High pressure CVD inside microstructured optical fibres

We report the fabrication of semiconductor structures within holey fibres via a pressure driven microfluidic chemical vapour deposition process, demonstrating templated growth of crystalline Group IV semiconductor structures and devices in extreme aspect ratio geometries

Conservation of the S10-spc-α Locus within Otherwise Highly Plastic Genomes Provides Phylogenetic Insight into the Genus Leptospira

S10-spc-α is a 17.5 kb cluster of 32 genes encoding ribosomal proteins. This locus has an unusual composition and organization in Leptospira interrogans. We demonstrate the highly conserved nature of this region among diverse Leptospira and show its utility as a phylogenetically informative region. Comparative analyses were performed by PCR using primer sets covering the whole locus. Correctly sized fragments were obtained by PCR from all L. interrogans strains tested for each primer set indicating that this locus is well conserved in this species. Few differences were detected in amplification profiles between different pathogenic species, indicating that the S10-spc-α locus is conserved among pathogenic Leptospira. In contrast, PCR analysis of this locus using DNA from saprophytic Leptospira species and species with an intermediate pathogenic capacity generated varied results. Sequence alignment of the S10-spc-α locus from two pathogenic species, L. interrogans and L. borgpetersenii, with the corresponding locus from the saprophyte L. biflexa serovar Patoc showed that genetic organization of this locus is well conserved within Leptospira. Multilocus sequence typing (MLST) of four conserved regions resulted in the construction of well-defined phylogenetic trees that help resolve questions about the interrelationships of pathogenic Leptospira. Based on the results of secY sequence analysis, we found that reliable species identification of pathogenic Leptospira is possible by comparative analysis of a 245 bp region commonly used as a target for diagnostic PCR for leptospirosis. Comparative analysis of Leptospira strains revealed that strain H6 previously classified as L. inadai actually belongs to the pathogenic species L. interrogans and that L. meyeri strain ICF phylogenetically co-localized with the pathogenic clusters. These findings demonstrate that the S10-spc-α locus is highly conserved throughout the genus and may be more useful in comparing evolution of the genus than loci studied previously

Mid-infrared transmission properties of amorphous germanium optical fibers

Germanium optical fibers have been fabricated using a high pressure chemical deposition technique to deposit the semiconductor material inside a silica capillary. The amorphous germanium core material has a small percentage of hydrogen that saturates the dangling bonds to reduce absorption loss. Optical transmission measurements were performed to determine the linear losses over a broad mid-infrared wavelength range with the lowest loss recorded at 10.6 µm. The extended transmission range measured in the germanium fibers demonstrates their potential for use in mid-infrared applications

Fusion of transparent semiconductors and microstructured optical fibers via high-pressure microfluidic chemical deposition

The introduction of a crystalline semiconductor material within the capillaries of a microstructured optical fiber (MOF) presents tremendous potential for the development of in-fiber optoelectronic devices. We have developed a high-pressure microfluidic process that allows us to adapt traditional chemical vapor deposition chemistries to incorporate materials within the capillaries of MOFs. Pressures up to 35MPa are used to force a precursor/carrier gas mixture through the capillaries enabling deposition within microscale capillaries over meters in length. The materials can be organized within the MOFs for in-fiber applications, or the MOF can be used as a template for the formation of highly uniform extreme aspect ratio tubes and wires. Our efforts in the deposition of silicon carbide within the microscale capillaries of MOFs from a single source precursor will be presented. Crystalline semiconductor materials such as SiC are of particular interest to us owing to their ability to generate light. The introduction of SiC into the capillaries presents tremendous potential for the development of in-fiber optoelectronic devices with potential applications including light generation, modulation, and amplification

Templated growth of II-VI semiconductor optical fiber devices and steps towards infrared fiber lasers

ZnSe and other zinc chalcogenide semiconductor materials can be doped with divalent transition metal ions to create a mid-IR laser gain medium with active function in the wavelength range 2-5 microns and potentially beyond using frequency conversion. As a step towards fiberized laser devices, we have manufactured ZnSe semiconductor fiber waveguides with low (less than 1dB/cm at 1550nm) optical losses, as well as more complex ternary alloys with ZnSxSe1-x stoichiometry to potentially allow for annular heterostructures with effective and low order mode core-cladding waveguiding

Low loss silicon fibers for photonics applications

Silicon fibers are fabricated using a high pressure chemical deposition technique to deposit the semiconductor material inside a silica capillary. The silicon is deposited in an amorphous state into pure silica capillaries and can be crystallized to polysilicon after the deposition via a high temperature anneal. Optical transmission measurements of various amorphous and polycrystalline core materials were performed in order to determine their linear losses. Incorporating silicon functionality inside the fiber geometry opens up new possibilities for the next generation of integrated silicon photonics devices

A magnifying fiber element with an array of sub-wavelength Ge/ZnSe pixel waveguides for infrared imaging

We demonstrate an array of tapered Ge-core/ZnSe-cladding waveguides in a silica fiber matrix for infrared image transfer and a pixel magnification of 3.5× at 3.39µm and 10.64µm wavelengths. The structure was synthesized by a high-pressure chemical vapor deposition technique to deposit the semiconductor waveguides within the holes of a silica based microstructured optical fiber. The core/cladding structure reduces the optical propagation loss through the waveguides, and good isolation between the pixels is demonstrated. With further material improvements, these structures could be useful for applications such as infrared endoscopic imaging

All-optical modulation of laser light in amorphous silicon-filled microstructured optical fibers

Amorphous silicon is deposited within optical fibers by a high pressure microfluidic deposition process and characterized via Raman spectroscopy. All-optical modulation of 1.55 µm light guided through the silicon core is demonstrated using the free carrier absorption generated by a 532 nm pump pulse. Modulation depths of up to 8.26 dB and modulation frequencies of up to 1.4 MHz are demonstrated

High-pressure chemical deposition for void-free filling of extreme aspect ratio templates

Extreme aspect ratio semiconductor structures are critical to modern optoelectronic technology because of their ability to waveguide light and transport electrons. Waveguides formed from almost any material by conventional micro/nanofabrication techniques typically have significant surface roughness that scatters light and is a constraining factor in most optoelectronic devices. For example, fabricated planar silica waveguides have optical losses 3 to 5 orders of magnitude higher than silica fibers, in part due to surface roughness. For these reasons silica nanofibers have been proposed as alternatives to fabricated silica or semiconductor channels for waveguiding of light in miniaturized optical devices, as they meet the strict requirements for surface roughness and diameter uniformity required for low loss. An additional advantage of these silica fibers is that they have a circular cross section that can simultaneously guide both transverse electric (TE) and transverse magnetic (TM) polarizations without cutoff. In contrast the rectilinear cross sections of microfabricated planar waveguides can effectively guide only one polarization without cutoff. However, semiconductors in general exhibit a far broader range of useful optoelectronic function than silica glass because of their ability to form hetero and homojunctions, serve as optical gain media over a broad range of wavelengths, and their superior non-linear optical properties

Confined high-pressure chemical deposition of hydrogenated amorphous silicon

Hydrogenated amorphous silicon (a-Si:H) is one of the most technologically important semi-conductors. The challenge in producing it from SiH4 precursor is to overcome a significant kinetic barrier to decomposition at a low enough temperature to allow for hydrogen incorporation into a deposited film. The use of high precursor concentrations is one possible means to increase reaction rates at low enough temperatures, but in conventional reactors such an approach produces large numbers of homogeneously nucleated particles in the gas phase, rather than the desired heterogeneous deposition on a surface. We report that deposition in confined micro-/nanoreactors overcomes this difficulty, allowing for the use of silane concentrations many orders of magnitude higher than conventionally employed while still realizing well-developed films. a-Si:H micro-/nanowires can be deposited in this way in extreme aspect ratio, small- diameter optical fiber capillary templates. The semi- conductor materials deposited have ~0.5 atom% hydrogen with passivated dangling bonds and good electronic properties. They should be suitable for a wide range of photonic and electronic applications such as nonlinear optical fibers and solar cell