There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

A topical review of numerical and experimental studies of supercontinuum generation in photonic crystal fiber is presented over the full range of experimentally reported parameters, from the femtosecond to the continuous-wave regime. Results from numerical simulations are used to discuss the temporal and spectral characteristics of the supercontinuum, and to interpret the physics of the underlying spectral broadening processes. Particular attention is given to the case of supercontinuum generation seeded by femtosecond pulses in the anomalous group velocity dispersion regime of photonic crystal fiber, where the processes of soliton fission, stimulated Raman scattering, and dispersive wave generation are reviewed in detail. The corresponding intensity and phase stability properties of the supercontinuum spectra generated under different conditions are also discussed.

Supercontinuum generation in photonic crystal fiber

This Review explains the concept of dissipative solitons and their application to high-energy mode-locked fibre laser cavities. Dynamics and effects such as dissipative soliton ‘explosions’ and ‘rain’ are summarized, and an outlook of the field is also provided.

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Dissipative solitons for mode-locked lasers

DC–DC converters with voltage boost capability are widely used in a large number of power conversion applications, from fraction-of-volt to tens of thousands of volts at power levels from milliwatts to megawatts. The literature has reported on various voltage-boosting techniques, in which fundamental energy storing elements (inductors and capacitors) and/or transformers in conjunction with switch(es) and diode(s) are utilized in the circuit. These techniques include switched capacitor (charge pump), voltage multiplier, switched inductor/voltage lift, magnetic coupling, and multistage/-level, and each has its own merits and demerits depending on application, in terms of cost, complexity, power density, reliability, and efficiency. To meet the growing demand for such applications, new power converter topologies that use the above voltage-boosting techniques, as well as some active and passive components, are continuously being proposed. The permutations and combinations of the various voltage-boosting techniques with additional components in a circuit allow for numerous new topologies and configurations, which are often confusing and difficult to follow. Therefore, to present a clear picture on the general law and framework of the development of next-generation step-up dc–dc converters, this paper aims to comprehensively review and classify various step-up dc–dc converters based on their characteristics and voltage-boosting techniques. In addition, the advantages and disadvantages of these voltage-boosting techniques and associated converters are discussed in detail. Finally, broad applications of dc–dc converters are presented and summarized with comparative study of different voltage-boosting techniques.

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Step-Up DC–DC Converters: A Comprehensive Review of Voltage-Boosting Techniques, Topologies, and Applications

The Internet of Things (IoT) is the next era of communication. Using the IoT, physical objects can be empowered to create, receive, and exchange data in a seamless manner. Various IoT applications focus on automating different tasks and are trying to empower the inanimate physical objects to act without any human intervention. The existing and upcoming IoT applications are highly promising to increase the level of comfort, efficiency, and automation for the users. To be able to implement such a world in an ever-growing fashion requires high security, privacy, authentication, and recovery from attacks. In this regard, it is imperative to make the required changes in the architecture of the IoT applications for achieving end-to-end secure IoT environments. In this paper, a detailed review of the security-related challenges and sources of threat in the IoT applications is presented. After discussing the security issues, various emerging and existing technologies focused on achieving a high degree of trust in the IoT applications are discussed. Four different technologies, blockchain, fog computing, edge computing, and machine learning, to increase the level of security in IoT are discussed.

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A Survey on IoT Security: Application Areas, Security Threats, and Solution Architectures

The current model of centralized electricity generation, transmission and distribution is under pressure to change for a variety of reasons; environmental concerns are driving a shift away from large coal-fired generation systems to increasing adoption of renewable energy sources, which tend to be distributed and not always available on demand, and hence requiring distributed storage support. Moreover, to support electric vehicles, energy needs to be provided as a service to consumers independent of location, rather than a product delivered and billed to a fixed location. In this work, we compare and contrast modern internet and energy networks and services, identifying key functionalities and the main technical challenges to be faced in transforming the electricity distribution system to a flexible yet reliable and robust platform for the exchange of electrical energy.

Towards an internet of energy

A dual wavelength actively modelocked erbium-doped fiber laser was constructed which generated pulses approximately 50 ps long with repetition rate 2.6 GHz at both 1544.1 nm and 1545.7 nm. The laser cavity incorporated a pair of dispersive gratings to produce temporal-spectral multiplexing of the pulses in the gain medium, which was observed to reduce cross-saturation effects.

Dual wavelength modelocked fiber laser

Range anxiety is an obstacle to the acceptance of electric vehicles (EVs), caused by drivers’ uncertainty regarding their vehicle's state of charge (SoC) and the energy required to reach their destination. Most estimation methods for these variables use simplified models with many assumptions that can result in significant error, particularly if dynamic and environmental conditions are not considered. For example, the combined efficiency of the inverter drive and electric motor varies throughout the route and is not constant as assumed in most range estimation methods. This study proposes an improved method for SoC and range estimation by taking into account location-dependent environmental conditions and time-varying drive system losses. To validate the method, an EV was driven along a selected route and the measured EV battery SoC at the destination was compared with that predicted by the algorithm. The results demonstrated excellent accuracy in the SoC and range estimation, which should help alleviate range anxiety.

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Accurate range estimation for an electric vehicle including changing environmental conditions and traction system efficiency

We report the demonstration of compact fluidic fibre lasers based on capillary tubes and photonic crystal fibres, featuring single channel and multiple laterally integrated fluidic lasers respectively. Their preparation was based on capillary action and lasing occurred without the need for external mirrors or lithographically defined microstructures. The fibre lasers were found to be tunable by varying the chromophore density in the liquid core and a functional wavelength selectivity mechanism inherent in both types of lasers provided a long free spectral range that does not correspond to the length of the fibres. The enhanced mode spacing is attributed to a Vernier resonant effect.

Fluidic fibre dye lasers

We characterize the soliton-train emission from an Er–Yb-doped fiber loop laser. We discuss the self-starting dynamics and pulse-repetition-rate control in this sliding-frequency soliton laser. We show that the laser truly self-starts after only one cavity round trip. In the steady state the laser emits a closely spaced train of solitons. We also show that the output pulse width may be controlled by the interplay of continuous frequency shifting, bandwidth-limited amplification, and nonlinear polarization rotation of the circulating solitons. The repetition rate is fixed by means of a weak intracavity feedback. The laser is tunable by shifting of the filter wavelength through the whole spectral band of the active fiber.

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Graham Town

Papers

Towards an internet of energy

Dual wavelength modelocked fiber laser

Accurate range estimation for an electric vehicle including changing environmental conditions and traction system efficiency

Fluidic fibre dye lasers

Tunable erbium-ytterbium fiber sliding-frequency soliton laser