Nonlinear Devices Research Articles

Thermal annealing enhanced morphological, nonlinear characteristic, and optical features of Victoria blue nanofilms for photonic application

Victoria blue thin films (VB) were produced using the spin coating technique (SCT) and subsequently annealed at temperatures ranging from 293 K to 463 K. The chemical structure and surface topography of VB films have been described using the Fourier-transform infrared (FT-IR) method and Scanning electron microscope (SEM). The transmittance and reflectance data were immediately used to derive optical features from 190 to 2500 nm in the wavelength range. The single oscillator model of Wemple-DiDomenico was used for determining the dispersion characteristics of VB films. Some dispersion parameters, such as dispersion energy (Ed), oscillator energy (Eο), optical conductivity (σ1, σ2) and dielectric constants (ε1and ε2) have been determined and clearly described. The values of χ3, f,M−1, M−3, ε∞,εL, N/m* , E0, Ed, n2andηopt for as deposited film are calculated as: 6.10 × 10-14, 71.30 (eV)2, 0.31, 0.040, 2.72, 4.04, 3.06 × 1046 kg−1 m−3, 6.34, 11.09, 7.6 × 10-13and 1.98, respectively. Based on this study, thermal annealing changes the optical properties of VB thin film, making it a preferable option for some photonic applications. On the other hand, the high values of these nonlinear parameters are crucial for creating low-power electronics such as optical computers. As a result, we strongly advise employing thermal annealing to change the linear and nonlinear properties of VB films, which might be the ideal choice for many photonic applications And nonlinear devices.

Two‐Photon Pumped Single‐Mode Lasing in CsPbBr3 Perovskite Microwire

AbstractAchieving high‐quality, frequency‐upconversion single‐mode lasing output is an important requirement for developing new nonlinear optoelectronic devices, such as on‐chip optical communication, nonlinear optical switches, and optical parametric amplifiers. Here, an individual CsPbBr3 microwire prepared by the anti‐solvent method is served as both gain media and microresonator to achieve two‐photon pumped frequency upconversion single‐mode lasing with the side‐mode suppression ratio of 18 dB. Meanwhile, the refractive index of orthorhombic perovskite is theoretically calculated based on first principles, and determining its square whispering‐gallery oscillation type by combining with the plane wave model and the steady‐state oscillation conditions of laser. The extracted exciton binding energy of 33.15 meV higher than the thermal ionization energy of room temperature (≈26 meV) suggests that the as‐grown CsPbBr3 microwires possess the capacity to achieve two‐photon pumped lasing output, as well further gaining deeper insights into the role of exciton‐phonon coupling in light emission.

Promoting second-harmonic generation in the LiNbO3 film combined with metasurface using plasmonic quasi bound states in the continuum

Metasurfaces have become a fascinating framework for nonlinear optics, with the advantages of a compact footprint and unprecedented flexibility to manipulate light. However, further advancements are necessary to enhance the efficiency of metasurfaces in nonlinear devices. Here, a novel approach for second harmonic generation (SHG) based on the LiNbO3 metasurface using leaked plasmonic bound states in the continuum (BIC) is proposed. The behavior of SHG in the guided mode resonance (GMR) under TE polarization and plasmonic modes under TM polarization is investigated. The structure consists of a plasmonic grating overlying a nonlinear lithium niobate dielectric waveguide layer that supports two different BIC, namely plasmonic BIC and GMR BIC. The evolution of second harmonics generation(SHG) near two groups of BIC is explored. The SHG of the plasmonic quasi-BIC is stronger than that based on the GMR quasi-BIC. In addition, the plasmonic accidental quasi-BIC produces stronger harmonic effects than the quasi-BIC based on symmetry-broken. Specifically, at a pump intensity of 30 MW/cm2, this accidental quasi-BIC results in SHG efficiency of 1.86 × 10−3. This work provides a valuable approach to achieving enhanced SHG using plasmonic and BIC. It opens up new possibilities for the utilization of LiNbO3 in integrated nonlinear nanophotonics and paves the way for the development of advanced nonlinear photonic devices.

Performance Analysis of a Backward/Forward Algorithm Adjusted to a Distribution Network with Nonlinear Loads and a Photovoltaic System

Context: The backward/forward (BF) algorithm is a sweep-type technique that has recently been used as a strategy for the power flow analysis of ill-conditioned networks. The purpose of this study is to evaluate the performance of the BF algorithm compared to that of a computational tool such as Simulink, with both strategies adjusted to the operating conditions of a distribution network with nonlinear components (loads and photovoltaic system), unbalanced loads, and harmonic distortion in the voltage and current signals. Method: The study case is a low-voltage distribution network with a radial topology, unbalanced loads, and nonlinear components. The BF algorithm is adjusted to consider two approaches of the Norton model: a coupled admittance matrix and a decoupled admittance matrix. The latter is also used in the network model created in Simulink. The performance of the algorithm is evaluated by analyzing 18 operation scenarios defined according to the presence and use intensity of the loads and solar irradiance levels (low and high). Results: In general, the three strategies could successfully determine the waveform and RMS values of the voltage signals with errors of less than 0,8 and 1,3%, respectively. However, the performance of the strategies for the estimation of current signals and power parameters shows errors of 5-300% depending on the level of solar irradiance at which the photovoltaic system operates. Conclusions: The results show that the BF strategy can be used to analyze unbalanced power grids with increasing penetration of renewable generation and the integration of nonlinear devices, but the performance of this strategy depends on the load model applied to represent the behavior of nonlinear devices and generation systems.

Active terahertz frequency conversion on silicon-based time-varying metasurface

Terahertz (THz) metasurfaces have emerged as the preferred material for active devices, with numerous potential applications. However, due to a lack of materials with an ultrafast response, functional devices with fascinating time-varying phenomena remain to be explored. In this study, we experimentally investigated a time-varying THz metasurface with silicon–gold hybrid structures. The results show that the transmission spectra undergo a remarkable transformation when an optical pump is used. A transient time boundary is introduced to study the time-varying response using the sudden change in silicon conductivity in the presence of an optical pump. We observed the generation of new spectral components, and the magnitude of the converted wave is linear with the incident power. The proposed silicon-based THz time-varying metasurface paves the way for developing THz sources and nonlinear optical devices.

Bulk-Switching Memristor-Based Compute-In-Memory Module for Deep Neural Network Training.

The constant drive to achieve higher performance in deep neural networks (DNNs) has led to the proliferation of very large models. Model training, however, requires intensive computation time and energy. Memristor-based compute-in-memory (CIM) modules can perform vector-matrix multiplication (VMM) in place and in parallel, and have shown great promises in DNN inference applications. However, CIM-based model training faces challenges due to non-linear weight updates, device variations, and low-precision. In this work, a mixed-precision training scheme is experimentally implemented to mitigate these effects using a bulk-switching memristor-based CIM module. Low-precision CIM modules are used to accelerate the expensive VMM operations, with high-precision weight updates accumulated in digital units. Memristor devices are only changed when the accumulated weight update value exceeds a pre-defined threshold. The proposed scheme is implemented with a system-onchip of fully integrated analog CIM modules and digital sub-systems, showing fast convergence of LeNet training to 97.73%. The efficacy of training larger models is evaluated using realistic hardware parameters and verifies that CIM modules can enable efficient mix-precision DNN training with accuracy comparable to full-precision software-trained models. Additionally, models trained on chip are inherently robust to hardware variations, allowing direct mapping to CIM inference chips without additional re-training.

Mitigation of Grid Current Harmonics by ABC- ANN based Shunt Active Power Filter

Harmonics are being introduced into power system networks as a result of the increasing use of nonlinear devices. These harmonics cause distortion of current and voltage signals, which in turn causes damage to power distribution systems. As a result, the suppression of harmonics is of extreme significance in power systems. This paper proposes Shunt Active Power Filters (SAPF) based on neural network algorithms like Artificial Neural Network (ANN) as a feasible approach to mitigating harmonic distortion and raising power quality in electrical distribution systems. This research shows that using shunt active power filters (SAPF), which use the Artificial Bee Colony Optimized Artificial Neural Network Controller (ABC-ANN), is an efficient method for enhancing power quality and minimizing harmonic distortion in distribution systems. The ABC-ANN algorithms have been produced for SAPF with the goal of improving system performance by reducing Grid current Harmonics .In the first stage of this work, PSO Technique is used to tune a standard PI controller to its optimum gain values (Ki ,Kp). Then, these target and input data of PSO tuned PI controller will be supplying inputs to the ANN controller. To find the optimal weight and bias values, this ANN controller has been tuned with the help of the ABC algorithm. Using MATLAB/SIMULINK software, we compare the performance of the proposed algorithm to that of other optimization algorithm like Differential Evaluation (DE) algorithm, as well as the PSO tuned PI controller and traditional PI controller. The findings from the simulation suggest that a SAPF utilizing an ABC trained ANN controller could improve THD in the supplying current while maintaining harmonics within IEEE-519 accepting levels.

Multiple surface lattice resonances of overlapping nanoparticle arrays with different lattice spacing.

Multiple surface lattice resonances generated with nanoparticle arrays are promising to enhance light-matter interactions at different spectral positions simultaneously, and it is important to tailor these resonances to desired frequencies for practical applications such as multi-modal nanolasing. To this end, this study proposes to generate multiple surface lattice resonances using overlapping nanoparticle arrays with different lattice spacing. Both full-wave numerical simulations and analytical coupled dipole approximation calculations reveal that for the overlapping structures composed with two different gold nanosphere arrays, both surface lattice resonances for the element structures are effectively excited. Considering that the optical responses are governed by the dipole-dipole interactions between the nanoparticles, it is interesting to find that the multiple surface lattice resonances are almost invariant by adjusting the relative shifts between the two arrays, which can be useful to tailor the high-quality factor resonances to desired spectral positions. In addition, due to the same reason, it is also shown that the multiple surface lattice resonances can be further finely tuned by selectively removing specific nanoparticles in the array. We anticipate that the tolerance to generate multiple surface lattice resonances and the flexible tunability make the overlapping nanoparticle arrays useful to design high performance linear and nonlinear nanophotonic devices.

Determination of optical constants via the single oscillator Drude-Voigt dispersion model in fluoroborate glass for optical lenses: Nonlinear optical properties

In this work, a new fluoroborate (B2O3+AlF3+NaF + CaF2) glass has been fabricated using the melt-quenching technique. Glass sample has been characterized via X-ray diffraction, scanning electron microscope, and optical spectrophotometric measurements for absorption, transmission, and reflection in the range of 350–750 nm. The optical absorption of this transparent glass is used to determine the absorption coefficients, which are then used to estimate the extinction coefficients. The refractive indices as a function of wavelengths are estimated using extinction coefficients and reflectance data of fluoroborate glass. Very important parameters such as density, molar volume, and molar polarizability have been extensively studied. Using these data, fundamental optical parameters such as average oscillator strength (6.42) and inherent absorption wavelength (119 nm) are evaluated using the Drude-Voigt single oscillator model. Compared with previously studied oxide-based glasses, the fluoroborate glass possesses a relatively high refractive index of 1.74 and an Abbe number of 49 in the visible region of 587.6 nm. The relationship between inherent absorption wavelength and Abbe number values is also discussed. Moreover, the values of refractive index and linear optical susceptibility are used to evaluate the third-order optical susceptibility (11.56 × 10−14 esu) and nonlinear refractive index (2.50 × 10−12 esu). These results suggest that fluoroborate glass is a potential material for optical lenses and nonlinear devices in the visible range.

Minimalistic System of Characteristics of Non-linear Baseband Pulse Devices and Its Measurement

Introduction. The general system of parameters, including compression points and intersection points of various harmonics, is unsuitable for devices operating under the influence of baseband pulses (for example, before the modulator in the transmitter, after the demodulator in the receiver). Previously, the authors have developed simple models in the form of nonlinear recursive filters, which give a satisfactory error in describing the response of a wide class of baseband pulse circuits. The system of nonlinear functions of such models can be considered as a new system of characteristics of nonlinear-dynamical baseband impulse circuits, for which it is necessary to develop a method that ensures their measurement with an acceptable error. In the general formulation, this problem is rather challenging; therefore, this article considers only a first-order nonlinear recursive filter. However, the obtained result gives satisfactory results for devices without flat top transient overshoot.Aim. To consider a method for measuring the characteristics of nonlinear-dynamical baseband impulse devices without overshoot on the flat top of the transient response.Materials and methods. The considered recursive filter is represented by an equivalent circuit consist of nonlinear resistive and capacitive elements. Therefore, the task is reduced to measuring their current-voltage characteristics (IV) and charge-voltage characteristics (CVC). IV characteristics are measured at the flat tops of the transient characteristics of the device. Having a certain IV, we obtain the opportunity to calculate the current (and then the charge) of the capacitive element. The experimental study was carried out on the example of a three-stage amplifier with an aperiodic transient response.Results. The transient characteristics of the filter are approximated by the model with an accuracy of no worse than 3.2 %.Conclusion. The considered system of functions can be obtained with a definable error that satisfactory for practice, which allows it to be considered as a new system of parameters for nonlinear baseband pulse devices.

Controllable optical bistability in a Fabry–Pérot cavity with a nonlinear three-dimensional Dirac semimetal

Optical bistability (OB) is capable of rapidly and reversibly transforming a parameter of an optical signal from one state to another, and homologous nonlinear optical bistable devices are core components of high-speed all-optical communication and all-optical networks. In this paper, we theoretically investigated the controllable OB from a Fabry–Pérot (FP) cavity with a nonlinear three-dimensional Dirac semimetal (3D DSM) in the terahertz band. The OB stems from the third-order nonlinear bulk conductivity of the 3D DSM and the resonance mode has a positive effect on the generation of OB. This FP cavity structure is able to tune the OB because the transmittance and the reflectance can be modulated by the Fermi energy of the 3D DSM. We believe that this FP cavity configuration could provide a reference concept for realizing tunable bistable devices.

Two-dimensional tellurium-based diodes for RF applications

The research of two-dimensional (2D) Tellurium (Te) or tellurene is thriving to address current challenges in emerging thin-film electronic and optoelectronic devices. However, the study of 2D-Te-based devices for high-frequency applications is still lacking in the literature. This work presents a comprehensive study of two types of radio frequency (RF) diodes based on 2D-Te flakes and exploits their distinct properties in two RF applications. First, a metal-insulator-semiconductor (MIS) structure is employed as a nonlinear device in a passive RF mixer, where the achieved conversion loss at 2.5 GHz and 5 GHz is as low as 24 dB and 29 dB, respectively. Then, a metal-semiconductor (MS) diode is tested as a zero-bias millimeter-wave power detector and reaches an outstanding linear-in-dB dynamic range over 40 dB, while having voltage responsivities as high as 257 V ⋅ W−1 at 1 GHz (up to 1 V detected output voltage) and 47 V ⋅ W−1 at 2.5 GHz (up to 0.26 V detected output voltage). These results show superior performance compared to other 2D material-based devices in a much more mature technological phase. Thus, the authors believe that this work demonstrates the potential of 2D-Te as a promising material for devices in emerging high-frequency electronics.

Neodymium oxide saturable absorber for generating Q-switched and mode-locked pulses in 1.55-micron region

Exploring new saturable absorber (SA) materials is important for the advancement fibre laser technology especially in the improving the performance of Q-switched and mode-locked fiber lasers, which have tremendous applications in areas such as material processing, telecommunications, biomedical imaging, and scientific research. Here, we prepared a layer of Neodymium Oxide (Nd2O3) film as a nonlinear optical device to obtain the Q-switched and mode-locked pulses in the Erbium-doped fiber laser (EDFL) cavity. The developed Nd2O3 film recorded excellent optical properties with the saturable absorption of 2.8%, saturation intensity of 0.8 MW /cm2 and non-saturable loss of 59.0%. By integrating the Nd2O3 film into a simple ring EDFL’s cavity, a stable and robust Q-switched laser operating at 1558 nm was realized as the pump power is set between 45 and 92 mW. The average output power improved from 4.70 to 9.57 mW as the strength of the pumping was raised from 45 to 92 mW. The repetition rate and pulse width are tunable from 71 to 89 kHz and 3.48–2.56 µs, respectively as the pump power is escalated within the same range. The fundamental frequency of electrical signal exhibits signal-to-noise ratio (SNR) of 62 dB and this signifies the excellent stability of the Q-switching operation. In an extended EDFL cavity, the Nd2O3SA can produce a mode-locked soliton pulse operating at 1559.29 nm. The laser run at repetition rate of 1.89 MHz and pulse duration of 3.73 ps while recorded the highest peak power of 1.7 kW at pump power of 97.62 mW.

Manipulation of nonlinear optical responses in layered ferroelectric niobium oxide dihalides

Realization of highly tunable second-order nonlinear optical responses, e.g., second-harmonic generation and bulk photovoltaic effect, is critical for developing modern optical and optoelectronic devices. Recently, the van der Waals niobium oxide dihalides are discovered to exhibit unusually large second-harmonic generation. However, the physical origin and possible tunability of nonlinear optical responses in these materials remain to be unclear. In this article, we reveal that the large second-harmonic generation in NbOX2 (X = Cl, Br, and I) may be partially contributed by the large band nesting effect in different Brillouin zone. Interestingly, the NbOCl2 can exhibit dramatically different strain-dependent bulk photovoltaic effect under different polarized light, originating from the light-polarization-dependent orbital transitions. Importantly, we achieve a reversible ferroelectric-to-antiferroelectric phase transition in NbOCl2 and a reversible ferroelectric-to-paraelectric phase transition in NbOI2 under a certain region of external pressure, accompanied by the greatly tunable nonlinear optical responses but with different microscopic mechanisms. Our study establishes the interesting external-field tunability of NbOX2 for nonlinear optical device applications.

Equivalent Circuits Application of Pin-Diodes and MEMS-Keys in Electrodynamic Modeling Problems

This article studies the possibility of using circuit formats to describe radio components in electrodynamic modeling problems. The study was carried out on the example of a controlled metamaterial in the form of an electromagnetic crystal with SPICE-models of equivalent circuits of pin-diodes and MEMS-keys. Also, the possibility of using Touchstone files as an alternative format for describing radio-electronic components was considered. The obtained results are illustrated by scatter matrix plots, as well as equivalent circuits and SPICE code. Obtained results can be used for the design of structures that combine active nonlinear radio components and microwave devices.

A generalized admittance criterion for dominant harmonic source determination without synchronous phasor measurements

The widespread integration of various nonlinear power electronic devices in modern power systems has made harmonic distortion more serious than ever before. Given the urgent need to improve power quality, the harmonic contribution evaluation (HCE) is of great importance since it can provide a strong basis for harmonic mitigation measures. However, the conventional HCE methods are not effective due to the lack of synchronous voltage and current phasor information in real-field practice. To overcome the phasor limitation, an HCE method based on a generalized admittance criterion (GAC) is proposed in this paper. The proposed GAC aims to determine the dominant harmonic source at the point of common coupling (PCC) from the utility side and customer side. Compared to the conventional method, the developed method only needs the RMS values of the PCC voltage, current, and phase angle difference. Therefore, the synchronous phasor information of voltage and current is no longer required. Meanwhile, a threshold to determine the dominant harmonic source is established by using the equivalent admittance ratio on both sides of PCC. The evaluation process of the proposed method is significantly simplified by comparing the generalized admittance limit with the proposed threshold, which also greatly improves the method evaluation accuracy. Moreover, the interference of background harmonic fluctuation is excluded by using the linear calibration-based harmonic admittance estimation method. Finally, multiple scenarios with various admittance characteristics were simulated to verify the performance of the proposed criterion, and the real-field measurement is also used to demonstrate the accuracy and validity of the proposed method.

Magnetically tunable zero-index metamaterials

Zero-index metamaterials (ZIMs) feature a uniform electromagnetic mode over a large area in arbitrary shapes, enabling many applications including high-transmission supercouplers with arbitrary shapes, direction-independent phase matching for nonlinear optics, and collective emission of many quantum emitters. However, most ZIMs reported to date are passive; active ZIMs that allow for dynamic modulation of their electromagnetic properties have rarely been reported. Here, we design and fabricate a magnetically tunable ZIM consisting of yttrium iron garnet (YIG) pillars sandwiched between two copper clad laminates in the microwave regime. By harnessing the Cotton–Mouton effect of YIG, the metamaterial was successfully toggled between gapless and bandgap states, leading to a “phase transition” between a zero-index phase and a single negative phase of the metamaterial. Using an S-shaped ZIM supercoupler, we experimentally demonstrated a tunable supercoupling state with a low intrinsic loss of 0.95 dB and a high extinction ratio of up to 30.63 dB at 9 GHz. We have also engineered a transition between the supercoupling state and the topological one-way transmission state at 10.6 GHz. Our work enables dynamic modulation of the electromagnetic characteristics of ZIMs, enabling various applications in tunable linear, nonlinear, quantum, and nonreciprocal electromagnetic devices.

Observation of spatial self-phase modulation excited by off-axis integer and fractional vortex beams

Spatial self-phase modulation (SSPM) is widely used to characterize the nonlinear refractive index of two-dimensional layered materials and design passive nonlinear photonic devices. In this work, we investigate the SSPM phenomena of black phosphorus dispersed in agarose solid under the excitation of on-axis and off-axis integer and half-integer vortex beams. It is found that with the increase of the off-axis distance of the Gaussian vortex beam, the pattern of the far-field self-diffraction intensity gradually breaks from the initial ring and finally evolves into a tail outside the self-diffraction ring. Moreover, for half-integer vortex beams, the size of the innermost tail of the self-diffraction ring is nearly half smaller than that of the second outer tail. The underlying mechanism of the observed SSPM phenomenon is also analyzed. Interestingly, the trailing number and rotation direction of the self-diffraction ring pattern quantitatively reflect the magnitude and sign of the topological charge (TC) of the off-axis vortex beam, respectively. This work provides a novel method to measure the TC of off-axis vortex beam in the nonlinear optics regime.

Ab-initio investigation of structural, opto-electronic, and thermodynamic properties of ZnAl2Se4 for photovoltaic applications

In this manuscript, the structural, opto-electronic, and thermodynamic properties of ZnAl2Se4 chalcogenide compounds were studied in detail using the full potential linearized augmented plane wave method. The exchange and correlation potentials used in density functional theory were calculated using local density approximation, the generalized gradient approximation (GGA) method, and the modified Becke–Johnson (mBJ) potential using Wien2k code. The obtained results were compared with each other as well as with available experimental data. At ambient conditions, ZnAl2Se4 is a direct wide bandgap (Г–Г) semiconductor with a bandgap of 2.1 and 3.3 eV with GGA and mBJ potentials, respectively. Density of states (DOS; total DOS and Partial Density Of States (PDOS)) and electron density contour plots were in similar accordance with bandgap, showing semiconductive behavior and covalent bonding nature. The optical properties like the real and imaginary parts of the dielectric constant, the energy loss function L( ω), and the conductivity σ( ω) were calculated. Optical aspects show interaction among phonon and electron in terms of long-range and short-range forces. The studied compound is very useful for various linear–nonlinear optical devices, so this compound is very valuable for several linear–nonlinear optical devices. So this manuscript represents a comprehensive approach for calculating the complete set of useful properties of the ZnAl2Se4 compound, which can provide support for understanding various device phenomena such as electrochemical sensing, photovoltaics, and nonvolatile electronic memories.

Efficient second harmonic generation at quasi-bound states in the continuum in hybrid nanostructures of 2D plasmonic array and waveguide

We numerically investigate the second harmonic generation (SHG) in hybrid plasmonic–photonic structures consisting of an array of periodic gold nanodisks covered by a nonlinear dielectric layer. In the designed hybrid systems, symmetry-protected bound states in the continuum (BICs) at normal incidence, and Friedrich–Wintgen BICs due to the coupling between localized surface plasmon resonances (LSPRs) and waveguide modes at oblique incidence, are observed under both transverse-electric (TE) and transverse-magnetic (TM) polarized illuminations. SHG near the BICs is studied, and the dramatically enhanced nonlinear optical response at quasi-BICs is obtained. Such enhancement is ascribed to the enhanced local field due to hybrid modes of LSPRs and photonic modes. The results indicate that hybrid plasmonic-dielectric systems supporting BICs at both TE- and TM-polarized incidences are promising platforms for linear and nonlinear photonic devices.