Design and fabrication of high quality-factor 1-d photonic crystal/photonic wire extended microcavities

We have successfully demonstrated experimentally the fabrication and measurement of high quality-factor one-dimensional photonic crystal/photonic wire extended cavities based on silicon-on-insulator. The cavities that we have investigated ranged from 3 to 8 m in length. A quality-factor of nearly 74 000 was measured at a cavity length of 5 m through the use of tapering both within and outside the cavity, showing good agreement with the finite-difference time-domain simulation approach use

Sedimentary framework of mainland fringing reef development, Cape Tribulation Area

Mainland fringing reefs with a diverse coral fauna have developed in the Cape Tribulation area primarily upon coastal sediment bodies such as beach shoals and creek mouth bars. Growth on steep rocky headlands is minor. The reefs have extensive sandy beaches to landward, and an irregular outer margin. Typically there is a raised platform of dead nef along the outer edge of the reef, and dead coral columns lie buried under the reef flat. Live coral growth is restricted to the outer reef slope. Seaward of the reefs is a narrow wedge of muddy, terrigenous sediment, which thins offshore. Beach, reef and inner shelf sediments all contain 50% terrigenous material, indicating the reefs have always grown under conditions of heavy terrigenous influx. The relatively shallow lower limit of coral growth (ca 6m below ADD) is typical of reef growth in turbid waters, where decreased light levels inhibit coral growth. Radiocarbon dating of material from surveyed sites confirms the age of the fossil coral columns as 33304110 ybp, indicating that they grew during the late postglacial sea-level high (ca 5500-6500 ybp). The former thriving reef-flat was killed by a post-5500 ybp sea-level fall of ca 1 m. Although this study has not assessed the community structure of the fringing reefs, nor whether changes are presently occurring, it is clear the corals present today on the fore-reef slope have always lived under heavy terrigenous influence, and that the fossil reef-flat can be explained as due to the mid-Holocene fall in sea-level. A medium term programme is required to record sediment loading and coral community structure, and to establish the environmental vulnerability of these reefs

Technical assistance in Nigeria : developing geoscience skills for tomorrow

The World Bank funded Nigerian Geochemical Mapping Technical Assistance Project was started in 2008 within the Nigerian Ministry of Mines and Steel Development, and is now nearing completion. Staff from the Nigerian Geological Survey Agency (NGSA), the Nigerian academic community, British Geological Survey, and Geological Survey of Finland, have worked alongside one another in a comprehensive program of practical training and knowledge exchange. This program has enabled researchers from a range of backgrounds and experience in Africa and Europe to exchange knowledge and develop important geoscience skills. As part of this program key skills in many areas including; GIS, statistics, QC, data management, laboratory analysis, sampling methodologies, has developed the knowledge and skills base within the Nigerian geosciences community, and has maintained momentum for Nigeria’s national geochemical mapping program. An important objective of the Project is knowledge exchange during training of Nigerian geoscientists in conducting regional geochemical surveys as part of a long term mapping program across Nigeria. Practical training in methodologies for geochemical mapping formed the basis of a major field campaign in 2009, during which over 100 personnel were trained in geochemical mapping techniques. A similar number of personnel were involved in specialist training through a series of workshops and training courses in Nigeria and the UK. Two field areas were selected for the geochemical mapping training — one in central Nigeria (the ‘Minna Cell’) and one in south-western Nigeria (the ‘South-western Cell’) — covering a combined area of 52 000 km2. Key challenges involved the procurement of field equipment and consumables, and modernisation of sample preparation laboratories and archiving facilities at the National Geosciences Research Laboratory, Kaduna. New sample preparation and analytical equipment has been purchased and the laboratory staff have received training in the use of the new equipment. In the long-term it is envisaged that the analytical facilities will be developed further, and that all samples will be prepared, analysed and archived in Nigeria. A national geochemical mapping programme involving multi-element analysis of stream sediment samples is used as a primary dataset in the exploration for new economic mineral deposits. Establishing a geochemical baseline is necessary in order to monitor the effects of anthropogenic activities e.g. contamination caused by industrial waste and mining activities, for environmental investigations and medical geology studies both in rural and in urban areas, as well as studies within the agricultural and forestry sectors

Fire and Climax Spruce Forests in Central Yukon

Observations made during recent studies into fire history of forests in central Yukon ... suggest that, in the event of long-continued absence of fire, mixed stands of black and white spruce ... might become mono-specific black spruce stands. It is, however, unlikely that fires will often be absent for the long time periods needed for this change to develop. ..

Analysis of resonant responses of split ring resonators using conformal mapping techniques

We report a novel method for modeling the resonant frequency response of infra-red light, in the range of 2 to 10 microns, reflected from metallic spilt ring resonators (SRRs) fabricated on a silicon substrate. The calculated positions of the TM and TE peaks are determined from the plasma frequency associated with the filling fraction of the metal array and the equivalent LC circuit defined by the SRR elements. The capacitance of the equivalent circuit is calculated using conformal mapping techniques to determine the co-planar capacitance associated with both the individual and the neighbouring elements. The inductance of the equivalent circuit is based on the self-inductance of the individual elements and the mutual inductance of the neighboring elements. The results obtained from the method are in good agreement with experimental results and simulation results obtained from a commercial FDTD simulation software package. The method allows the frequency response of a SRR to be readily calculated without complex computational methods and enables new designs to be optimised for a particular frequency response by tuning the LC circuit

Optical properties of split ring resonator metamaterial structures on semiconductor substrates

Metamaterials based on single-layer metallic Split Ring Resonators (SRR) and Wires have been demonstrated to have a resonant response in the near infra-red wavelength range. The use of semiconductor substrates gives the potential for control of the resonant properties of split-ring resonator (SRR) structures by means of active changes in the carrier concentration obtained using either electrical injection or photo-excitation. We examine the influence of extended wires that are either parallel or perpendicular to the gap of the SRRs and report on an equivalent circuit model that provides an accurate method of determining the polarisation dependent resonant response for incident light perpendicular to the surface. Good agreement is obtained for the substantial shift observed in the position of the resonances when the planar metalisation is changed from gold to aluminium

Characterisation at infrared wavelengths of metamaterials formed by thin-film metallic split-ring resonator arrays on silicon

The infrared reflectance spectra at normal incidence for split-ring resonator arrays fabricated in thin films of three different metals on a silicon substrate are reported. The results are compared with a finite difference time domain simulation of the structures and a simple and novel equivalent-circuit method for the calculation of the first and second resonant wavelengths

Coupling strength control in photonic crystal/photonic wire multiple cavity devices

Resonance splitting has been demonstrated for two coupled micro-cavities with control of the free spectral range between the resonance peaks, together with a normalised transmission level of approximately 60%. Coupled micro-cavity-based structures that were separated by two closely spaced in-line coupler sections between the two micro-cavities have also been successfully fabricated and measured. The coupling strength of the two cavities was controlled via the use of hole tapering in the middle section between the two cavities. 2D finite-difference time-domain simulation shows close agreement with the results of measurements

Increasing optical metamaterials functionality

Gold Split Ring Resonators (SRRs) were fabricated on silicon substrates by electron beam lithography and lift-off, with overall dimensions of approximately 200 nm. Reflectance spectra from the SRRs are similar to those published elsewhere. New devices are proposed based on the additional functionality afforded by the use of a silicon substrate

Transmission of PhC coupled-resonator waveguide (PhCCRW) structure enhanced via mode matching

A method for increasing the coupling efficiency between ridge optical waveguides and PhCCRWs is described. This increase is achieved via W1 channel waveguide sections, formed within a two-dimensional triangular lattice photonic crystal using mode-matching. The mode-matching is achieved by low quality-factor modified cavities added to both the input and output ports of the PhCCRW. A three dimensional finite-difference time-domain method has been used to simulate light propagation through the modified PhCCRW. We have fabricated PhCCRWs working at 1.5µm in silicon-on-insulator material. Measurements and simulations show that the overall transmission is improved by a factor of two