Equivalent optical waveguides

We develop a comparison method which identifies a waveguide with properties that are well known and are very similar to the one under investigation. It has a very simple mathematical basis which allows a trivial derivation of the moment method for circular cross-sectional fibers includingW-fibers, and an extension to noncircular optical waveguides. We first use the scalar approximation, and then extend to the full vector theory which accounts for polarization. Our concern is with fundamental mode propagation constants and higher mode cutoffs.     

Reactions and wetting behaviour in the aluminium-fused silica system

Wetting of fused silica by molten aluminium at temperature of 800 to 1000° C and 3×10^–5 Torr was dependent on the formation of a reaction zone by redox reactions. The reaction zone consisted of three layers. It was postulated that reactions proceeded by interdiffusion of Si²⁺, Al⁺, Al²⁺ and Al³⁺: the layer adjacent to the metal drop was primarily AlO stabilized by a solid solution of SiO; and adjacent to fused silica, a spinel of AlO and Al₂O₃ stabilized by SiO. On cooling these dissociated into Al, Si and -Al₂O₃ and/or-Al₂O₃.     

Simplified numerical analysis of optical fibres and planar waveguides

A convenient and efficient numerical technique is presented for determining modal properties of an optical fibre or planar waveguide. A simple recurrence relation, suitable for programming on only a pocket calculator, leads to parameters such as group velocity and cutoff wavelengths. The method is particularly useful for analysing single mode fibres, and an example of current interest is given.     

Influence of Microcracking and Slow Crack Growth on the Planar Coupling Coefficient in PZT

The difference in the planar coupling coefficient, k_p, of two PZT specimens with different grain sizes under the same poling treatment was attributed to a greater tendency for microcracking in the large grain-size specimens. In the absence of microcracking, as shown in small grain-size specimens, the decrease in k_p and failure of the poled specimens is attributed to slow crack growth. The optimum poling conditions for small grain-size specimens were evaluated in terms of reducing the slow crack-growth effect.     

New method for equivalent-step-index fibre determination

We propose a new method for determining equivalent-step index fibres: the far-field intensity halfangle is measured for a range of wavelengths and the data fitted by the step-fibre formula. A simple analytical formula aids the analysis. Proven experimental techniques can be used and no Gaussian or other theoretical approximations are involved.     

Influence of mixing medium on sintering and coupling coefficient of PZT ceramics

Mixtures of PZT, PbO and a water solution of PVA were prepared with distilled water and isopropyl alcohol. Better cold pressing behavior and more uniform microstructures free of large pores were obtained with use of the alcohol. Nature of grain boundaries was essentially unaffected as indicated by K_p measurements.     

Large-scale quantum mechanical simulations of high-<Emphasis Type="Italic">Z</Emphasis> metals

High-Z metals constitute a particular challenge for large-scale ab initio electronic-structure calculations, as they require high resolution due to the presence of strongly localized states and require many eigenstates to be computed due to the large number of electrons and need to accurately resolve the Fermi surface. Here, we report recent findings on high-Z metals, using an efficient massively parallel planewave implementation on some of the largest computational architectures currently available. We discuss the particular architectures employed and methodological advances required to harness them effectively. We present a pair-correlation function for U, calculated using quantum molecular dynamics, and discuss relaxations of Pu atoms in the vicinity of defects in aged and alloyed Pu. We find that the self-irradiation associated with aging has a negligible effect on the compressibility of Pu relative to other factors such as alloying.     

Sintering of α-Al2O3/quartz, and α-Al2O3/cristobalite related to mullite formation

Cristobalite and quartz react differently in mixtures with α-Al₂O₃ at 1415°C. With cristobalite, an eutectic liquid forms in accordance with the metastable phase equilibrium diagram for α-Al₂O₃-SiO₂ (cristobalite) in the absence of mullite. With quartz, a liquid first forms on the surfaces of quartz because of the occurence of an intermediate liquid phase on transformation of quartz to cristobalite. These liquids act as precursors to the formation of mullite by reacting with α-Al₂O₃. Mullite was detected earlier in the cristobalite-containing mixtures under similar firing conditions because the growth of mullite becomes significant with the formation of the eutectic liquid at the α-Al₂O₃-cristobalite interface since it is already saturated with Al₂O₃. The kinetics of sintering are affected by the rates of the step reactions.