Sensor properties of hollow-core photonic crystal fibers

A new class of hollow-core photonic crystal fibers (PCFs) with various modifications of spatial lattices is considered. The influence of the PCF structure geometry on the photonic band gap (PBG) in the visible spectral range is demonstrated. A relationship between a change in the PCF core refractive index due to filling of the hollow core with various liquids and the PBG position is established. PCFs show new possibilities for use as biological and chemical sensors.     

High selectivity Boolean olfaction using hollow-core wavelength-scalable Bragg fibers

A new odorant detection scheme, based on infrared absorption of volatile organics inside an optofluidic channel array, is discussed in terms of its selectivity. The sensor unit of the array is a hollow core Bragg fiber that selectively (spectrally) guides an incident continuum radiation. The presence of infrared absorbing molecules in the channel results in the quenching of the otherwise transmitted signal. Each fiber unit in the array is designed and fabricated so that it is sensitive to specific chemical bonds and the bond environment, but at the same time, each fiber is also broadly sensitive to a large number of chemicals due to their infrared absorbance spectra. The cumulative array response data, using an appropriate threshold, enable selective binary sampling of the infrared fingerprint of hundreds of molecules. The selectivity of the system is quantitatively investigated with computer simulations and found to be exponentially increasing with the number of fibers in the array. Relatively simple data analysis using binary logic combined with the high selectivity of the novel scheme paves the way for ubiquitous application of electronic noses in toxic gas detection, food quality control, environmental monitoring, and breath analysis for disease diagnostics.     

Fluoride and tellurite glasses for thin-film IR viewers

We have studied optical characteristics of Er³⁺-, Ho³⁺-, and Yb³⁺-doped ZBLAN and TWL glasses. Their luminescence was excited at wavelengths of 975, 378, and 449 nm. The 975-nm radiation excited the Yb³⁺ (² F _7/2 → ² F _5/2), and the excitation energy was then transferred to the Er³⁺ and Ho³⁺. The short-wavelength excitation led to cross-relaxation processes: (⁴ F _7/2, ² F _7/2) → (⁴ I _11/2, ² F _5/2) for the Er³⁺-Yb³⁺ pair (378 nm) and (⁵ F ₃, ² F _7/2) → (⁵ I ₅, ² F _5/2) for the Ho³⁺-Yb³⁺ (449 nm). At the three excitation wavelengths, we observed green luminescence in the range 525–550 nm. Using the glasses studied here, we prepared thin colorless lacquer films potentially attractive for hidden information recording and hidden labeling of various objects and materials.     

High contrast glasses for all-solid fibers fabrication

We present composition development of borosilicate glasses for fabrication of high refractive index contrast, all-solid photonic crystal fibers. An oxide system composed of SiO₂B₂O₃Al₂O₃Li₂ONa₂OK₂O was adjusted to match thermal properties of selected highly nonlinear, lead bismuth gallium silicate glass. A high difference of refractive index of 0.376 is achieved at a wavelength of 1550 nm. We proved experimentally that the developed pair of glasses enables to draw optical fibers, and we propose a design of a photonic crystal fiber structure for broadband supercontinuum generation.     

IR spectra and structures of tellurite glasses

It is shown with IR spectral investigations that the short range order of certain tellurite glasses, obtained from monomineral crystalline phases, is similar to that of the crystals. They may contain the following polyhedra: TeO₄-trigonal bipyramids (C_2v symmetry), deformed TeO₄ groups, TeO₃ trigonal pyramids (C_3v point symmetry), or combinations of these polyhedra. The introduction of V₂O₅ and MoO₃ in the binary glasses leads to a TeO₄ → TeO₃ transition. MoO₃ delays the decay of TeO₄ groups in a wider concentration range.     

IR study of Pb-Sr titanate borosilicate glasses

The infrared spectra (IR) of various glass compositions in the glass system, [(Pb _x Sr_1−x )O·TiO₂]-[2SiO₂·B₂O₃]-[BaO·K₂O]-[La₂O₃], were recorded over a continuous spectral range (400–4000 cm⁻¹) to study their structure systematically. IR spectrum of each glass composition shows a number of absorption bands. These bands are strongly influenced by the increasing substitution of SrO for PbO. Various bands shift with composition. Absorption peaks occur due to the vibrational mode of the borate network in these glasses. The vibrational modes of the borate network are seen to be mainly due to the asymmetric stretching relaxation of the B-O bond of trigonal BO₃ units. More splitting is observed in strontium-rich composition.     

Dispersion analysis of hollow-core modes in ultralarge-bandwidth all-silica Bragg fibers with nanosupports

Dispersion of the fundamental confined modes in hollow-core all-silica Bragg fibers with nanosupports is analyzed. The transfer-matrix formalism is applied. Anomalies in the group-velocity dispersion are evidenced at long wavelengths, toward the upper limit of the bandgap. The results confirm that, as in microstructured photonic crystal fibers, this anomalous dispersion is due to prevention of the confined hollow-core modes from crossing the surface modes, the avoided crossings are more apparent in the variation of group velocity with wavelength. The dependence of these avoided crossings on the hollow-core radius and the layer thicknesses is briefly analyzed.     

Native oxide glasses for indium gallium arsenide

Epitaxial films of indium gallium arsenide on indium phosphide are important for optoelectronic applications in the 1.0 to 1.7 μm wavelength region. Oxide glasses having essentially the same metal ratios as the epitaxial films, thermal expansion coefficients near 7.5 × 10^?6 and glass transition temperatures from 560 to 640°C have been prepared. They can be sputtered readily as water insoluble amorphous films that can be etched easily, even after prolonged heat treatment at 600°C, and are useful for thermal diffusion masks.     

Characterization of ZBGAN glasses

The physical and electrical properties of a ZrF₄-BaF₂-GdF₃-AIF₃-NaF (ZBGAN) glass have been studied. The addition of NaF increases the glass-forming ability of the base composition glass yet does not degrade the optical characteristics. The viscosity decreased with increasing NaF, suggesting that the increased glass-forming ability was due to the confusion principle. The electrical conductivity decreased with increasing NaF for low temperatures but increased at higher temperatures. The activation energy showed an increase with increasing NaF. The data suggest that the conductivity is not due to the total fluorine ion concentration.     

Characterization of fluorine-doped silica glasses

Fluorine-doped silica glasses containing up to 2 wt% were prepared by the vapour-phaseaxial-deposition (VAD) sintering process. The characteristics of these glasses were investigated by Raman spectroscopy, vacuum-ultraviolet-ultraviolet (v.u.v-u.v.) spectroscopy, and viscosity measurements. From the Raman spectroscopic investigation, it has been shown that the Si-F bond structure in the fibres is the same as that in bulk glass and is not affected by codoped additives such as B₂O₃. From the u.v.-v.u.v, spectroscopic investigation, it has been shown that the absorption band at 7.6 eV in high-purity silica glass is removed with the addition of fluorine. This addition produces a silica glass with most excellent transparency in u.v. and v.u.v. regions. Also it was observed that the optimum addition is around 1 wt%. This fact proves that fluorine incorporation in glass prevents the generation of defects related to optical loss in fibres. From the viscosity study, it was found that the viscosity decreases with an increase of the fluorine content in glass and the activation energy also decreases with increasing fluorine content.     

Methods for improving the mechanical properties of oxide glasses

Methods are reviewed for improving the mechanical properties of oxide glasses. These are divided into surface and bulk techniques and include thermal and chemical strengthening, controlled crystallization, and particle, fibre and whisker reinforcement. The merits and limitations of individual techniques are compared and discussed. In conclusion, a number of applications for these materials are briefly outlined.     

Electrical conductivity of ion-exchanged oxide glasses

Bulk glasses in the system Na₂O-CaO-Al₂O₃-B₂O₃-SiO₂ have been subjected to a sodium silver exchange reaction. The application of a suitable combination of electric field and temperature brings about switching to a high conducting state (HIE). The critical electric field,E _c, has a value in the range 2 to 20 V cm^–1 andE _c values decrease as a function of temperature. The resistivity in the HIE state is of the order of 10 cm and the activation energy is 0.01 eV. Wagner's asymmetric polarization cell measurements show that the conductivity is ionic in nature. No switching is observed in the case of glasses subjected to a sodium copper exchange reaction carried out on these glasses at 525 ° C for 12h. This is ascribed to the microstructure exhibited by such exchanged samples which consists of copper-rich droplet phases dispersed within a copper-deficient matrix. The rather large inter-droplet separation makes it difficult for the copper-rich phase to grow to its percolation limit.     

Magnetic properties of nickel-strontium-borate oxide glasses

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Silver halide photonic crystal fibers for the middle infrared

Photonic crystal fibers are normally holey silica fibers, which are opaque in the mid- and far-infrared. We have fabricated novel fibers by multiple extrusions of silver halide crystalline materials, which are highly transparent in the mid-infrared. These fibers are composed of two solid materials; The core consists of pure AgBr, and the cladding includes AgCl fiberoptic elements arranged in two concentric hexagonal rings around the core. Flexible fibers of outer diameter 1 mm and length of approximately 1 m were fabricated, and their optical properties were measured. These fibers exhibited core-clad behavior and would be extremely useful for IR laser power transmission, IR radiometry, and IR spectroscopy.     

High-purity As-S-Se and As-Se-Te glasses and optical fibers

We describe a procedure for the preparation of As-S-Se and As-Se-Te glasses with low contents of gas-forming impurities (hydrogen, oxygen, and carbon) via melting of extrapure-grade elements in an evacuated silica ampule and purification of the melt by chemical distillation. The impurity concentrations in the glasses thus prepared have been reduced to the following levels: hydrogen, <0.02; oxygen, 0.2; carbon, <0.02; silicon, <0.4 ppm by weight. Using the double-crucible method, we have fabricated glass fibers with various ratios of the core and cladding diameters (1: 25 to 9: 10), protected with a tetrafluoroethylene/1,1-difluoroethylene copolymer coating, which have an average bending strength of 0.5–1 GPa. The minimal optical losses are 150 dB/km at 6.6 μm in multimode As-Se-Te glass fibers and 60 dB/km at 4.8 μm in As-S-Se glass fibers. The effect of microinhomogeneities in the melt on the optical performance of arsenic sulfoselenide glass fibers fabricated by the double-crucible method is examined.     

Electrical conductivity in iron-containing oxide glasses

The electrical properties of silicate, borate, phosphate and tellurite glasses containing iron are reviewed. The highest electrical conductivity has been observed in iron-tellurite glasses. The problem of the structure and influence of different glass modifiers on the electrical conduction of iron-containing glasses is discussed.     

Two-liquid phase structure of photoconducting oxide glasses

An electron microscopic study of a series of photoconducting oxide glasses in the systems CdO/B₂O₃/SiO₂, CdO/B₂O₃/GeO₂ and PbO/Al₂O₃/SiO₂, has shown the essential diphasic nature of these materials. The samples were examined by replica techniques, in transmission and by scanning electron microscopy. Two-liquid features have been identified, as has very fine-scale crystallisation, both on the basis of textures of fracture surfaces and of electron diffraction patterns. Physical models proposed to explain the electronic properties of glasses such as these must take account of this obvious two-phase nature of such materials.