AlGaAs Research Articles

Multiple electron pumping

The need to pump single electrons with a high degree of accuracy and fidelity has led to the development of a range of different pump and turnstile designs. Previous pumping mechanisms have all demonstrated that pumping more than one electron per cycle degrades the quantisation of the measured current. This unreliable delivery of multiple electrons per cycle has limited the use of on-demand single electron sources in electron quantum optic experiments. We present highly quantised current with multiple electrons pumped per cycle. We experimentally demonstrate that in our pumps an increase in electron throughput per cycle does not lead to an appreciable degradation in the accuracy of the produced current.Our pump is realised in an aluminium gallium arsenide two-dimensional electron gas, where electrons are pumped through a one-dimensional split-gate confinement potential under the influence of an applied source-drain voltage V_{text{SD}}, and where the pump is driven by a trapezoidal arbitrary waveform. This combination of a split-gate potential, V_{text{SD}} bias and trapezoidal wave form has led to the observation of robust quantised plateaus where not just a single electron, but a multiple integer number of electrons are pumped per cycle with a high degree of robustness and without the need of a magnetic field. For seven electrons per cycle, we report an increase of over two orders of magnitude in pumping accuracy from 2.72 times 10^{-2} in devices operating in the conventional pumping regime, to 1.64 times 10^{-4} in pumps operating in what we call the long plateau regime, a regime accessed under a change in a split-gate pumps applied V_{text{SD}} voltage. This pump will find direct use in quantum transport measurements where the metrological accuracy of single electrons pumped per cycle is not required and the low throughput per cycle of electrons is limiting.

High-Power Laser Diodes Based on InGaAs(P)/Al(In)GaAs(P)/GaAs Heterostructures with Low Internal Optical Loss

High-Power Laser Diodes Based on InGaAs(P)/Al(In)GaAs(P)/GaAs Heterostructures with Low Internal Optical Loss

The growth and spectroscopic properties of Yb:KNGM crystal: A promising ultrashort pulse laser material

Yb3+-doped mixed laser crystals are widely recognized as materials capable of generating ultrashort pulses and have garnered significant attention in recent times. In this study, we thoroughly examined the structure and spectroscopic properties of a novel mixed molybdate crystal, Yb:KNGM. Notably, we made detailed observations of an exceptionally broad absorption band with a full width at half maximum (FWHM) of 78 nm. The broad absorption band indicates that the commercially available InGaAs laser diode (LD) can be effectively utilized for high pumping efficiency purpose. The absorption and emission cross-section at 967 and 1014 nm were calculated to be 1.56 × 10−20 cm2 and 2.05 × 10−20 cm2, respectively. The FWHM of the emission band reaches a substantial range of 62 nm, making it highly conducive to the production of ultrashort pulse lasers. The bandgap (Eg) was fitted as 3.26 eV by Tauc formula. Positive gain cross-section can be achieved while the β is only higher than 0.2 and a large FWHM of 41 nm was discovered when β is 0.5. The aforementioned merits provide compelling evidence that Yb:KNGM crystal holds great promise as a laser crystal for the application of wild tunable and ultrashort pulse lasers pumped by LD.

Effects of Photobiomodulation Using Low-Level Laser Therapy on Alveolar Bone Repair

Alveolar bone repair is a complex and extremely important process, so that functions such as the mastication, occlusion and osseointegration of implants can be properly reestablished. Therefore, in order to optimize this process, many procedures have been used, such as grafting with biomaterials and the application of platelet-rich fibrin (PRF). Another method that has been studied is the use of photobiomodulation (PBM) with the use of low-level laser therapy (LLLT), which, through the absorption of photons by the tissue, triggers photochemical mechanisms in the cells so that they start to act in the search for homeostasis of the affected region. Therefore, the objective of this review was to analyze the use of LLLT as a possible auxiliary tool in the alveolar bone repair process. A search was carried out in scientific databases (PubMed/MEDLINE, Web of Science, Scopus and Cochrane) regarding the following descriptors: “low-level laser therapy AND alveolar bone repair” and “photobiomodulation AND alveolar bone repair”. Eighteen studies were selected for detailed analysis, after excluding duplicates and articles that did not meet predetermined inclusion or non-inclusion criteria. According to the studies, it has been seen that LLLT promotes the acceleration of alveolar repair due to the stimulation of ATP production, activation of transcription and growth factors, attenuation of the inflammatory process and induction of angiogenesis. These factors depend on the laser application protocol, and the Gallium Aluminum Arsenide—GaAlAs laser, with a wavelength of 830 nm, was the most used and, when applications of different energy densities were compared, the highest dosages showed themselves to be more efficient. Thus, it was possible to conclude that PBM with LLLT has beneficial effects on the alveolar bone repair process due to its ability to reduce pain, the inflammatory process, induce vascular sprouting and, consequently, accelerate the formation of a new bone matrix, favoring the maintenance or increase in height and/or thickness of the alveolar bone ridge.

RUL prediction for bivariate degradation process considering individual differences

Remaining useful life (RUL), is essential for prediction and health management. Because of unit-to-unit heterogeneity in degradation, it is intractable to perform precise degradation trajectories of an individual bivariate individual system. First, for predicting the RUL of an individual system, the parameter in the nonlinear transformation path of the degradation model is proposed as an indicator to characterize the heterogeneity of the degradation process, which is used for accurate degradation prediction. Furthermore, a prediction method based on this improved degradation model is presented for the RUL estimation of degrading systems. An improved parameter updating way based on the Bayesian approach is developed for parameter posterior estimation. The proposed prediction method is illustrated and validated through a publicly available GaAs lasers dataset and a practical degrading system case data. The results show that the new method is superior to the conventional method in prediction accuracy.

Optimization of strip-based hybrid plasmonic terahertz waveguide with distributed Bragg reflector layers

In view of recent developments in the utilization of terahertz (THz) communications technology for the increasing demands of high speed and data rates for various wireless applications, this research work targets the design and analysis of distributed Bragg reflector (DBR)-based hybrid plasmonic THz waveguide. This THz waveguide operates at a frequency range from 2.5 to 3.5 THz. The proposed DBR-based hybrid plasmonic THz waveguide consists of DBR layers of gallium arsenide (GaAs) and aluminum arsenide, high-density polyethylene (HDPE) as substrate, a GaAs stripe for wave-guidance, and few layers of graphene layers in HDPE for better confinement. To increase the light confinement between DBR and graphene, a GaAs strip is placed into HDPE. By altering the width and height of the GaAs strip, the parameters birefringence, mode field diameter (MFD), confinement loss, effective mode area, beat length, and dispersion have been fully examined. The obtained simulation results shows high birefringence of 0.6276, maximum MFD of 45 mm, low confinement loss of 7.5 × 10 − 9 mm − 1, high effective mode area of 16.5 mm2, and low anomalous dispersion of 0.0023 (ps/THz/cm) in the range of 2.5 to 3.5 THz. This optimized THz waveguide may helps to enable in guided THz applications for photonic integrated circuits.

Conventional arrayed waveguide grating (CAWG) devices for high stability and low insertion loss in near infrared wavelength band

Abstract This study has presented the different suggested compounds based (CAWG) like silicon dioxide (SiO2), lithium niobate (LiNbO3) and gallium aluminum arsenide (Ga(1-x)Al(x)As) taking into consideration their operating wavelength range, their operating temperature range, their physical properties, and also their ability to be used in the manufacture of optical devices. The optimum performance was given in case of using the following materials such as SiO2, LiNbO3 and Ga(1-x)Al(x)As materials, so these materials have been used as a proposed materials based CAWG devices, which have been investigated for high stability and low insertion loss in near infrared wavelength band. The comparison between these proposed materials are clarified through the design parameters of CAWG device such as the order of diffraction (m), path length adjacent waveguides difference (ΔL), focal length (L f ), free spectral range (FSR), max no. of I/O wavelength channels (N max), and arrayed waveguides (P) number.

Integrated optics based on electro optic modulators for long distance links and high bit rate communication

Abstract This paper has clarified the gallium aluminum arsenide and plastic modulators and its element circuit modeling design considerations for high signal processing distance links communications. Modulator circuit model design considerations and equations analysis are taken into account. Modulator source resistance, modulator inductance, and modulator capacitance based electro-optic modulator (EOM) is studied and analyzed against temperature variations. In addition to the switching voltage for EOM is analyzed at both 1300 nm and 1550 nm wavelength versus temperature variations. The operation efficiency and maximum modulation resonance frequency are studied for previous and proposed EOM versus modulator length variations. The lower modulator resistance, modulator capacitance, and modulator inductance can be achieved with the proposed EOM. As well as the proposed EOM has outlined the optimum operational efficiency and maximum resonance modulation frequency compared to the previous EOM.

Heterogeneous Degradation Modeling Based on Hierarchical Bayesian Model and Wiener Process

In this paper, a hierarchical Bayesian model is presented with heterogeneous degradation data populations based on Wiener process and Gaussian mixture model, where the actual degradation path is described by Wiener process, and the Gaussian mixture model is used to capture the heterogeneity between data populations. The Bayesian parameters estimation method is carried out via hierarchical priors and Gibbs sampling algorithm, and DIC and WAIC are the two selection criteria for the optimal model to fit the data. A set of GaAs laser numerical example indicates that the heterogeneous degradation data population with two sub-populations provides a better reliability assessment result than assuming a homogeneous population.

56-fs diode-pumped SESAM mode-locked Yb:YAl3(BO3)4 laser.

We report on the first sub-60 fs pulse generated from a diode-pumped SESAM mode-locked Yb-laser based on a non-centrosymmetric Yb:YAl3(BO3)4 crystal as a gain medium. In the continuous-wave regime, pumping with a spatially single-mode, fiber-coupled 976 nm InGaAs laser diode, the Yb:YAl3(BO3)4 laser generated 391 mW at 1041.7 nm with a slope efficiency as high as 65.1%, and a wavelength tuning across 59 nm (1019 to 1078 nm) was achieved. By implementing a commercial SESAM to initiate and sustain the soliton type mode-locking, and using only a 1 mm-thick laser crystal, the Yb:YAl3(BO3)4 laser delivered pulses as short as 56 fs at a central wavelength of 1044.6 nm with an average output power of 76 mW at a pulse repetition rate of ∼67.55 MHz. To the best of our knowledge, this result represents the shortest pulses ever achieved from Yb:YAB crystal.

Bayesian Estimation of Time to Failure Distributions Based on Skew Normal Degradation Model: An Application to GaAs Laser Degradation Data

In this paper, the Bayesian method which involves informative and weakly informative priors are considered to estimate the parameters and percentiles of the time to failure distribution. The parameters of the time to failure distribution and its percentiles are determined based on linear degradation model where the degradation parameter is assumed to follow the skew normal distribution. For the prior distributions, location and scale parameters of the skew normal distribution is assumed to follow the uniform distribution while the shape parameter is assumed to follow gamma distribution. Two gamma priors are considered, either informative or weakly informative prior, depending on the assumed values of the hyper parameters. The performance of the method under the different prior assumptions is compared using a simulation study based on Markov Chain Monte Carlo method as well as a real data application. It is found that the parameter estimation based on informative prior is more precise as opposed to the weakly informative prior, especially in the case of small sample size. In addition, the skew normal degradation model is compared to the log-logistic degradation model through a simulation study and a real application of GaAs laser data. When modeling the percentiles of the time to failure distribution, results found based on the skew normal distribution is generally found to be more precise, particularly for the higher percentile values.

A Novel Microstructure of 2‐Bit Optical Analog to Digital Converter Based on Kerr Effect Nonlinear Nanocavities in 2D Photonic Crystal

In this paper, an all‐optical analog‐to‐digital converter based on nonlinear with silicon materials is designed and simulated. The proposed structure consists of three nonlinear nanocavity that control the optical signal power intensity. The nonlinear material used is aluminum gallium arsenide (AlGaAs). Aluminum gallium arsenide (AlGaAs) with a linear refractive index of n0 = 1.4 and a nonlinear refractive index of n2 = 1.5 × 10−17. Due to the small path length of the waveguides, the optical signals move a short distance and as a result, the power optical losses along the path are reduced and on the other hand, the speed of the structure is increased. The transmission percentage is between 90% and 100%. The overall dimensions of the structure are 324 μm2. The plane wave expansion (PWE) method is used to calculate the band structure. The two‐dimensional finite difference time domain (2D‐FDTD) method is used to calculate the transmission power spectrum and the simulation results.

Second order nonlinear optics in AlGaAs metasurfaces

Recently, nonlinear optics at the nanoscale level has emerged as a promising branch of nanophotonics. In this work, we focus our attention on Aluminum Gallium Arsenide (AlGaAs) nanoantennas and metasurfaces for efficient and controlled second harmonic photon emission. After a brief introduction concerning the main studies in this field, we present the latest results achieved in AlGaAs platforms both in the lossless and absorption regimes.

Stochastic Uncertain Degradation Modeling and Remaining Useful Life Prediction Considering Aleatory and Epistemic Uncertainty

Remaining useful life (RUL) prediction based on the degradation model is vital for the maintenance and management of complex equipment. It is necessary to describe the aleatory uncertainty in internal changes during equipment degradation and quantify the epistemic uncertainty caused by a lack of sufficient knowledge simultaneously. This article proposes a novel framework for the degradation model and RUL prediction with aleatory and epistemic uncertainties. First, the probability theory is combined with the uncertainty theory to establish a stochastic uncertain degradation model. Following that, a new stochastic uncertain maximum likelihood estimation (SUMLE) method is proposed based on probability function and uncertainty distribution to identify model parameters. The Bayesian inference is adopted to update the model parameters in the current time. Afterward, the above dual-source uncertainty is incorporated into RUL prediction. The distribution function of the RUL is derived, which can be updated in real-time according to the arrival of new degradation observations. Finally, the experimental studies on gallium arsenide (GaAs) laser and gyroscope degradation data are conducted to interpret the superiority of the proposed method over based on the stochastic process or uncertain process separately for predicting the RUL.

Anticariogenic Sanative Effect of Aluminum Gallium Arsenide Crystals on Hydroxyapatite Crystals

Dental caries is a progressive disease with varying phases of demineralization and remineralization, and the scope of reversing the carious lesion is increased if it is diagnosed before there is surface cavitation. Preventive management strategies are directed towards making the enamel more resistant towards acid dissolution. The caries preventive protocol has always been fluoride-centric. Repeated application of fluoride gives rise to acquired fluoride resistance strains of Streptococci mutans which can be transient or permanent. The need of the hour is an effective remineralizing protocol which is one which brings about a change in enamel crystal and makes it more resistant to the acidic challenges of the oral cavity. The authors have devised a protocol in which irradiation with aluminum gallium arsenide crystals LASER can bring about a sanative change in crystal and lead to greater acid resistance of the enamel crystal and thus potentiate the remineralization of non-cavitated lesions. The concept of aluminum gallium arsenide–assisted caries inhibition and the proposed hypothesis of the mechanism of action is discussed.

The 1.5 μm spectroscopic properties of Yb,Er:GSAG crystal: A promising 1.5 μm laser gain medium

The 1.5 μm lasers exhibit excellent eye safety characteristics that make them crucial for laser ranging, radar and optical communication. In this work, the 1.5 μm spectroscopic properties of a mixed garnet crystal, Yb,Er:GSAG, were investigated. The strongest absorption at 940 nm overlaps well with the currently mature InGaAs laser diodes. Under 940 nm excitation, a strong emission band with peak wavelength at 1534 nm was detected. The Judd-Ofelt calculation was performed based on the measured absorption spectrum, and the three intensity parameters Ωt (t = 2,4,6) were fitted as 0.974 × 10−20 cm2, 0.477 × 10−20 cm2 and 0.352 × 10−20 cm2, respectively. The absorption cross-section at 940 nm and emission cross-section at 1534 nm were calculated as 0.59 and 0.81 × 10−20 cm−1, respectively. Lastly, a positive gain cross-section can be achieved at 1534 nm when the population inversion ratio β is only higher than 0.2. The results imply that this crystal is a promising 1.5 μm near infrared laser gain medium.

Multiple tunnel diode peaks in I–V curves of a multijunction laser power converter

How to characterize tunnel diodes (TDs) in multijunction photovoltaic cells is a challenge. Here, we investigate a locally illuminated six-junction InGaAs laser power converter (LPC) by measuring the wide-voltage-range I–V curves. Multiple TD peaks are observed in the reverse breakdown area of the dark-state I–V curve, while with increased laser power, the peaks break into more subpeaks successively, and the subcell photocurrent steps are found to shrink due to the moving subpeaks at the right side of the steps. A model of a multijunction LPC under localized illumination is proposed, and the shrinkage of a step originates from the larger local overproduced subcell photocurrent than the local peak current of the very TD below this subcell. Therefore, the correspondences between TD peaks in the I–V curves and their physical locations in the structure of the LPC are determined. This work gives in-depth insight into the current limiting mechanism of TDs in multijunction photovoltaic devices under non-uniform illumination and expands the knowledge of multijunction photovoltaic devices.

Reliability modelling considering multi-dimensional cognitive uncertainties based on uncertainty theory

Aiming at the multi-dimensional cognitive uncertainties in performance degradation modelling for small samples, a reliability assessment method is proposed based on uncertainty theory. First, a degradation model is established based on the uncertain process, which considers cognitive uncertainties from the time fluctuation, the measurement error, and the individual differences in initial value and degradation rate, and the reliability function is derived. Then, a two-step parameter estimation method for the degradation model is proposed based on the α-path and the least square, which is verified by numerical simulation. Finally, the effectiveness and superiority of the proposed method are verified by the cases of GaAs lasers and magneto-optic data storage disks, and parameter sensitivity analysis is conducted. The results indicate that uncertainty affects product reliability greatly. For small samples, thedegradation models considering multi-dimensional uncertainties based on the Liu process has smaller fitting errors than that based on the Wiener process.

Fourier Transformation Infrared Spectroscopic Analysis of Enamel Following Different Surface Treatments: An Invitro Study

Dental caries is an oral disease that has a global footprint. The first onslaught is subsurface, and at this stage, it can be remineralized. This study attempts to analyze the compositional changes that occur during demineralization and different surface treatment remineralization protocols. Aim: The aim of this study is to evaluate the compositional changes caused by different surface treatments on demineralized enamel. Methodology: Six extracted intact posterior teeth were selected and sectioned mesiodistally to achieve two halves. Each half was further divided into six equal sizes to achieve 12 samples per tooth. Except for one sample, which served as the control for that particular tooth, the remaining samples were placed in a demineralizing solution (acetate 0.1 Mol/L, calcium 0.1 Mol/L, phosphate 0.1 Mol/L and fluoride 0.1 mg/L pH 5.0) for 24 h. The samples were then assigned to groups and surface-treated as described below. The samples were grouped as follows so as to subject each sample to the following different surface treatments: Group 1: control, Group 2: Demineralized, Group 3: Laser 1 Watt, Group 4: Laser 2 Watts, Group 5: Laser 3 Watts, Group 6: Laser 3.5 Watts, Group 7: CPP-ACPF, Group 8: CPP-ACPF & Laser 3.5 Watts, Group 9: Enafix, Group 10: Enafix & Laser 3.5 Watts, Group 11: MI Paste and Group 12: MI Paste & Laser 3.5 Watts. The laser used for irradiating the samples in the respective laser groups utilized different wattages of an 810 nm aluminum–gallium–arsenide laser for 30 s. The samples were analyzed using Fourier transform infrared spectrometry coupled with attenuated total reflectance (FTIR-ATR). A qualitative analysis was performed. Result: The 3.5 watts aluminum–gallium–arsenide laser followed by CPP-ACPF caused compositional changes in the organic and inorganic components of the enamel tissues, and these changes were similar to those of the control teeth. Conclusion: Aluminum–gallium–arsenide laser irradiation alone does cause compositional changes and makes the enamel conducive for remineralization.

On Wiener Process Degradation Model for Product Reliability Assessment: A Simulation Study

This paper examines the application of the Wiener process as a degradation model. Its appropriateness as a degradation model is discussed and demonstrated with the aid of Monte Carlo simulations. In particular and for monotonically degrading systems, this paper demonstrates that the irreversible accumulation of damage can be modelled by the Wiener maximum process. First passage times of the Wiener and its maximum process are also revealed to coincide. Practical advantages of assessing system reliability from degradation data are highlighted by applying the Wiener process model to a real gallium arsenide (GaAs) laser data for telecommunication systems. The real data application results demonstrate that degradation analysis allows for conclusions about system reliability to be reached earlier without compromising estimation accuracy—a major practical advantage.