This paper reviews the field of poled glass and poled fibre devices with a specific focus on silicate glasses and fibres. The technology is presented along with detailed discussion of the mechanism involving charge separation and trapping. The potential role of field induced crystallisation is discussed and several emerging applications are presented.

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In this work, we present the fabrication of chalcogenide photonic crystal fibres (PCFs) with a solid core for three different glass composition containing a variety of chalcogens. We show that the Stack and Draw technique currently used for silica PCFs can be problematic in the case of chalcogenides glasses. We prove that excess losses are related to the interface between the capillaries. We also present correct PCF design enables a significant improvement of final fibre losses. We obtained a lowest attenuation of 3 dB/m at 1.55 μm, of 4.5 dB/m at 3.39 μm and 6 dB/m at 9,3 μm.

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Highly nonlinear fiber with step-index type and microstructure type were fabricated using Bi₂O₃ based high refractive index glasses. Step-index type fiber with effective core area of 3.3 μm² was fabricated using core and cladding glass whose refractive index is 2.22 and 2.13. This fiber exhibits high nonlinearity (γ = 1300 W^-1km^-1) because of high nonlinearity of the glass material and the small effective core area. The fiber also exhibits low loss (-1.9 dB/m) and fusion spliceability to silica fiber. Microstructure type fiber which shows low GVD and high nonlinearity simultaneously was fabricated by a novel inflating method. This fiber has a guiding core structure to reduce the fusion splicing loss when air holes collapse. Wide wavelength tuning range due to small GVD in four wave mixing experiment was demonstrated.

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This paper reviews some of the interesting applications of semiconductor nanocrystals embedded in glasses. Because of their unique electronic and optical properties, semiconductor quantum dots (QDs) found wide applications in photonics. They are inexpensive and robust material and have attracted a great attention in the application of 1.3-1.5 μm optical communication. Embedding semiconductor QDs in spherical microcavities is also an attractive system both for fundamental physics research in the field of cavity quantum electrodynamics and for its potential application in lasing materials. Energy transfer processes and coupling-strength between nanocrystals can be studied and demonstrated using semiconductor nanocrystals doped glasses. It has been established that an efficient energy transfer occurs between QDs having a significant band gap energy difference, i.e., between dots of markedly different sizes. We demonstrate that a promising way to enhance energy transfer between different subsets of QDs is to red-shift the emission sufficiently far from the host absorption so that self-absorption by the host becomes negligible.

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This paper reviews tellurite-based fibers and their applications to optical communication networks. First, an investigation of tellurite-based glass and the fabrication of conventional step-index fibers and photonic crystal fibers (PCF) are described. By purifying the raw materials and employing a novel PCF fabrication process, low background losses were achieved for an Er³⁺-doped, an undoped tellurite-based fiber and a tellurite-based PCF. Second, the optical properties of Er³⁺-doped tellurite-based glass and fiber, and the gain characteristics of erbium doped tellurite fiber amplifiers (EDTFAs) were studied. A seamless, low noise and gain flattened C + L band EDTFA was realized, and an S + C + L band amplifier was constructed by combining an EDTFA and a thulium-doped fluoride fiber amplifier (TDFFA) in parallel. Third, it is confirmed that the Raman scattering characteristic of tellurite-based fiber has such a large gain coefficient and Stokes shift that it is possible achieve a wideband tellurite-based fiber Raman amplifier. To overcome several problems, a distributed/discrete hybrid tellurite- and silica-based fiber Raman amplifier (FRA) was constructed as an S + C + L band WDM repeater with a gain bandwidth of 127-nm. Fourth, Brillouin amplification and the simulated performance of slow light generation in a tellurite-based fiber were investigated. The fiber exhibits the largest time delay per unit power of 19.9 ns/mW. Finally, a carrier-envelope offset (CEO)-locked frequency comb with low fiber coupling pulse energy (230 pJ) was demonstrated by using a tellurite-based PCF. This method has the potential to lock the CEO with a lower pulse energy and thus provide a low-noise and high-accuracy optical frequency comb at telecommunication wavelengths. These tellurite-based fibers with low background loss thus offer attractive functions for applications in the optical communication field.

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Properties and applications of self-assembled sub-wavelength structures and related form birefringence produced by femtosecond laser writing in silica glass are reviewed.

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Silica-based waveguide devices as represented by planar lightwave circuits (PLCs) are key devices for constructing photonic networks with huge data transmission capacity and flexibility. As a result of recent progress on optical communication networks, dynamically controlled silica-based optical devices have become both significant and practical. The thermo-optic (TO) effect is employed to control optical signals. The devices that have been developed include TO switches, variable optical attenuators (VOAs), and devices in which they are integrated. The silica-based waveguide phase shifters that employ the TO effect in these devices are compact, highly reliable, and suitable for large-scale integration. This paper reviews the large scale matrix switches including an 8 × 8 TO switch and a 32 × 32 TO switch. And a 40-ch VOA integrated AWG multiplexer with tap couplers, micromirrors, and monitor photodiodes is also demonstrated.

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Optical properties of PbS quantum dots (QDs) precipitated inside the oxide glass matrix were investigated. Photoluminescence (PL) spectra were recorded with peak wavelengths located at 1170-1680 nm with peak width of 150-500 nm. Radii of QDs in glasses were 2.0-3.7 nm depending upon the thermal treatment conditions. Changes in temperatures and excitation intensities resulted in the shift of photoluminescence bands as large as 70 nm, due to the laser-induced local heating. Photoluminescence from PbS QDs showed darkening and brightening behavior. Intensity of the photoluminescence increased with time at low temperature (< 150 K) especially when the excitation intensity was low. Photo-darkening was observed when temperature and/or illumination intensities increased. Competition between the photo-brightening and photo-darkening determined the final steady-state photoluminescence intensity.

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A glass material and a spherical glass encapsulation process for LEDs were developed. An LED encapsulated by the spherical glass exhibits high directional characteristic and emits collimated lights. This glass encapsulated LEDs are potent for light sources for displays such as portable projection systems and LCD back lights.

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In this paper, the last glass-ceramics recently made from chalco-halide glasses is presented. Various glass-ceramics were obtained from compositions belonging to different systems such as Ge-(Sb/Ga)-(S/Se)-MX (MX: alkali halide). XRD experiments and SEM observations were performed to determine the crystallization mechanism in these chalcogenide glasses. While alkali halide such as CsCl is rejected from the glassy network in antimony based glasses leading to its crystallization, some gallium based glasses present a quasi-arranged structure which tends to reach a higher stability by crystallizing as Ga₄GeSe₈ or Ga₂Se₃. Thus, the amount of alkali halides introduced in antimony based glasses limits the crystallization rate to 20% of the glassy matrix. Furthermore, the crystallization of gallium based phases having a refractive index close to the matrix one lowers the scatterings permitting to keep an excellent infrared transmittance with a crystallized proportion of about 40%.

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The thermal properties of BaO-TiO₂-GeO₂-SiO₂ based glasses have been investigated. The temperature differences, ΔT, between the crystallization onset temperature and glass transition temperature were over 95°C. The wide range of ΔT enables the fabrication of practical fibers with a core/clad structure including partial crystallization. The rod-in-tube method was used for fabricating fiber preform, and the fiber drawing was successfully achieved. The double clad fiber with the core diameter of 6.5 μm, the 1st clad diameter of 24.5 μm, and the 2nd clad diameter of 125 μm was obtained over 100 m in length. The propagation loss of the fiber was 1.8 dB/cm. The crystallization onset temperature of the 1st cladding is lower than other glasses, so that only the 1st cladding is selectively crystallized by post-heating for active devices. Furthermore, the 1st cladding contains CuO to assist heating by absorbing the energy of laser irradiation. Fusion splicing to the conventional silica fiber was also achieved, in spite of the different thermal properties of BTGS glass and silica glass, by precisely controlling the heating power and heating position of the fiber. The splicing loss with less than 1.5 dB per point was achieved.

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Dy³⁺-doped selenide glasses and their optical fibers in the Ge-Ga-Sb-Se glass-forming system were fabricated and their mid infrared (MIR) emission (2.5-5 μm) characteristics were analyzed. Optimum concentration for 3 μm emission band was determined as 0.02 mol% due to cross relaxation between Dy³⁺ ions. Sensitizers such as Pr³⁺, Ho³⁺, Tb³⁺ or Tm³⁺ ions were co-doped to improve MIR emissions from Dy³⁺. Pr³⁺ provided the highest emission intensity of Dy³⁺:⁶H_13/2 → ⁶H_15/2 but suffered from the efficient energy transfer between two ions involved. Tm³⁺ showed further enhancement due to its co-excitation wavelength of 1.8 μm.

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By excitation with 800 nm femtosecond laser, we observed the green up-conversion fluorescence at 526 nm (²H_11/2-⁴I_15/2) and 548 nm (⁴S_3/2-⁴I_15/2) for Er³⁺ ions doped in 76TeO₂·20Nb₂O₅·4ZnO glass. From I_H,S ~ Pⁿ relationship (I_H,S; fluorescence intensity of ²H_11/2-⁴I_15/2 and ⁴S_3/2-⁴I_15/2, P: laser power density, n: the number of photons absorbed per visible photon emitted), the n values of 1.4 and 1.3 were obtained at room temperature for I_H and I_S, respectively, and approached "2" at lower temperatures and at lower excitation power densities. This indicates that two photons were involved in the excitation of the up-conversion fluorescence. Considering the up-conversion intensity at various repetition frequencies on fs laser excitation and the emission decay behaviors as well as the results of Judd-Ofelt analysis, we could explain this excitation mechanism in terms of energy transfer (ET: ⁴I_11/2 + ⁴I_11/2 → ⁴F_7/2 + ⁴I_15/2, and ⁴I_9/2 + ⁴I_9/2 → ⁴S_3/2 + ⁴I_13/2). We shall also discuss on a back transfer process of the latter ET for the reduction of the n value at room temperature.

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Eu²⁺ and Sm³⁺ co-doped silicate glasses were prepared under reducing atmosphere in a system SiO₂-Al₂O₃-CaO and the glass-ceramics were obtained by heat-treatment at temperatures between 1000 and 1400°C. Broad emission band were observed between 400 and 550 nm due to the 5d→4f transition of Eu²⁺, as well as sharp emission peaks at 563, 600, 646 and 713 nm due to the 4f→4f transition of Sm³⁺ in the samples. Emission color became white under ultraviolet or violet excitation for the glass ceramics heat-treated at above 1100°C. Ceramming temperature dependence of the color coordinates, emission spectra were investigated and discussed with the precipitated crystal phases. We have successfully obtained the glass ceramic phosphor emitting white color, suitable for a white LED without organic resin for power illumination.

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The photoelastic constants (PECs) of transparent SnO-P₂O₅ (SP) glasses with 52-72 mol% SnO were determined using a frequency stabilized transverse Zeeman He-Ne laser (STZL) at 633 nm. The SP glass samples were melted at 950°C in carbon crucibles and at 1050°C in alumina crucibles. The melting conditions affect the values of glass transition temperature and OH content but have almost no effect on PEC. The PEC varies monotonically with increasing SnO concentration from -0.73 to -1.98 × 10^-12 Pa^-1.

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A barium titanosilicate, BaTiSi₂O₇, with suzukiite (BaVSi₂O₇)-type structure has a unique Ti-O unit, which consists of mirror-symmetrical TiO₅ pyramids pair, and possesses a visible orange photoluminescence (PL) by an ultraviolet excitation at room temperature. However, the origin of orange PL has not been fully understood. Therefore, the purpose of this study is to elucidate the origin and mechanism of orange PL in suzukiite-type BaTiSi₂O₇. It has been proposed that two types of oxygen-defect in the pyramidal TiO₅ unit pair contribute to the efficient orange PL, i.e., the extrinsic oxygen-vacancy due to the lack of oxygen in the TiO₅ unit, and the intrinsic oxygen-vacancy, which exists in the TiO₅ unit pair due to its structural peculiarity.

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The glasses with (25-x)La₂O₃·xGd₂O₃·25B₂O₃·50GeO₂ composition corresponding to the (La,Gd)BGeO₅ were prepared, and the substitution effect of gadolinium ions (Gd³⁺) on crystallization behavior and phase formation was examined by DTA, XRD and Raman techniques in detail. Ferroelectric (La,Gd)BGeO₅ phase with hexagonal stillwellite structure were crystallized in the composition range of x = 0-15. Although no significant change in physical properties was observed in the whole composition range, crystallization behavior was drastically changed as the progressive substitution of Gd³⁺ was carried out (i.e., crystallization of monoclinic phase of (La,Gd)BGeO₅ and high-pressure phase of Gd₂Ge₂O₇ with a triclinic structure). Structure of the glasses and crystallized phases, and the phase formation mechanism were also discussed.

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We examined the crystallization behavior of double clad fiber composed by BaO-TiO₂-GeO₂-SiO₂ based glasses in detail. Formation of needle-like fresnoite-type Ba₂Ti(Ge,Si)₂O₈ were observed at the interface between the first and second clad. In addition, we employed the two-step heat-treatment (i.e., 728°C, 20 h + 749°C, 1 h) in fabrication of the crystallized fiber in order to obtain the highly-oriented fresnoite phase in the fiber structure. The first treating temperature, 728°C, which gives the maximum nucleation rate, was determined by differential thermal analysis. It was demonstrated that the two-step heat-treatment was effective for improvement of the orientation of fresnoite-type phase in the first clad of the double clad fiber.

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Luminescence characteristics of Er³⁺-doped Li₂O-Al₂O₃-SiO₂ (LAS) glass and glass-ceramic were evaluated by measuring their absorption spectra, fluorescence spectra and fluorescence lifetime. The absorption cross section of ⁴I_13/2 - ⁴I_15/2 transition at 1.5 μm increased after cerammization. In contrast, fluorescence intensity of the 1.5 μm emission, fluorescence lifetime, τ_f and the Quantum efficiency, η calculated from τ_f and spontaneous emission probabilities decreased after cerammization. The decrease of τ_f and η was attributed to the increase of the nonradiative decay rate, W_nr caused by accumulation of Er³⁺ ions in the glass matrix containing OH ions by cerammization.

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Fluorine-doped silica glass fiber was fabricated as fiber-core for transmittance of deep ultraviolet wavelength region. By examining the effect of oxyhydrogen flame onto the core-glass (conventional cleaning process called fire-polishing process), it was found to create oxygen-deficiency centers. Additionally, fire-polishing process changes the distribution of fluorine concentration near core-cladding interface and leads to the deterioration of the optical characteristics of the fiber. By conducting preform fabrication without fire-polishing, the obtained fluorine-doped silica glass fiber showed high transmittance of more than 92% m^-1 at 266 nm and excellent durability after 4 G pulses of 7 mJcm^-2 laser irradiation.

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We report on fabrication of the BaO-TiO₂-GeO₂ glass thin films on a fused silica substrate by RF sputtering, and investigation of the crystallization behavior, surface texture and the optical non-linearity in the glass thin film by means of AFM, XRD, Raman and Maker fringe techniques. Although the Ba₂TiGe₂O₈, hereafter abbreviated to BTG, phase with second-order optical nonlinearity was mainly crystallized, the precipitation of the sub-phase of BaGe₄O₉ was also confirmed in the heat-treated glass thin films. In the glass thin film heat-treated at heat-treatment temperature (T_HT) = 730-750°C, the (211) preferential orientation of BTG phase and an upheaval about 300-400 nm were confirmed at the surface. These transparent crystallized glass thin films indicated a clearly Maker fringe patterns, demonstrating a second-order optical nonlinearity, and the effective second-order nonlinear optical constant, d_eff, was estimated to be ~0.8 pm/V.

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Due to the possibility of high Er³⁺ doping and their broadband emission, the bithmuth-oxide-based glasses can be a promising candidate of host materials for a compact waveguide amplifier with high performance. By a novel fabrication process, we have developed a Bi₂O₃-based waveguide device with propagation loss as low as 0.13 dB/cm, which is comparable to the silica-based waveguides. We have achieved an ultra-compact Er-doped waveguide amplifier with 1 cm² size by designing a spiral light-wave circuit with low bending loss. This EDWA showed gain values over 15 dB, noise figures lower than 8 dB and gain flatness less than 2 dB over the whole C-band region. The output power of this EDWA reached higher than 12 dBm.

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Raman scattering measurements were performed in the benitoite-type BaTiSi₃O₉, BaZrSi₃O₉, BaSnSi₃O₉ and tetragermanate-type BaGe₄O₉ phases in order to elucidate the spectroscopic and structural features of D_2/vG(T₃O₉)-type compounds (expressed by Smith's notation) with the GO₆ octahedral unit isolated by the T₃O₉ ring. The Raman band assignments in middle and high wavenumber region wes also carried out. In addition, the wavenumber of antisymmetric stretching vibration mode, ν_as, for Si-O-G bond was calculated by means of combination of the simple molecular model and Badger's rule, and compared with the experimental results. It was suggested that the ν_as was governed by the force constant of T-O_ax bond, which was connected with the G⁴⁺.

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Benitoite (BaTiSi₃O₉) phases, which were partially-substituted by germania (GeO₂) in order to stabilize the phase, were synthesized, and their optical properties were examined. The benitoite phase was crystallized by a small quantity of Ge-introduction into the benitoite composition. Clear blue emission with the peak at ~430 nm, due to the transition of ³T₁ → ¹A₁ in the TiO₆ octahedra, was observed at room temperature during the ultraviolet excitation, being sufficient for a visual confirmation. On the other hand, the reduction in blue emission intensity by the Ge-introduction was confirmed. This was qualitatively explained on the basis of configurational-coordinate mode without discrepancy.

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A series of d ⁰ ions, i.e., Ti⁴⁺, Zr⁴⁺, Nb⁵⁺, Ta⁵⁺, Mo⁶⁺, and W⁶⁺, has been incorporated into silicate glass matrix by utilizing a conventional melt-quenching method, and their optical properties have been examined. When the resultant glasses are excited by ultraviolet light, intense emissions are observed in the blue to orange wavelength regions of the visible spectrum, depending on the kind of d ⁰ ions. We suggest that the nd ⁰ (n = 3, 4, 5) energy levels play an important role in the emergence of intense visible emissions. The results indicate that glasses doped with d ⁰ ions are potential materials in displays and nonlinear devices.

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Phase evolution and ferroelectric behavior in 0.8BaTiO₃-(0.2-x) BiScO3-xPbTiO₃ ceramics, x = 0-0.20, has been investigated in this paper. The phase assemblage and lattice parameters indicate the appearance of tetragonal-rhombohedral phase transition and the existence of a MPB region in the composition range x = 0.15-0.20. All these compositions exhibit relaxor ferroelectric behavior due to cation disorder for the substitution on the A-site by Bi and on the B-site by Sc. The dielectric permittivity of the specimens as well as the polarization decreases with increasing BiScO₃. However, close to MPB region, the composition with dominance of rhombohedral phase (x = 0.15) exhibits higher remnant polarization than that with tetragonal for the more reorientational directions of the rhombohedral phase than that of the tetragonal one (x = 0.17).

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The carbothermal reduction of TiO was investigated and compared with that of TiO₂ using a thermodynamic approach and experiments. Cubic-TiO powder was synthesized using a high-energy mill to understand the reduction and carburization process. During the reduction and carburization process, TiO is found to be changed into TiC and Ti₂O₃ simultaneously at low temperatures. This change is ascribed to the low thermodynamic stability of TiO compared with that of Ti₂O₃. The instability of TiO is found to result in a higher driving force for the carburization of TiO to TiC than that for relatively stable Ti₂O₃.

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Porous silicon carbide (SiC) ceramics with different pore size were prepared from SiC powders, an aluminum yttrium garnet (Y₃Al₅O₁₂, YAG) as a sintering additive, and three different sizes of templates (polymer microbeads) by a sacrificial template technique. Their microstructure and mechanical strengths were evaluated as a function of template size, i.e., pore size. Porosity of these porous SiC ceramics increased with increasing the template content, regardless of template size. Pore size was proportional with the template size. The growth of faceted grains was accelerated with increasing the template size. Both flexural and compressive strengths decreased with increasing the porosity whereas both strengths increased with decreasing the template size, i.e., pore size. Typical flexural and compressive strengths of the porous SiC ceramics fabricated using 8 μm-templates were ~55 MPa and ~240 MPa at ~45% porosity, respectively.

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A facile process was introduced to prepare zirconia-coated hematite particles (Fe₂O₃(@)ZrO₂) in an aqueous solution. The amorphous ZrO₂ shell was homogeneously deposited on the hematite surface, and the thickness of ZrO₂ precursor shell is about 2-3 nm. The method shows a strategy for surface modification with an ultrathin inorganic layer.

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