Nonlinear Applications Research Articles

High Q transparency, strong third harmonic generation, and giant nonlinear chirality driven by toroidal dipole-quasi-BIC

Electromagnetically induced transparency (EIT), nonlinearity, and optical chirality hold significant applications in many areas such as optical switches, slow-light devices, chiral harmonic conversion, and optical storage. In this work, we theoretically propose an asymmetric all-dielectric metasurface supporting toroidal dipole-quasi-bound states in the continuum (TD-q-BICs). High quality (Q) EIT, strong third harmonic generation (THG), and giant nonlinear chirality are achieved via the extremely enhanced electric field energy localized in the Si plate by the TD-q-BIC. A huge transition from high Q EIT with transmission of ∼0.99 to strong chirality with circular dichroism (CD) of ∼0.9 is realized by tuning the angle and polarization state of incident light. Strong THG with efficiency of 4.5 × 10−3 under linear polarization light is due to the highly localized electric field supported by the TD-q-BIC and perfect nonlinear CD chirality with theoretically value of ∼1 originates from the large discrepancy in electric field distributions under different circularly polarized light. Our work provides an innovative paradigm to construct TD-q-BICs-governed EIT analogs, THG, and nonlinear chirality for the development of multifunction nanophotonic meta-devices.

Multi-wing chaotic system based on meminductor and its application in image encryption

Meminductor is a novel type of nonlinear device following the memristor, characterized by its memory properties. Currently, research on meminductors is still in its infancy, with their physical devices yet to be formally realized. Therefore, conducting fundamental research on their nonlinear circuit properties and applications is of great significance. In this paper, a new multi-wing chaotic system is proposed based on the mathematical model of a magnetically controlled meminductor. By varying the values of its parameters, the system can generate two-wing, three-wing, and four-wing chaotic attractors. Various analytical methods are employed to study the dynamical behaviours of the proposed chaotic system. The results demonstrate that the system is highly sensitive to its initial conditions and control parameters, which makes it suitable for image encryption. Based on the new system, we propose a new algorithm for image encryption that combines the newly established four-dimensional multi-wing chaotic system with bit plane decomposition technique, firstly, the high four-bit planes containing 94% image information are disordered by S-type permutation, then the disordered bit planes perform operation of XOR with the random matrix generated by chaotic sequences, and finally, the encrypted image is obtained by merging the bit planes.

Versatile Metamaterial: Exploring the Resonances of Symmetry‐Protected Modes for Multitasking Functionality

AbstractIn this work, an experimental study supported by numerical modeling that demonstrates the possibility of exciting Symmetry Protected‐Bound states In the Continuum (SP‐BICs) in a 1D silicon grating fabricated on a lithium niobate substrate is presented. bBoth transverse electric and magnetic polarization states are investigated, leading to the excitation of four quasi‐ Bound states In the Continuum (quasi‐BIC) resonances, exhibiting distinct behaviors. Under standard illumination conditions (plane of incidence perpendicular to the 1D grating lines), two of these resonances are highly sensitive to illumination conditions, while the other two resonances involving unconventional illumination directions (plane of incidence parallel to the grating lines) are more robust to the angle of incidence, but just as sensitive to external stresses in terms of resonance wavelength and quality factor. Additionally, temperature detection is experimentally demonstrated with a Sensitivity of ST = 0.81∼nm °C−1, a state‐of‐the‐art value achieved due to significant electromagnetic field enhancement inside the lithium niobate substrate at the quasi‐BIC resonance. These findings pave the way for their use in various sensing applications (such as biology, electromagnetic, and temperature sensing), as well as nonlinear applications like second harmonic generation, and electro‐ and acousto‐optic modulation.

An insight into the solitonic features of the nonlinear generalized higher-order Schrödinger equation using the solver method

For many nonlinear applications described by the dynamics of nonlinear Schrödinger equation with higher-order terms (HONLSE) such as nonlinear optics, space plasma physics molecular biology, astrophysics, quantum mechanics, superfluid, fluid mechanics, and fiber optics communications, a unique closed-form solution have been obtained using energy equation. In addition, some new solitary solutions HONLSE have been obtained via the unified solver method. The resultant solutions behave as breathers, super solitons, envelope breathers, blow up, localized super waves, periodical super shock, train super solitons, and shock structures. The modulations of Kerr nonlinear, chromatic dispersive, and wave packet drift parameters on the wave characteristics of the obtained solutions have been investigated. It was reported that the model parameters affect the amplitude, steepness, and width of the resultant structures. The provided solution can be used as a box solver for a variety of natural science systems described by distinct nonlinear equations.

Broadband nonlinear refraction transients in C-doped GaN based on absorption spectroscopy

Optical nonlinear response and its dynamics of wide-bandgap materials are key to realizing integrated nonlinear photonics and photonic circuit applications. However, those applications are severely limited by the unavailability of both dispersion and dynamics of nonlinear refraction (NLR) via conventional measurements. In this work, the broadband NLR dynamics with extremely high sensitivity (λ/1000) can be obtained from absorption spectroscopy in GaN:C using the refraction-related interference model. Both the absorption and refraction kinetics are found to be significantly modulated by the C-related defects. Especially, we demonstrate that the refractive index change Δn of GaN:C is negative and can be used to realize all-optical switching applications owing to the large NLR and ultrafast switching time. The NLR under different non-equilibrium carrier distributions originates from the capture of electrons by CN+ defect state, while the absorption modulation originates from the excitation of tri-carbon defects. We believe that this work provides a better understanding of the GaN:C nonlinear properties and an effective solution to broadband NLR dynamics of transparent thin films or heterostructure materials.

Statics and dynamics of a lunar anchored tethered system

Space tethered system has various attractive potential applications and now serves as promising lunar infrastructures hopefully. In this paper, statics and dynamics of a lunar anchored space tethered system in the restricted Earth-Moon three-body system will be studied to enable future potential applications. Nonlinear dynamics and potential applications of a space tether system extending from the lunar surface to the Earth’s side are investigated. The static equilibrium equations of the system with a distributed mass tether are established at the L1 side without considering small perturbations caused by eccentricity to analyze internal stress, detailed cross-sectional profiles, and counterweight mass. The elastic deformations are discretized using the assumed modes method, and the Lagrangian approach is used to derive the dynamical equations of the system with a viscoelastic tether considering the elastic elongation within the elliptical Earth-Moon restricted three-body system (EEMRTB). The oscillations of the tether as well as the distribution of stress and strain are addressed using numerical analysis considering both construction difficulty and power generation capacity, the ideal design parameter ranges are provided based on the nonlinear dynamic analysis. Additionally, a brief analysis of the accessible regions within the Earth-Moon system is also conducted. The validity, accuracy and advantage of the established dynamics are clarified.

Spectral period doubling and encoding of dissipative optical solitons via gain control

Period-doubling bifurcation, as an intermediate state between order and chaos, is ubiquitous in all disciplines of nonlinear science. However, previous experimental observations of period doubling in ultrafast fiber lasers are mainly restricted to self-sustained steady state, controllable manipulation and dynamic switching between period doubling and other intriguing dynamical states are still largely unexplored. Here, we propose to expand the vision of dissipative soliton periodic doubling, which we illustrate experimentally by reporting original spontaneous, collisional, and controllable spectral period doubling in a polarization-maintaining ultrafast fiber laser. Specifically, the spontaneous period doubling can be observed in both single- and double-pulses. The mechanism of the switchable state and periodic doubling was revealed by numerical simulation. Moreover, state transformation of individual solitons can be resolved during the collision of triple solitons involving stationary, oscillating, and period doubling. Further, controllable deterministic switching between period doubling and other dynamical states, as well as exemplifying the application of period-doubling-based digital encoding, is achieved under programmable pump modulation. Our results open a new window for unveiling complex Hopf bifurcation in dissipative systems and bring useful insights into nonlinear science and applications.

Wafer-scale fabrication of InGaP-on-insulator for nonlinear and quantum photonic applications

The development of manufacturable and scalable integrated nonlinear photonic materials is driving key technologies in diverse areas, such as high-speed communications, signal processing, sensing, and quantum information. Here, we demonstrate a nonlinear platform—InGaP-on-insulator—optimized for visible-to-telecommunication wavelength χ(2) nonlinear optical processes. In this work, we detail our 100 mm wafer-scale InGaP-on-insulator fabrication process realized via wafer bonding, optical lithography, and dry-etching techniques. The resulting wafers yield 1000 s of components in each fabrication cycle, with initial designs that include chip-to-fiber couplers, 12.5-cm-long nested spiral waveguides, and arrays of microring resonators with free-spectral ranges spanning 400–900 GHz. We demonstrate intrinsic resonator quality factors as high as 324 000 (440 000) for single-resonance (split-resonance) modes near 1550 nm corresponding to 1.56 dB/cm (1.22 dB/cm) propagation loss. We analyze the loss vs waveguide width and resonator radius to establish the operating regime for optimal 775–1550 nm phase matching. By combining the high χ(2) and χ(3) optical nonlinearity of InGaP with wafer-scale fabrication and low propagation loss, these results open promising possibilities for entangled-photon, multi-photon, and squeezed light generation.

Optimization of photocurrent and surface wettability of new As10Bi30Se30Te30 thin films through annealing at different temperatures for optoelectronic applications

Group V-VI-based metal-doped double chalcogenides are essential in thermoelectric and suitable optoelectronic devices. The present investigation is based on optimising various optical, structural, and electrical behaviours of quaternary As10Bi30Se30Te30 films through thermal annealing at different temperature scales. The structural study by X-ray diffraction (XRD) exhibited the presence of various Bi2Se3, Bi2SeTe2, and Bi2Te3 phases in the annealed films. The crystallinity gradually enhanced after the annealing process. The microstructural modifications in the material have been confirmed through the Raman spectra. The elemental confirmation was verified from the energy dispersive X-ray (EDX) spectra, whereas the cross-sectional scanning electron microscopy (SEM) view showed the annealing-induced modifications in the films. The granular structure in the films is seen from the surface morphology study. The reduction of the energy gap from 1.36 ± 0.002 eV to 1.26 ± 0.001 eV upon annealing induced the increment in refractive index from 3.08 to 3.15. With annealing, the non-linear refractive index varied from 4.341x10−10 esu to 5.218 x10−10 esu. This indicates the narrowing of the bandgap and enhancement in the non-linear optical response of the material after the annealing process. The 3rd-order nonlinear susceptibility is also increased by annealing, thus making it suitable for nonlinear device applications. Annealing-induced surface change in the material enhances its surface wettability and makes it more hydrophilic. The linear enhancement in photocurrent with the voltage is ohmic and makes it suitable for various optoelectronic applications.

Non-linear MHD modelling of transients in tokamaks: a review of recent advances with the JOREK code

Abstract Transient MHD events like edge localized modes (ELMs) or disruptions are a concern for magnetic confinement fusion power plants. Research with the MHD code JOREK towards understanding control of such instabilities is reviewed here. Experimental validation for unmitigated vertical displacement events (VDEs) progressed. The mechanism of vertical force mitigation by impurity injection was identified. Two-way eddy current coupling to CARIDDI was completed. Shattered pellet injection (SPI) was simulated in JET, KSTAR and ASDEX Upgrade (AUG) and ITER. Benign runaway electron (RE) beam termination in JET and ITER was studied. Coupling of kinetic REs to the MHD is ongoing and a virtual RE synchrotron radiation diagnostic was developed. Regarding pedestal physics, regimes devoid of large ELMs in AUG were simulated and predictive JT60-SA simulations are ongoing. For ELM suppression by resonant magnetic perturbations (RMPs), AUG, ITER and EAST simulations were performed. A free boundary RMP model was validated against experiments. Evidence for penetrated magnetic islands at the pedestal top based on AUG experiments and simulations was found. Simulations of the naturally ELM-free quiescent H-mode (QH) in AUG and HL-3 show external kink mode formation prevents pedestal build-up towards an ELM within windows of the edge safety factor. With kinetic neutral particles, high field side high density (HFSHD) formation in ITER was simulated and with kinetic impurities, tungsten transport in AUG RMP plasmas was studied. To capture turbulent transport, electro-static full-f PiC models for ion temperature gradient (ITG) and trapped electron modes (TEM) were established and benchmarked. Application to RMP plasmas shows enhanced turbulence in comparison to unperturbed states. Energetic particle (EP) interactions with MHD were studied. Flux-pumping that prevents the safety factor on axis from dropping below unity was simulated. First non-linear stellarator applications include current relaxation in l=2 stellarators, while verification for advanced stellarators progresses.

Structure and properties of Er3+- modified (Bi0.5Na0.5)0.945Ba0.055TiO3-based lead-free ferroelectric ceramics

Er3+-modified (Bi0.5Na0.5)0.945Ba0.055Ti0.98(Fe0.5Sb0.5)0.02O3 (BNBT-FS) lead-free ferroelectric ceramics with large electrostrain and electrostrictive response were fabricated in our work. Results showed that Er3+-doping induced the destruction of ferroelectric order and significantly enhanced the field-induced strain. For 0.2 mol% modified sample, the unipolar strain reached 0.463 % under the electric field of 80 kV/cm, yielding a large normalized strain d33* (Smax/Emax) of 579 pm/V. For 0.4 mol% modified sample, high electrostrictive effect with temperature-insensitive electrostrictive coefficient Q33 (0.022–0.026 m4/C2 in the temperature range of 25–100°C) was obtained. The large electrostrain and electrostrictive response in the present materials show the great potential of the materials for nonlinear actuators applications.

Experimentally validated passive nonlinear capacitor in piezoelectric vibration applications

Abstract Piezoelectric vibration isolation and energy harvesting applications have been extensively studied in the literature. The studies include linear and nonlinear approaches. Linear methods are simpler but possess inherent limitations. On the other hand, nonlinear ones could perform better over a broader operating frequency range. Nonlinearity can be introduced in the mechanical domain or electrical domain actively or passively. Since electrical components can be on smaller scales compared to mechanical counterparts, inducing nonlinearity on the mechanical system through the electrical domain can be more practical. Moreover, passive structures require no energy supply and controller therefore they are simpler and more reliable than active ones. In this paper, a novel way to attain passive hardening stiffness was suggested by introducing an electrical component in a shunt circuit for passive nonlinear piezoelectric vibration isolation or energy harvesting applications and the induced structural non-linearity is demonstrated experimentally. A passive nonlinear component is suggested to be a hardening capacitor obtained by the P–N junction. An analytic model is derived for parallel connected macro-fiber composite (MFC) piezoelectric material attached bimorph configuration on a cantilever beam and the model is solved numerically. MFC integrated bimorph model, and P–N junction approximate model are presented. The frequency response of the coupled system is obtained by using numerical models and experiments. Both numerical analysis and experiments validated the hardening stiffness effect of the P–N junction. To the best of the authors’ knowledge, this study is the first study to demonstrate that nonlinear capacitance of P–N junctions can be used to attain nonlinearity in a mechanical system.

Optimal Sparsity in Nonlinear Nonparametric Reduced Order Models for Transonic Aeroelastic Systems

Machine learning and artificial intelligence algorithms typically require a large amount of data for training. This means that for nonlinear aeroelastic applications, where small training budgets are driven by the high computational burden associated with generating data, the usability of such methods has been limited to highly simplified aeroelastic systems. This paper presents a novel approach for the identification of optimized sparse higher-order polynomial-based aeroelastic reduced order models (ROMs) to significantly reduce the amount of training data needed without sacrificing fidelity. Several sparsity promoting algorithms are considered, including rigid sparsity, least absolute shrinkage and selection operator (LASSO) regression, and orthogonal matching pursuit (OMP). The study demonstrates that through OMP, it is possible to efficiently identify optimized s-sparse nonlinear aerodynamic ROMs using only aerodynamic response information. This approach is exemplified in a three-dimensional aeroelastic stabilator model experiencing high-amplitude freeplay-induced limit cycles. The comparison shows excellent agreement between the ROM and the full-order aeroelastic response, including the ability to generalize to new freeplay and velocity index values, with online computational savings of several orders of magnitude. The development of an optimally sparse ROM extends previous higher-order polynomial-based ROM approaches for feasible application to complex three-dimensional nonlinear aeroelastic problems, without incurring significant computational burdens or loss of accuracy.

A DFT investigation of Ti-substituted [formula omitted] for tailored photovoltaic properties

Transition Metal Chalcogenide Perovskites (TMCP) have been in the spotlight due to their exceptional optoelectronic properties. CaZrS3 is one among them with an experimental bandgap of 1.90 eV. If its bandgap is tuned to lower values, it can be employed in additional photovoltaic applications, such as solar cell absorbers. In this work, the transition metal element Zr in CaZrS3 is substituted with Ti atoms in different proportions and the optoelectronic properties are investigated using Density Functional Theory (DFT). The optoelectronic calculations are all done using the DFT+U method including the spin–orbit coupling. With substitutional alloying, we successfully tuned the energy gap from 1.91 eV to 1.18 eV and the photovoltaic properties were also observed to be modified. For the substituted CaZr1−xTixS3 samples, large birefringence is observed. This indicates enhancement in optical anisotropy via substitutional alloying which is significant in both linear and nonlinear optoelectronic applications like polarizers, wave plates etc.

‘Bridge-builders’ and ‘boundary spanners’: a qualitative study of youth workers’ perceptions of their roles and practices with vulnerable young people in school-based settings

ABSTRACT This paper presents a qualitative study of 22 youth workers’ perceptions of their roles and practices in seven school-based settings in a large post-industrial city in regional Australia. Youth workers are often engaged in school-based settings working with vulnerable young people, yet knowledge of how workers perceive and conceptualize their role and practice in these settings remains limited. Through focus group interviews, youth workers were asked how they engage, and work with vulnerable students, how they conceptualize their roles and the bodies of knowledge to which those practices and roles pertain. We find that youth work in school-based settings requires the dynamic and non-linear application of the practices of youth accompaniment, family support and youth-centred advocacy, underpinned by respect for the dignity, autonomy and agency of the young person. We argue that the complex application of these practices positions youth workers as ‘bridge-builders’ and ‘boundary-spanners’. Bridge-builders assist young people to connect and engage with support services. Boundary-spanners build relationships across service providers to network different organizations and professionals for better collaboration and support of young people. These findings have implications for youth policy and practice in the area of youth work with vulnerable young people in school-based settings.

Complex dynamics in nonlinear small time-delayed optoelectronic oscillator and application in fast reservoir computing and pulse generation

We investigated a time-delayed optoelectronic oscillator (OEO) that displays a wide range of complex dynamic behavior under small time delay. The phase-space trajectory distributions in different dynamic regimes were compared which brings a new perspective on the underlying mechanism of the transition process. It was found that bifurcation is always possible no matter how small the time delay is even if the universal adiabatic approximation model is invalid. Hereby we proposed a versatile simple oscillator which has a potential capacity as memory carrier and high-dimensional state spatial mapping ability that brings 1000 times computing-efficiency improvements of reservoir computing over the large time delay one. Furthermore, we demonstrated a new approach for a tunable optoelectronic pulse generator (repetition rate at 0.2 MHz and 0.25 GHz) which depends critically on time-delayed input electrical pulse. The proposed oscillator is also a promising system for the applications of fast chaos-based communication.

Novel stochastic embedded solitons with quadratic nonlinear susceptibility in the presence of multiplicative noise

This paper addresses the modeling of optical systems with stochastic quadratic nonlinearity for the first time, a novel and challenging research area within nonlinear optics. By incorporating multiplicative white noise and quadratic nonlinear susceptibility, the study presents an innovative approach to recovering optical solutions. Leveraging the G′G -expansion method and extended Kudryashov’s method, new stochastic exact solutions are derived, encompassing bright, dark, singular, and trigonometric solitons. Graphical representations aid in understanding these solutions’ characteristics. Insights into the stochastic nature of optical solutions under various conditions are provided, offering valuable contributions to nonlinear optics and potential applications in telecommunications and materials science.

Giant nonlinear optical wave mixing in a van der Waals correlated insulator.

Optical nonlinearities are one of the most fascinating properties of two-dimensional (2D) materials. While tremendous efforts have been made to find and optimize the second-order optical nonlinearity in enormous 2D materials, opportunities to explore higher-order ones are elusive because of the much lower efficiency. Here, we report the giant high odd-order optical nonlinearities in centrosymmetric correlated van der Waals insulator manganese phosphorus triselenide. When illuminated by two near-infrared femtosecond lasers, the sample generates a series of profound four- and six-wave mixing outputs. The near-infrared third-order nonlinear susceptibility reaches near the highest record values of 2D materials. Comparative measurements to other prototypical nonlinear optical materials [lithium niobate, gallium(II) selenide, and tungsten disulfide] reveal its extraordinary wave mixing efficiency. The wave mixing processes are further used for nonlinear optical waveguide with multicolor emission. Our work highlights the promising prospect for future research of the nonlinear light-matter interactions in the correlated 2D system and for potential nonlinear photonic applications.

Topology-optimized photonic topological crystalline insulators with multiband helical edge states

Abstract Photonic topological crystalline insulators (PTCIs) with helical edge states provide an alternative way to achieve robust electromagnetic wave transport and processing. However, most existing PTCIs only involve a single topological bandgap, and generally support a pair of gapped helical edge states, restricting the scope of applications in various fields such as multiband waveguides, filters, and communication systems. Here, we design dual-band PTCIs, in which multiple helical edge modes appear within two distinct bulk gaps, for transverse electric (TE) and transverse magnetic (TM) modes, respectively, by introducing the topology optimization method into the photonic crystals with glide symmetry. For PTCIs with TE modes, the mismatched frequency ranges of edge modes hosted by two orthometric boundaries offer an opportunity to realize a photonic demultiplexer. For PTCIs with TM modes, we show the enhanced second harmonic (SH) generation through the coupling of multiband edge modes by matching the frequency ranges of edge modes within the first and second bandgaps to fundamental and SH waves, respectively. This work provides a new way for designing multiband PTCIs with helical edge states, having promising potentials in developing multiband topological photonic devices for both linear and nonlinear applications.

Analytical Linearization of Aerodynamic Loads in Unsteady Vortex-Lattice Method for Nonlinear Aeroelastic Applications

This paper presents the analytical linearization of aerodynamic loads (computed with the unsteady vortex-lattice method), which is formulated as tangent matrices with respect to the kinematic states of the aerodynamic grid. The loads and their linearization are then mapped to a nonlinear structural model by means of radial-basis functions, allowing for a two-way strong interaction scheme. The structural model comprises geometrically exact beams formulated in a director-based total Lagrangian description, circumventing the need for rotational degrees of freedom. The structural model is spatially discretized into finite elements and temporally discretized with the help of an implicit scheme that identically preserves momenta and energy. The resulting nonlinear discrete equations are solved by applying Newton’s method, requiring calculating the Jacobians of the whole aeroelastic system. The correctness of the linearized loads is then shown by direct comparison with their numerical counterparts. In addition, we employ our strongly coupled aeroelastic model to investigate the nonlinear static and dynamic behavior of a suspension bridge. With this approach, we successfully investigate the numerical features of the aeroelastic system under divergence and flutter conditions.