Shintaro Mizuno

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.

Fabrication of metal nanocluster and nanoparticles in the CaO-Bi2O3-B2O3-Al2O3-TiO2 glass by irradiation of XeCl pulsed laser

We report the fabrication of nanoparticles that contain metal nanoclusters at the surface of the CaO-Bi(2)O(3)-B(2)O(3)-Al(2)O(3)-TiO2 glass using XeCl laser irradiation. We have demonstrated that the surface morphology such as that containing nanoparticles or a smooth flat surface can be controlled by laser irradiation conditions; the laser fluence, repetition rate, and temperature of the glass. The transmission electron microscope (TEM) images of the cross section of the nanoparticles show that the metal nanoclusters were formed inside the nanoparticle by XeCl pulsed laser irradiation, a unique phenomenon different from TiO2-crystallization achieved by conventional heat-treatment of the glass. Since formation of nanoparticles containing metal nanocluster is a phenomenon different from previous papers about XeCl laser irradiation of oxide glasses, the combined process of pulsed laser irradiation and heat-treatment will open a wide variety of optical glass devices.

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.

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.

Photo-induced structure ordering in crystallized glass from nano-particles to single-crystal patterning

Challenges for laser-induced structure ordering from nano-particles to single-crystal patterning in glasses are 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 laser-induced structure ordering in glass will be presented as follows: (1) UV-laser induced structure ordering of nano-particles in tellurite-based glasses and possible photonic integrated circuits with innovative minute scale. (2) Single crystalline patterning by atom heat laser processing in Sm-doped glasses for optical waveguides with second-order nonlinearity.