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.

/pdf/dissipative-solitons-for-mode-locked-lasers-1fudg0a89g.pdf

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.

/pdf/step-up-dc-dc-converters-a-comprehensive-review-of-voltage-6dlytctzg2.pdf

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.

/pdf/a-survey-on-iot-security-application-areas-security-threats-1gb31j78px.pdf

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

Linear Bragg grating resonators have recently been attracting much attention as the search for fibre compatible transmission filters continues. However, these structures are limited to applications that require only narrow stopbands. There remains applications that would benefit from the availability of broader bandwidth filters; either multi-passband or single passband. With that in mind an investigation into the feasibility of fabricating chirped Bragg grating resonators ensued. Two types of chirped resonator structures have been considered: Fabry-Perot and Moire gratings. The Fabry-Perot resonators comprise of two chirped gratings displaced by some distance along the length of the fibre. The Moire gratings comprise again of two chirped gratings but where the gratings are written directly on top of each other in the fibre one grating is shifted slightly in wavelength.

https://ieeexplore.ieee.org/iel3/3420/10086/00478113.pdf

Efficient fibre grating transmission filters

Gallium Nitride (GaN) HEMTs have increasingly been used in high frequency switching power converters. The combination of high voltage, high current, high temperature and low-on resistance enables higher efficiency and lower form factor as compared to Silicon devices. FET switch operate in the linear ohmic region. However, the presence of trap centres in GaN HEMTs alter the on-resistance and shifts the threshold voltage, causing current collapse and degrades the efficiency. Pulsed I-V measurements of a commercial foundry GaN MMIC HEMT revealed drain current collapse and on-resistance modulation in the ohmic region of the HEMT loadline. A trap model based on SRH theory was used to characterize trapping effects that alter the drain current in the linear region of operation.

SRH based trap model for GaN MMIC power switches

Microstructured polymer optical fiber was fabricated in which bubbles were randomly distributed in the cladding to both guide and scatter light. The effect of fabrication conditions on the fiber structure and properties is discussed.

Fabrication conditions for randomly microstructured polymer optical fibers

Ultrafast optical pulse-code generation was demonstrated using an optical fibre Bragg grating. Single 1.8 ps input pulses were converted into a train of output pulses separated by 21.5 ps, each with controlled amplitude, representing a digital codeword.

Graham Town

Papers

Efficient fibre grating transmission filters

SRH based trap model for GaN MMIC power switches

Fabrication conditions for randomly microstructured polymer optical fibers

Optical pulse code generation using optical fibre gratings

Electric vehicles in the grid – intermittent storage balancing intermittent generation