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

We describe an optical chemical sensor using a multi-channel directional coupler with slot waveguides.

Optical chemical sensor using a multi-channel directional coupler with slot waveguides

A simplified uplink communication scheme for millimeter-wave (mm-wave) radio-over-fiber system employing RF self-homodyning at the base station (BS) is proposed and experimentally demonstrated. The proposed scheme establishes a simple low-speed data transmission from the BS to the central station and simplifies the BS and uplink optical transport by removing most of the required high speed optoelectronic and RF devices.

Simplification of base station and uplink optical transport in millimeter-wave radio-over-fiber system employing RF self-homodyning

This paper presents a new shoot-through control method applicable for an impedance source galvanically isolated DC/DC converter. In impedance source converters, the introduction of shoot-through states increases the switching speed of H-bridge switches about two to three times the switching frequency. This approach reduces the switching transient of all switches of inverters by commutating them once in a switching cycle. The shoot-through states are generated by alternatively switching the single leg of the inverter whereas, in baseline modulation approach, all the switches are turned on during shoot-through states. This method decreases the switching loss of front-end converters and independent controllability of active and shoot through states. This modulation technique is applied and validated to a voltage-feed Quasi-Z source isolated DC-DC converter with a voltage doubling rectifier.

A new PWM Shoot-through control for voltage-fed quasi-z-source DC/DC converters

The Maxwell-Garnett and Bruggeman effective medium models are extended to a total differential model to predict differential changes in the optical properties of polymer nanocomposites in response to external influences. A Mie scattering model was used to model the transmission properties of these materials.

Total differential optical properties of polymer nanocomposite materials

A compact quasi-Z-source DC/DC converter is presented with high voltage gain, isolated output, and improved efficiency. The improvements in size and performance were achieved by using a square wave inverter with only two output switches driving an isolating transformer in push-pull mode, followed by a voltage doubling output rectifier. The converter is well-suited to applications requiring a high voltage gain, especially renewable energy sources such as photovoltaic and fuel-cell power supplies. To demonstrate the converter's performance a prototype designed to output 400 V at 500 W was constructed and tested. The efficiency at full load varied from 89.0% to 97.4% as the input voltage changed from 44 V to 82 V.

Graham Town

Papers

Optical chemical sensor using a multi-channel directional coupler with slot waveguides

Simplification of base station and uplink optical transport in millimeter-wave radio-over-fiber system employing RF self-homodyning

A new PWM Shoot-through control for voltage-fed quasi-z-source DC/DC converters

Total differential optical properties of polymer nanocomposite materials

A high voltage gain quasi Z-source isolated DC/DC converter