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A continue wave of high-speed vertical-cavity surface-emitting lasers (VCSELs) for 980 nm short-reach communication is presented. The design of such devices is based on five strained InGaAs/GaAsP quantum wells QWs that enclosed between 20.5-periods p-doped top and 37-periods n-doped bottom epitaxially grown AlGaAs/GaAs distributed Bragg reflectors. VCSEL with current flow apertures of different area is fabricated and characterized at a range oxide aperture diameters ∅ ~ 6 to 19 μm. These devices essentially used for improving the output optical power and exhibiting high modulation bandwidth at room temperature (RT). Experimental results of output light–current–voltage at threshold currents as low as 0.45 mA, together with the threshold current, current density, maximum power and maximum wall blug efficiency as a function of oxide aperture diameter at various temperature, are achieved. Optical spectra and small-signal analysis are performed for different bias currents (I) and oxide aperture diameters (∅) in a wide range of temperatures. A small-signal modulation bandwidth (f-3dB) around 24 GHz is reached with ∅ ~ 6 μm when I ~ 5.5 mA at RT of T ~ 25 °C. [ABSTRACT FROM AUTHOR]

The demand for innovative and cost-effective in-situ consolidation technologies in soft clay stimulated the effort to employ electrokinetic phenomena in soils under an electric field. This work explains the principles of electrophoresis and electroosmosis in soft clay under an electric field and discusses the implacations of these results for field implementation of the technique. The experimental work reported here was carried out to shed light on the principles by considering various influencing factors. The results show that there is a threshold current (about 15 mA) for electroosmosis and electrophoresis in soft clay. Below the threshold current, electrophoresis plays a major role and is accompanied by weak electroosmosis. The particle size, dry density, and boundary rise height of electrophoretic soil in anode chamber are mainly affected by soil moisture content, electrode in electrolyte length, and bottom of electrode to soil surface distance. The closer the soil moisture content is to the average value of the liquid limit and plastic limit, the denser the electrophoretic soil will be. Above the threshold current, almost only electroosmosis occurs. The greater the current, the greater the electroosmosis. In practical engineering application, electrodes are usually directly inserted into the soft clay. This results in the current usually being much greater than the threshold current, meaning the electrophoretic phenomenon in the soil can be negligible.

When a fault occurs on the transmission line, the relay should send the faulty signal to the circuit breaker to trip or isolate the line. Timely detection is integral to fault protection and the management of transmission lines in power systems. This paper focuses on using the threshold current and voltage to reduce the time of delay and trip time of the instantaneous overcurrent relay protection for a 330 kV transmission line. The wavelet transforms toolbox from MATLAB and a Simulink model were used to design the model to detect the threshold value and the coordination time for the backup relay to trip if the primary relay did not operate or clear the fault on time. The difference between the proposed model and the model without the threshold value was analysed. The simulated result shows that the trip time of the two relays demonstrates a fast and precise trip time of 60% to 99.87% compared to other techniques used without the threshold values. The proposed model can eliminate the trial-and-error in programming the instantaneous overcurrent relay setting for optimal performance.

In this paper, a diode laser design method based on optimization of the thickness and material composition of the quantum well (QW) in order to achieve the minimum current threshold and maximum output optical power is introduced. In the proposed structure, an asymmetric waveguide structure was used to control the confinement factor and decrease free carrier loss. The laser design, operating at 808 nm, was optimized by using a 10 nm Al0.126Ga0.774In0.1As for the QW and a 900 nm Al0.4Ga0.6As for the waveguide (WG). The experimental results show that the optical power can be enhanced effectively with the proposed structure. The experimental results also show the slope efficiency in 1 mm cavity length is improved sufficiently to a value of 1.36 W/A. Furthermore, the present QW structure provides internal quantum efficiency and internal loss of 0.93 and 0.38 cm−1, respectively. [ABSTRACT FROM AUTHOR]

In edge-emitting high power laser diodes, the longitudinal spatial hole burning (LSHB) effect induced by the inhomogeneous photon and carrier distributions and the non-linear process, two-photon absorption (TPA), are demonstrated to the key causes of power saturation at the high injection level even in the absence of thermal roll-over. Laser diodes based on extreme, double/triple asymmetric (EDAS/ETAS) epitaxial structures show great potentials in high-power and high-efficiency applications owing to the reduced series resistance, low optical loss, and suppressed power saturation. In this paper, a novel semi-analytical calculation method is proposed to systematically analyze the impact of LSHB and TPA effects on the output characteristics of EDAS/ETAS-based broad area lasers (BALs). By leveraging the feature that it is flexible to adjust the confinement factor of ETAS epitaxial structure without compromising the internal loss and resistance level, the laser parameters are first optimized to minimize power saturation of ETAS-based BALs under pulsed and Continuous Wave (CW) operation. [ABSTRACT FROM AUTHOR]

Design rules are proposed for UVA vertical-cavity surface-emitting laser diodes, and the modal gain and cavity properties are analyzed using an electro-optical numerical model. To achieve a low threshold current, it is important to align the gain-peak and resonance wavelengths, but the quantum-confined Stark effect makes that difficult because the former wavelength shifts with changing current density. The relationship between the gain peak and the injection current is discussed. Also, the quantum-well design affects the gain characteristics, and the gain properties with different quantum-well number, composition, and width are discussed. [ABSTRACT FROM AUTHOR]

Monolithic multi-wavelength VCSEL arrays, with wavelengths of individual VCSELs precisely set in a post-epitaxial growth process, would enable compact multi-color light sources and transmitters for various sensing and datacom applications. Here we report on a numerical study of the requirements of spectral matching and balancing of DBR reflectances, optical confinement factor, and optical gain for uniformity of threshold current and slope efficiency over wavelength with wavelength set by intra-cavity phase tuning. The requirements are verified by an experimental demonstration of intra-cavity phase tuned VCSELs in the spectral range 1043–1067 nm with a wavelength spacing of 8 ± 1 nm enabled by precise Ar ion-beam etching. Small variations of threshold current and slope efficiency are achieved by close to ideal spectral matching and balancing. The VCSELs are GaAs-based with a dielectric SiO2/TiO2 top-DBR. We conclude that high uniformity of threshold current and slope efficiency is demanding in terms of spectral matching and balancing and requires not only very precise etching for intra-cavity phase tuning and precise thickness of the layers in the dielectric top-DBR, but also precise thickness and composition of the layers in the epitaxial semiconductor part. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the effects of variation of thickness and the number of quantumwells as well as the contact length were investigated. In this paper, a vertical cavity surfaceemitting laser was simulated using of software based on finite element method. Thenumber of quantum wells was changed from 3 to 9 and the results which are related tooutput power, resonance wavelength and threshold current were extracted. Outputspecifications in terms of quantum wells thicknesses of 3.5nm to 9.5nm were evaluated.Contact thickness is also changed from 0.5μm to 3μm. Results showed that as the numberof quantum wells increased, the resonance wavelength also increased and photon energydecreased. By reducing the thickness of the quantum well, the threshold current andradiation wavelength were also decreased. By increasing the contact length, thresholdcurrent and output power increased. Temperature inside the network and density ofphoton were increased as the contact length increased

To meet the rising demand for a high-speed and power-efficient optical link for cryogenic data operation, we report a 6.8- $\mu \text{m}$ oxide-aperture VCSEL with a record bandwidth ≥50 GHz at cryogenic temperatures. A high-speed packaged oxide-VCSEL demonstrates optical data transmission capability from 12.5 to 44 Gb/s NRZ and 51.56 Gb/s PAM-4 at 77K. [ABSTRACT FROM AUTHOR]

The multi-mode vertical-cavity surface-emitting lasers (MM-VCSELs) with different photonic crystal (PhC) designs in core and cladding regions are compared for transmitting the complex formatted QAM-OFDM data over 100-m OM5 multi-mode fiber (MMF). Among the designs with using flat core/cladding (denoting as Coreflat/Cladflat) and/or PhC core/cladding (denoting as Corephc/Cladphc) for the MM-VCSEL, the Coreflat+Cladflat VCSEL with the highest threshold current and large emission aperture provides the highest differential quantum efficiency of 0.11 and output power of 2 mW, whereas the Coreflat+Cladphc2 VCSEL with two periods of cladding PhC reveals the lowest threshold current of 2 mA, the highest modulation bandwidth of 15 GHz, the lowest relative intensity noise peak of -126 dBc/Hz and background level of -143 dBc/Hz. After pre-compensation, the Coreflat+Cladphc2 VCSEL chip can achieve the highest OFDM bandwidth of 18 GHz for 72-Gbit/s transmission in the BtB case. With additionally adding 1 period of core PhC, the Corephc1+Cladphc2 VCSEL possesses a single-mode lasing spectrum to facilitate the suppression of modal dispersion after MMF propagation. Hence, the Corephc1+Cladphc2 VCSEL exhibits the same bit rate of 60 Gbit/s as compared to the Coreflat+Cladphc2 VCSEL after 100-m OM5-MMF. After improving the analog bandwidth for waveform synthesis, the data rate of Coreflat+Cladphc2 VCSEL can successfully deliver 76-Gbit/s and 72-Gbit/s single-band 16-QAM OFDM data streams for BtB and 100-m OM5 MMF conditions via the pre-leveling technology. To date, the ultimate raw data rate achieves 92-Gbit/s with employing the multi-band QAM-OFDM data format. [ABSTRACT FROM AUTHOR]

Designing of single-mode ZnO nanowire laser has been achieved. Studying its properties has also been considered. Analysis of single-mode rate equations indicates that the laser has threshold current of 53 mA, the output power of 30 mW at bias current of 70 mA and the slope efficiency around 1.77 mW/mA for the output power from both mirrors. The critical diameter for nanowire has been calculated and it is found to be 128 nm. The number of nanowire rods through designed area of dimensions (21µm×21µm) has also been calculated. The cavity of nanowire laser is (F-P). The results are compared with some experimental work of ZnO nanowire lasers and good agreement is found.

The splitting and threshold currents of vacuum arc cathode spots in axial magnetic fields (AMFs) up to 220 mT are investigated experimentally. Measurements are made on electrodes of Cu and CuCr25 with electrode separations of 2 and 6 mm. The electrode diameter is 30 mm. All the experiments are conducted in a demountable vacuum chamber evacuated continuously by a turbo-molecular pump to a pressure of the order of 10−3 Pa. The spots are photographed using a high-speed digital camera with an exposure time of 2 μs. The AMF is applied by means of two permanent magnets placed symmetrically inside the chamber. The experimental results indicate that the splitting and threshold current decrease in the presence of AMF and tend to certain constant values when the field gets stronger. The splitting and threshold currents are considerably larger than Cu electrodes than those with CuCr25 electrodes. With increasing electrode separation, the splitting current decreases while the threshold current increases. Possible explanations are proposed to account for the experimental observations. [ABSTRACT FROM AUTHOR]

This work deals with the modeling and simulation of quantum well lasers based on a heterostructure formed by indium gallium antimonide (InGaSb) and gallium antimonide (GaSb). The objective is to study the feasibility of a laser operating continuously in the near infrared for applications in the detection of polluting gases. Important device parameters such as the optical gain and threshold current density are investigated in detail. The results show that the optical gain is close to 4000 cm−1 and tends to increase with the carrier density in the active region but decreases with temperature and the quantum well thickness. The dependence of the laser threshold current density on the optical losses and temperature is also evaluated. [ABSTRACT FROM AUTHOR]

The output characteristics of vertical cavity surface emitting lasers (VCSELs) arrays are largely influenced by temperature. We systematically studied thermal properties in 20-element oxide-confined VCSEL arrays via both theory and experiment. The output power, conversion efficiency, and threshold current dependent on ambient temperatures were measured. According to the relationship of wavelength shift and dissipated power, the device thermal resistance dependent on ambient temperature was obtained. The actual temperature in active region was successfully extracted. A 3-D heat diffusion model was established to simulate temperature distribution accurately. [ABSTRACT FROM AUTHOR]

This paper presents a generic SPICE model for threshold current controlled memristive devices. This work relates to mathematical development to allow this kind of behavior and it exhibits its relationship with the equivalent circuit adopted to achieve this goal. The operating logic is described and the code for its computational implementation is presented and explained. The functionality of the model implemented is demonstrated through several simulation experiments, whose results clearly show the switching resistance dependency on the electrical current through the device and highlight some important fingerprints of memristive devices. The acquisition and the data analysis from tests also help to prove the excellent convergence performance of the model presented and to elucidate the parameter settings. Finally, the paper reinforces the relevance of this new proposition by addressing one of its potential applications, demonstrating its use in the implementation of memristive stateful logic based on material implication. [ABSTRACT FROM AUTHOR]

The demand for innovative and cost-effective in-situ consolidation technologies in soft clay stimulated the effort to employ electrokinetic phenomena in soils under an electric field. This work explains the principles of electrophoresis and electroosmosis in soft clay under an electric field and discusses the implacations of these results for field implementation of the technique. The experimental work reported here was carried out to shed light on the principles by considering various influencing factors. The results show that there is a threshold current (about 15 mA) for electroosmosis and electrophoresis in soft clay. Below the threshold current, electrophoresis plays a major role and is accompanied by weak electroosmosis. The particle size, dry density, and boundary rise height of electrophoretic soil in anode chamber are mainly affected by soil moisture content, electrode in electrolyte length, and bottom of electrode to soil surface distance. The closer the soil moisture content is to the average value of the liquid limit and plastic limit, the denser the electrophoretic soil will be. Above the threshold current, almost only electroosmosis occurs. The greater the current, the greater the electroosmosis. In practical engineering application, electrodes are usually directly inserted into the soft clay. This results in the current usually being much greater than the threshold current, meaning the electrophoretic phenomenon in the soil can be negligible., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors.)

We discuss the effect of self-heating on performance of injection microdisk lasers operating in continuous-wave (CW) regime at room and elevated temperature. A model is developed that allows one to obtain analytical expressions for the peak optical power limited by the thermal rollover effect, the corresponding injection current and excess temperature of the device. The model predicts, there exists the maximum temperature of microlaser operation in CW regime and the minimum mircrodisk diameter, at which CW lasing is possible. The model allows one to determine the dependence of the device characteristics on its diameter and the inherent parameters, such as thermal resistance, electrical resistance, non-radiative recombination and characteristic temperature of the threshold current. It is found that a rapid growth of the threshold current density with decreasing the diameter (which takes place even in the absence of the self-heating effect) is the main internal reason leading to the dependence of the temperature characteristics of the mirodisk laser on its size. In the calculations, we used a set of parameters extracted from experiments with InGaAs quantum dot microdisk lasers. The simulation results (in particular, the light-current curve and the dependence of the minimum microdisk diameter on ambient temperature) comply well with the measured dependences. [ABSTRACT FROM AUTHOR]

Hybrid dc switches (HDCSs) have attracted considerable attention due to the low ON-state loss and fast current interruption. With low current interruption, there is no arc generation between the contacts. However, arc discharge occurs between the contacts after the contact opens for a high circuit current. Arc discharge is a harmful phenomenon. It erodes the surface of the contacts and decreases the insulation strength between the contacts. This article presents a new configuration of contacts that can increase the threshold current for arc-free commutation. The contact has a cuboid shape with a join of copper and carbon. When the contacts are in the closing position, the copper and carbon materials of the contacts come in contact. Then, a low contact resistance can be achieved. When the contacts start opening, the contact spots of the copper start decreasing until rupture, but carbon, which has a higher resistivity than copper, still remains in contact. With a higher resistance of the contacts, the current is further commutated to the semiconductor device until the current at the contacts becomes low. After the contacts rupture, the low surge voltage from the inductance in the circuit cannot ignite arc discharge. Thus, arc-free commutation can be achieved. [ABSTRACT FROM AUTHOR]

A systematic study of the quasi-Fermi level pinning in various interband cascade lasers (ICLs) is reported. These ICLs, with either type-II or type-I quantum well active regions, cover the mid-infrared wavelength range from 3 to $6~\mu \text{m}$ and can operate in continuous wave (cw) at room temperatures and above. It was found that the quasi-Fermi level can be pinned in many ICLs over a wide range of temperature, which is associated with an observed drop of differential resistance at threshold. For the first time, the quasi-Fermi level pinning was demonstrated in ICLs at room temperature. The temperature dependence of the quasi-Fermi level pinning in ICLs was also examined. A pinning factor is introduced to evaluate how well the quasi-Fermi level is pinned in ICLs with different configurations and lasing wavelengths. Also, it was found that the quasi-Fermi level pinning disappeared in some ICLs where an obvious drop of differential resistance could not be observed at the threshold. Furthermore, the quasi-Fermi level pinning was found to be correlated to the doping concentration in electron injectors in ICLs. Possible mechanisms and implications related to the quasi-Fermi level pinning are discussed. [ABSTRACT FROM AUTHOR]

Racetrack memory (RTM) is a novel spintronic memory-storage technology that has the potential to overcome fundamental constraints of existing memory and storage devices. It is unique in that its core differentiating feature is the movement of data, which is composed of magnetic domain walls (DWs), by short current pulses. This enables more data to be stored per unit area compared to any other current technologies. On the one hand, RTM has the potential for mass data storage with unlimited endurance using considerably less energy than today’s technologies. On the other hand, RTM promises an ultrafast nonvolatile memory competitive with static random access memory (SRAM) but with a much smaller footprint. During the last decade, the discovery of novel physical mechanisms to operate RTM has led to a major enhancement in the efficiency with which nanoscopic, chiral DWs can be manipulated. New materials and artificially atomically engineered thin-film structures have been found to increase the speed and lower the threshold current with which the data bits can be manipulated. With these recent developments, RTM has attracted the attention of the computer architecture community that has evaluated the use of RTM at various levels in the memory stack. Recent studies advocate RTM as a promising compromise between, on the one hand, power-hungry, volatile memories and, on the other hand, slow, nonvolatile storage. By optimizing the memory subsystem, significant performance improvements can be achieved, enabling a new era of cache, graphical processing units, and high capacity memory devices. In this article, we provide an overview of the major developments of RTM technology from both the physics and computer architecture perspectives over the past decade. We identify the remaining challenges and give an outlook on its future. [ABSTRACT FROM AUTHOR]

Using a finite element method to numerically solve the time-dependent Ginzburg-Landau equations, we studied the dynamic properties of the mesoscopic superconducting strips. We obtain the different voltage-current, free energy-time, and vortex evolution patterns for different temperatures conditions and applied current. Our results show that the temperature and the applied current directly influence the dynamics of the superconducting condensate and lead to the variations of threshold current and the periodic oscillations of the free energy across the strips with a frequency. [ABSTRACT FROM AUTHOR]

In this paper, we present experimental results of spontaneous emission clamping in the threshold for vertical-cavity surface-emitting lasers (VCSELs) with oxide current confinement. We show that the spontaneous emission not wholly clamps in the threshold. We propose a new method for determining the threshold current value using the study of the clamping phenomena. This method has an advantage over the commonly used methods in the accuracy because the current of the spontaneous emission clamping is betted defined than the current of the slope change of the stimulated emission light-current curve. The estimated uncertainty of the method is no more than 20 µA. [ABSTRACT FROM AUTHOR]

This work investigates the degradation processes affecting the long-term reliability of 1.3 μm InAs quantum-dot lasers epitaxially grown on silicon. By submitting laser samples to constant-current stress, we were able to identify the physical mechanisms responsible for the optical degradation. More specifically, the samples (i) exhibited a gradual increase in threshold current, well correlated with (ii) a decrease in sub-threshold emission, and (iii) a decrease in slope efficiency. These variations were found to be compatible with a diffusion process involving the propagation of defects toward the active region of the device and the subsequent decrease in injection efficiency. This hypothesis was also supported by the increase in the defect-related current conduction components exhibited by the electrical characteristics, and highlights the role of defects in the gradual degradation of InAs quantum dot laser diodes. Electroluminescence measurements were used to provide further insight in the degradation process. [ABSTRACT FROM AUTHOR]

An exact problem of the electromagnetic wave propagation in a multilayer heteronanostructure with complex values of the dielectric constant (permittivity) is solved. The contribution to the refractive index of an additive to the dielectric constant due to the injected carriers is taken into account. A heterostructure based on a nanosystem used for the manufacture of lasers in the range 0.94–1.14 μm is considered. The methods and approaches used are also applicable for optimizing multilayer structures based on other solid solutions and those with several quantum wells. Based on the calculations of the temperature dependence of the radiation characteristics of injection lasers based on heteronanostructures, it was shown that the anomalous behavior of the temperature dependence of the threshold current is associated with a weakening of the waveguide properties of their active region. In accordance with the calculation results, the heteronanotructures parameters of injection lasers were optimized with respect to the thickness and dielectric properties of the waveguide nanolayer material, which made it possible to significantly reduce the temperature dependence of their radiative characteristics. [ABSTRACT FROM AUTHOR]

This paper introduces the fault current behavior of full-bridge modular multilevel converters (MMCs) and hybrid MMCs, with a consideration of a non-simultaneous blocking of the two half-bridges in each sub-module. In order to protect insulated gate bipolar transistor (IGBTs) in the full-bridge sub-module, both sides of a full-bridge sub-module are not blocked at the same time point. It is assumed that the first blocking of both sides is random in each sub-module, so there are many possible voltages in each arm after the first blocking. Because of this, there are also many possible fault current slopes after the first blocking. The influence of this sequential blocking on the maximum fault current is analyzed in the study. This paper also determines the threshold current, which has to be decreased due to this phenomenon. An optimization method of threshold current is also proposed. Other new MMC sub-modules can also use this new blocking method to reduce the stress of IGBTs, whose working principle is also introduced in this paper. [ABSTRACT FROM AUTHOR]

We report on AlInGaN-based blue and green edge-emitting lasers designed for low-current operation and low power consumption. By properly optimizing cavity length and mirror coatings, threshold currents below 5 mA are achieved on single-mode blue laser diodes (LDs) emitting at 460 nm. For output power levels below 10 mW, the LDs with an optimized chip design exhibit a decreased power consumption and an increased power stability against temperature variations compared to LDs with a standard chip design. Extended to green emitters, the new design results in single-mode LDs emitting at 515 nm with threshold currents close to 15 mA. [ABSTRACT FROM AUTHOR]

The electromigration (EM) technique is a method that is used to ensure the physical growth of metallic micro/nanowires. In the EM technique, the atomic diffusion of metals is intentionally accelerated by controlling the input current and heating the substrate, thus forming a hillock owing to the accumulation of atoms, which is transformed into small-diameter metallic micro/nanowires. The metallic micro/nanowires can be fabricated by discharging the atoms through a hole, which is artificially introduced in the passivation. The fabrication of metallic micro/nanowires has been successfully demonstrated using the EM technique, and the wire growth behavior is dependent on the characteristics of the artificial hole. However, very little information is available about the quantitative assessment of wire fabrication performance even though several experimental attempts have been conducted in prior studies. Additionally, the effect of structural parameters, such as the hole size, on the fabrication performance has not yet been adequately investigated. This study quantitatively evaluates the fabrication performance that is influenced by the hole size in terms of the growth rate of wires and threshold current used for fabrication. Based on the experimental results, the fabrication loss related to the hole size is experimentally revealed; further, an empirical formula for the fabrication loss has been developed. The optimal hole size to achieve the high performance of the micro/nanowire growth using the EM technique can be obtained with this finding.