight channel waveguide modulator exhibits stable- and high-intensity modulation efficiency (82%) using a simple cross-polarization setup after the polarization dependence is reduced. We demonstrate an all wet-etching process to fabricate polymeric EO modulators.

Bleaching of sol-gel glass film with embedded gold nanoparticles by thermal poling

Gold clusters embedded in glass are expected to be hard to dissolve in the form of ions since gold is essentially a nonreactive metal. In spite of that, bleaching of Au-doped nanocomposite sol-gel glass film on a soda-lime glass substrate is demonstrated in which electric-field thermal poling is employed to effectively dissolve randomly distributed gold nanoparticles (15nm in diameter) embedded in a low conductivity sol-gel glass film with a volume filling factor as small as 2.3%. The surface plasmon absorption band at 520nm is suppressed in the region covered by the anodic electrode. The phenomenon is explained by the ionization of the gold nanoparticles and the redistribution of gold ions in the glass matrix due to the action of the extremely high electrostatic field locally developed during poling.

Control of Optical Properties of Thin Films Doped with Au Fine Particles by the Sol-Gel Method

We have developed tinted glasses with thin films doped with Au particles by the sol-gel method for automotive windows. Pink-colored glasses are mass-produced. The observed color is from absorption due to surface plasma resonance of Au particles. The squeeze-out of fine Au particles out of gel films was restrained by an organic additive. The index of the matrix was adjusted by the mixing ratio of TiO2 (refractive index n = 2.20) to SiO2 (n = 1.46). The absorption of Au particles is more intense with the higher index of the matrix, and its peak varies from 530 nm for n = 1.46 to 630 nm for n = 2.20, which yields a transmission color from pink to blue. The combination of the color of the glass substrate and the absorption by the Au particles in the thin films with various indices yields a variety of tinted glasses such as pink, orange, blue, blue-green and gray.

Anisotropic nanometal particles on TiO2 film using sol-gel method

Recently, people have become interested in fine metal particles such as Au,Ag,Pt and Pd because of their importance in applications such as optical devices, electronic devices and heterogeneous catalysis. (1 to approximately 3) In particular, anisotropic fine metal particles have been researched as one of the key technologies to light control. We propose a new technique for preparation of anisotropic Au fine particles. SiO2 film dispersed Au fine particles was prepared by sol-gel method on TiO2 film made by sputtering. Silicon alkoxides and Au salts were used as raw materials for SiO2 film dispersed Au fine particles. The gel film was given heat- treatment at 300 degrees Celsius, and then Au salts we decomposed into Au fine particles. It was identified by TEM (transmission electron microscope) observation that anisotropic Au fine particles were trapped at the interface between SiO2 film and TiO2 film. In addition, compositional distribution in depth direction was investigated. It was confirmed by X-ray photoelectron spectroscopy that Au was distributed on the interface between TiO2 film and SiO2 film and the SiO2 film surface. Furthermore, the polarized light spectrum of Au fine particles separated out on the interface between TiO2 film and SiO2 film were measured, and as a result a polarized absorption spectrum caused by a minor axis and a major axis of Au fine particles were observed.