Comparisons between gigabit NRZ, CAP and optical OFDM systems over FEC enhanced POF links using LEDs

Simulations have been performed to compare the link power budget and power dissipation of carrierless amplitude and phase modulation-64 (CAP-64) and 64-quadrature amplitude modulation-orthogonal frequency division multiplexing (64-QAM-OFDM) systems over feedforward error correction (FEC) enhanced plastic optical fibre (POF) links using light emitting diodes (LEDs). It is shown that CAP-64 outperforms 64-QAM-OFDM and supports record high 2.1Gb/s over 50m POF transmission. The CAP-64 and 64-QAM-OFDM links consume similar powers which are 2 (2.5) times of that of NRZ for the single POF link (twin POF links) case. © 2012 IEEE.

Optimized vertical carbon nanotube forests for multiplex surface-enhanced raman scattering detection

The highly sensitive and molecule-specific technique of surface-enhanced Raman spectroscopy (SERS) generates high signal enhancements via localized optical fields on nanoscale metallic materials, which can be tuned by manipulation of the surface roughness and architecture on the submicrometer level. We investigate gold-functionalized vertically aligned carbon nanotube forests (VACNTs) as low-cost straightforward SERS nanoplatforms. We find that their SERS enhancements depend on their diameter and density, which are systematically optimized for their performance. Modeling of the VACNT-based SERS substrates confirms consistent dependence on structural parameters as observed experimentally. The created nanostructures span over large substrate areas, are readily configurable, and yield uniform and reproducible SERS enhancement factors. Further fabricated micropatterned VACNTs platforms are shown to deliver multiplexed SERS detection. The unique properties of CNTs, which can be synergistically utilized in VACNT-based substrates and patterned arrays, can thus provide new generation platforms for SERS detection. © 2012 American Chemical Society.

One-pot synthesis of intercalating ZnO nanoparticles for enhanced dye-sensitized solar cells

In this letter we report a facile one-pot synthesis of intercalated ZnO particles for inexpensive, low-temperature solution processed dye-sensitised solar cells. High interconnectivity facilitates enhanced charge transfer between the ZnO nanoparticles and a consequent enhancement in cell efficiency. ZnO thin films were formed from a wide range of nanoparticle diameters which simultaneously increased optical scattering whilst enhancing dye loading. A possible growth mechanism was proposed for the synthesis of ZnO nanoparticles. The intercalated ZnO nanoparticle thin films were integrated into the photoanodes of dye-sensitised solar cells which showed an increase in performance of 37% compared to structurally equivalent cells employing ZnO nanowires. © 2012 Elsevier B.V.

Energy transfer and enhanced 1.54 μm emission in Erbium-Ytterbium disilicate thin films.

α-(Yb1-xErx)2Si2O7 thin films on Si substrates were synthesized by magnetron co-sputtering. The optical emission from Er3+ ions has been extensively investigated, evidencing the very efficient role of Yb-Er coupling. The energy-transfer coefficient was evaluated for an extended range of Er content (between 0.2 and 16.5 at.%) reaching a maximum value of 2 × 10⁻¹⁶ cm⁻³s⁻¹. The highest photoluminescence emission at 1535 nm is obtained as a result of the best compromise between the number of Yb donors (16.4 at.%) and Er acceptors (1.6 at.%), for which a high population of the first excited state is reached. These results are very promising for the realization of 1.54 μm optical amplifiers on a Si platform.

Enhanced down conversion of photons emitted by photoexcited Er xY2-xSi2O7 films grown on silicon

Photon cutting with efficiencies up to 400% is demonstrated in Erx Y2-x Si2 O7 films grown on Si and its concentration dependence is analyzed. The cutting is the result of cross-energy-transfer processes occurring within a single rare earth (Er3+) acting as both sensitizer and activator. Similarities with upconversion are revealed and possible applications in solar cells are discussed. © 2010 The American Physical Society.

Enhanced light emission in active silicon-on-insulator photonic crystal slabs and slot waveguides

We present experimental measurements on Silicon-on-insulator (SOI) photonic crystal slabs with an active layer containing Er3+ ions-doped Silicon nanoclusters (Si-nc), showing strong enhancement of 1.54 μm emission at room temperature. We provide a systematic theoretical analysis to interpret such results. In order to get further insight, we discuss experimental data on the guided luminescence of unpatterned SOI planar slot waveguides, which show enhanced light emission in transverse-magnetic (TM) modes over transverse-electric (TE) ones. ©2007 IEEE.

Enhanced infra-red emission from sub-millimeter microelectromechanical systems micro hotplates via inkjet deposited carbon nanoparticles and fullerenes

In this paper, we demonstrate a micro-inkjet printing technique as a reproducible post-process for the deposition of carbon nanoparticles and fullerene adlayers onto fully CMOS compatible micro-electro-mechanical silicon-on-insulator infrared (IR) light sources to enhance their infrared emission. We show experimentally a significant increase in the infrared emission efficiency of the coated emitters. We numerically validate these findings with models suggesting a dominant performance increase for wavelengths <5.5 μm. Here, the bimodal size distribution in the diameter of the carbon nanoparticles, relative to the fullerenes, is an effective mediator towards topologically enhanced emittance of our miniaturised emitters. A 90% improvement in IR emission power density has been shown which we have rationalised with an increase in the mean thickness of the deposited carbon nanoparticle adlayer. © 2013 AIP Publishing LLC.

Surface acoustic waves in liquid helium for enhanced single-electron transport applications

High frequency Rayleigh and Sezawa modes propagating in the ZnO/GaAs system capable of operating immersed in liquid helium have been engineered. In the case of the Rayleigh mode, the strong attenuation produced by the liquid is counteracted by the strengthening of the mode induced by the ZnO. However, in the case of the Sezawa modes, the attenuation is strongly reduced taking advantage of the depth profile of their acoustic Poynting vectors, that extend deeper into the layered system, reducing the energy radiated into the fluid. Thus, both tailored modes will be suitable for acoustically-driven single-electron and single-photon devices in ZnO-coated GaAs-based systems with the best thermal stability provided by the liquid helium bath. © 2012 IEEE.

Enhanced integrated modelling approach to reconfiguring manufacturing enterprises

Dynamism and uncertainty are real challenges for present day manufacturing enterprises (MEs). Reasons include: an increasing demand for customisation, reduced time to market, shortened product life cycles and globalisation. MEs can reduce competitive pressure by becoming reconfigurable and change-capable. However, modern manufacturing philosophies, including agile and lean, must complement the application of reconfigurable manufacturing paradigms. Choosing and applying the best philosophies and techniques is very difficult as most MEs deploy complex and unique configurations of processes and resource systems, and seek economies of scope and scale in respect of changing and distinctive product flows. It follows that systematic methods of achieving model driven reconfiguration and interoperation of component based manufacturing systems are required to design, engineer and change future MEs. This thesis, titled Enhanced Integrated Modelling Approach to Reconfiguring Manufacturing Enterprises , introduces the development and prototyping a model-driven environment for the design, engineering, optimisation and control of the reconfiguration of MEs with an embedded capability to handle various types of change. The thesis describes a novel systematic approach, namely enhanced integrated modelling approach (EIMA), in which coherent sets of integrated models are created that facilitates the engineering of MEs especially their production planning and control (PPC) systems. The developed environment supports the engineering of common types of strategic, tactical and operational processes found in many MEs. The EIMA is centred on the ISO standardised CIMOSA process modelling approach. Early study led to the development of simulation models during which various CIMOSA shortcomings were observed, especially in its support for aspects of ME dynamism. A need was raised to structure and create semantically enriched models hence forming an enhanced integrated modelling environment. The thesis also presents three industrial case examples: (1) Ford Motor Company; (2) Bradgate Furniture Manufacturing Company; and (3) ACM Bearings Company. In order to understand the system prior to realisation of any PPC strategy, multiple process segments of any target organisation need to be modelled. Coherent multi-perspective case study models are presented that have facilitated process reengineering and associated resource system configuration. Such models have a capability to enable PPC decision making processes in support of the reconfiguration of MEs. During these case studies, capabilities of a number of software tools were exploited such as Arena®, Simul8®, Plant Simulation®, MS Visio®, and MS Excel®. Case study results demonstrated effectiveness of the concepts related to the EIMA. The research has resulted in new contributions to knowledge in terms of new understandings, concepts and methods in following ways: (1) a structured model driven integrated approach to the design, optimisation and control of future reconfiguration of MEs. The EIMA is an enriched and generic process modelling approach with capability to represent both static and dynamic aspects of an ME; and (2) example application cases showing benefits in terms of reduction in lead time, cost and resource load and in terms of improved responsiveness of processes and resource systems with a special focus on PPC; (3) identification and industrial application of a new key performance indicator (KPI) known as P3C the measuring and monitoring of which can aid in enhancing reconfigurability and responsiveness of MEs; and (4) an enriched modelling concept framework (E-MUNE) to capture requirements of static and dynamic aspects of MEs where the conceptual framework has the capability to be extended and modified according to the requirements. The thesis outlines key areas outlining a need for future research into integrated modelling approaches, interoperation and updating mechanisms of partial models in support of the reconfiguration of MEs.

Observation of locked phase dynamics and enhanced frequency stability in synchronized micromechanical oscillators

Even though synchronization in autonomous systems has been observed for over three centuries, reports of systematic experimental studies on synchronized oscillators are limited. Here, we report on observations of internal synchronization in coupled silicon micromechanical oscillators associated with a reduction in the relative phase random walk that is modulated by the magnitude of the reactive coupling force between the oscillators. Additionally, for the first time, a significant improvement in the frequency stability of synchronized micromechanical oscillators is reported. The concept presented here is scalable and could be suitably engineered to establish the basis for a new class of highly precise miniaturized clocks and frequency references. © 2013 American Physical Society.