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Employing Monte-Carlo simulations we investigate parameters and optimize geometry of IR quantum-dot detectors with diffusion-limited capture into the dots surrounded by potential barriers. Our results show that structures with modulation doping of interdot matrix provide an effective separation of the localized and conducting electron states. In these structures, the capture time is mainly determined by the quantum dot concentration and the height of potential barriers around dots. The capture is not sensitive to the dot positions. It also weakly depends on the electric field up to the characteristic value, at which significant electron heating allows hot electrons to overcome the barriers. Optimizing the carrier capture and transit times, we show that quantum-dot structures have a lot of potentials for increasing the photoconductive gain and for the development of IR room-temperature detectors.

Here we report our research on quantum-dot structures with collective barriers surrounding groups of quantum dots (planes, clusters etc) and preventing photoelectron capture. Employing Monte-Carlo simulations, we investigate photoelectron kinetics and calculate the photoelectron lifetime as a function of geometrical parameters of the structures, dot occupation, and electric field. Results of our simulations demonstrate that the capture processes are substantially suppressed by the potential barriers and enhanced in strong electric fields. Detailed analysis shows that the effects of the electric field can be explained by electron heating, i.e. field effects become significant, when the shift of the electron temperature due to electron heating reaches the barrier height. Optimized photoelectron kinetics in quantum-dot structures with collective barriers allows for significant improvements in the photoconductive gain, detectivity, and responsivity of photodetectors based on these structures.

In this work we calculate and analyze modal gain for terahertz lasers based on HgCdTe heterostructures with quantum wells (QWs) taking into account the symmetry-enforced light hole-heavy hole mixing at the quantum well interfaces. We have found that modal gain for a structure with 5 HgTe QWs of the 5.2 nm width can be 33 cm⁻¹ at 9 THz.

The model used for analyzing the gain characteristics of Er-doped waveguide amplifier (EDWA) is based on the rate-propagation equations with intensity profiles of pump and signal light (IPPSL). This simulation indicates that the IPPSL have significant effect on the gain of signal light. The results show that a gain change 2.3 dB of signal light at 1534 nm is obtained for a 4 cm long channel waveguide amplifier with different intensity profiles pumped by 80 mW at 980 nm. Experiment also shows that a gain change about 2.31 dB at 1534 nm for the channel waveguide of 4 cm length is obtained for different IPPSL. Thus, the effect of IPPSL should be considered to enhance the pump efficiency in the design of EDWA.

A new avalanche photodiode device applied to a visible light communication (VLC) system is designed using a standard 0.18 $\mu$m complementary metal oxide semiconductor process. Compared to regular CMOS APD devices, the proposed device adds a $P$-well layer above the deep $N$-well/$P$-substrate structure, and an $N+$/$P+$ layer is deposited upon it. The $N+$/$P+$ layer acts as an avalanche breakdown layer of the device, and an STI structure is used to prevent the edge break prematurely. The simulation results shows that the avalanche breakdown voltage is as low as 9.9 V, dark current is below $1\times 10^{-11}$ A under −9.5 V bias voltage, and the 3 dB bandwidth is of 5.9 GHz. It is due to the use of the 0.18 $\mu$m CMOS process-specific STI protection ring and short-circuits the connection of the deep $N$-well/$P$-substrate, and the dark current is reduced to be lower than two orders of magnitude compared to regular CMOS APD. Gain and noise characteristics are accurately calculated from Hayat dead-space model applied to this CMOS APD. So, this device’s gain and excess noise factor are 20 and 2.5, respectively.

Here, we investigate the impact of space-time reverse (STR) problems, a result of parity-time symmetry in optics and quantum mechanics, on soliton propagation in optical fibers. The STR problems are characterized by the existence of a field and its reverse. The research introduces a new classification of two scenarios: non-interactive and interactive fields and reverse fields. The solutions for the generalized Fokas–Lenells equation (gFLE) with STR and third-order dispersion are derived. To tackle this, adaptive transformations for the field and its reverse are introduced, employing a unified method. In the non-interactive scenario, both exact and approximate solutions are found. However, in the interactive case, only exact solutions are discovered. This work reveals that the presence of the field and its reverse unveils new soliton structures, including bright–dark envelope solitons and right and left envelope-solitons. In the non-interactive case, the field displays a right envelope-soliton, while the reverse field exhibits a left envelope-soliton (or vice versa). The study hypothesizes that the presence of a reverse field might impede soliton propagation in optical fibers.

The research also includes an analysis of modulation instability (MI), determining that MI is initiated when the coefficient of Raman scattering exceeds a critical value. Furthermore, the study examines the modulated wave gain and explores global bifurcation through phase portrait by constructing the Hamiltonian function.

In this paper, we optimized the performance of a 2.4 GHz variable gain low-noise amplifier for WLAN applications which provides high dynamic range with relatively low power consumption. First, the differential evolution algorithm was used to optimize the width of input transistors, then the tunable on-chip switching stage method was applied to control the amplifier gain when the input signal increases. The optimization was performed in terms of gain, noise figure (NF), IIP3 and power dissipation. The LNA has achieved a variable gain from 16.55 to 20.45 dB with excellent NF between 1.63 and 1.74 dB. Furthermore, the proposed circuit achieves a third order input intercept point of 6.6 dBm. It consumes only 10 mW from a 1.5 V supply.

A power-efficient, voltage gain enhancement technique for op-amps has been described. The proposed technique is robust against Process, Voltage and Temperature (PVT) variations. It exploits a positive feedback-based gain enhancement technique without any latch-up issue, as opposed to the previously proposed conductance cancellation techniques. In the proposed technique, four additional transconductance-stages (gm stages) are used to boost the gain of the main gm stage. The additional gm stages do not significantly increase the power dissipation. A prototype was designed in 65nm CMOS technology. It results in 81dB voltage gain, which is 21dB higher than the existing gain-boosting technique. The proposed op-amp works with as low a power supply as 0.8V, without compromising the performance, whereas the traditional gain-enhancement techniques start losing gain below a 1.1V supply. The circuit draws a total static current of 295$\mu$A and occupies 5000$\mu$m² of silicon area.

A new compact $1\times 4$ microstrip patch antenna array design for future 5G applications is presented in this paper. The proposed antenna array consists of square slot loaded with four radiating patch elements. The corporate feed network has been implemented for the excitation of the array. The feed line is connected to the square slot patch through a quarter-wave transformer matching network. The proposed array is designed on an FR-4 substrate with a dielectric constant of 4.4, thickness of 1.6mm and loss tangent (tan$\delta )$ of 0.02. It has a compact dimension of 9.590$\times$ 17.802$\times 1.6\text{m}{\text{m}}^3$. The proposed structure has been designed and simulated by using commercially available HFSS software. The simulated results (reflection coefficient, gain, efficiency, radiation pattern) are verified through the measurement process to confirm the validity of the design concept. The measurement results are in good agreement with the simulated results. The proposed structure resonates at 38.1GHz with a $-$10dB impedance bandwidth of about 3700MHz (36.5GHz to 40.2GHz). The reflection coefficient at 38.1GHz is $-$34dB, with a maximum gain of 7.81dB. The proposed square slot loaded patch antenna array is very promising for 5G communications at 38GHz band (37–40GHz).

A compact low-cost metamaterial circular monopole antenna for LTE applications is presented here. This paper addresses an asymmetric circular split-ring radiator for 2.6GHz (LTE-7 band), 3.5GHz (LTE-22 band). The design here employs split rings with varying split gaps in the consecutive ring layers of the radiating element which helped in achieving better impedance matching for obtaining multiband operation. The work presented here demonstrates the feasibility of achieving double negative material property, without loading the SRR’s separately in the system. The antenna was modeled using a 1.6mm thick FR-4 lossy material. The simulated results were compared with measured results and found to be in good agreement with each other. Employing asymmetric split ring as radiator helped in achieving 29% of size reduction in the patch layer. The modified split-ring radiator achieved directional radiation pattern and minimum side-lobe levels with a peak gain of 1.29 and 0.204dB at the lower band and upper band, respectively. The compact dimension $45\times 40{\text{mm}}^2$ of the radiating system makes it suitable for LTE-WLAN/Wi-Max applications.

In this paper, optimum transistor sizing of CMOS differential amplifier using tunicate swarm algorithm (TSA) is proposed. The designing of CMOS differential amplifier is activated to determine the best feasible design parameter values. This work proposes the optimized values of various parameters of a CMOS differential amplifier for better performance. TSA is chosen to optimize the circuit area. TSA has the ability to solve complex functions, like MOS transistor size and bias current. TSA is employed to optimize the parameters of circuit design, like area, power dissipation MOS transistor size, and also used to enhance other circuit specifications, while fulfilling circuit design criteria. The design objectives of CMOS differential amplifier are considered the fitness function of TSA algorithm. Then, weight parameters of CMOS differential amplifier design are optimized using TSA. By CMOS differential amplifier using TSA algorithm, we can optimize circuit design parameters with higher probability of yielding optimal results regarding circuit area lessening, lesser power dissipation and MOS transistor sizes. The proposed method is implemented in the MATLAB platform. The proposed CMOS-DA-TSA method attains 52.01%, 50.29% and 44.30% minimum slew rate, 64.61%, 75.30% and 55.92% minimum power dissipation compared to the existing methods like CMOS-ACD-SOA, CMOS-PAI-FOPSO and CMOS-PSO-MOL, respectively.

We review simple connectionist and firing rate models for mutually inhibiting pools of neurons that discriminate between pairs of stimuli. Both are two-dimensional nonlinear stochastic ordinary differential equations, and although they differ in how inputs and stimuli enter, we show that they are equivalent under state variable and parameter coordinate changes. A key parameter is gain: the maximum slope of the sigmoidal activation function. We develop piecewise-linear and purely linear models, and one-dimensional reductions to Ornstein–Uhlenbeck processes that can be viewed as linear filters, and show that reaction time and error rate statistics are well approximated by these simpler models. We then pose and solve the optimal gain problem for the Ornstein–Uhlenbeck processes, finding explicit gain schedules that minimize error rates for time-varying stimuli. We relate these to time courses of norepinephrine release in cortical areas, and argue that transient firing rate changes in the brainstem nucleus locus coeruleus may be responsible for approximate gain optimization.

The optimal usage of designed fuel pellets is one of the very important parameters in inertial confinement fusion (ICF) systems. In this research, time-dependent dynamical equations for D/D fuel are written by considering impurity of ⁶Li. Then dependency of gain on temperature, density and pellet radius is studied using Runge–Kutta method. The obtained results show that the energy gain will be maximized at the initial temperature 35 keV, density, 5000 g/cm³ and ratio impurity of ⁶Li, 0.05.

We have considered soliton pulse compression in a dispersion decreasing ideal elliptical birefringent fiber with phase modulation. We have shown that there is exact balancing between the effective gain and the effective phase modulation and as a result arrive at the fundamental soliton solution. For the various dispersion decreasing profiles we have considered, we have shown that the hyperbolic profile is the best suitable choice for the dispersion decreasing profile as it provides fairly good compression even after compensating for the fiber loss.

The polarized spectra of the intensity and gain of the amplified spontaneous emission (ASE) have been measured for two glycerin solutions of a laser dye Rhodamine-640 (RhA and RhB with concentrations of 3 × 10^-4 and 3 × 10^-3 M/L, respectively). The solutions were pumped by the linearly polarized light. The ASE polarization ratio r strongly depends on the pump pulse energy, which is continuously increasing up to one for RhA and saturating at the level of r ≈ 0.8 for RhB. The gain spectra have been measured by variation of the amplification length for ASE. With increasing pump beam energy, the maximum gain continuously grows for RhA and saturates for RhB, reaching the values of 14–15 and 6 cm^-1 for both materials for the polarization parallel to the pump beam polarization. At a particular spectral point, the gain coefficient has also been measured by the direct amplification of the probe beam of a microlaser on a cholesteric liquid crystal.

The spectra of amplified spontaneous emission (ASE) intensity and gain have been measured for solutions of laser dye Rhodamine-640 in glycerin with light scattering TiO₂ nanoparticles. Such solutions typically manifest random lasing in backscattering geometry. In this work, the conventional transverse pump geometry is used, and the ASE gain spectra are measured using a variation of the length of the illuminated (pumped) stripe. In this geometry, with increasing concentration of nanoparticles, the "unidirectional" gain along the stripe decreases dramatically. At the same time, strong narrowing of the ASE bandwidth is observed even in the absence of net gain. The experimental results help one to understand the role of the scattering particles in the light amplification. On the one hand, the particles increase a zigzag type of the light path within the amplifying medium, which results in bandwidth narrowing and strong amplification of chaotic light beams. On the other hand, the amplification of a seed beam propagating in a selected direction is dramatically suppressed. The results are discussed using simple modeling of ASE amplification and qualitative arguments.

This paper reports on the simulative and comparative study on the effects of multi quantum well (MQW) design parameters on the spectral linewidth of a wafer-bonded GaAs/InP-based, 1.5 μm long-wavelength vertical-cavity surface-emitting laser (LW-VCSEL). The device employs InGaAsP MQWs sandwiched between GaAs/AlGaAs and GaAs/AlAs distributed Bragg reflectors (DBR) and utilizes a bottom-emitting, air-post design for current confinement. Among the modeled LW-VCSEL devices, the best linewidth achieved was 41.29 MHz at a peak wavelength of 1.57 μm for 8 MQWs with well thicknesses of 5.5 nm each and barrier thicknesses of 8 nm; equivalent to the experimental device developed in the past. Comparison of linewidth values calculated using developed analytical equations that link the MQW parameters to the spectral linewidth versus the actual linewidth from fabricated devices yields error ratios of ~ 6% proving a robust approximation has been achieved.

In this paper, we present a novel erbium–ytterbium doped fiber amplifier (EYDFA) + Raman + EYDFA hybrid optical amplifier (HOA) for a super-dense wavelength division multiplexing (SD-WDM) system application. The performance of the 100-channel system has been investigated for an overall data rate and channel spacing of 100Gb/s and 0.4nm, respectively, over a wavelength span of 1550–1589.9nm. HOA has been optimized for Raman length, EYDFA lengths, pump powers and Er${}^{+}$ concentrations to achieve high average gain and low gain variation ratio of 40.41dB and 0.40respectively. The optimized configuration of the proposed HOA has been compared with EYDFA + Raman and Raman + EYDFA HOA configurations. The achieved high and flat gain with an acceptable output optical signal to noise ratio (OSNR) in case of EYDFA + Raman + EYDFA HOA; makes it an optimum choice for SD-WDM systems.

We demonstrate a polarization-insensitive multiple-quantum-well optical amplifer for 1.3 μm wavelength in AlGaInAs-InP material system, using three tensile strained wells with strain of 0.36% in the active region. The amplifiers were fabricated forming ridge waveguide structure, which showed excellent polarization insensitivity (less than 0.6 dB) over the entire range of wavelength (1.28 μm ~ 1.34 μm) and a gain of 22.5 dB at the bias current of 200 mA and 1304 nm wavelength.

In this paper, a method based on prospect theory is proposed to solve the multiple attribute decision making (MADM) problem with three formats of attribute aspirations. According to the idea of prospect theory, reference points concerning attributes are first determined. Then, for the three formats of attribute aspirations, the calculation formulae of alternatives' gains/losses concerning attributes are given. By calculating each alternative's gain/loss, a gain–loss matrix is constructed. Further, using the value function from prospect theory and the simple additive weighting method, the overall prospect value of each alternative is calculated. Based on the obtained overall prospect values, a ranking of alternatives can be determined. Finally, a case study is given to illustrate the use of the proposed method.