Scattering Matrix Method Research Articles

GaAs quantum transport: Scrutinizing the effects of pressure, temperature and Rashba-Dresselhaus spin-orbit interactions for next-generation spintronic devices

This research investigates the spin-dependent transmission attributes and associated Giant Magnetoresistance (GMR) effect emerging from spin-polarized electron tunneling in a GaAs quantum well superlattice (QWS). The influence of Rashba and Dresselhaus spin-orbit interactions (SOIs) on transport properties is analyzed under the framework of the scattering matrix method. Our quantitative findings revealed that these spin-orbit couplings (SOCs) introduce inherent spin-filtering mechanisms, significantly influencing transmission probabilities. Furthermore, numerical estimations proved that external perturbations including pressure, temperature and structural modifications considerably impact the quantum transport characteristics of the scrutinized system. Additionally, major outcomes suggest that precise manipulation of spin-dependent transport in GaAs QWS holds promise for advancing spintronics technology. It is found that with well-tuned parameter values, the SOCs behave as a spin-dependent barrier modifying the band shape and its anisotropy. This study offers novel insights into the fundamental physics governing spin-dependent transport within quantum superlattices with promising implications for the development of advanced spintronic devices.

Propagation characteristics of obliquely incident terahertz waves in inhomogeneous microplasma

The transmission characteristics of terahertz (THz) waves in a non-uniform microplasma are investigated by using the scattering matrix method. The electron density distribution in microplasma is simulated by Epstein and parabolic models. The effects of physical parameters, such as the incidence angle of THz waves, microplasma size, electron density, and collision frequency, on the propagation of THz waves are numerically analyzed. The results show that lower frequency THz waves are difficult to penetrate the microplasma with high electron density and high collision frequency. The microplasma density distribution, especially the gradient variation of the density in the first layer, has a large effect on the reflection of THz waves. Thus, THz waves can be used to diagnose the physical parameters of microplasmas.

Electrodynamic modeling of slot gratings by the generalized scattering matrix method – spherical wave decomposition

An algorithm is presented for the electrodynamic analysis of a two-dimensional waveguide slot array of finite dimensions. To solve the boundary value problem, the generalized scattering matrix method is used. The complex problem for a structure with large electrical dimensions is divided into two subproblems: wave scattering on one lattice element and the interaction of waves within the lattice. In accordance with this method, the electromagnetic field of a solitary lattice element is represented in the form of an expansion in incident and scattered spherical waves. The solution to the first subproblem is given by the scattering operator, which relates the amplitudes of the incident and scattered waves. The solution to the second subproblem yields an interaction matrix that relates the amplitudes of waves incident on the mth array element with the amplitudes of waves scattered by the nth element. Application of the scattering operator and interaction matrix to the analysed lattice leads to a system of linear algebraic equations for the amplitudes of the scattered waves. A non-periodic slot grating, focused in the Fresnel zone, containing up to a thousand elements is analysed. The obtained numerical results are in good agreement with the known behaviour of focused leaky wave gratings. Possible areas of application of the method are discussed.

Generalization of the Method of Scattering Matrices to Problems in Nonlinear Dispersion Media

Generalization of the Method of Scattering Matrices to Problems in Nonlinear Dispersion Media

Terahertz wave propagation characteristics in SMM-based three-dimensional plasma fluid

During the return to the atmosphere of a hypersonic vehicle in adjacent space, a plasma sheath forms on the surface of the vehicle, which blocks normal electromagnetic communications. The ‘blackout’ phenomenon caused by plasma sheaths has received much attention. This paper focuses on the American RAM-C vehicle as the research object, and utilizes the fluid simulation software USim to numerically simulate the pressure, temperature, and electron density under different flight conditions, and based on the simulation results, selects the appropriate electron density and plasma collision frequency, introduces the terahertz (THz) wave, and adopts the scattering matrix method (SMM) to study the propagation characteristics of the vertically incident non-uniform magnetized plasma with the terahertz wave. Among other things, the transmission characteristics of terahertz waves in the plasma are affected by the flight altitude and flight angle of attack of the vehicle. The conclusions indicate that the transmissivity of terahertz wave transmission in plasma increases, and the reflectivity and absorptance decrease with increasing flight altitude and flight angle of attack. Under the condition of controlling other flight parameters unchanged, the plasma frequency and collision frequency decrease with the increase of flight altitude. The larger the flight angle of attack is, the larger the plasma frequency and collision frequency are. The electron density on the wall surface of the vehicle was also tested, and it was found that the lowest electron density was found at the tail end of the leeward surface. This study can provide some theoretical references for mitigating the ‘blackout’ phenomenon of re-entry vehicles.

Modeling full PCSELs and VCSELs using modified rigorous coupled-wave analysis.

An integrated rigorous coupled-wave analysis (RCWA) algorithm is presented in this paper, which can simulate full vertical-cavity surface-emitting laser (VCSEL) and photonic crystal surface-emitting laser (PCSEL) structures. A classic RCWA can only analyze a structure when the light source is incident from the top, bottom, or both sides of the device. However, for VCSEL applications, the light source is generated in the middle and propagates in both directions. A bidirectional scattering matrix method and doubling algorithm are implemented in RCWA. The resonant wavelength and Q factor of a VCSEL can then be found in the output spectrum. The accuracy and execution speed are compared with those of the Lumerical finite-difference time-domain (FDTD) method for several VCSEL and PCSEL designs. The results show that the maximum discrepancy between RCWA and FDTD is less than 3 nm, and the difference in the far-field divergence angle is less than 0.5°. The speed of RCWA also outperforms FDTD simulation significantly.

Finite-element assembly approach of optical quantum walk networks

We present a finite-element approach for computing the aggregate scattering matrix of a network of linear coherent scatterers. These might be optical scatterers or more general scattering coins studied in quantum walk theory. While techniques exist for two-dimensional lattices of feed-forward scatterers, the present approach is applicable to any network configuration of any collection of scatterers. Unlike traditional finite-element methods in optics, this method does not directly solve Maxwell’s equations; instead it is used to assemble and solve a linear, coupled scattering problem that emerges after Maxwell’s equations are abstracted within the scattering matrix method. With this approach, a global unitary is assembled corresponding to one time step of the quantum walk on the network. After applying the relevant boundary conditions to this global matrix, the problem becomes non-unitary and possesses a steady-state solution that is the output scattering state. We provide an algorithm to obtain this steady-state solution exactly using a matrix inversion, yielding the scattering state without requiring a direct calculation of the eigenspectrum. The approach is then numerically validated on a coupled-cavity interferometer example that possesses a known, closed-form solution. Finally, the method is shown to be a generalization of the Redheffer star product, which describes scatterers on one-dimensional lattices (2-regular graphs) and is often applied to the design of thin-film optics, making the current approach an invaluable tool for the design and validation of high-dimensional phase-reprogrammable optical devices and study of quantum walks on arbitrary graphs.

A 2D chiral microcavity based on apparent circular dichroism

Engineering asymmetric transmission between left-handed and right-handed circularly polarized light in planar Fabry–Pérot (FP) microcavities would enable a variety of chiral light-matter phenomena, with applications in spintronics, polaritonics, and chiral lasing. Such symmetry breaking, however, generally requires Faraday rotators or nanofabricated polarization-preserving mirrors. We present a simple solution requiring no nanofabrication to induce asymmetric transmission in FP microcavities, preserving low mode volumes by embedding organic thin films exhibiting apparent circular dichroism (ACD); an optical phenomenon based on 2D chirality. Importantly, ACD interactions are opposite for counter-propagating light. Consequently, we demonstrated asymmetric transmission of cavity modes over an order of magnitude larger than that of the isolated thin film. Through circular dichroism spectroscopy, Mueller matrix ellipsometry, and simulation using theoretical scattering matrix methods, we characterize the spatial, spectral, and angular chiroptical responses of this 2D chiral microcavity.

Propagation characteristics of obliquely incident THz waves in inhomogeneous fully ionized dusty plasma using the scattering matrix method

The scattering matrix method is applied to investigate the propagation characteristics of obliquely incident terahertz (THz) waves in inhomogeneous fully ionized dusty plasma. The propagation coefficients of THz waves are analyzed with different physical parameters in the case of parabolic electron density distribution. The results show that the transmissivity of lower frequency THz waves have a noticeable variation with the change of physical parameters. However, the transmissivity values can rapidly approach 1 in higher frequency band. We notice that there is a critical value fc≈0.045 THz. When f>fc, the transmissivity increases as the dust particles density and radius increase. However, it is somewhat opposite when f<fc. Significantly, the THz waves exhibit a greater propensity for penetrating fully ionized dusty plasma compared with the weakly ionized dusty plasma. To a certain degree, the investigation results provide new ideas for addressing the issue of “blackout”.

Frequency selection mechanism of sub-terahertz wave propagation within the sharp-coned plasma sheath

The propagation characteristics of sub-terahertz (sub-THz) waves through the sharp-coned plasma sheath are investigated, revealing a frequency selection phenomenon. Two significant electron density gradients within the sharp-coned plasma sheath, which result in high reflection coefficients, are identified. These strong reflective interfaces divide the plasma into distinct regions, and the frequency selection mechanism is analyzed using the improved scattering matrix method. This research finds that the combination of these reflective interfaces and the intervening plasma forms a “resonator structure,” leading to the observed frequency selection. A quantitative relationship between plasma parameters and the frequency selection phenomenon is analyzed. The results indicate that the reflection coefficients of the reflective interfaces increase, making the frequency selection more pronounced, when the thickness of the interfaces decreases or the peak electron density increases. In addition, a lower collision frequency leads to reduced absorption effects and a more pronounced frequency selection. The phenomenon suggests that enhancing transmissivity at lower frequencies may be feasible, providing a theoretical insight into the application of sub-THz waves in mitigating communication blackouts.

975 nm multimode semiconductor lasers with high-order Bragg diffraction gratings

The 975 nm multimode diode lasers with high-order surface Bragg diffraction gratings have been simulated and calculated using the 2D finite difference time domain (FDTD) algorithm and the scattering matrix method (SMM). The periods and etch depth of the grating parameters have been optimized. A board area laser diode (BA-LD) with high-order diffraction gratings has been designed and fabricated. At output powers up to 10.5 W, the measured spectral width of full width at half maximum (FWHM) is less than 0.5 nm. The results demonstrate that the designed high-order surface gratings can effectively narrow the spectral width of multimode semiconductor lasers at high output power.

Omnidirectional mirror based on the aperiodic and hybrid-order aperiodic-periodic chirped multilayers

We propose an innovative design of highly reflective omnidirectional mirror based on chirped-type aperiodic and hybrid-order aperiodic-periodic multilayered structures in the spectral range from 400 nm to 3000 nm that contains a larger part of solar radiation. The aperiodic sequences considered are Fibonacci (FIB) and Thue-Morse (ThMo), while a power law function has been adopted to tune the thickness of layers. The chirping functions parameters were optimized to obtain maximum averaged reflectivity over the entire angular range. The numerical calculations were performed by a recursive formula via the scattering matrix method. For all the structures, the chirping effect improved the omnidirectional properties of multilayers in terms of average reflectivity and quasi omnidirectional spectral width (q-ODW). In detail, it was revealed that the ThMo based structures provide the best performance in terms of both averaged reflectivity and q-ODW. For ThMo chirped multilayer the q-ODW reached the value of 1605 nm with incident angular span 0-60°. On the other hand, the hybrid-order structure based on ThMo shows an q-ODW up to 2500 nm. Finally, for all the investigated structures the average reflectivity reaches a value larger than 0.93 using nearly 100 layers.

Investigation of random laser effect in structural disordered aperiodic multilayer

The gap states of a random Fibonacci-on-average multilayer exhibit strong localization and high Q-factors, indicating potential suitability for random lasing applications. This study investigates the gain threshold behavior of random lasing within the visible spectrum. Using the scattering matrix method with complex refractive indices, our simulations examine the relationship between the gain threshold, structural disorder, and the number of layers. The results contribute to the understanding of random lasing behavior of this type of quasi-crystal.

An efficient determination of field distributions in E-plane dielectric loaded waveguides

ABSTRACT This paper proposes a new, fast, and efficient method for determining the electromagnetic field distribution in two-port E-plane dielectric-loaded uniform rectangular waveguides. The analysis region is divided into individual blocks in the absence and presence of dielectric obstacles. The non-zero electric and magnetic field components are constructed throughout the system via the proposed method by utilizing the generalized scattering matrix method between blocks for unimodal or multimodal excitation. The resulting field distributions are compared to those obtained from commercial software, with very close agreement achieved, but with a significantly reduced computational time for the proposed method. The method is applicable in a straightforward manner and has been tested on both a filter device with relatively complex geometry and a disjoint system with a modal coupling challenge between its elements. The field components' accuracy is also tested by calculating the Poynting vector along the system. Additionally, this approach provides the global scattering parameters at the physical ports as a co-product. The proposed method has the potential to be applied to various two-port networks by using the proposed method according to the considered problem.

Nonlinear harmonic wave manipulation in nonlinear scattering medium via scattering-matrix method

Nonlinear harmonic wave manipulation in nonlinear scattering medium via scattering-matrix method

Scattering of Sound Waves in Two Stepped Non-uniformly Lined Duct

Scattering of sound waves in two stepped cylindrical duct which walls are coated with different acoustically absorbent materials is investigated by using Wiener-Hopf technique directly and by determining scattering matrices. First, by using Fourier transform technique we obtain a couple of modified Wiener-Hopf equations whose solutions involve four sets of infinitely many unknown expansion coefficients providing systems of linear algebraic equations. Then we determine scattering matrices of the problem and we state the total transmitted field by using generalized scattering matrix method. Numerical results are compared for different parameters.

Optical properties of polyaniline/modified graphene oxide nanocomposites

In this research, the complex refractive index of polyaniline (PANI)/hexamethylene diisocyanate-modified graphene oxide (HDI-GO) nanocomposites has been obtained. The PANI/HDI-GO nanocomposites were prepared via in situ polymerization of aniline monomer in the presence of HDI-GO nanofillers, and their crystalline structure and surface morphology were investigated via X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements. Then, the experimental reflectance and transmittance for pure PANI and PANI/HDI-GO nanocomposite films with HDI-GO contents of 0.5, 1 and 2 wt% deposited on glass substrates were measured using UV-Vis spectrophotometry within the spectral region 300–900 nm. Then, the refractive index and extinction coefficient have been obtained using a novel method developed by the authors. The model is based on the generalized Scattering Matrix Method, which is used to obtain the theoretical values for the thin film/substrate reflectance and transmittance. Root mean square errors obtained are systematically lower than 0.21%, which corroborates the excellent accuracy of the model. The proposed method does not require sophisticated equipment, just a spectrophotometer, to obtain the complex refractive index of a thin film from transmittance and reflectance measurements.

Analysis and design of transition radiation in layered uniaxial crystals using tandem neural networks

With the flourishing development of nanophotonics, a Cherenkov radiation pattern can be designed to achieve superior performance in particle detection by fine-tuning the properties of metamaterials such as photonic crystals (PCs) surrounding the swift particle. However, the radiation pattern can be sensitive to the geometry and material properties of PCs, such as periodicity, unit thickness, and dielectric fraction, making direct analysis and inverse design difficult. In this paper, we propose a systematic method to analyze and design PC-based transition radiation, which is assisted by deep learning neural networks. By matching boundary conditions at the interfaces, effective Cherenkov radiation of multilayered structures can be resolved analytically using the cascading scattering matrix method, despite the optical axes not being aligned with the swift electron trajectory. Once properly trained, forward deep learning neural networks can be utilized to predict the radiation pattern without further direct electromagnetic simulations. In addition, tandem neural networks have been proposed to inversely design the geometry and/or material properties for the desired effective Cherenkov radiation pattern. Our proposal demonstrates a promising strategy for dealing with layered-medium-based effective Cherenkov radiation detectors, and it can be extended to other emerging metamaterials, such as photonic time crystals.

Application of the scattering matrix method for investigating the propagation characteristics of terahertz waves in magnetized dusty plasma

A scattering matrix method is applied to investigate propagation characteristics of oblique incident terahertz waves into magnetized dusty plasmas. The numerical results agree well with those given by the Wenzell–Kramer–Brillouin method. Three different electron density distributions are taken into account, and both the right- and left-hand circularly polarized (RCP and LCP) waves are analyzed. Transmission properties of terahertz (THz) waves with different physical parameters, such as external magnetic, dust particle density, and dust particle radius, are discussed systematically. There exists a transmissivity peak at the lower-frequency band for RCP waves when an external magnetic field is presented. The value of the peak nearly keeps invariant, and its location moves toward the higher-frequency direction if the magnetic field enhances. Increasing the dust particle density or radius can make the value of a transmissivity peak larger. The transmissivity of higher-frequency RCP THz waves decreases if the external magnetic field increases. However, for LCP waves, there is no transmissivity peak. It increases monotonously as the frequency of a THz wave increases. Different from the RCP waves, enhancing the external magnetic field is better for the LCP waves to penetrate the dusty plasma. Our results may provide some theoretical basis for alleviating the problem of “blackout.”

Propagation Characteristics of Broadband Terahertz Waves in an Inhomogeneous Plasma With Sheath

Using terahertz (THz) waves as the communication carrier is an effective way to overcome the blackout when a spacecraft reenters the atmosphere. A blackout plasma typically has a sheath, but the physical mechanism of broadband THz wave propagation and attenuation in sheath plasma has not been clarified. This article presented experimental and theoretical studies of the propagation characteristics of broadband THz waves in a neon plasma with a sheath for plasma densities ranging from 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sup> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">18</sup> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> . The experimental results showed that a broadband THz wave at a frequency of 1.9 THz had a high attenuation of about 22 dB in the plasma. We simulated the propagation characteristics of the THz wave in the plasma, based on a five-layer plasma model by using the scattering-matrix method. When the sheath plasma density, simulation parameter, was 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sup> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> , the experimental attenuation curve of THz wave in plasma was consistent with the simulation curve. This work clarified the determinants of THz wave attenuation in sheath plasma, which lays a foundation for overcoming the black barrier problem.