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Detergent extracts of Trypanosoma cruzi epimastigotes catalysed the hydrolysis of a range of amino-acyl and peptidyl p-nitro-anilides and aminomethylcoumarins. At least three enzymes were detected that cleave Z-Phe-Arg-MCA. Two of these were optimally active at alkaline pH, the other at pH 4·0. Of the two enzymes with alkaline pH optima, one was a cysteine peptidase and was unable to cleave Bz-Arg-MCA readily, whilst the other cleaved Bz-Arg-MCA and was inhibited by diisopropyl fluorophosphate. The acidic enzyme was similar to cathespin L of other eukayrotes with respect to its pH profile, substrate-specificity and inhibitor-sensitivity. Evidence was presented that epimastigotes contain a cysteine-type dipeptidyl aminopeptidase, one or more aminopeptidases, and a serine peptidase that cleaves Boc-Ala-Ala-pNA. Digitonin solubilization of the activities from cells supports the hypothesis that the cathespin L-like enzyme and the dipeptidyl aminopeptidase are lysosomal, whilst the Bz-Arg-MCA hydrolase, the aminopeptidases and the Boc-Ala-Ala-pNA serine peptidase are cytosolic

Optical wavefront interferometry has evolved into increasingly compact and portable forms with optimizations and novel developments from multi-component, bulk-optic configurations to miniaturized multi-core fiber forms; each presents its own advantages, challenges and opportunities.

The escalation of global communication traffic has intensified the need for faster data processing techniques and systems. A combination of excessive browsing and downloading from of the world-wide web and high definition television technologies necessitates a replacement of today’s electronic-based data processing with all-optical systems. The light signal, which is carried within thin strands of optical fibre, will be manipulated at speeds and capacities far beyond the capability of existing electronics without the signal having to leave the transmitting fibre. To date, signal regeneration, switching, and encoding/decoding of information have all been demonstrated in conventional silica-based optical fibres. However, the long fibre lengths and high powers necessary to achieve this represent a significant drawback. In order to realize efficient, compact and ultrafast data processing schemes with low energy consumption new fibres will have to be fabricated that incorporate enhanced material functionalities such as high nonlinearities. A recent and promising new fibre platform that incorporates semiconductor materials into the core of a silica glass cladding has opened a route to realize this goal. In this poster, I will describe my research on the demonstration of all-optical signal processing in micron-sized resonators fabricated from silicon core optical fibres.

The first splicing experiments between silicon optical fibres (SOFs) and conventional fibres are investigated. An optimized fusion splicing approach for a polycrystalline SOF is demonstrated and the material properties after splicing are characterized.

A silicon microsphere was fabricated inside a fiber forming a hybrid Fabry-Pérot microcavity. The large difference in indices and thermal-optic coefficients of the sphere and its silica cladding are exploited for high-sensitivity temperature sensing.

We demonstrate an erasable grating coupler which allows optical device testing throughout the fabrication process without impairing final circuit performance. Refractive index variation is introduced using ion implantation and can be subsequently removed using laser annealing.

We review our progress in the development of nonlinear devices from the silicon optical fibre platform. The nonlinear performance will be benchmarked through demonstrations of high speed all-optical wavelength conversion, modulation, and continuum generation.

Nonlinear silicon photonics in the mid-infrared (mid-IR) is attracting increased interest with applications ranging from broadband telecommunications to sensing and spectroscopy. Recent reports have shown that hydrogenated amorphous silicon (a-Si:H) can exhibit low transmission losses, a high refractive index similar to the crystalline material, an even higher Kerr nonlinearity, though is much cheaper to produce. In this paper we extend the characterization of our a-Si:H core fibres beyond the telecommunications window of ~1.5µm and present the first measurements of the transmission properties up to the edge of the mid-infrared regime. The results show that the nonlinear figure of merit (FOMNL = n2/βTPAλ) increases dramatically over this region, with FOMNL > 20 around 2µm and above in Fig. 1(a) which open up the possibility of these fibres for nonlinear applications in the mid-IR regime.&more...

Low loss germanium-on-silicon waveguides are characterized over 2-3µm and demonstrated for all-optical modulation based on free-carrier absorption. The results indicate the suitability of this platform for optical processing in the mid-infrared.

Silicon photonic devices are becoming an increasingly popular platform for nonlinear optical applications owing to the high Kerr nonlinearity and tight optical confinement. Although typically these devices are fabricated from silicon planar wafers using standard photolithographic and etching techniques, more recently alternative fiber-based platforms have emerged [1]. In this paper we will review methods to fabricate novel micro-scale devices from our silicon fiber platform using standard fiber post-processing techniques. Fig. 1 shows two geometries that are unique to the fiber platform; microcylindrical silicon resonators [2] and tapered silicon core waveguides [3]. The ability to arbitrarily tailor the dimensions in these devices to manipulate the light confinement is of particular interest for low power, high speed nonlinear optical processing. For example, we will show that the ultra-small mode volume of the resonators can be exploited for ultrafast Kerr optical switching and modulation, whilst the longitudinally varying waveguide parameters of the tapers can be used for nonlinear pulse shaping at modest power levels.

Unary and compound semiconductors have been deposited into microstructured optical fibers to make junction-based fiber devices, very high power infrared fibers, mid-infrared fiber lasers, and nonlinear hydrogenated amorphous silicon fibers.

Silicon waveguides are becoming an increasingly popular platform for nonlinear optical signal processing. The incorporation of silicon into the optical fiber geometry provides an important step towards integrating semiconductor functionality with conventional fiber infrastructures, as well as allowing for the construction of robust devices with novel waveguiding properties. In this paper we review our progress in characterizing the nonlinear transmission properties of the hydrogenated amorphous silicon (a-Si:H) core fibers fabricated using a high pressure chemical deposition technique [1]. a-Si:H is emerging as a important material for nonlinear photonics owing to its high nonlinearity, low fabrication costs, and low transmission losses. Although, to date, this material has largely been characterized at telecommunications wavelengths [2], we have recently extended our investigations to present the first characterization of both the nonlinear absorption and refractive index over a wavelength region that crosses the two-photon absorption (TPA) edge, stretching towards the mid-infrared regime. These results will be discussed in relation to future device development, where we will demonstrate the potential for all-optical control using both cross-phase and cross-absorption modulation.

In this paper we describe a new class of silicon photonic crystal fibre (SiPCF) that brings together two powerful optical technologies, the photonic crystal fibre (PCF) and the semiconductor optical fibre. The PCF is now a well established fibre paradigm that has proven to be a very versatile waveguide and has found applications in nonlinear optics, fibre lasers, and sensors. The versatility of the PCF is due to its microstructured cladding which enables complex manipulation of the waveguide’s characteristics, and also allows for enhanced light interaction with materials that are infiltrated into the cladding voids. The most typical form of semiconductor optical fibre has a fused silica cladding and guides light in the high refractive index semiconductor core. Although semiconductor optical fibres are a nascent technology, practical applications, such as nonlinear pulse shaping and all optical modulation, have begun to emerge in the last couple of years. However, material losses are currently preventing this fibre type from becoming a major disruptive technology and, with this in mind, we present the first steps to decouple the functionality of the semiconductor from its material losses. We achieve this by filling the holes of a modified total internal reflection guiding silica PCF with hydrogenated amorphous silicon (a-Si:H) inclusions. We will show that the resulting SiPCF guides light in the low loss core via the antiresonant reflecting optical waveguiding (ARROW) mechanism.