The Design of Single Mode Large Cross-section Glass-based Waveguides for Photonic Integrated Circuits

This paper presents our recent simulation results and novel designs of single mode large cross-section glass-based waveguides for photonic integrated circuits (PICs). Simulations were performed using an in-house Finite Difference (FD) based mode solver and the FD Beam propagation Method (FD-BPM). Our simulation results show that this innovative technology could provide a simplified means to couple optical energy efficiently between optical components in a single chip. This would provide the base for the future large-scale integration of optical components in PICs. The novel idea of using single mode large cross-section glass-based waveguides as an optical integration platform is an evolutionary innovative solution for the monolithic integration of optical components, in which the glass-based structures act both as waveguides and as an optical bench for integration. This allows easy and efficient optical coupling between optical components and optical fibres, removing costly and tedious alignment problems and considerably reducing optical coupling losses in PICs. We expect that the glass-based waveguide PICs technology will enable the emergence of a new generation of compact, reliable, high speed, and multifunctional devices.     

Size control of dendrimer-templated silica

One of the most significant challenges facing the biomimetic synthesis of materials is achieving the requisite level of dimensional and spatial control. Typical reaction conditions for biomimetic silica synthesis allow for continued growth and ripening leading to the formation of larger nanospheres on the order of 200-600 nm in diameter. Herein, we have used polyamidoamine and polypropylenimine dendrimers as templates to expand the reaction conditions of biogenic silica production to produce a more robust synthesis leading to size-selective precipitation of silica nanospheres. Through the use of defined concentrations of phosphate buffer and main group metal chloride salts, we have shown that the biomimetic silica growth process is controlled by cationic neutralization of the anionic silica nanosphere surface. Neutralization minimizes electrostatic repulsions, allowing for agglomerization and continued growth of nanospheres. By controlling these concentrations, we can selectively produce silica nanospheres of desired dimensions between 30 and 300 nm without adversely affecting the template's activity.     

Reduction and methyl transfer kinetics of the alpha subunit from acetyl coenzyme a synthase

Stopped-flow was used to evaluate the methylation and reduction kinetics of the isolated alpha subunit of acetyl-Coenzyme A synthase from Moorella thermoacetica. This catalytically active subunit contains a novel Ni-X-Fe4S4 cluster and a putative unidentified n = 2 redox site called D. The D-site must be reduced for a methyl group to transfer from a corrinoid-iron-sulfur protein, a key step in the catalytic synthesis of acetyl-CoA. The Fe4S4 component of this cluster is also redox active, raising the possibility that it is the D-site or a portion thereof. Results presented demonstrate that the D-site reduces far faster than the Fe4S4 component, effectively eliminating this possibility. Rather, this component may alter catalytically important properties of the Ni center. The D-site is reduced through a pathway that probably does not involve the Fe4S4 component of this active-site cluster.     

High-performance liquid chromatographic method to resolve and determine lipopolysaccharide sub-groups of Escherichia coli endotoxin in isolated perfused rat liver perfusate.

A high-performance liquid chromatographic method was developed for resolving heterogeneous preparations of fluorescently labelled endotoxin derived from Escherichia coli (Serotype 0111:B4) into separate lipopolysaccharide sub-groups. The endotoxin was chromatographed on an analytical gel permeation column using a mobile phase of acetonitrile (20%, v/v) and 100 mM phosphate buffer (pH 7.75). Four fluorescent peaks were resolved, representing sub-groups of markedly different molecular sizes. Three of the four sub-groups contained the core polysaccharide 2-keto-3-deoxyoctonate, confirming that they contained lipopolysaccharide. Fluorescein isothiocyanate (FITC)-labelled endotoxins derived from Vibrio cholerae and Salmonella minnesota chromatographed using the same system eluted with distinctly different patterns of peaks from each other and from E. coli. Extraction of E. coli FITC-endotoxin from a buffer solution using a phenol-diethyl ether method and subsequent chromatography allowed the determination of three of the four fluorescent sub-groups over the concentration range 1-15 micrograms/ml.     

Trends in microdisk laser research and linear optical modelling

Research into microdisk lasers demonstrates new achievements both in the technology and in the associated physical effects and applications. Melting and rounding of the disk edge boosts the Q-factors due to improved surface smoothness. In-plane cavity shape is widely used as a design instrument. Optimal shaping of pumped area lowers the threshold power. Photonic molecules made of several microdisks as “photonic atoms” show lasing at several closely spaced frequencies. A microdisk with a single quantum dot as an active region is considered as the most promising system for realisation of a single photon emitter necessary for quantum computing. These new effects and devices can be simulated with accurate numerical techniques, developed recently for “warm-cavity” linear modelling, that are able to bring a new vision of the physics of lasing.     

Facet reflectivity in the presence of a diffracting corner

Results and new theory are presented for the uncoated and coated facet reflectivity of a shallowly buried waveguide, taking account of the diffracting corner present at the air–semiconductor interface. The corner effects are shown to be most significant in the case of coated facets. The analysis also predicts the asymmetry introduced into the radiation pattern.     

Practice of thin-layer chromatography

Ohne Zusammenfassung

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Practice of thin-layer chromatography By J.C. Touchstone and M.F. Dobbins, John Wiley & Sons, New York, Chichester, Brisbane, Toronto, 1978