Burst switched optical networks supporting legacy and future service types

Focusing on the principles and the paradigm of OBS an overview addressing expectable performance and application issues is presented. Proposals on OBS were published over a decade and the presented techniques spread into many directions. The paper comprises discussions of several challenges that OBS meets, in order to compile the big picture. The OBS principle is presented unrestricted to individual proposals and trends. Merits are openly discussed, considering basic teletraffic theory and common traffic characterisation. A more generic OBS paradigm than usual is impartially discussed and found capable to overcome shortcomings of recent proposals. In conclusion, an OBS that offers different connection types may support most client demands within a sole optical network layer

Studies of advanced integrated nano-photonic devices in silicon

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 267-285).Electronic-photonic integrated circuits (EPICs) are a promising technology for overcoming bandwidth and power-consumption bottlenecks of traditional integrated circuits. Silicon is a good candidate for building such devices, due to its high-index contrast and low propagation loss at telecom wavelengths. The current thesis presents recent advances in demonstrating discrete components built in silicon-on-insulator (SOI) platforms, around 1550 nm, that can be used as building blocks for future EPIC systems. The first part of this thesis investigates electro-optic modulators based on one-dimensional photonic crystal microcavities, with femtojoule switching energies, as well as on-chip optical interconnects using the super-collimation effect in two-dimensional photonic crystals, both in hole- and rod-based configurations. The second part focuses on microring-based structures, demonstrating wide thermal tunability and hitless operation of single-ring filters, as well as three more advanced categories of devices suitable for wavelength-division multiplexing (WDM) applications. These are twenty-channel second-order tunable filterbanks (both in dual- and counter-propagating configurations), reconfigurable optical add-drop multiplexers (ROADMs) with telecom-grade specifications, and a dynamical slow light cell for delay lines and optical memory elements. All the devices demonstrated in this thesis can be integrated on the same chip. The small device footprints and the use of the SOI platform are ideal for integration with a standard CMOS process, enabling the fabrication of novel electronic-photonic integrated circuits. These new EPIC systems may one day play an important role in the scaling of current computing systems and taking advantage of the WDM capability to increase operational bandwidth, while keeping the power consumption at low levels.by Marcus Dahlem.Ph.D

Investigation of graphene as electrode in n-type OFETs and its use in nanometric devices

This work aims to investigate the use of CVD-graphene as electrode material in nanometric channel n-type Organic Field Effect Transistors (OFETs) based on thermally evaporated thin films of the perylene-3,4,9,10-tetracarboxylic acid diimide derivatives (PDIF-CN2 and PDI8-CN2). We firstly explored the electrical response of nano devices with standard bottom-contact/ distributed bottom gate architecture. By a thorough comparison with short channel transistors made with gold electrodes, output characteristics of the graphene-based devices suggests that SCLC contribution is suppressed. Moreover, current on/off ratios independent of the channel length (L) and enhanced response for high longitudinal biases are demonstrated for (L) down to 140 nm. Further advances have been reached by the use of a proper device architecture for nano devices with patterned local gate tracks and an ultra-thin films (8nm) of Hafnium Dioxide as high-k gate dielectric. The largely improved gate modulation results in a proper output currents saturation for channel length down to 200nm, with supply biases of few volts. Through impedance spectroscopy, overlap capacitances and the overall AC response of CVD-graphene electrodes have been investigated as well. The cut-off frequency of the nanodevice has been indirectly evaluated considering the DC transconductance and the measured overlap capacitance of the graphene electrodes. Values of the order of 150 kHz has been obtained for channel lengths of 200nm. Lastly, the organic/graphene interfaces and their injection and extraction phenomena have been further investigated in micrometric architectures. In particular, the problem of contact resistances have been analyzed via Scanning Kelvin Probe Force Microscopy (SKPFM) and the energetics of the interfaces has been reconstructed by the analysis of UV Photoelectron Spectroscopy (UPS) and X-ray Photoelectron Spectroscopy (XPS)

Design, fabrication and spectroscopy of strain-turnable quantum dots in nanowire antennas

Single-photon sources with high brightness, resolution-limited linewidths, and wavelength tunability are promising for future quantum technologies. This thesis investigates elastically tunable quantum dots(QDs) inside nanowire antennas which are fabricated and studied using photoluminescence spectroscopy and time correlated single photon counting at cryogenic temperature. For the nanofabrication, a new electron beam lithography system and a reactive ion etch chamber have been calibrated and maintained. GaAs nanowires with diameters as low as 120 nm and aspect ratios as high at 1:18 were successfully fabricated. These nanowires were structurally characterized by single electron microscopy. A sample with nanowires containing QDs was vertically bonded to a piezoelectric crystal. To carry out experiments at low temperature, two commercial and one home-built pulsed-tube cryostats were assembled. A miniature confocal microscope, which can be used inside the home built cryostat, was assembled and characterised. A confocal microscope to carryout spectroscopy at telecom wavelength,to be used with the commercial cryostats, was assembled and used in experiments by other group members. A third microscope for near infrared spectroscopy was assembled, to carry out spectroscopic characterization of the strain tunable device. And reveals that the nanowire geometry influences the extraction efficiency (η). For the brightest nanowire, we estimated η ≈57 %. We find that non-resonant excitation leads to static (fluctuating) charges, likely at the nanowire surface, causing DC Stark shifts (inhomogeneous broadening); for low excitation powers, the effects are not observed, and resolution-limited linewidths are obtained. Despite significant strain-field relaxation in the high-aspect-ratio nanowires, we achieve up to 1.2 meV tuning of a dot’s transition energy

SIMULATION AND ANALYSIS OF VEHICULAR AD-HOC NETWORKS IN URBAN AND RURAL AREAS

According to the American National Highway Traffic Safety Administration, in 2010, there were an estimated 5,419,000 police-reported traffic crashes, in which 32,885 people were killed and 2,239,000 people were injured in the US alone. Vehicular Ad-Hoc Network (VANET) is an emerging technology which promises to decrease car accidents by providing several safety related services such as blind spot, forward collision and sudden braking ahead warnings. Unfortunately, research of VANET is hindered by the extremely high cost and complexity of field testing. Hence it becomes important to simulate VANET protocols and applications thoroughly before attempting to implement them. This thesis studies the feasibility of common mobility and wireless channel models in VANET simulation and provides a general overview of the currently available VANET simulators and their features. Six different simulation scenarios are performed to evaluate the performance of AODV, DSDV, DSR and OLSR Ad-Hoc routing protocols with UDP and TCP packets. Simulation results indicate that reactive protocols are more robust and suitable for the highly dynamic VANET networks. Furthermore, TCP is found to be more suitable for VANET safety applications due to the high delay and packet drop of UDP packets.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format

Optical MEMS

Optical microelectromechanical systems (MEMS), microoptoelectromechanical systems (MOEMS), or optical microsystems are devices or systems that interact with light through actuation or sensing at a micro- or millimeter scale. Optical MEMS have had enormous commercial success in projectors, displays, and fiberoptic communications. The best-known example is Texas Instruments’ digital micromirror devices (DMDs). The development of optical MEMS was impeded seriously by the Telecom Bubble in 2000. Fortunately, DMDs grew their market size even in that economy downturn. Meanwhile, in the last one and half decade, the optical MEMS market has been slowly but steadily recovering. During this time, the major technological change was the shift of thin-film polysilicon microstructures to single-crystal–silicon microsructures. Especially in the last few years, cloud data centers are demanding large-port optical cross connects (OXCs) and autonomous driving looks for miniature LiDAR, and virtual reality/augmented reality (VR/AR) demands tiny optical scanners. This is a new wave of opportunities for optical MEMS. Furthermore, several research institutes around the world have been developing MOEMS devices for extreme applications (very fine tailoring of light beam in terms of phase, intensity, or wavelength) and/or extreme environments (vacuum, cryogenic temperatures) for many years. Accordingly, this Special Issue seeks to showcase research papers, short communications, and review articles that focus on (1) novel design, fabrication, control, and modeling of optical MEMS devices based on all kinds of actuation/sensing mechanisms; and (2) new developments of applying optical MEMS devices of any kind in consumer electronics, optical communications, industry, biology, medicine, agriculture, physics, astronomy, space, or defense

Engineering handbook

2003 handbook for the faculty of Engineerin

An experimental assessment of computational fluid dynamics predictive accuracy for electronic component operational temperature

Ever-rising Integrated Circuit (IC) power dissipation, combined with reducing product development cycles times, have placed increasing reliance on the use of Computational Fluid Dynamics (CFD) software for the thermal analysis of electronic equipment. In this study, predictive accuracy is assessed for board-mounted electronic component heat transfer using both a CFD code dedicated to the thermal analysis of electronics, Flotherm, and a general-purpose CFD code, Fluent. Using Flotherm, turbulent flow modelling approaches typically employed for the analysis of electronics cooling, namely algebraic mixing length and two-equation high-Reynolds number k-e models, are assessed. As shown, such models are not specific for the analysis of forced airflows over populated electronic boards, which are typically classified as low-Reynolds number flows. The potential for improved predictive accuracy is evaluated using candidate turbulent flow models more suited to such flows, namely a one-equation SpalartAllmaras model, two-layer zonal model and two equation SST k-co model, all implemented in Fluent. Numerical predictions are compared with experimental benchmark data for a range of componentboard topologies generating different airflow phenomena and varying degrees of component thermal interaction. Test case complexity is incremented in controlled steps, from single board-mounted components in free convection, to forced air-cooled, multi-component board configurations. Apart from the prediction of component operational temperature, the application of CFD analysis to the design of electronic component reliability screens and convective solder reflow temperature profiles is also investigated. Benchmark criteria are based on component junction temperature and component-board surface temperature profiles, measured using thermal test chips and infrared thermography respectively. This data is supplemented by experimental visualisations of the forced airflows over the boards, which are used to help assess predictive accuracy. Component numerical modelling is based on nominal package dimensions and material thermal properties. To eliminate potential numerical modelling uncertainties, both the test component geometry and structural integrity are assessed using destructive and non-destructive testing. While detailed component modelling provides the à priori junction temperature predictions, the capability of compact thermal models to predict multi-mode component heat transfer is also assessed. In free convection, component junction temperature predictions for an in-line array of fifteen boardmounted components are within ±5°C or 7% of measurement. Predictive accuracy decays up to ±20°C or 35% in forced airflows using the k-e flow model. Furthermore, neither the laminar or k-e turbulent flow model accurately resolve the complete flow fields over the boards, suggesting the need for a turbulence model capable of modelling transition. Using a k-co model, significant improvements in junction temperature prediction accuracy are obtained, which are associated with improved prediction of both board leading edge heat transfer and component thermal interaction. Whereas with the k-e flow model, prediction accuracy would only be sufficient for the early to intermediate phase of a thermal design process, the use of the k-co model would enable parametric analysis of product thermal performance to be undertaken with greater confidence. Such models would also permit the generation of more accurate temperature boundary conditions for use in Physics-of-Failure (PoF) based component reliability prediction methods. The case is therefore made for vendors of CFD codes dedicated to the thermal analysis of electronics to consider the adoption of eddy viscosity turbulence models more suited to the analysis of component heat transfer. While this study ultimately highlights that electronic component operational temperature needs to be experimentally measured to quality product thermal performance and reliability, the use of such flow models would help reduce the current dependency on experimental prototyping. This would not only enhance the potential of CFD as a design tool, but also its capability to provide detailed insight into complex multi-mode heat transfer, that would otherwise be difficult to characterise experimentally

Online learning of physics during a pandemic: A report from an academic experience in Italy

The arrival of the Sars-Cov II has opened a new window on teaching physics in academia. Frontal lectures have left space for online teaching, teachers have been faced with a new way of spreading knowledge, adapting contents and modalities of their courses. Students have faced up with a new way of learning physics, which relies on free access to materials and their informatics knowledge. We decided to investigate how online didactics has influenced students’ assessments, motivation, and satisfaction in learning physics during the pandemic in 2020. The research has involved bachelor (n = 53) and master (n = 27) students of the Physics Department at the University of Cagliari (N = 80, 47 male; 33 female). The MANOVA supported significant mean differences about gender and university level with higher values for girls and master students in almost all variables investigated. The path analysis showed that student-student, student-teacher interaction, and the organization of the courses significantly influenced satisfaction and motivation in learning physics. The results of this study can be used to improve the standards of teaching in physics at the University of Cagliar

Nanoparticle devices for brain-inspired computing.

The race towards smarter and more efficient computers is at the core of our technology industry and is driven by the rise of more and more complex computational tasks. However, due to limitations such as the increasing costs and inability to indefinitely keep shrinking conventional computer chips, novel hardware architectures are needed. Brain-inspired, or neuromorphic, hardware has attracted great interest over the last decades. The human brain can easily carry out a multitude of tasks such as pattern recognition, classification, abstraction, and motor control with high efficiency and extremely low power consumption. Therefore, it seems logical to take inspiration from the brain to develop new systems and hardware that can perform interesting computational tasks faster and more efficiently. Devices based on percolating nanoparticle networks (PNNs) have shown many features that are promising for the creation of low-power neuromorphic systems. PNN devices exhibit many emergent brain-like properties and complex electrical activity under stimulation. However, so far PNNs have been studied using simple two-contact devices and relatively slow measuring systems. This limits the capabilities of PNNs for computing applications and questions such as whether the brain-like properties continue to be observed at faster timescales, or what are the limits for operation of PNN devices remain unanswered. This thesis explores the design, fabrication, and testing of the first successful multi- contact PNN devices. A novel and simple fabrication technique for the creation of working electrical contacts to nanoparticle networks is presented. Extensive testing of the multi-contact PNN devices demonstrated that electrical stimulation of multiple input contacts leads to complex switching activity. Complex switching activity exhibited different patterns of switching behaviour with events occurring on all contacts, on few contacts, or only on a single contact. The device behaviour is investigated for the first time at microsecond timescales, and it is found that the PNNs exhibit stochastic spiking behaviour that originates in single tunnel gaps and is strikingly similar to that observed in biological neurons. The stochastic spiking behaviour of PNNs is then used for the generation of high quality random numbers which are fundamental for encryption and security. Together the results presented in this thesis pave the way for the use of PNNs for brain-inspired computing and secure information processing