Large Bandwidth Research Articles

Compact THz Polarization Splitter with Large Bandwidth Based on Cascade Hexagonal Porous Two-Core PCF

ABSTRACT A novel cyclic olefin copolymer (COC)-based terahertz (THz) polarization beam splitter (PBS) employing photonic crystal fiber (PCF) with cascade hexagonal porous two-core structure is proposed. The porous two-core is achieved by replacing the original two large air holes with three layers of small air holes. The mode coupling characteristics between the even and odd modes in the x- and y-polarization directions for the proposed THz PBS are explored using the time-domain finite difference (FDTD) method. The influence of PBS structural parameters on its coupling length is investigated. Numerical analysis results indicate that the bandwidths of 227.8 GHz (ranging from 1.8970 to 2.1248 THz) and 147 GHz (ranging from 1.928 to 2.075 THz) are acquired for the x- and y-polarization fundamental modes, respectively. The highest extinction ratios (ERs) are 114.5 dB and 72.3 dB, and the minimum insertion losses (ILs) are 0.0142 dB and 0.0369 dB for the x- and y-polarization fundamental modes, respectively. Moreover, the length of the proposed PBS is merely 11.655 mm. The proposed PBS will find potential applications in polarization-diverse THz systems, including broadband line-of-sight communication, real-time security checks, and high-resolution imaging.

Frequency experimental identification approach for single-phase induction motor common-mode parameters

Introduction. The presence of broad-spectrum and high-amplitude electromagnetic interference (EMI) within a single-phase induction motor (SPIM) drive poses a significant threat to both the system and other electronic equipment. High-frequency (HF) models of electrical motors play a critical role in overcoming these challenges, as they are essential for characterizing electromagnetic compatibility (EMC) in drives and designing effective EMI filters. The novelty of this study proposes an enhanced HF motor model based on transfer functions (TFs) to accurately represent the motor’s behavior at HFs for frequency-domain analyses in the range of 100 Hz to 30 MHz. Purpose. The equivalent HF model for a SPIM is discussed in this paper. The suggested equivalent circuit describes a motor’s common-mode (CM) properties. Methodology. HF model was developed by a frequency-domain analysis utilizing an experimental setup and MATLAB software. The motor impedance analysis is based on the measurement of variations in motor characteristics as a function of frequency in the CM setup. Originality. TF has been tuned using an asymptotic identification method of Bode to match the behavior of the real impedances of the motor parameters as a function of the frequency in the CM configuration. This tuned TFs are then synthesized into a comprehensive wideband EMC equivalent circuit model using the Foster network technique, which can be then simulated in any Spice-based simulator tools. Results. The proposed mathematical model was employed to conduct simulations, and the resulting predictions were validated against experimental data. CM response of the EMC equivalent circuit at low, medium, and HFs were compared between simulations and experimental measurements using Lt-Spice simulator software. Practical value. It is observed that results show satisfactory agreement with the measurements over a large frequency bandwidth [100 Hz–30 MHz], and the equivalent model of SPIM can be cascaded with other electronic and electrical modules to form a complete single-phase electric drive system model for fast analysis and prediction of system level EMI and electromagnetic sensitivity. References 37, table 5, figures 13.

Highly Efficient Slow‐Light Mach–Zehnder Modulator Achieving 0.21 V cm Efficiency with Bandwidth Surpassing 110 GHz

AbstractHigh‐speed electro‐optic modulators are key components in modern communication networks and various applications that require chip‐scale modulation with large bandwidth, high modulation efficiency, and compact footprint. However, fundamental trade‐offs make it challenging to achieve these metrics simultaneously, and thus new methodologies must be explored. To this end, a Mach–Zehnder modulator harnessing slow‐light waveguides and capacitively loaded slow‐wave electrodes are presented on silicon‐nitride‐loaded lithium niobate on an insulator platform. The increased group index and reduced microwave loss significantly improve the modulation efficiency. With the 1‐mm‐length modulation section, a low half‐wave voltage length product Vπ·L of 0.21 V cm is obtained, which is one order of magnitude smaller than that of conventional thin film lithium niobate Mach–Zehnder modulators, and a modulation bandwidth of surpassing 110 GHz is achieved. The digital signal processor‐free non‐return‐to‐zero signal and eight‐level pulse amplitude modulation signal of up to 180 and 300 Gbps, respectively, are generated by the modulator, which provides ultra‐large bandwidth, ultra‐high efficiency, and a compact solution for next‐generation electro‐optic systems.

Real-Time Reconfigurable Radio Frequency Arbitrary-Waveform Generation via Temporal Pulse Shaping with a DPMZM and Multi-Tone Inputs

Benefitting from a large bandwidth and compact configuration, a time-domain pulse-shaping (TPS) system provides possibilities for generating broadband radio frequency (RF) arbitrary waveforms based on the Fourier transform relationship between the input–output waveform pair. However, limited by the relatively low sampling rate and bit resolution of an electronic arbitrary-waveform generator (EAWG), the diversity and fidelity of the output waveform as well as its reconfiguration rate are constrained. To remove the EAWG’s limitation and realize dynamic real-time reconfiguration of RF waveforms, we propose and demonstrate a novel approach of RF arbitrary-waveform generation based on an improved TPS system with an integrated dual parallel Mach–Zehnder modulator (DPMZM) and multi-tone inputs. By appropriately adjusting the DC bias voltages of DPMZM and the power values, as well as the center frequencies of the multi-tone inputs, any desired RF arbitrary waveform can be generated and reconfigured in real time. Proof-of-concept experiments on the generation of different user-defined waveforms with a sampling rate up to 27 GSa/s have been successfully carried out. Furthermore, the impact of modulation modes and higher-order dispersion on waveform fidelity is also discussed in detail.

A frequency-agile retrodirective tag for large-scale sub-terahertz data backscattering

Backscattering is a promising power-efficient communication technique providing sustainable wireless links with a low carbon footprint. This approach is a critical enabler for dense IoT networks, which are forecast to grow to 41 billion by 2025. However, existing backscatter designs are limited to the sub-6 GHz bands or narrowband operation in the millimeter-wave regime; therefore, they fail to concurrently support many interference-free low-power users. Enabling a frequency-agile wideband backscatter design in the sub-terahertz offers a two-pronged advantage for densely deployed backscatter networks: spatial reuse enabled by directionality and frequency multiplexing enabled by the large available bandwidth. We present the first sub-THz backscatter architecture that operates above 100 GHz. Our design relies on a detailed understanding of reciprocity in leaky-wave devices and offers a realistic joint localization and communication protocol for sub-THz backscatter networks.

Ring-assisted, racetrack, and Mach-Zehnder modulator: which one offers the lowest voltages and chirp-free operation?

This study presents a comparison between resonant and non-resonant electro-optical modulator configurations. The focus lies on finding the configuration with the highest modulation amplitude at the lowest drive voltage while achieving a large electro-optical bandwidth. It is found that the ring-assisted Mach-Zehnder modulator (RaMZM) offers chirp-free and resonantly enhanced modulation without bandwidth limitations imposed by the ring. In contrast, a racetrack modulator (RTM) offers resonant enhancement at the cost of a chirped modulated signal and with a bandwidth limitation. The traditional non-resonant Mach-Zehnder modulator (MZM) configuration requires higher modulation voltages while offering chirp-free operation with a flat frequency response. The RaMZM, therefore, looks like an ideal candidate for encoding information in backbone networks where small modulation voltages and perfect control over the phase of a signal are needed. The results are supported by experiments that show driverless plasmonic modulation at 220 GBaud 2PAM, 160 GBaud 4PAM and 100 GBaud 8PAM with record low peak voltages of 0.5 V.

Fabrication of core-shell Fe4N@C with sea-island structure by one-step nitriding method as efficient electromagnetic wave composite absorber

Porous structure design and magnetic-dielectric composite are effective ways to develop electromagnetic wave (EMW) absorbing materials with light-weight, thin-thickness, large effective absorption bandwidth (EAB), and strong reflection loss (RL). This article presents a simple one-step nitridation method for synthesizing Fe4N@C compounds with sea-island like and core-shell structures. The optimal RL value of Fe4N@C is up to -60.01dB, and the EAB (frequency range for RL< -10 dB) is 5GHz (11.1-16.1GHz) with a thickness of 1.9mm. The EAB reaches 5.5GHz (12.5-18GHz) when the matching thickness is 1.7mm. The multi-component design achieved excellent impedance matching properties. The carbon frame connects the core-shell particles to form a three-dimensional porous structure, providing multiple reflection losses. Therefore, this work provides a convenient way to design efficient and lightweight EMW absorbers with special structures.

In-situ relative calibration of Bragg crystals with Monte Carlo line ratio analysis.

X-ray line emission spectra can thoroughly characterize hot plasmas, especially when line shapes and ratios convey distinct aspects of plasma conditions. However, the high spectral resolution required for observing line shapes is often at odds with the large bandwidth required to observe many line ratios across a wide spectral range. One strategy to obtain high spectral resolution over a wide bandwidth is to use multiple crystals with calibrated reflectivity so that line intensities across different crystals can be compared. Here, we explore the use of a low-resolution, wide-bandwidth mica survey spectrometer to infer relative reflectivity of two high-resolution, narrow-bandwidth quartz crystals. A Monte Carlo error analysis determines comparable x-ray line ratios measured from both spectrometers, resulting in an in situ calibration factor and associated uncertainty for the relative reflectivity of the high-resolution crystals.

Design and fabrication of lithium niobate asymmetrical mode resonators toward C-band and Ku-band

Abstract This work presents a laterally excited bulk wave resonator (XBAR) based on the suspended Z-cut lithium niobate thin film. In order to systematically analyze the influence of geometric structure on the performance of resonators, including electromechanical coupling coefficient (kt 2) and quality factor (Q), the pitch of inter-digital transducers and lateral reflective boundary width (D) were optimized via finite element analysis simulation. Besides, the XBARs with the broadband piston mode structure (BPM-XBAR) were further studied, and the transverse displacement was weakened after optimization, hence enhancing the Q value of the targeted mode. Consequently, the fabricated devices exhibited first order asymmetrical (A1) mode resonance at 5.87 GHz with kt 2 of 12.98% and Q of 218, a nearly 70% increase in Q value. The third order asymmetrical (A3) mode resonance occurred at 17.18 GHz with kt 2 of 7.91%. The above devices have the potential to construct large bandwidth and low loss filters toward the C-band and Ku-band.

COSMO: Dynamic Uploading Scheduling in mmWave-Based Sensor Networks with Mobile Blockers

Wireless sensor networks (WSNs) leveraging millimeter wave (mmWave) communication for bandwidth-demanding applications is considered in this paper. Despite the large bandwidth, the delivery of delay-sensitive information collected by sensors may still face significant latency due to the vulnerability to intermittent link blockage. Hence, the guarantee of low age of information (AoI) in mmWave WSNs is not straightforward. In this paper, the wireless sensing and dynamic programming techniques are jointly exploited to relieve the above issue. The former tracks the human blockers and predicts the chance of link blockage; the latter optimizes the transmission of multiple sensors based on the prediction. Particularly, the long-term optimization of sampling, uplink time and power allocation policies in a sensor network can be formulated as an infinite-horizon Markov decision process (MDP) with discounted cost, where the state transition probabilities can be predicted via wireless sensing. A novel low-complexity solution framework, namely COSMO, with a guaranteed performance in the worst case, is proposed. Simulations show that compared with heuristic benchmarks, benefiting from the prediction of the link blockage, COSMO can significantly suppress the average system cost, which consists of both AoI and energy consumption.

6 GHz lamb wave acoustic filters based on A1-mode lithium niobate thin film resonators with checker-shaped electrodes

The first-order antisymmetric (A1) mode lamb wave resonator (LWR) based on Z-cut LiNbO3 thin films has attracted significant attention and is widely believed to be a candidate for next-generation reconfigurable filters with high frequency and large bandwidth (BW). However, it is challenging for traditional interdigitated electrodes (IDTs) based LWR filters to meet the requirement of a clean frequency spectrum response and enough out-of-band (OoB) rejection. To solve the problem, we propose LWRs with checker-shaped IDTs for the design of filters that meet the Wi-Fi 6E standard. By taking advantage of checker-shaped IDTs with unparalleled boundaries, the fabricated 6-GHz resonators successfully suppress higher-order A1 spurious modes, demonstrating a spurious-free impedance response and a high figure-of-merit (FOM) up to 104. Based on the demonstrated checker-shaped electrode design, the filter features a center frequency (f0) of more than 6 GHz, a 3 dB BW exceeding 620 MHz, and an excellent OoB rejection >25 dB, consistent with the acoustic-electric-electromagnetic (EM) multi-physics simulations. Furthermore, through the capacitance-inductance matching network technology, the filter’s voltage standing wave ratio (VSWR) is successfully reduced below 2, showing an excellent 50 Ω impedance matching. This study lays a foundation for ultra-high-frequency and ultra-wideband filters for the Wi-Fi 6/6E application.

A review on free space optical communication links: 5G applications

Abstract Free space optical (FSO) communications has garnered significant attention as a potential substitute for radio frequency (RF) wireless communication in short and long range transmissions. Free-space optical (FSO) communication is a method where an optical beam is sent across an unguided channel, gaining favour in high-speed wireless networks due to its large optical bandwidth, fast data transmission, lack of licencing requirements, secure nature, and easy setup. Despite several inherent advantages that FSO has over existing radio frequency (RF) communication technologies, its link performance is severely hampered by atmospheric fog and turbulence, which not only reduce optical irradiance but also cause the modulated optical beam to deviate from its intended path, impacting the quality of the received signal. This review paper discusses FSO technology, channel impairments under varied atmospheric attenuation conditions, advantages, and applications. Various channel models in terms of probability density functions are described, which characterise the statistical nature of the irradiance fluctuations of optical transmission through scattering and atmospheric turbulence. Key objectives that need to be addressed in the near future, particularly in fifth-generation (5G) and beyond, includes enhancing capacity, boosting data rates, minimising latency, and enhancing service quality. Last but not the least, several uses of FSO that facilitates 5G and future technologies have also been covered in this study.

Generation of GHz surface acoustic waves in (Sc,Al)N thin films grown on free-standing polycrystalline diamond wafers by plasma-assisted molecular beam epitaxy

Abstract Telecommunication of the next generation demands filters that can operate in the 10 GHz range with sufficient bandwidths. For surface-acoustic-wave (SAW) devices this prerequisite translates into high sound velocities and high piezoelectric couplings. Wurtzite AlN on diamond, which exploits the strong piezoelectricity of AlN with the very high SAW velocity of diamond, has been considered a promising platform. A significant boost (up to a factor of 4) of the piezoelectric response can be obtained by alloying AlN with Sc. Here, the main challenge lies in the synthesis of highly-oriented thin (Sc,Al)N films on diamond. In this work, we aim at establishing a platform for SAW devices using plasma-assisted molecular beam epitaxy for the deposition of Sc0.2Al0.8N on diamond. We investigate the structural properties related to SAW generation gearing towards applications at high frequencies. To this end, we prepare (Sc,Al)N thin films using plasma-assisted MBE on polished polycrystalline diamond wafers and demonstrate the efficient generation of SAW modes with frequencies up to 8 GHz. Systematic studies of the dependence of the SAW velocity and electromechanical coupling coefficient on the Sc0.2Al0.8N film thickness is presented for various SAW modes. Our result demonstrates the potential of this material combination for future application that requires large bandwidth in the ultra-high frequency range.&amp;#xD;

Enhancing Detection Frequency and Reducing Noise Through Continuous Structures via Release-Controlled Transfer Toward Light-Based Wireless Communication.

Organic photodetectors (OPDs) have received considerable attention owing to their superior absorption coefficient and tunable bandgap. The introduction of bulk-heterojunction (BHJ) structure aims to maximize charge generation, however, its response speed is constrained by the random distribution of donor and acceptor. Herein, a multiple-active layer design consisting of a single acceptor layer and a bulk-heterojunction layer (A/BHJ structure) is introduced, which combines the benefits of both the planar junction and the BHJ, improving photo-sensing. A transfer process is employed for this structure, which involves calculating the energy release rate at each interface, considering temperature and velocity. Consequently, the OPD with the A/BHJ structure is successfully fabricated through transfer printing, resulting in reduced dark current, superior detectivity (1.06 × 1013 Jones), and rapid response, achieved by creating a high hole injection barrier and suppressing trap sites within the interfaces. By thoroughly investigating charge dynamics in the structure, the A/BHJ structure-based OPD attains large bandwidth detection with high signal-to-noise. An efficient wireless data communication system with digital-to-analog conversion is showcased using the A/BHJ structure-based OPD.

Time Lens Photon Doppler Velocimetry (TL-PDV) for extreme measurements

Capturing extreme surface velocities with >50 km/s dynamic range, which arise in shock physics such as inertial confinement fusion (ICF), is beyond the reach of conventional photon Doppler velocimetry (PDV) systems due to the need for extremely large electrical bandwidth under such conditions. The recent ignition in ICF calls for new velocimetry that can measure velocities exceeding 100 km/s. Time lens PDV (TL-PDV) is a solution where the high frequency beat signal from a conventional PDV system is periodically temporally magnified in the optical domain using a time lens. Here we experimentally demonstrate TL-PDV for the first time, validate the performance over a 74 km/s velocity range with high accuracy using a temporal magnification factor of 7.6, and verify excellent agreement with conventional PDV for laser driven micro-flyer experiments. TL-PDV currently provides the largest velocity dynamic range among PDV systems and is scalable to even higher velocities, which makes it an ideal candidate for material characterization under the most extreme conditions such as optimizing fuel efficiency in ICF experiments.

The effect of conduction loss on microwave absorption performance of Fe-doped NiCo2O4 spinel oxide

Strong absorption and large bandwidth are two contributors to material’s electromagnetic wave absorbing performance. While spinel ferrite materials have garnered extensive attention in the realm of microwave absorption, their relatively low conductivity remains a practical challenge.In this work, NiCo2-xFexO4 (x = 0, 0.04, 0.06 and 0.08) precursor was prepared by hydrothermal and after-sintered method. It was found that Fe doping exhibit excellent EM absorption properties. Specially, when the Fe content is 0.08, the maximum reflection loss −48.90 dB at 15.40 GHz and the maximum effective bandwidth 4.20 GHz are achieved. More importantly, the absorption frequency can be broadened from Ku to C band even to S band with proper adjusting Fe content. Doping with Fe enhances conduction loss and make a significant contribution to dielectric loss, as a result, the impedance matching degree of the Fe-NiCo2O4 composite is influenced by the synergistic effect of its dielectric and magnetic properties. This work provides a simple way for enhancing the microwave absorption capabilities of ferrite materials and provides insight into understanding conduction loss in microwave absorption.

Understanding the machining mechanism in ultrasonic vibration-assisted nanogrinding of GaN

As a typical difficult-to-machine material, gallium nitride (GaN) crystals have the merits of excellent chemical stability and large bandwidth, which can be used in fields of space optical components, photoelectric devices, and electronic communication. The smooth surface of GaN is the basis of these applications. Grinding of GaN has thus drawn increasing attention. Furthermore, vibration-assisted nanogrinding has the potential to reduce grinding forces compared with conventional nanogrinding. In this study, ultrasonic-vibration-assisted nanogrinding of GaN with a single grit is conducted based on molecular dynamic (MD) simulations. The plastic deformation mechanism of GaN single crystals as well as the influence of grinding parameters, such as vibration period and amplitude, on the grinding outcomes are investigated. The MD simulations reveal that plastic deformation of GaN in the vibration-assisted nanogrinding process is dominated by amorphous transformation, dislocation, stacking faults, lattice distortion, and formation of nanocrystals. Furthermore, amorphous GaN atoms are mainly induced in front of the grit and at either side of the grinded groove. In the grinding process, the periodic fluctuation of grinding force components, which include the normal, tangential, and horizontal forces, are stable. A smaller grinding force is obtained when grinding with a small vibration period. Moreover, a small vibration period and large vibration amplitude lead to improved grinding efficiency, suppressing the grinding force and subsurface damage, and improving the grinding quality. The findings in this study facilitate an understanding of the plastic deformation mechanism of GaN single crystals and also provide guidance for parameter optimization during vibration-assisted nanogrinding.

Survey on Optical Wireless Communication with Intelligent Reflecting Surfaces

Optical Wireless Communication (OWC) technology has gained significant attention in recent years due to its potential for providing high-data-rate wireless connections through the large license-free bandwidth available. A key challenge in OWC systems, similar to high-frequency Radiofrequency (RF) systems, is the presence of dead zones caused by obstacles like buildings, trees, and moving individuals, which can degrade signal quality or disrupt data transmission. Traditionally, relays have been used to mitigate these issues. Intelligent Reflecting Surfaces (IRSs) have recently emerged as a promising solution, enhancing system performance and flexibility by providing reconfigurable communication channels. This paper presents an overview of the application of IRSs in OWC systems. Specifically, we categorize IRSs into two main types: mirror array-based IRSs and metasurface-based IRSs. Furthermore, we delve into modeling approaches of mirror array-based IRSs in OWC and analyze recent advances in IRS control, which are classified into system power or gain optimization-oriented, system link reliability optimization-oriented, system data rate optimization-oriented, system security optimization-oriented, and system energy optimization-oriented approaches. Moreover, we present the principles of metasurface-based IRSs from a physical mechanism perspective, highlighting their application in OWC systems through the distinct roles of light signal refraction and reflection. Finally, we discuss the key challenges and potential future directions for integrating IRS with OWC systems, providing insights for further research in this promising field.

THz band drone communications with practical antennas: Performance under realistic mobility and misalignment scenarios

For 6G non-terrestrial communications, drones will offer uninterrupted connectivity for surveillance, sensing, and localization. They will also serve as drone base stations to support terrestrial base stations, providing large bandwidth, high-rate, and ultra-reliable low latency services. In this paper, for the first time in the literature, we depict the true performance of Terahertz (THz) band communications among drones by applying various channel selection and power allocation schemes with practical THz antennas within (0.75–4.4) THz under realistic mobility and misalignment scenarios. Through numerical simulations, we unveil the capacity of drone links under different channel selection and power allocation schemes within 10s to 100s of Gbps at distances (1–100) m, when drones are in motion and subject to (mis)alignment due to mobility and even under beam misalignment fading. However, when exposed to real drone mobility traces, the performance of all channel selection schemes drops significantly, sometimes by up to six orders of magnitude, due to the occasional reverse orientations of antennas. In addition to the capacity analysis, we report available frequency bands (transmission windows) considering all schemes and mobility patterns. We also identify a band that is commonly available under all considered mobility and misalignment settings, and we evaluate its performance in terms of spectral and energy efficiencies, which can be useful in designing THz transceivers for drone communications. Our findings emphasize the essence of active beam control solutions to achieve the desired capacity potential of THz drone communications, while also highlighting the challenges of utilizing the THz band for drone communications.

Upgrade of DIII-D radial interferometer-polarimeter for large bandwidth, low noise, and toroidal mode number measurements.

Near ion-cyclotron frequency (fci) fluctuations, such as those originating from Global and Compressional Alfvén Eigenmodes (GAEs/CAEs), are expected to be present in future fusion reactors but are not well understood due to the limited availability of core measurements in present-day tokamaks. The measurement bandwidth of the Radial Interferometer-Polarimeter (RIP) diagnostic has been upgraded from 1 to 5MHz to detect these fluctuations in DIII-D. RIP adopts the three-wave technique for simultaneous polarimetric and interferometric measurements. Solid-state microwave sources operating at 650GHz are used as probe beams and provide 5MHz bandwidth for both polarimetric and interferometric measurements. Bandwidths of related hardware, including mixer amplifier, signal cable, and digital phase demodulator, are increased correspondingly. Measurement noise is minimized by reducing the time delay between reference and probe signals to nanosecond level and employing correlation-based techniques. Using the upgraded diagnostic, CAE/GAE-like bursting fluctuations are observed in neutral-beam heated plasmas with toroidal magnetic field Bφ ≈ 1 T. Current upgrades being undertaken would enable the evaluation of toroidal mode number for these modes. This work opens the possibility of better understanding near ion-cyclotron frequency fluctuations in fusion relevant plasmas.