Optical waveguide fabrication in silica using flame hydrolysis

This thesis is concerned with the fabrication, assessment and application of doped silica waveguides using Flame Hydrolysis Deposition. Deposition apparatus has been designed and constructed. This equipment consists of a gas supply assembly, a bubbler cabinet, a deposition box and a chemical scrubber. An optimum sintering regime for the low density silica soot has been established consisting of 60 minutes at 1250oC. This regime is dependent on the levels of P2O5, GeO2 and/or TiO2 doping in the silica host. Independent control of layer thickness and index is achieved. Refractive index can be varied by changing the doping levels, and thickness, by increasing the number of traversals of the hydrolysing flame. Film homogeneity in terms of layer thickness was found to be difficult to control and up to 30% variation in thickness was obtained in some samples. Thermophoretic effects were shown to play an important part in the deposition process. Titanium and phosphorus doped films were found to suffer film degradation and aging. This led to the formation of titanium rich crystals and crystal agglomerates which produced Rayleigh/ Mie scatter in the sintered films. No such problem was found with Germanium, and all films were subsequently fabricated using Germanium and Phosphorus. No out-of-plane scatter was observed in the sintered films. Ridge waveguides were fabricated using lithography and Reactive Ion Etching in a CHF3 plasma, giving waveguides with smooth side walls. Loss assessment was carried out using two techniques, both of which were non-destructive. One involved a video camera to scan across the waveguide and detect the out-of-plane scatter. This technique was sensitive to scattering centres and was less accurate for short lengths of guide. Loss figure varied from 0.2 to over 5 dB/cm depending on the scan length. The second technique involved turning the waveguide into a Fabry-Perot resonator, by coating the end faces of the waveguide. Temperature induced cycles in the output intensity could be used to obtain the waveguide attenuation. This technique was sensitive to the facet angles of the guides which could contribute significantly to the loss measured. Such resonances were obtained in only one sample and gave a loss figure of over 9 dB/cm which is considered unreliable. Films were doped with both Nd3+ and Er3+ using a solution doping technique and fluorescence spectra were obtained for both. Increased scatter was observed in the planar films with such doping. Holographic gratings were fabricated on planar waveguides with a view to their incorporation as feedback elements in a laser structure. Second Harmonic Generation was observed for the first time in planar rib waveguide structures doped with Phosphorus and Germanium. In a `seeding' experiment where 1064nm radiation was launched at the same time as a second harmonic `seed', a two-hundred fold increase was observed in generated second harmonic signal over the background level

Use of semiconductor optical amplifiers in signal processing applications

We describe a 42.6 Gbit/s all-optical pattern recognition system which uses semiconductor optical amplifiers (SOAs). A circuit with three SOA-based logic gates is used to identify the presence of specific port numbers in an optical packet header

42.6 Gbit/s fully integrated all-optical XOR gate

We demonstrate an SOA-based all-optical high-speed Mach-Zehnder interferometer exclusive- OR (XOR) gate fabricated in a silica III-V hybrid-integration technology platform.  The device includes integrated time delays for rapid differential operation as well as integrated phase shifters for fine tuning of power splitters and interferometer bias enabling highly optimized XOR gate operation.  XOR functionality is verified through inspection of the output pulse sequence and the carrier-suppressed output spectrum.  A 2.3 dB penalty for a 42.6 Gb/s RZ-OOK signal at a 10-9 bit error rate is observed

High-speed electronics for short-link communication

High-speed electronic integrated circuits are essential to the development of new fiber-optic communication systems. Close integration and co-design of photonic and electronic devices are becoming more and more a necessity to realize the best performance trade-offs. This paper presents our most recent results and a brief introduction to our research in recently started EU projects

All-optical header processing in a 42.6Gb/s optoelectronic firewall

A novel architecture to enable future network security systems to provide effective protection in the context of continued traffic growth and the need to minimise energy consumption is proposed. It makes use of an all-optical pre-filtering stage operating at the line rate under software control to distribute incoming packets to specialised electronic processors. An experimental system that integrates software controls and electronic interfaces with an all-optical pattern recognition system has demonstrated the key functions required by the new architecture. As an example, the ability to sort packets arriving in a 42.6Gb/s data stream according to their service type was shown experimentally

Energy‐efficient colourless photonic technologies for next‐generation DWDM metro and access networks

Within the scope of our EU FP7 C3PO project, we are developing novel, energy-efficient, colourless photonic technologies for low-cost, next-generation dense wavelength-division-multiplexed metro transport and access networks. The colourless transmitters use reflective arrayed photonic integrated circuits, particularly hybrid reflective electroabsorption modulators, and multi-wavelength laser sources, with custom power-efficient driver circuitry. A low-loss piezoelectric beam-steering optical matrix switch allows for dynamic wavelength reconfigurability. Simplifying the required optical and electronic hardware, as well as avoiding the need for expensive, thermally-stabilised tuneable lasers, will yield cost and energy savings for data switching applications in future metro, access, and datacentre interconnection networks. We report on recent advancement towards these low-power optical networks, providing the latest systems results achieved with key enabling hybrid photonic integrated devices and electronic driver/receiver arrays for our targeted applications

Molecular profiling of signet ring cell colorectal cancer provides a strong rationale for genomic targeted and immune checkpoint inhibitor therapies

We would like to thank all patients whose samples were used in this study. We are also thankful to the Northern Ireland Biobank and Grampian Biorepository for providing us with tissue blocks and patient data; and Dr HG Coleman (Queen’s University Belfast) for her advice on statistical analyses. This work has been carried out with financial support from Cancer Research UK (grant: C11512/A18067), Experimental Cancer Medicine Centre Network (grant: C36697/A15590 from Cancer Research UK and the NI Health and Social Care Research and Development Division), the Sean Crummey Memorial Fund and the Tom Simms Memorial Fund. The Northern Ireland Biobank is funded by HSC Research and Development Division of the Public Health Agency in Northern Ireland and Cancer Research UK through the Belfast CRUK Centre and the Northern Ireland Experimental Cancer Medicine Centre; additional support was received from Friends of the Cancer Centre. The Northern Ireland Molecular Pathology Laboratory which is responsible for creating resources for the Northern Ireland Biobank has received funding from Cancer Research UK, Friends of the Cancer Centre and Sean Crummey Foundation.Peer reviewedPublisher PD

Diagnosis of phosphorus monolayer doping in silicon based on nanowire electrical characterisation

The advent of high surface-to-volume ratio devices has necessitated a revised approach to parameter extraction and process evaluation in field-effect transistor technologies. In this work, active doping concentrations are extracted from the electrical analysis of Si nanowire devices with high surface-to-volume ratios. Nanowire resistance and Si resistivity are extracted, by first extracting and subtracting out the contact resistance. Resistivity (ρ) is selected as the benchmark parameter to compare different doping processes with each other. The impacts of nanowire diameter scaling to 10 nm and of nanowire spacing scaling to <20 nm are extracted for monolayer doping and beam-line ion implantation. Despite introducing significant crystal damage, P beam-line ion implantation beats allyldiphenylphosphine (ADP) P monolayer doping with a SiO2 cap in terms of lower Si resistivity and higher dopant activation, with dependencies on the nanowire width greater than on nanowire spacing. Limitations in ADP P monolayer doping with a SiO2 cap are due to the difficulties in dopant incorporation, as it is based on in-diffusion, and P atoms must overcome a potential barrier on the Si surface

Effect of Hookworm Infection on Wheat Challenge in Celiac Disease – A Randomised Double-Blinded Placebo Controlled Trial

Background and Aims: The association between hygiene and prevalence of autoimmune disease has been attributed in part to enteric helminth infection. A pilot study of experimental infection with the hookworm Necator americanus was undertaken among a group of otherwise healthy people with celiac disease to test the potential of the helminth to suppress the immunopathology induced by gluten

Heimler Syndrome is Caused by Hypomorphic Mutations in the Peroxisome-Biogenesis Genes PEX1 and PEX6

Heimler syndrome (HS) is a rare recessive disorder characterized by sensorineural hearing loss (SNHL), amelogenesis imperfecta, nail abnormalities and occasional or late onset retinal pigmentation. We ascertained eight families with HS, and - using a whole exome sequencing approach - identified biallelic mutations in PEX1 or PEX6 in six of them. Loss of function mutations in both genes are known causes of a spectrum of autosomal recessive peroxisome biogenesis disorders (PBDs), including Zellweger syndrome. PBDs are characterized by leukodystrophy, hypotonia, SNHL, retinopathy, and skeletal, craniofacial, and liver abnormalities. We demonstrate that each HS family has at least one hypomorphic allele that results in extremely mild peroxisomal dysfunction. Although individuals with HS share some subtle clinical features found in PBDs, the overlap is minimal and the diagnosis was not suggested by routine blood and skin fibroblast analyses used to detect PBDs. In conclusion, our findings define Heimler syndrome as a mild PBD, expanding the pleiotropy of mutations in PEX1 and PEX6