Widely tunable terahertz semiconductor laser sources

Terahertz Quantum Cascade Lasers (THz QCLs) and Terahertz Difference Frequency Generation Quantum Cascade Laser sources (DFG-QCLs) are two types of semiconductor THz radiation sources that are compact and amenable to production in mass quantities. THz QCL can generate over 1W of power under cryogenic temperatures, while THz DFG-QCL can be operated under room temperature over 1mW level output. For either case, widely tunable solution is highly desired for spectroscopy applications. For THz QCLs, operation is still limited to cryogenic temperature and broad tuning is not available. Our experimental study shows that using variable barriers is a viable approach to enhance the design space for THz QCLs. We also propose to tune the spectral output of these devices using an optically projected variable distributed feedback grating. Tuning will be achieved by changing the projected grating period. Preliminary experimental results support the idea but higher pumping light intensity is required for this method to work. For THz DFG-QCLs, very broad tuning in 1-6 THz range has been demonstrated using rotating diffraction grating in an external cavity setup. Similar tuning range can also be achieved in a monolithic configuration. Based on the previous work which demonstrated an electrical monolithic tuner with 580 GHz tuning range, we design and test in this dissertation a linear array of 10 DFG-QCL devices to cover a 2 THz tuning range. An independent gain control scheme is developed to achieve high yield (~100%) of individual device. It is implemented via independent current pumping of two electrically isolated sections. Surface DFB grating and independent current pumping scheme used in our DFG QCLs is found to be useful for mid-IR QCL array sources. We propose a longitudinal integration scheme of multiple grating sections. It enables a single ridge to emit single mode radiation at different wavelengths upon selection. This helps to reduce mid-IR QCL array far field span. We demonstrated single ridge devices that can emit 2 or 3 different wavelengths upon selection.Electrical and Computer Engineerin

Mid-infrared quantum cascade laser arrays with electrical switching of emission frequencies

We present a design of quantum cascade laser arrays made of ridge-waveguide devices in which the emission frequency can be electrically switched between several specified values. Our approach relies on fabricating multiple independently-biased distributed feedback grating sections along the laser ridge waveguides. Switchable single-mode lasing from the laser facet is achieved by balancing the injection pumping of the different grating sections. Our method provides a robust solution that can increase the tuning bandwidth of the quantum cascade laser arrays without increasing the size of the array emission aperture

Differential privacy in edge computing-based smart city Applications:Security issues, solutions and future directions

Fast-growing smart city applications, such as smart delivery, smart community, and smart health, are generating big data that are widely distributed on the internet. IoT (Internet of Things) systems are at the centre of smart city applications, as traditional cloud computing is insufficient for satisfying the critical requirements of smart IoT systems. Due to the nature of smart city applications, massive IoT data may contain sensitive information; hence, various privacy-preserving methods, such as anonymity, federated learning, and homomorphic encryption, have been utilised over the years. Furthermore, limited concern has been given to the resource consumption for data privacy-preserving in edge computing environments, which are resource-constrained when compared with cloud data centres. In particular, differential privacy (DP) has been an effective privacy-preserving method in the edge computing environment. However, there is no dedicated study on DP technology with a focus on smart city applications in the edge computing environment.To fill this gap, this paper provides a comprehensive study on DP in edge computing-based smart city applications, covering various aspects, such as privacy models, research methods, mechanisms, and applications. Our study focuses on five areas of data privacy, including data transmitting privacy, data processing privacy, data model training privacy, data publishing privacy, and location privacy. In addition, we investigate many potential applications of DP in smart city application scenarios. Finally, future directions of DP in edge computing are envisaged. We hope this study can be a useful roadmap for researchers and practitioners in edge computing enable smart city applications

Prolonged vs intermittent intravenous infusion of β-lactam antibiotics for patients with sepsis: a systematic review of randomized clinical trials with meta-analysis and trial sequential analysis

Abstract Background The prolonged β-lactam antibiotics infusion has been an attractive strategy in severe infections, because it provides a more stable free drug concentration and a longer duration of free drug concentration above the minimum inhibitory concentration (MIC). We conducted this systematic review of randomized clinical trials (RCTs) with meta-analysis and trial sequential analysis (TSA) to compare the effects of prolonged vs intermittent intravenous infusion of β-lactam antibiotics for patients with sepsis. Methods This study was prospectively registered on PROSPERO database (CRD42023447692). We searched EMBASE, PubMed, and Cochrane Library to identify eligible studies (up to July 6, 2023). Any study meeting the inclusion and exclusion criteria would be included. The primary outcome was all-cause mortality within 30 days. Two authors independently screened studies and extracted data. When the I 2 values < 50%, we used fixed-effect mode. Otherwise, the random effects model was used. TSA was also performed to search for the possibility of false-positive (type I error) or false-negative (type II error) results. Results A total of 4355 studies were identified in our search, and nine studies with 1762 patients were finally included. The pooled results showed that, compared with intermittent intravenous infusion, prolonged intravenous infusion of beta-lactam antibiotics resulted in a significant reduction in all-cause mortality within 30 days in patients with sepsis (RR 0.82; 95%CI 0.70–0.96; P = 0.01; TSA-adjusted CI 0.62–1.07). However, the certainty of the evidence was rated as low, and the TSA results suggested that more studies were needed to further confirm our conclusion. In addition, it is associated with lower hospital mortality, ICU mortality, and higher clinical cure. No significant reduction in 90-day mortality or the emergence of resistance bacteria was detected between the two groups. Conclusions Prolonged intravenous infusion of beta-lactam antibiotics in patients with sepsis was associated with short-term survival benefits and higher clinical cure. However, the TSA results suggested that more studies are needed to reach a definitive conclusion. In terms of long-term survival benefits, we could not show an improvement

Nonlinear optics with quantumengineered intersubband metamaterials

Intersubband transitions in n-doped semiconductor heterostructures provide the possibility to quantum engineer one of the largest known nonlinear optical responses in condensed matter systems, limited however to electric field polarized normal to the semiconductor layers. Here we show that by coupling of electromagnetic modes in plasmonic metasurfaces with quantum-engineered intersubband transitions in semiconductor heterostructures one can create ultra-thin highlynonlinear metasurfaces for normal light incidence. Structures discussed here represent a novel kind of hybrid metalsemiconductor metamaterials in which exotic optical properties are produced by coupling electromagneticallyengineered modes in dielectric and plasmonic nanostructures with quantum-engineered intersubband transitions in semiconductor heterostructures. Record values of effective optical nonlinearities of over 400 nm/V are experimentally measured for metasurfaces optimized for efficient second harmonic generation at 9.7 ??m pump wavelength under normal incidence

A Low-Leakage Epitaxial High‑κ Gate Oxide for Germanium Metal–Oxide–Semiconductor Devices

Germanium (Ge)-based metal–oxide–semiconductor field-effect transistors are a promising candidate for high performance, low power electronics at the 7 nm technology node and beyond. However, the availability of high quality gate oxide/Ge interfaces that provide low leakage current density and equivalent oxide thickness (EOT), robust scalability, and acceptable interface state density (<i>D</i>_it) has emerged as one of the most challenging hurdles in the development of such devices. Here we demonstrate and present detailed electrical characterization of a high-κ epitaxial oxide gate stack based on crystalline SrHfO₃ grown on Ge (001) by atomic layer deposition. Metal–oxide–Ge capacitor structures show extremely low gate leakage, small and scalable EOT, and good and reducible <i>D</i>_it. Detailed growth strategies and postgrowth annealing schemes are demonstrated to reduce <i>D</i>_it. The physical mechanisms behind these phenomena are studied and suggest approaches for further reduction of <i>D</i>_it