Tyndall National Institute at UCC in Cork, Ireland named for John Tyndall, scientist, is one of Europe's leading research centres, specialising in ICT hardware research, commercialisation of technology and the education of next generation researchers. Tyndall has over 450 researchers, engineers, students and support staff focused on research and the commercialisation of technology through industry collaboration. Tyndall’s research spans a range of technologies from atoms to systems in the areas of photonics, microsystems and micro-nanoelectronics and addresses key challenges in the areas of Communications, Energy, Health and the Environment. Queen Elizabeth II visited the research centre as part of her state visit to Ireland on 20 May 2011. Wikipedia.
Zhao J.,Tyndall National Institute
Optics Express | Year: 2014
We experimentally demonstrate and numerically investigate a discrete-Fourier-transform (DFT) based offset quadrature-amplitudemodulation (offset-QAM) orthogonal frequency division multiplexing (OFDM) system. We investigate the scheme using a set of square-rootraised-cosine functions and a set of super-Gaussian functions as signal spectra. It is shown that offset-QAM OFDM exhibits negligible penalty for all investigated spectra, in contrast to rectangular-function based Nyquist FDM (N-FDM) and sinc-function based conventional OFDM (C-OFDM). The required guard interval (GI) length for dispersion compensation in offset-QAM OFDM is analyzed and shown to scale with twice the subcarrier spacing rather than the full OFDM bandwidth. Experimental results show that 38-Gb/s offset-16QAM OFDM supports 600-km fiber transmission with negligible penalty in the absence of GI while a GI length of eight is required in C-OFDM. Further numerical simulations show that by avoiding the GI, 112-Gb/s polarization multiplexed offset-4QAM OFDM can achieve 23% increase in net data rate over C-OFDM under the same transmission reach. We also discuss the design of the pulse-shaping filter in the DFT-based implementation and show that when compared to NFDM, the required memory length of the filter for pulse shaping can be reduced from 60 to 2 in offset-QAM OFDM regardless of the fiber length. © 2014 Optical Society of America.
Usman M.,Tyndall National Institute
Physical Review B - Condensed Matter and Materials Physics | Year: 2012
The demonstration of isotropic polarization response from semiconductor quantum dots (QDs) is a crucial step towards the design of several optoelectronic technologies. Among many parameters that impact the degree of polarization (DOP [n - ]) of a QD system, the shape asymmetry is a critical factor. We perform multi-million-atom simulations to study the impact of the elliptical shapes on the electronic and polarization properties of single and vertically stacked InAs QDs. The comparison between a low aspect ratio (AR) and a high AR QD reveals that the electronic and the polarization properties strongly depend on the AR of the QD; the elongation of a tall QD allows tuning of the DOP [n - ] over a much wider range. We then extend our analysis to an experimentally reported vertical stack of nine QDs (9-VSQDs) that has shown significant potential to achieve isotropic polarization properties. We analyze the contribution from the shape asymmetry in the large, experimentally measured, in-plane polarization anisotropy. Our analysis shows that the orientation of the base elongation controls the sign of the DOP [n - ]; however, the magnitude of the base elongation has only a very little impact on the magnitude of the DOP [n - ]. We further predict that the elliptical shape of the 9-VSQDs can only tune either DOP  or DOP [1̄10] for the isotropic response. Our model results, in agreement with the TEM findings, suggest that the experimentally grown 9-VSQDs has either a circular or a slightly [1̄10] elongated base. Overall, the detailed investigation of DOP [n - ] as a function of the QD shape asymmetry provides a theoretical guidance for the continuing experimental efforts to achieve tailored polarization properties from QD nanostructures for the design of optical devices. © 2012 American Physical Society.
O'Brien S.,Tyndall National Institute
Optics Letters | Year: 2014
We present a design method and numerical results describing the construction of distributed feedback grating filters that support discrete combs of transmission resonances. These filter designs define open superstructure grating resonators with transmission channels that can be placed at predetermined frequencies, such as those defined by the wavelength division multiplexing grid or by a secondary frequency comb source. Focusing on a specific example with 40 GHz channel spacing, we optimize an active structure that defines three low-threshold lasing modes. How our design approach relates to filter synthesis techniques based on cascaded grating resonators is also discussed. © 2014 Optical Society of America.
Elliott S.D.,Tyndall National Institute
Langmuir | Year: 2010
Wepresent mechanisms for atomic layer deposition of Ru, Rh, Pd, Os, Ir, or Pt metal from homoleptic precursors and oxygen. The novel mechanistic feature is that combustion of ligands produces transient hydroxyl groups on the surface, which can undergo Brønsted-type elimination of a further ligand or water from the surface. Each ligand therefore releases one electron for reduction of the metal. The growth reaction may be described as oxide-catalyzed redox decomposition of the precursor. To validate the mechanism against experiment, we derive analytical expressions for product ratios and the growth rate in terms of saturating coverages. © 2010 American Chemical Society.
Nolan M.,Tyndall National Institute
Physical Chemistry Chemical Physics | Year: 2011
In recent experiments Tada et al. have shown that TiO 2 surfaces modified with iron oxide display visible light photocatalytic activity. This paper presents first principles simulations of iron oxide clusters adsorbed at the rutile TiO 2 (110) surface to elucidate the origin of the visible light photocatalytic activity of iron oxide modified TiO 2. Small iron oxide clusters adsorb at rutile (110) surface and their presence shifts the valence band so that the band gap of the composite is narrowed towards the visible, thus confirming the origin of the visible light activity of this composite material. The presence of iron oxide at the TiO 2 surface leads to charge separation, which is the origin of enhanced photocatalytic efficiency, consistent with experimental photoluminesence and photocurrent data. Surface modification of a metal oxide is thus an interesting route in the development of visible light photocatalytic materials. © the Owner Societies 2011.