Thas Nirmalathas

Provision of Independent Services in WDM-Passive Optical Networks using Closely Separated Dual Baseband Channels

We demonstrate a simple scheme for the generation and separation of two independent high bandwidth baseband optical channels using a single laser and modulator for provision of independent services in WDM passive optical networks.

All-Graphene Planar Double-Quantum-Dot Resonant Tunneling Diodes

This paper proposes a new class of resonant tunneling diodes (RTDs) that are planar and realizable with a single graphene nanoribbon. Unlike conventional RTDs, which incorporate vertical quantum well regions, the proposed devices incorporate two confined planar quantum dots within the single graphene nanoribbon, giving rise to a pronounced negative differential resistance (NDR) effect. The proposed devices, termed here as planar double-quantum-dot RTDs, and their transport properties are investigated using quantum simulations based on nonequilibrium Greens function formalism and the extended Huckel method. The proposed devices exhibit a unique current-voltage waveform consisting of a single pronounced current peak with an extremely high, in the order of 104, peak-to-valley ratio. The position of the current peak can be tuned between discrete voltage levels, allowing digitized tunability, which is exploited to realize multi-peak NDR devices.

Wavelength Reuse Scheme for Source Free Optical Network Units in WDM Passive Optical Networks

We demonstrate a wavelength reuse scheme facilitated through sub-carrier downstream transmission that achieves source free optical network units in a WDM-PON. The scheme only requires baseband detection for both downstream and upstream data recovery.

A Geographic Primitive-Based Bayesian Framework to Predict Cyclone-Induced Flooding*

AbstractThe effectiveness of managing cyclone-induced floods is highly dependent on how fast reasonably accurate predictions can be made, which is a particularly difficult task given the multitude of highly variable physical factors. Even with supercomputers, collecting and processing vast amounts of data from numerous asynchronous sources makes it challenging to achieve high prediction efficiency. This paper presents a model that combines prior knowledge, including rainfall data statistics and topographical features, with any new precipitation data to generate a probabilistic prediction using Bayesian learning, where the advantages of data-oriented and heuristic modeling are combined. The terrain is partitioned into geographic primitives (GPs) based on manual inspection of flood propagation vector fields in order to simplify the stochastic system identification. High calculation efficiency is achieved through statistically summarizing simultaneous events spread across geography into primitives, allowing ...

Natural Disasters, When Will They Reach Me?

The expected time of impact, also known as the mean first passage time (MFPT) to reach failure, is a criticalmetricin the management of natural disasters. The complexity of the dynamics governing natural disasters lead to stochastic behaviour. This book shows that state transitions of many such systems translate into random walks on their respective state spaces, biased and shaped by environmental inhomogeneity. Thus the probabilistic treatment of those random walks gives valuable insights of expected behaviour. A comprehensive case study of predicting cyclone induced flood is followed by a discussion of generic methods that predict MFPT addressing directional bias. This is followed by discussing MFPT prediction methods in systems showing network inhomogeneity. All presented methods are illustrated using real datasets of natural disasters. The book ends with a short discussion of possible future research areas introducing the problem of predicting MFPT for bush-fire propagation.

Performance of Planar, Rib, and Photonic Crystal Silicon Waveguides in Tailoring Group-Velocity Dispersion and Mode Loss

Nanophotonic technologies have attracted a lot of attention to co-develop optical and electronic devices on silicon (Si) that further miniaturize modern optical communication systems. Optical properties of these miniaturized devices are highly dependent on waveguide geometry and can be tailored for various applications with minor changes in cross-sectional areas. This paper investigates the performance of widely discussed planar, rib, and photonic crystal Si waveguides by manipulating the dimensions of Si core designed for single mode operation across the 1.2 to 1.6 μm telecommunication bands. Each of the waveguide is studied and compared for a set of properties, including effective refractive index, group index, group-velocity dispersion, and mode loss, with and without narrow bends, which can be instrumental in selecting the correct type and geometry of the waveguide required for any specific application.

A computationally efficient framework for stochastic prediction of flood propagation

This paper presents a computationally efficient method to forecast floods stochastically. The main purpose of the method is to encapsulate prior knowledge as off-line calculations leading to earliest possible warnings. The computational efficiency is improved through exploiting the stereotypical features of hydrology and its dependence on topography by combining the parallel water-flow processes into parallel calculation through a probability transition matrix. Efficiency is improved further with the use of properties of Markov matrices in the general equation of the model. Extensive simulations on real rainfall data over parts of Queensland, Australia, during January 2012, revealed that this method was capable of improving the calculation efficiency by over 18 times with respect to gradient based calculations.

Ultra Dense WDM Passive Optical Network based on RSOAs Facilitated through a Simple and Stable Seeding Source

We propose a simple and stable seeding source that enables ultra dense WDM-PON based on injection locking devices and for the first time experimentally demonstrate a 12.5 GHz channel spaced DWDM-PON with 1.25 Gb/s transmission.

Characterization of geometry and depleting carrier dependence of active silicon waveguide in tailoring optical properties

Changes in refractive index and the corresponding changes in the characteristics of an optical waveguide in enabling propagation of light are the basis for many modern silicon photonic devices. Optical properties of these active nanoscale waveguides are sensitive to the little changes in geometry, external injection/biasing, and doping profiles, and can be crucial in design and manufacturing processes. This paper brings the active silicon waveguide for complete characterization of various distinctive guiding parameters, including perturbation in real and imaginary refractive index, mode loss, group velocity dispersion, and bending loss, which can be instrumental in developing optimal design specifications for various application-centric active silicon waveguides.

Indoor infrared optical wireless localization system with background light power estimation capability

The indoor user localization function is in high demand for high-speed wireless communications, navigations and smart-home applications. The optical wireless technology has been used to localize end users in indoor environments. However, its accuracy is typically very limited, due to the ambient light, which is relatively strong. In this paper, a novel high-localization-accuracy optical wireless based indoor localization system, based on the use of the mechanism that estimates background light intensity, is proposed. Both theoretical studies and demonstration experiments are carried out. Experimental results show that the accuracy of the proposed optical wireless indoor localization system is independent on the localization light strength, and that an average localization error as small as 2.5 cm is attained, which is 80% better than the accuracy of previously reported optical wireless indoor localization systems.