Surface Analysis and Treatment of Extruded Fluoride Phosphate Glass Preforms for Optical Fiber Fabrication

Fabrication of fluoride phosphate glass optical fibers using the extrusion method for preform fabrication has been studied using the commercial Schott N‐FK51A glass. The extrusion step was found to create a surface layer of differing composition from the bulk glass material, leading to defects drawn down onto the optical fiber surface during fiber fabrication, resulting in high loss and fragile fibers. Similar phenomena have also been observed in other fluoride‐based glasses. Removal of this surface layer from preforms prior to fiber drawing was shown to improve optical fiber loss from >5 dB/m to 0.5–1.0 dB/m. The removal of this surface layer is therefore necessary to produce low‐loss fluoride phosphate optical fibers.     

New Materials and Processes for Integrated Optics

Materials and processes for integrated optics are faced with increasing demands from telecommunications and instrumentation applications. Progress in three aspects of novel materials and processes are described: titanium-diffused sapphire waveguides and lasers, interferometric excimer laser ablation of waveguide gratings, and surface studies by waveguide surface plasmon resonance.     

Influence of magnesium on dielectric properties of Ca9–xMgxBi(VO4)7 ceramics

Solid solution of Ca_9‐xMg_xBi(VO₄)₇ in powder and ceramic forms are obtained by solid‐state reactions. Details of their crystal structures are determined for x = 0.25 and x = 0.5 by synchrotron radiation diffraction and the Rietveld method. The refinement has confirmed that Mg²⁺ is replacing Ca²⁺ in M5 position of a polar (S.G. R3c) β‐Ca₃(PO₄)₂‐type structure. Thermal analysis, dielectric and second harmonic generation experiments in broad temperature regions have proved this polar structure is formed for 0 ≤ x ≤ 0.7. Magnesium for calcium substitution enhances optical nonlinear activity of Ca_9‐xMg_xBi(VO₄)₇ in 0 < x ≤ 0.5. Two phase transitions have been found, one of which from polar to centrosymmetric phase is accompanied by dielectric constant peak of ferroelectric type. The other is upper on temperature, marked with smaller dielectric anomaly, and goes between 2 centrosymmetric phases. Temperatures of the phase transition only slightly depend on x, the first being near 1050 K, the second near 1100 K. Electric conductivity quickly rises with temperature in the polar phase. At higher temperature it changes according to the Arrhenius law with small activation energy, E_a ~ 0.7 eV for bulk conductivity and E_gb ~ 2.0‐2.5 eV for grain boundary conductivity. The analysis of bulk and grain boundary conductivities agrees with Ca²⁺‐ion fast transport in ceramics. The bulk conductivity slowly decreases with magnesium content, the grain boundary conductivity does not notably depend on the composition.     

Optical and Mechanical Properties of α/β Composite Sialons

Two-phase α/β composites have been produced with a combination of high hardness, fracture toughness, and strength. Compared with a single-phase α-sialon, the composite showed around a twofold increase in both fracture toughness and bending strength, with only minimal reduction in hardness. Despite being a two-phase material, the optical properties of the composite were very good, showing transparency in sections of around 0.5 mm thickness. The optical properties were in fact better for the composite than for the single-phase α-sialon. Work to date on transparent sialons has focused on single-phase α-materials, which have inherently low fracture toughness unless elongated microstructures are developed. However, this microstructural development appears to adversely affect optical transparency. In this work it has been shown that good combination of mechanical properties can be achieved while maintaining optical transparency in two-phase composite sialons. The development of such materials should widen their range of application.     

Thermal and optical properties of La2O3–Ga2O3– (Nb2O5 or Ta2O5) ternary glasses

La₂O₃–Ga₂O₃–M₂O₅ (M = Nb or Ta) ternary glasses were fabricated using an aerodynamic levitation technique, and their glass‐forming regions and thermal and optical properties were investigated. Incorporation of adequate amounts of Nb₂O₅ and Ta₂O₅ drastically improved the thermal stabilities of the glasses against crystallization. Optical transmittance measurements revealed that all the glasses were transparent over a wide wavelength range from the ultraviolet to the mid‐infrared. The refractive indices of the glasses increased and the Abbe number decreased upon substituting Ga₂O₃ with Nb₂O₅, and the decrease in the Abbe number was significantly suppressed when Ta₂O₅ was incorporated into the glass. As a result, excellent compatibility between high refractive index and lower wavelength dispersion was realized in La₂O₃–Ga₂O₃–Ta₂O₅ glasses. Analysis based on the single‐oscillator Drude–Voigt model provided more systematical information and revealed that this compatibility was due to an increase in the electron density of the glass.     

On Structure,Optical Properties and Photodegradated Ability of Aurivillius‐Type Bi3TiNbO9 Nanoparticles

Bi₃TiNbO₉ nanoparticles with an acceptor dopant of Ni²⁺ ion were prepared by the conventional Pechini sol–gel synthesis. The X‐ray polycrystalline diffraction measurements (XRD) and the Rietveld refinements of Bi₃TiNbO₉ samples were completed. The surface property of Bi₃TiNbO₉ nanoparticles was investigated by transmission electron microscope, scanning electron microscope), and N₂ adsorption–desorption isotherms. Bi₃TiNbO₉ nanoparticles showed an optical band gap with energy of 3.1 eV in the UV region. While the Ni²⁺‐doping could greatly reduce the band energy of Bi₃TiNbO₉:xNi²⁺ nanoparticles to 2.79 eV (x = 0.05) and 2.61 eV (x = 0.1). This indicates that the Ni‐doped samples could be excited by UV–visible light. The photocatalytic abilities were tested by the photodegradation on methylene blue solution (MB) and phenol solutions excited by visible light. Accordingly, the photocatalytic activity was improved by the Ni‐doping in B‐sites in this Aurivillius‐type structure. The results concluded that Bi₃TiNbO₉:Ni²⁺ would be a possible candidate as a visible light‐driven photocatalyst. The effective photocatalysis was discussed on the structure characteristic and experiment such as polarized Aurivillius (Bi₂O₂)²⁺ layers, luminescence, and decay lifetimes, etc.     

Tellurite Glasses for Broadband Amplifiers and Integrated Optics

The present investigation discusses the advantage of using RE-ion-doped (Nd³⁺, Tm³⁺, and Er³⁺) TeO₂ glasses for developing fiber and planar broadband amplifiers and lasers. The spectroscopy of RE-ion-doped fibers and glasses is discussed along with the thermal properties of glass hosts. The results of emission from the ³H₄ level in single-mode Tm³⁺-doped tellurite fiber show that the emission band overlaps with Er³⁺ emission from the ⁴I_13/2 level and Nd³⁺ emission from the ⁴F_3/2 level in silicate and tellurite glasses, thereby enabling the development of amplifiers and lasers between 1350 and 1650 nm. Recent results using Z-scan measurements of nonlinear refractive index and absorption demonstrate that the third-order nonlinearity in undoped TeO₂ glasses is of the order of 2 × 10⁻¹⁵ to 3 × 10⁻¹⁵ cm²·W⁻¹ between 1300 and 1550 nm. These results are briefly discussed in view of an amplifier operation combined with ultrafast all-optical switching.     

The effect of phase transition of crednerite/delafossite CuMn1−xCrxO2 on optical,thermal, and power factor properties

This study aims to investigate the effect of the phase transition of CuMn_1−xCr_xO₂ compound on the Jahn–Teller effect which in turn affects the optical, thermal, and thermoelectric power factor properties. The CuMn_1−xCr_xO₂ samples were synthesized by a solid-state reaction method. The ab initio computation was applied to evaluate the electronic and optical properties in order to confirm the experiment data. The appearance of the phase transition from crednerite CuMnO₂ to delafossite CuCrO₂ was confirmed by X-ray diffraction (XRD) and the ab initio computation through displaying the mixed crednerite/delafossite phase; and, the existence of the Jahn–Teller effect was confirmed by the X-ray photoelectron spectroscopy (XPS) technique exhibiting the occurrence of mixed-state Mn³⁺/Mn⁴⁺ ions. The results obtained from XRD, XPS, and the ab initio computation implied the decrease of the Jahn–Teller behavior with increased x content under the influence of the phase transition from the crednerite phase to the delafossite phase of CuMn_1−xCr_xO₂. Surprisingly, the Jahn–Teller distortion reduction caused an increase in the energy gap of the optical property, electrical resistivity, and activation energy in thermally activated band conduction. The effect suffered the specific heat behavior by being separated into two groups of crednerite and delafossite, and enhanced the small polaron behavior by increasing the activation energy of thermally activated band conduction. The phase transition reduced the results of thermal conductivity, thermopower, and thermoelectric power factor properties. In other words, the effect of the phase transition from the crednerite CuMnO₂ phase to the delafossite CuCrO₂ phase on CuMn_1−xCr_xO₂ compound reduced the Jahn–Teller effect with increased Cr content which in turn caused changes in the optical, thermal, and thermoelectric power factor properties. The effect of the phase transition is advantageous for the improvement of material properties.     

Improved Fluorescence from Tm-Ho- and Tm-Ho-Eu-Codoped Transparent PbF2 Glass-Ceramics for S+-Band Amplifiers

Tm³⁺-Ho³⁺- and Tm³⁺-Ho³⁺-Eu³⁺-ion-codoped oxyfluoride transparent glass-ceramics containing PbF₂ nanocrystals were prepared, and the near-infrared fluorescence properties of the Tm³⁺ ions were investigated for their potential use as a 1.4 μm amplifier. For all samples, the lifetime of the Tm³⁺:³ H ₄ level increased with heat treatment because of the decrease of the phonon energy as PbF₂ crystals were formed. Moreover, it was revealed that codoping with Ho³⁺ or Eu³⁺ was effective in suppressing the lifetime of the Tm³⁺:³ F ₄ level by energy transfer to the Ho³⁺:⁵ I ₇ or Eu³⁺:⁷ F ₆ level. For the codoped samples, the heat treatments decreased the Tm³⁺:³ F ₄ lifetime and increased the Tm³⁺:³ H ₄ lifetime. This was attributed to the concentration of rare-earth ions in the fluoride crystallites. These properties improved the population inversion of the 1.4 μm transition.     

Optical Amplification at 1.3 μm in a Praseodymium-Doped Sulfide-Glass Fiber

Praseodymium-doped glasses were prepared in the Ga-Na-S (GNS) system and their optical properties were studied. A single-mode fiber with an attenuation loss of 1.2 dB/m at a wavelength of 1.31 μm was fabricated using an extrusion method, and the amplification characteristics were measured in the bidirectional pumping configuration. We demonstrated a gain coefficient of 0.81 dB/mW at a wavelength of 1.34 μm, which is the highest we have ever reported, and achieved a net gain of 32 dB for a pump power of 90 mW. Highly efficient optical amplification at a wavelength of 1.3 μm was demonstrated in the praseodymium-doped GNS fiber.     

Fabrication of Translucent Magnesium Aluminum Spinel Ceramics

A precursor for magnesium aluminum spinel powder, composed of crystalline ammonium dawsonite hydrate (NH₄Al(OH)₂CO₃·H₂O) and hydrotalcite (Mg₆Al₂(CO₃)(OH)₁₆·4H₂O) phases, was synthesized via precipitation, using ammonium bicarbonate as the precipitant. The precursor was characterized by differential thermal analysis/thermogravimetry, X-ray diffractometry, and scanning electron microscopy. Reactive spinel powder, which could be densified to translucency under vacuum at 1750°C in 2 h without additives, was obtained by calcining the precursor at 1100°C for 2 h.     

New Red-Shade Ceramic Pigments Based on Y2Sn2−xCrxO7−δ Pyrochlore Solid Solutions

New high-stability red-shade ceramic pigments based on pyrochlore solid solutions Y₂Sn_{2− x} Cr _x O_7−δ ( x = 0–1, 0 < δ= 0–1/2 x ) were developed employing conventional solid-state reaction synthesis. The relationship between their optical properties and microstructure was analyzed by X-ray diffractometry and ultraviolet–visible-light spectroscopy. Decomposition of the structure with formation of the perovskite YCrO₃ observed for chromium substitutions x ≥ 5 was attributed mainly to high concentration of defects. The structural and optical parameters of the materials were found to correlate with the concentration of a species with higher oxidation state than Cr(III), such as Cr(IV) or Cr(V).     

Preparation and photoluminescence properties with the site‐selected excitations of Bi3+‐activated Ba3Sc4O9 phosphors

A series of novel Bi³⁺‐doped Ba₃Sc₄O₉ phosphors were synthesized through the solid‐state reaction. Their photoluminescence, decay curves, and thermal quenching properties were investigated in detail. The Ba₃Sc₄O₉:Bi³⁺ phosphors could be efficiently excited in the ultraviolet and near‐ultraviolet region (300‐400 nm), and the photoluminescence properties possess an obvious site‐selected excitations phenomenon. When excited at the ultraviolet light (320‐360 nm), the phosphors present a green or a bluish green emission, and when excited at the near‐ultraviolet light (370‐390 nm), the phosphors always show a yellow emission. The emission spectra excited at the different wavelength can be decomposed into four components, which accord with the four cationic sites in the structure of Ba₃Sc₄O₉. The influence of the Bi³⁺ concentration on the photoluminescence properties is also investigated. Upon excitation at 330 and 377 nm, the Ba₃Sc₄O₉:Bi³⁺ both have good thermal quenching properties; their emission intensity of the peak at 150°C both exceed 60% of the initial value. The above results indicate that the Ba₃Sc₄O₉:Bi³⁺ phosphor is a promising candidate to provide green or yellow components for UV or near‐UV LEDs.