Microstructured Fibre Taper with Constant Outer Diameter

Department of Electrical Engineerin

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Development and applications of dispersion controlled high nonlinearity microstructured fibres

In this thesis I investigate aspects of dispersion controlled high nonlinearity all silica holey fibre, including design, fabrication, sample applications, and modelling.Microstructured fibre fabrication allows for great flexibility in core and cladding structure designs, with the large available refractive index contrast between glass and air. This allows the control of waveguide dispersion across a wide wavelength range, which can be used to offset the material dispersion of the core glass. Therefore, this technology provides improved overall dispersion control via fibre design. This often requires a complex arrangement of air holes in the structure.The full fabrication procedures for small-core holey fibres are presented. In particular, the fabrication of fibres with a graded-hole-size structure is reported. A structural accuracy of ±6% is achieved and improvements are proposed for future work.A systematic study of the Supercontinuum Generation phenomenon is presented in this thesis. By using fibres with different dispersion profiles, pumping at 1.06 μm, the nonlinear effects such as Self-Phase-Modulation, Four-Wave-Mixing and Self-Soliton-Frequency-Shift, which dominate the spectral broadening in fibres with one or two zero-dispersion wavelengths are identified accordingly.The latest work has been focussed on controlled structural variation of holey fibres along their length to obtain fibre with a longitudinal variation of dispersion and nonlinearity. I fabricated a dispersion-decreasing holey fibre and performed the first demonstration of soliton compression in a holey fibre. A compression factor of 2 has been achieved with pJ pulses at 1.06 μm. Further numerical modelling has been carried out from a holey fibre design contour map, to optimize holey fibre tapers for soliton compression at 1.55 μm. A compression factor of 6 is possible in a 15-m holey fibre taper with a loss of 0.1 dB/m

OPTICAL PROPERTIES OF PHOTONIC CRYSTAL FIBERS WITH A FIBER CORE OF ARRAYS OF SUBWAVELENGTH CIRCULAR AIR HOLES: BIREFRINGENCE AND DISPERSION

We propose a kind of novel photonic crystal fibers (PCFs) based on a fiber core with arrays of subwavelength circular air holes, achieving the flexible control of the birefringence or the dispersion property of the PCFs. A highly birefringent (HB) PCF is achieved by employing arrays of subwavelength circular air hole pairs in the fiber core, which are arranged as a conventional hexagonal lattice structure with a subwavelength lattice constant. The HB-PCF is with uniform and ultrahigh birefringence (up to the order of 0.01) in a wavelength region from 1.25 μm to 1.75 μm or even a larger region, which, to the best of our knowledge, is the best birefringence property of the PCFs. A dispersion-flattened (DF) PCF with near-zero dispersion is achieved by employing arrays of subwavelength circular air holes in the fiber core arranged as a conventional hexagonal lattice structure with a subwavelength lattice constant, which contributes negative waveguide dispersion to the PCF. The proposed design of the DF-PCF provides an alternate approach for the dispersion control of the PCF. Besides the high birefringence and the flattened near-zero dispersion, the proposed PCFs with a fiber core of arrays of subwavelength circular air holes have the potential to achieve a large mode area single mode PCF.Department of Electrical Engineerin

Initial viral load and the outcomes of SARS

BACKGROUND: Severe acute respiratory syndrome (SARS) is caused by a novel coronavirus. It may progress to respiratory failure, and a significant proportion of patients die. Preliminary data suggest that a high viral load of the SARS coronavirus is associated with adverse outcomes in the intensive care unit, but the relation of viral load to survival is unclear. METHODS: We prospectively studied an inception cohort of 133 patients with virologically confirmed SARS who were admitted to 2 general acute care hospitals in Hong Kong from Mar. 24 to May 4, 2003. The patients were followed until death or for a minimum of 90 days. We used Cox proportional hazard modelling to analyze potential predictors of survival recorded at the time of presentation, including viral load from nasopharyngeal specimens (measured by quantitative reverse transcriptase polymerase chain reaction [PCR] of the SARS-associated coronavirus). RESULTS: Thirty-two patients (24.1%) met the criteria for acute respiratory distress syndrome, and 24 patients (18.0%) died. The following baseline factors were independently associated with worse survival: older age (61–80 years) (adjusted hazard ratio [HR] 5.24, 95% confidence interval [CI] 2.03–13.53), presence of an active comorbid condition (adjusted HR 3.36, 95% CI 1.44–7.82) and higher initial viral load of SARS coronavirus, according to quantitative PCR of nasopharyngeal specimens (adjusted HR 1.21 per log(10) increase in number of RNA copies per millilitre, 95% CI 1.06–1.39). INTERPRETATION: We found preliminary evidence that higher initial viral load is independently associated with worse prognosis in SARS. Mortality data for patients with SARS should be interpreted in light of age, comorbidity and viral load. These considerations will be important in future studies of SARS