Limited Bandwidth Research Articles

Self-measurement and calibration of amplitude-frequency response for coherent optical transmitters with limited DAC resolution

Precise measurement and calibration of the amplitude-frequency response (AFR) of coherent optical transmitters (Tx) are paramount for generating high-quality signals, especially when the transmitter has insufficient bandwidth. The previously proposed self-measurement and calibration (SMC) method based on multi-tone signals (MTS) is cost-effective, fast, and convenient. However, this method exhibits a compromised AFR measurement precision in high-frequency regions, especially when the digital-to-analog converters (DAC) of the Tx have a limited resolution. To solve this problem, we optimize the amplitudes and phases of the MTS by pre-emphasis and the sequential quadratic programming (SQP) algorithm to improve the accuracy in the high-frequency region. Numerical simulations show a notable reduction in AFR measurement error, from about 4 dB to 0.8 dB, when employing a DAC with a four-bit resolution. Additionally, experiments utilizing a 22 GHz 3-dB bandwidth transmitter to generate 61 GBaud dual-polarization 16QAM signals demonstrate a 60% BER reduction. The proposed SMC method is attractive for high-baud rate systems employing Tx with limited bandwidth and DAC resolution.

Network impact analysis on the performance of Secure Group Communication schemes with focus on IoT

Secure and scalable group communication environments are essential for many IoT applications as they are the cornerstone for different IoT devices to work together securely to realize smart applications such as smart cities or smart health. Such applications are often implemented in Wireless Sensor Networks, posing additional challenges. Sensors usually have low capacity and limited network connectivity bandwidth. Over time, a variety of Secure Group Communication (SGC) schemes have emerged, all with their advantages and disadvantages. This variety makes it difficult for users to determine the best protocol for their specific application purpose. When selecting a Secure Group Communication scheme, it is crucial to know the model’s performance under varying network conditions. Research focused so far only on performance in terms of server and client runtimes. To the best of our knowledge, we are the first to perform a network-based performance analysis of SGC schemes. Specifically, we analyze the network impact on the two centralized SGC schemes SKDC and LKH and one decentralized/contributory SGC scheme G-DH. To this end, we used the ComBench tool to simulate different network situations and then measured the times required for the following group operations: group creation, adding and removing members. The evaluation of our simulation results indicates that packet loss and delay influence the respective SGC schemes differently and that the execution time of the group operations depends more on the network situations than on the group sizes.

Pure-quartic soliton self-frequency shift in a mode-locked fiber laser

The pure-quartic soliton (PQS) offers the advantage of a wide spectrum and approximately Gaussian temporal profile, which has the potential to obtain high-energy ultrafast laser pulses. Thus, exploring the role of stimulated Raman scattering in the formation and propagation of PQSs in fiber lasers is crucial, especially considering the greater propensity for highpower and short PQS pulses compared to traditional solitons. Here, we present the modeling of a self-frequency shift (SFS) fiber laser based on the PQS, emphasizing the impact of fourth-order dispersion and the Raman effect. The significant red-shift in wavelength is discovered as the pump energy increases, revealing that the emergence of SFS is a universal attractor in mode-locked PQS fiber laser systems. Our simulations demonstrate that such wavelength tunability is a direct byproduct of the gain bandwidth limit and the stimulated Raman scattering for PQSs inside the fiber cavity, while the evolution dynamics in the gain and passive fiber show obvious differences. However, we find that the effect of SFS in a PQS fiber laser is compromised by a trade-off with the degradation of pulse quality, such as reshaping the oscillating tail and destroying the symmetry of the emission pulse. This Raman-induced nonlinear process under high pump energy facilitates the discovery of the comprehensive complexity of science for PQSs suffering from higher-dimensional forms of nonlinear effects in fiber lasers.

Fixed-time control of teleoperation systems based on adaptive event-triggered communication and force estimators

Abstract A fixed-time control strategy based on adaptive event-triggered communication and force estimators is proposed for a class of teleoperation systems with time-varying delays and limited bandwidth. Two force estimators are designed to estimate the operator force and environment force instead of force sensors. With the position, velocity, force estimate signals, and triggering error, an adaptive event-triggered scheme is designed, which automatically adjusts the triggering thresholds to reduce the access frequency of the communication network. With the state information transmitted at the moment of event triggering while considering the time-varying delays, a fixed-time sliding mode controller is designed to achieve the position and force tracking. The stability of the system and the convergence of tracking error within a fixed time are mathematically proved. Experimental results indicate that the control strategy can significantly reduce the information transmission, enhance the bandwidth utilization, and ensure the convergence of tracking error within a fixed time for teleoperation systems.

Enhancements to quantum communication performance utilizing a prototype photonic lantern and multiplexed single-photon detection.

The optical interfacing between a free-space channel and single-photon detectors (SPDs) can greatly impact the inherent performance of a free-space quantum key distribution receiver. Direct coupling to detectors creates engineering challenges, and a single-mode fiber requires adaptive optics. Using a multimode fiber (MMF) is common; however, larger core diameters limit the achievable bandwidth. We demonstrate a prototype multimode fiber-based photonic lantern that allows us to retain the benefits of the large multimode coupling while transitioning to multiple, less multimodal fibers, reducing bandwidth limitation.

Ultra-broadband illusion acoustics for space and time camouflages

Invisibility cloaks that can suppress wave scattering by objects have attracted a tremendous amount of interest in the past two decades. In comparison to prior methods that were severely limited by narrow bandwidths, here we present a practical strategy to suppress sound scattering across an ultra-broad spectrum by leveraging illusion metamaterials. Consisting of a collection of subwavelength tunnels with precisely crafted internal structures, this illusion metamaterial has the ability to guide acoustic waves around the obstacles and accurately recreate the incoming wavefront on the exit surface. Remarkably, two ultra-broadband illusionary effects are produced, disappearing space and time shift. Sound scatterings are removed at all frequencies below a limit determined by the tunnel width, as confirmed by full-wave simulations and acoustic experiments. Our strategy represents a universal approach to solve the key bottleneck of bandwidth limitation in the field of cloaking in transmission, and establishes a metamaterial platform that enables the long-desired ultra-broadband sound manipulation such as acoustic camouflage and reverberation control, opening up exciting new possibilities in practical applications.

Compact Ultra-Wide Band Two Element Vivaldi Non-uniform Slot MIMO Antenna for Body-Centric Applications

This work presents a novel compact two-port Vivaldi Non-uniform Slot MIMO Antenna (VNSMA) to overcome the challenges of traditional ultra-wideband (UWB) antennas, such as large size, limited bandwidth (BW), high mutual coupling, and suboptimal performance in wearable devices. Designed based on Vivaldi non-uniform slot profile antenna (VNSPA) theory, this antenna offers superior performance metrics and significantly advances wearable antenna technology. The novelty of this work is investigating different positions for the two compact UWB VNSA to get better performance with smaller sizes, wider impedance matching BW, and lower mutual coupling (MC) where side by side at an angle of 180ᵒ is determined to be the best configuration. Detailed parametric studies were performed on this configuration for better performance, where the MC was further reduced by etching the ground plane with a vertical slot between the two antennas and L slots around the Microstrip to Slot (M/S) transition, respectively. Furthermore, BW and gain enhancements were obtained by etching exponential tapered and triangular slots at its two edges. Using the Finite Integration Technique (FIT), Computer Simulation Technology (CST) software is used for the simulations in this work. The VNSMA is tested on a CST Gustav human phantom and gives excellent results with low specific absorption rate (SAR) values at several UWB frequencies. The proposed VNSMA provides good, measured outcomes of S11 < -11.08 dB with wide BW of 12.5 GHz (2.33–14.83 GHz) covering high isolation of -23 dB (for most of frequency band), moderate-high gain of 5.89 dBi, radiation efficiency of 66-90%, low Envelope Correlation Coefficient (ECC) of 0.002 and high diversity gain (DG) of 9.99 dBi, stable radiation patterns, and average group delay of 1.2 ns. This innovative design, which optimizes antenna positioning and incorporates ground plane modifications, achieves remarkable improvements in BW, which covers multiple bands, including WLAN (2.4–2.485 GHz), X-band (8-12 GHz), and part of Ku band (12-18 GHz). The findings demonstrate the antenna's potential for various high-resolution microwave imaging applications, particularly in medical diagnostics like breast and brain cancer detection, showcasing its impact in wearable technology and healthcare.

LS-based multipath channel measurement method using software defined radio platform

Multipath channel measurement is the foundation of multipath channel modeling and analysis. Recently, the software defined radio (SDR) has provided new ideas for the design of multipath channel measurement systems due to universality and reconfigurability. Therefore, this paper introduces a multipath channel measurement method applicable to various SDR platforms. At first, to enhance the resolution of multipath measurements, a signal processing approach combining the least squares (LS) estimation algorithm within the SDR framework is proposed. Furthermore, to mitigate LS estimation errors stemming from high correlation among baseband signals, a scrambled measurement signal is introduced and its effectiveness is demonstrated through eigenvalue decomposition. Next, the systematic errors of In-phase and Quadrature(IQ) imbalance and bandwidth limitation are further analyzed and addressed within the SDR framework. Finally, the proposed measurement method is implemented based on a practical universal software radio peripheral (USRP) device and validated under simulated and real channels. The proposed measurement method mainly focuses on the baseband signal processing within the software component of SDR, making it applicable to most general USRP devices. The experiment results demonstrate that multipath channel measurement results with high accuracy can be obtained.

Methodology for assessing the effectiveness of the impact intermittent noise interference to a radar station with adaptive detection threshold formation

Problem statement. For aviation suppression equipment, it is characteristic to separate the modes of interference and reconnaissance radiation in time due to the problem of their electromagnetic compatibility. It is also possible to alternately suppress various objects with a limited bandwidth of the interference station. This leads to periodic interruptions of the noise interference and, consequently, a decrease in its spectral density. A feature of radar stations of the latest and modernized means of intercepting air defense systems aimed at hitting targets in a complex interference environment is adaptive control of parameters and modes of operation of various subsystems. In particular, modern radar stations provide for the adaptive formation of a detection threshold based on estimates of the statistical characteristics of such interference. Such estimates are formed over the interference integration interval, the size of which is generally selected from the condition of insignificant influence of signals reflected from the targets on them. Moreover, for the most correct consideration of the interference situation in the vicinity of the detected target, the strobe pulses of the false alarm probability stabilization circuit, forming the integration interval, are placed on both sides of the analyzed range resolution element. Goal. To evaluate the effect of intermittent noise interference parameters on the operation of radar stations with adaptive detection threshold foration. Assumptions. When developing the methodology, the following typical assumptions were made: in target detection mode, the radar station emits pulse signals with a low or medium pulse repetition rate; the signal reflected from the target, noise interference and internal noise are independent normal random processes; interference and internal noise have a uniform spectral density within the bandwidth of the radar receiver; the receiving path of the radar station has a traditional structure, which includes: an intermediate frequency amplifier, a linear amplitude detector, an integrator and a threshold device. Results. For the first time, the obtained technique takes into account the influence of time and energy parameters of intermittent noise interference on the probability of correct target detection by a radar station with adaptive detection threshold formation. Reducing the duration of the interference pulse in the period of intermittent noise interference leads to a nonlinear increase in the probability of correct target detection. To maximize this indicator, it is necessary to ensure a sufficiently high accuracy in estimating the statistical characteristics of the power of intermittent noise interference. The reliability of the results obtained using the developed methodology is confirmed by the fact that the effectiveness of intermittent noise interference, while excluding pauses in its radiation, is reduced to the effectiveness of continuous noise interference. Practical significance. The developed technique makes it possible to clarify the technical requirements for radar stations that implement flexible control of the target detection mode under the influence of intermittent noise interference of unknown intensity.

Multimodal vortex-induced vibration mitigation and design approach of bistable nonlinear energy sink inerter on bridge structure

Large-scale structures, e.g., long-span bridge structures, are prone to induce multi-modal vibrations due to their densely spaced low modal frequencies. Due to the limited frequency bandwidth of linear dynamic absorbers, they are incapable of effectively mitigating vibrations across multiple modes. To this end, the bistable nonlinear energy sink inerter (BNESI) is used to mitigate the multimodal vortex-induced vibration (VIV) of the beam structure. The highly nonlinear equilibrium differential equations of the beam-BNESI system are numerically solved, and the simulated annealing (SA) algorithm is employed to determine the optimal VIV reduction ratio and BNESI parameters. In comparison to the cubic-type nonlinear energy sink inerter (CNESI), BNESI is found to possess more stable equilibrium positions, smaller stiffness coefficients, and higher VIV mitigation efficiency. The selection of design modes has been found to influence the efficiency of multimodal VIV mitigation, with the use of the intermediate modal order as the design mode resulting in the highest efficiency for multimodal VIV mitigation. The performance-based multimodal VIV mitigation design can be realized with three parameters, i.e., inertance ratio, damping coefficient, and stiffness coefficient. Moreover, the performance-based multimodal VIV mitigation approach and models proposed in this study demonstrate a high level of precision.

Dynamic clustering based on Minkowski similarity for web services aggregation

This research, introduces a new dynamic clustering method offering a new approach utilizing Minkowski Distance methods for calculating similarity of xml messages to effectively compress and aggregate them. The increase in Web services utilization has led to bottlenecks and congestion on network links with limited bandwidth. Furthermore, Simple Object Access Protocol (SOAP) is an eXtensible Markup Language (XML) based messaging system often utilized on the internet. It leads to interoperability by facilitating connection both users and their service providers across various platforms. The large amount and huge size of the SOAP messages being exchanged lead to congestion and bottlenecks. Aggregation tools for SOAP messages can effectively decrease the significant amount that traffic generated. This has shown a notable enhancement in performance. Enhancements can be made by using similarity methods. These techniques group together multiple SOAP messages that share a significant level of similarity. Present techniques utilizing grouping for aggregating XML messages have demonstrated efficiency and compression ratio limitations. Practically, the proposed model groups messages into clusters based on minimum distance, supporting Huffman (variable-length) and (fixed-length) encoding compressing for aggregating multiple compressed XML web messages into a single compact message. Generally, the suggested model’s performance has been evaluated through a comparison with K-Means, Principle Component Analysis (PCA) with K-Means, Hilbert, and fractal self-similarity clustering models. Minkowski distance clustering model has shown excellent performance, especially in all message sizes like small, medium, large, V.large. Technically, the model achieved superior average Compression Ratio and it has outperformed all other models.

Fe3C/Fe implanted hierarchical porous carbon as efficient electromagnetic wave absorber

The rapid development of communication technology has led to severe microwave pollution, which presents a challenge for microwave-absorbing composites. Current research suggests achieving superior microwave absorption requires the use of multi-component operation and ingenious structural design. Consequently, the present study has prepared continuous porous carbon (CPC) materials doped with large amounts of Fe3C/Fe nanoparticles (Fe@CPC) using carbonization and acid etching. By balancing the advantages of the above strategies, it is possible to address issues such as poor impedance match, single loss capacity, easy oxidation of magnetic metals/alloys, and the limited absorption bandwidth of conventional absorbing materials at the same time. The material exhibits a minimum reflection loss of −23.2 dB with an efficient absorption range of 5.3 GHz at 1.9 mm at a filler content of just 10 wt% in the paraffin matrix. In this paper, the samples with a continuous porous structure were prepared by a simple method, and the properties were excellent due to the appropriate preparation method and the synergistic effect of the multi-component composite. The porous structure facilitates the presence of a considerable number of active sites, which enables the loading of a substantial quantity of metal ions. Furthermore, nanoparticles are capable of aggregating and dispersing on the surface. This paper presents a theoretical framework for understanding the synergistic effect of microwave radiation through interfacial polarization and micro-scale magnetic interaction. Nevertheless, there are still obstacles to overcome in terms of achieving precise control over the structural design and ensuring the compatible integration of metal components.

Monolithically integrated EP-based optical isolator

Exceptional points (EPs) display peculiar degeneracies, where complex eigenvalues and associated eigenvectors coalesce simultaneously, resulting in a defective Hamiltonian. Meanwhile, the negative imaginary part of the energy eigenvalues related to a finite spectral linewidth at the resonant energy, which could provide a solution to tackle the isolation bandwidth limitation of MRR-based optical isolators without sacrificing the insertion loss. Here, a second-order EP2 system constructed by SiN-based cascaded racetrack resonators is proposed, while the metal strip operating as an integrated electromagnet provides magnetic fields required for non-reciprocal phase shifting (NRPS). Owing to the existence of the NRPS perturbation, the system is pushed away from EP and consequently triggers complex frequency splitting, resulting in the isolation bandwidth proportional to the square-root perturbation instead. The results show that the isolation bandwidth of the EP isolator is increased by 163% and 22% compared to single-racetrack and cascaded-racetrack isolators with 2.85 dB insertion loss and 34.3 dB isolation ratio, respectively. The presented EP-based optical isolator shows tremendous potential for high-density monolithic integration and packaging.

Performance Analysis of Deep Learning based Signal Constellation Identification Algorithms for Underwater Acoustic Communications

This research delves into the evaluation of Deep learning signal constellation identification (DL-SCI) algorithms in underwater acoustic communications using Orthogonal Frequency Division Multiplexing (OFDM). It distinctly examines at how effective the recurrent neural networks (RNNs), particularly, Gated Recurrent Unit (GRU) and Long Short-Term Memory (LSTM) algorithms in predicting the signal constellation when applied to different underwater acoustic channels characteristics. Unlike manual feature selection in machine learning (ML), in this paper, DL-SCI exploits the labelled OFDM signals at the transmitter to detect and decode them at the receiver. In order to measure their effectiveness performance metrics, Bit Error Rate (BER) and parameters derived from the confusion matrix such as accuracy and precision are used. The study highlights the importance of utilizing zero cyclic prefix techniques which can exploit the inherent bandwidth limitation effectively. Furthermore, when examining complexity, it is observed that both GRU and LSTM algorithms require less floating-point operations (FLOPS) compared to traditional methods such as Minimum Mean Square Error (MMSE) and Least Squares (LS). Interestingly GRU shows performance in terms of complexity when compared to LSTM. Moreover, GRU outperforms LSTM by achieving a 4 dB improvement for long subcarriers. These results emphasize the effectiveness of learning techniques in enhancing performance and efficiency in acoustic communications.

Direct amplitude-only hologram realized by broken symmetry.

Holographic displays have been a long-standing ambition for decades to realize true-to-life reconstruction. However, their practical adoption is hindered by their subpar image quality compared to two-dimensional displays, which is fundamentally limited by restricted spatial frequency bandwidth and artifacts. We address the limitation by using a symmetry-broken amplitude-only spatial light modulator, demonstrating image quality comparable to that of two-dimensional displays. The broken conjugate symmetry induced by phase noise of modulators eliminates conjugate image that causes issues in amplitude-only holograms and allows direct reconstruction without additional optical elements. The proposed method provides enhanced robustness against artifacts caused by sub-pixel structures of modulators, enabling experimental reconstruction of high-quality holograms. The full bandwidth and the robustness result in a 5-decibel improvement in peak signal-to-noise ratio compared to state-of-the-art holograms. Furthermore, the hologram has 24 times higher optical efficiency and a smaller volume than the traditional amplitude-only holograms while real-time synthesis is enabled by using a neural network.

Unscented-Kalman-Filter-Based Remote State Estimation for Complex Networks With Quantized Measurements and Amplify-and-Forward Relays.

In this article, the remote estimation problem is addressed for a class of discrete-time complex networks under the influence of probabilistic quantization and amplify-and-forward (AF) relays. The underlying complex network model, which is inherently nonlinear and stochastic, is affected by additive process and measurement noises. Owing to the limited bandwidth of the transmission channel, the measurement outputs are quantized by a probabilistic quantizer prior to transmission. To enhance the signal quality over long-distance transmissions, the quantized measurements are sent to AF relays and subsequently forwarded to the estimator. Utilizing the unscented Kalman filter approach, a novel state estimator is designed to minimize an upper bound on the estimation error covariance. Moreover, sufficient conditions are derived to ensure that the estimation error is exponentially bounded in the mean-square sense. Lastly, the efficacy of the proposed scheme is illustrated through numerical simulations.

Snapshot coherent diffraction imaging across ultra-broadband spectra

Ultrafast imaging simultaneously pursuing high temporal and spatial resolution is a key technique to study the dynamics in the microscopic world. However, the broadband spectra of ultra-short pulses bring a major challenge to traditional coherent diffraction imaging (CDI), as they result in an indistinct diffraction pattern, thereby complicating image reconstruction. To address this, we introduce, to our knowledge, a new ultra-broadband coherent imaging method, and empirically demonstrate its efficacy in facilitating high-resolution and rapid image reconstruction of achromatic objects. The existing full bandwidth limitation for snapshot CDI is enhanced to ∼60% experimentally, restricted solely by our laser bandwidth. Simulations indicate the applicability of our method for CDI operations with a bandwidth as high as ∼140%, potentially supporting ultrafast imaging with temporal resolution into ∼50-attosecond scale. Even deployed with a comb-like harmonic spectrum encompassing multiple octaves, our method remains effective. Furthermore, we establish the capability of our approach in reconstructing a super-broadband spectrum for CDI applications with high fidelity. Given these advancements, we anticipate that our method will contribute significantly to attosecond imaging, thereby advancing cutting-edge applications in material science, quantum physics, and biological research.

Frequency comb generation from the ultraviolet to mid-infrared region based on a three-stage cascaded PPLN chain

Optical frequency combs (OFCs) have enabled significant opportunities for high-precision frequency metrology and high-resolution broadband spectroscopy. Although nonlinear photonics chips have the capacity of frequency expansion for OFCs, most of them can only access the limited bandwidths in the partial infrared region, and it is still hard to satisfy many measurement applications in the ultraviolet-to-visible region. Here, we demonstrate a compact broadband OFC scheme via the combination of three χ(2) nonlinearities in a three-stage periodically poled lithium niobate (PPLN) chain. With a supercontinuum spectrum OFC delivered into the PPLN chain, the intra-pulse diffidence frequency generation, optical parametric amplification, and high-order harmonic generation were carried out in sequence. It is crucial that the harmonics of the 1st–10th orders are simultaneously obtained with an offset-free OFC spectrum from 0.35 to 4.0 μm. In view of the great potential for integration and spectral expansion, this wideband frequency comb source will open a new insight for the valuable applications of two-dimensional material analysis, biofluorescence microscopy, and nonlinear amplitude-phase metrology.

Development of an innovative patch antenna design and implementation using ENG materials for health care systems and 5G networks

The object of this study is a new design of an overhead microstrip antenna, including Epsilon Negative (ENG) metamaterials and L-shaped parasitic overlays aimed at achieving dual-band operation and improving the performance of modern wireless communication systems. The research is aimed at solving the problem of limited bandwidth and dual-band functionality in conventional antenna designs. This study solves the problem of limited bandwidth and dual-band functionality in conventional microstrip patch antenna designs, which are crucial for modern wireless communication systems. The inclusion of L-shaped parasitic overlays effectively expands the bandwidth in each frequency range. The results indicate significant improvements: at the upper resonant frequency, a 10 dB return loss bandwidth of 27.84 % (2.88–3.81 GHz) and a 3 dB axial ratio bandwidth of 5.05 % (2.90–3.05 GHz) are achieved, while at the lower resonant frequency, a return loss bandwidth is 10 dB, which is 6.11 % (2.22–2.36 GHz). These improvements indicate a significant increase in antenna performance compared to conventional designs, which is confirmed by comparing the simulation results with the measurement results. Distinctive features contributing to these results include the use of ENG metamaterials, which improve electromagnetic properties and signal propagation; vertical transitions, which provide efficient dual-band operation; and L-shaped parasitic overlays, which significantly expand bandwidth. These characteristics combine to eliminate the limitations of traditional designs, which makes the proposed antenna suitable for use in a wide frequency range in modern wireless communication systems.

Metamaterial Broadband Absorber Induced by Synergistic Regulation of Temperature and Electric Field and Its Optical Switching Application.

Nowadays, metamaterial absorbers still suffer from limited bandwidth, poor bandwidth scalability, and insufficient modulation depth. In order to solve this series of problems, we propose a metamaterial absorber based on graphene, VO2, gallium silver sulfide, and gold-silver alloy composites with dual-control modulation of temperature and electric field. Then we further investigate the optical switching performance of this absorber in this work. Our proposed metamaterial absorber has the advantages of broad absorption bandwidth, sufficient modulation depth, and good bandwidth scalability all together. Unlike the single inspired layer of previous designs, we innovatively adopted a multi-layer excitation structure, which can realize the purpose of absorption and bandwidth width regulation by a variety of means. Combined with the finite element analysis method, our proposed metamaterial absorber has excellent bandwidth scalability, which can be tuned from 2.7 THz bandwidth to 12.1 THz bandwidth by external electrothermal excitation. Meanwhile, the metamaterial absorber can also dynamically modulate the absorption from 3.8% to 99.8% at a wide incidence angle over the entire range of polarization angles, suggesting important potential applications in the field of optical switching in the terahertz range.