Wideband Generation Research Articles

Wideband and low-spurious optical waveform generator for optically addressable quantum systems manipulation and control

Optical manipulation of quantum systems requires stable laser sources able to produce complex waveforms over a large frequency range. In the visible region, such waveforms can be generated using an acousto-optic modulator driven by an arbitrary waveform generator, but these suffer from a limited tuning range typically of a few tens of MHz. Visible-range electro-optic modulators are an alternative option offering a larger modulation bandwidth, however they have limited output power which drastically restricts the scalability of quantum applications. There is currently no architecture able to perform phase-stabilized waveforms over several GHz in the visible or near infrared region while providing sufficient optical power for quantum applications. Here we propose and develop a modulation and frequency conversion set-up able to deliver optical waveforms over a large frequency range, with a high spurious extinction ratio, scalable to the entire visible/near infrared region with high optical power. The optical waveforms are first generated at telecom wavelength and then converted to the emitter wavelength through a sum frequency generation process. By adapting the pump laser frequency, the optical waveforms can be tuned to interact with a broad range of optical quantum emitters or qubits such as alkali atoms, trapped ions, rare earth ions, or fluorescent defects in solid-state matrices. Using this architecture, we were able to detect and study a single erbium ion in a nanoparticle. We also generated high bandwidth signals at 606 nm, which would enable frequency multiplexing of on-demand read-out Pr3+:Y2SiO5 quantum memories.

Thermoacoustic phased-array radiators – Theory, characteristics, and applications

Standard non-invasive acoustic non-destructive testing (NDT) methods like testing in contact or using immersion tank arrangements are limited since the probes need to be in direct contact with the test piece or using a fluid as coupling media. Air-coupled ultrasonic testing avoids these limitations and enables new testing methods. Two up-and-coming transducer technologies are recognized as promising: transducers using ferroelectrets and transmitters based on the thermoacoustic principle. Thermoacoustic radiators based on thin-film technology offer a resonant-free generation of ultrasound. The resonance-free operation enables the wideband generation of acoustics waves and promises advantages for existing NDT methods. Using specially shaped substrates and electrodes enables the fabrication of planar and focused thermoacoustic radiators. This contribution presents the latest results of our ongoing research regarding thermoacoustic radiators, which is the thermoacoustic phased-array. Phased-array transducers offer the on-the-fly change of the steering angle and the position of the focal point without moving or modifying the transducer itself. Combining both technologies, thermoacoustic emitter and the phasedarray principle broaden the spectrum of classical NDT applications and modern approaches like the excitation of guided waves or structural health monitoring. In detail, we modelled the sound field of a self-fabricated thermoacoustic phased-array radiator, characterised the emitter elementwise and tested several application scenarios (e.g., transmission, beam steering, focusing and the excitation of guided waves).

Monolithically integrated laser with DBR for wideband and low time delay signature chaos generation

Chaotic laser has attracted a large amount of attention due to its broad spectrum, noise-like characteristics, and photonic integrated chaotic semiconductor lasers have further expanded the application field of chaotic laser for their small size and stable properties. Therefore, a monolithically integrated laser with a distributed Bragg reflector (DBR) is designed. This proposed chaotic laser consists of a distributed feedback (DFB) laser section, a phase section, and a DBR section. DBR grating can provide wavelength detuning to generate mode beating, which enhances chaotic bandwidth and distributed feedback to suppress time delay signature (TDS). The transmission line laser model (TLLM) of chaotic laser is constructed and chaotic characteristics of the integrated chip are investigated. A chaotic signal with a bandwidth of 12.34 GHz and TDS less than 0.065 is obtained. In addition, a map of dynamic states in the parameter space of phase section current and DBR section current is shown, and a wide range of chaotic regions are obtained. The results show that the broadband chaotic laser with a low TDS can be obtained by controlling the parameters reasonably, which is beneficial to realize the application of chaotic laser.

A Monolithically Integrated Two-Section Laser for Wideband and Frequency-Tunable Photonic Microwave Generation

A monolithically integrated two-section laser is presented for wideband and frequency-tunable photonic microwave generation. The laser consists of two back-to-back DFB sections forming a mutually coupled structure. By properly adjusting the bias currents of two sections, the laser can stably work at the state of period-one oscillation over a wide range of frequency detuning. Based on this, continuous and linear tuning of photonic microwave signals can be achieved. Experimental results confirm that a large tunable range from 12.45 to 80.30 GHz can be realized using this laser.

Wideband and high-dimensional chaos generation using optically pumped spin-VCSELs.

We propose and numerically demonstrate wideband and high-dimensional chaos signal generation based on optically pumped spin-polarized vertical-cavity surface-emitting lasers (spin-VCSELs). Here, we focus on the chaotic characteristics of spin-VCSELs under two scenarios: one is a spin-VCSEL with optical feedback and the other is optical heterodyning the outputs of two free-running spin-VCSELs. Specifically, we systematically investigate the influence of some key parameters on the chaotic properties, i.e., bandwidth, spectral flatness (SF), time delay signature (TDS), correlation dimension (CD), and permutation entropy (PE), and reveal the route to enhance these properties simultaneously. Our simulation results demonstrate for the first time that spin-VCSELs with simple auxiliary configurations allow for chaos generation with desired properties, including effective bandwidth up to 30 GHz and above, no TDS of greater than 0.2, the flatness of 0.75 and above, and the high complexity/dimensionality over a wide range of parameters under both schemes. Therefore, our study may pave the way for potential applications requiring wideband and high-dimensional chaos.

Wideband and flat-spectrum chaos generation from a semiconductor laser with strong dispersive light feedback

Wideband and flat-spectrum chaos generation from a semiconductor laser with strong dispersive light feedback

Photonic Generation of Wideband Chirped Microwave Waveforms

A chirped microwave waveform with a large time-bandwidth product (TBWP) can find important applications in modern radar systems and microwave imaging systems. Microwave photonics, a field that studies the generation and processing of microwave signals in the optical domain to take advantage of the ultra-wide bandwidth offered by photonics, has been considered an effective solution for high-frequency and large-bandwidth microwave waveform generation. In this paper, an overview on photonic generation of wideband chirped microwave waveforms is provided. Three major methods are discussed including chirped microwave waveform generation based on spectral shaping and frequency-to-time (SS-FTT) mapping, frequency and bandwidth multiplication, and Fourier-domain mode-locking of an optoelectronic oscillator (OEO). The performance of the techniques for chirped microwave waveform generation is studied. Techniques to generate chirped microwave waveforms based on photonic integrated circuits (PICs) are also discussed.

Nature-inspired orbital angular momentum beam generator using aperiodic metasurface

This article presents the design of reflective nature-inspired metasurfaces for generation of wideband and high purity circularly polarized (CP) orbital angular momentum (OAM) waves. It has been shown in this article that the breaking of the transitional periodicity and the combination of aperiodic nature-inspired distribution of sub-wavelength sized meta-atoms based on Pancharatnam–Berry (PB) phase theory can lead to OAM beams of high purity with improved bandwidth. The distribution of the PB anisotropic meta-atoms across the proposed metasurface aperture is non-uniform and distributed along logarithmic spirals similar to sunflower seeds, i.e. outwardly logarithmic spiral lattices of no transitional periodicity. The proposed reflective CP-OAM beam generator metasurface diameter is 140 mm, thickness ≈ 0.11λ 17GHz and has 600 anisotropic spatially rotated PB meta-atoms of sub-wavelength size of 5 mm ≈ 0.28λ 17GHz. Four OAM metasurface generators have been designed to produce OAM waves of various modes from 1 to 4. Both simulation and experimental results have demonstrated that the proposed metasurfaces can efficiently generate CP-OAM beams from 13.1 GHz to 20.5 GHz (BW = 44%) with high mode purity >90%.

Non-destructive laser-ultrasonic Synthetic Aperture Focusing Technique (SAFT) for 3D visualization of defects

The Laser Ultrasonic (LU) technique has been widely studied. Detected ultrasonic signals can be further processed using Synthetic Aperture Focusing Techniques (SAFTs), to detect and image internal defects. LU-based SAFT in frequency-domain (F-SAFT) is developed to visualize horizontal hole-type defects in aluminum. Bulk acoustic waves are non-destructively generated by irradiating a laser line-source, and detected using a laser Doppler vibrometer at a point away from the generation. The influence of this non-coincident generation-detection on the equivalent acoustic velocity used in the algorithm is studied via velocity mappings. Because the wide-band generation characteristic of the LU technique, frequency range selections in acoustic wave signals are implemented to increase Signal-to-Noise Ratio (SNR) and reconstruction speed. Results indicate that by using the LU F-SAFT algorithm, and incorporating optimizations such as velocity mapping and frequency range selection, small defects can be visualized in 3D with corrected locations and improved image quality.

Wideband and high efficiency orbital angular momentum generator based on bi-layer metasurface

A broadband and high-efficieny bi-layer metasurface is proposed in this paper. The unit cell of the metasurface is formed by symmetrically etching two cross-type metal patches on both sides of a dielectric plate. Furthermore, the two metal patches have a displacement of half a period along the <i>y</i>-axis. By employing the displacement, the transmission bandwidth of the bi-layer metasurface is significantly expanded. In order to obtain a physical insight into bandwidth broadening, a π-type equivalent circuit that presents the electromagnetic coupling between within the bi-layer metasurfaces is successfully extracted to investigate the influence of electromagnetic coupling on transmission performance. The results show that by shifting the metal patches along the <i>y</i>-axis by half a period, the coupling impedance (<i>Z</i><sub>12</sub> or <i>Z</i><sub>21</sub>) of bi-layer metasurface can be significantly modified, which further changes the electromagnetic coupling of the bi-layer metasurface. Correspondingly, the impedances <i>Z</i><sub>p</sub> and <i>Z</i><sub>s</sub> in the π-type circuit are changed to approximately meet the resonant condition of circuit in broadband, resulting in the bandwidth expansion of the proposed device. By using Pancharatnam-Berry phase theory, we redesign the proposed metasurface unit cell into a broadband orbital angular momentum generator. The simulation and measurement results verify that the bi-layer metasurface can convert a left-hand circularly polarized wave into a right-hand circularly polarized wave carrying orbital angular momentum in a frequency range between 11 GHz and 12.8 GHz, demonstrating the performance of device.

Generation of Broadband High-Purity Dual-Mode OAM Beams Using A Four-Feed Patch Antenna: Theory and Implementation

A broadband four-feed circular patch antenna is demonstrated to generate high-purity dual-mode vortex beams carrying orbital angular momentum (OAM) for the first time. The electric field formula of the circularly polarized (CP) component is derived for analyzing radiation characteristics of different OAM modes, such as the CP property, phase and amplitude distributions. Theoretical calculation and numerical simulation results show that the four-feed patch antenna operating in the TMn1 mode can generate ±n OAM waves. A prototype of a four-feed circular TM21-mode patch antenna is fabricated and measured to verify the effectiveness of the theoretical analysis. The proposed antenna consists of a four-feed patch with an air-coupled parasitic patch and a four-way phase-shifting feeding network. Experimental results show that the proposed antenna can generate a left-hand CP OAM with mode l = +2 and a right-hand CP OAM with mode l = −2. The OAM beams are generated in a wide band from 5.50 to 6.50 GHz with a mode purity over 90%. The proposed method is very suitable for the generation of wideband, dual-mode and high-purity OAM beams in the microwave and millimeter wave bands.

Sub-terahertz wideband vector beam generator based on superwavelength lattice dielectric grating

Segmented orientation of a half wave plate will convert a linear polarization into a cylindrical vector polarization. In this work, the half wave plate is achieved by 3D printed low-index dielectric grating, whose segmented rotation forms a vector beam generator. The radially and azimuthally polarized beam is experimentally measured at 140 GHz when passing through the printed sample. Further study shows that the grating lattice affects the bandwidth of the vector beam generator. The frequently used subwavelength lattice design shows narrow bandwidth due to the undesired eigenmode dispersion and interaction. In contrast, the superwavelength lattice design offers wideband and efficient vector beam generation thanks to the weak diffraction of the low-index material and the proper eigenmode dispersion. The mechanism can be applied similarly to other type of polarization control to enrich sub-terahertz elements.

A new dual C‐shaped rectangular dielectric resonator based antenna for wideband circularly polarized radiation

This article presents a new dual C-shaped rectangular dielectric resonator (DR) based antenna for generation of wideband circularly polarized (CP) radiation. The proposed antenna comprises of a pair of C-shaped rectangular dielectric DR and a metal strip with a coaxial probe. By utilization of a metal strip at the side surface of C-shaped rectangular DR, the wideband CP radiation is achieved from the proposed dielectric resonator antenna (DRA). Fundamental orthogonal modes (TExδ11 and TEy1δ1) are excited using the rectangular DRA with a metal strip for the generation of CP fields. The proposed antenna with dual C-shaped rectangular CP DRA provides the measured −10 dB reflection coefficient bandwidth of 30.07% (3.22 GHz-4.36 GHz) with measured 3-dB axial ratio bandwidth of 14.81% (3.25 GHz-3.77 GHz) at the boresight. The proposed antenna covers the useful Wi-MAX band.

Analysis of wideband circularly polarized ring slot antenna using characteristics mode for bandwidth enhancement

In this article, a coplanar waveguide fed ring slot antenna is proposed for the generation of circular polarization. It is shown that the bandwidth can be improved by adding a stub. Characteristics mode analysis is used to understand the wideband behavior and generation of circular polarization in different antenna configurations. Parametric analysis is used to optimize the performance of the antenna. The proposed antenna is fabricated and the measured results are compared with the simulated performance. The measured impedance bandwidth (|S11| ≤ －10 dB) is 64.6% (2.25 GHz–4.4 GHz) and a 3 dB axial ratio bandwidth is 64.6% (2.25 GHz–4.4 GHz).

A simplified lumped model for the optimization of post-buckled beam architecture wideband generator

Buckled beams structures are a classical kind of bistable energy harvesters which attract more and more interests because of their capability to scavenge energy over a large frequency band in comparison with linear generator. The usual modeling approach uses the Galerkin mode discretization method with relatively high complexity, while the simplification with a single-mode solution lacks accuracy. It stems on the optimization of the energy potential features to finally define the physical and geometrical parameters. Therefore, in this paper, a simple lumped model is proposed with explicit relationship between the potential shape and parameters to allow efficient design of bistable beams based generator. The accuracy of the approximation model is studied with the effectiveness of application analyzed. Moreover, an important fact, that the bending stiffness has little influence on the potential shape with low buckling level and the sectional area determined, is found. This feature extends the applicable range of the model by utilizing the design of high moment of inertia. Numerical investigations demonstrate that the proposed model is a simple and reliable tool for design. An optimization example of using the proposed model is demonstrated with satisfactory performance.

On-Chip THz Spectroscope Exploiting Electromagnetic Scattering With Multi-Port Antenna

This paper presents a new methodology to extract spectral information of radiated THz signals to enable a fully integrated broadband THz spectroscope in silicon. A classical down-conversion spectrum analysis architecture requires on-chip generation of LO signals covering GHz-THz frequencies to analyze an incident spectrum covering that range. This paper presents a method to exploit the interaction between the front-end antenna and the incident signal to extract spectral information eliminating the need for extremely wideband LO generation and the entire receiver architecture following the antenna. The central premise is that the incident THz signal excites a spectrum-dependent current distribution on the antenna surface and this work presents a method to measure and then estimate the incident spectrum from the impressed current distribution on an on-chip antenna. The chip is implemented in $0.13~\mu \text {m}$ SiGe BiCMOS technology and measures 2.6 mm $\times 1.9$ mm. Measurement results are presented for various incident spectra between 40–330 GHz. In addition, the paper presents a method for extracting time-domain information by exploiting the variable nonlinearities of the integrated detectors. By modifying a classical single-port antenna into a 2D multi-port scatterer, the paper presents a synthesizer-free THz spectroscope which consists of an integrated scatterer and multitude of low-power sensors capable of sub-wavelength measurement of near-field interactions which are exploited for spectral estimation.

Bandwidth increasing mechanism by introducing a curve fixture to the cantilever generator

A nonlinear wideband generator architecture by clamping the cantilever beam generator with a curve fixture is proposed. Devices with different nonlinear stiffness can be obtained by properly choosing the fixture curve according to the design requirements. Three available generator types are presented and discussed for polynomial curves. Experimental investigations show that the proposed mechanism effectively extends the operation bandwidth with good power performance. Especially, the simplicity and easy feasibility allow the mechanism to be widely applied for vibration generators in different scales and environments.

A Goal-Oriented Error Estimator for Reduced Basis Method Modeling of Microwave Devices

This letter proposes a novel a-posteriori error estimator suitable for the reduced order modeling of microwave circuits. Unlike the existing error estimators based on impedance function residuals, the new one exploits the residual error associated with the computation of the scattering matrix. The estimator can be effectively used in the Reduced Basis Method (RBM) to automatically generate reduced-order models. The results of numerical experiments show that the new error estimator predicts the errors in the computed S-parameters more accurately than the other existing approaches, and that it can be used to automate the generation of wideband reduced models.

Design of wideband vibration-based electromagnetic generator by means of dual-resonator

This paper describes the design of a wideband electromagnetic energy harvester that utilizes a novel dual-resonator method to improve the operational frequency range of the vibration-based generator. The device consists of two separate resonator systems (coil and magnet), which each comply with their respective resonance frequencies. This is because both resonators are designed in such a way that both magnet and coil components will oscillate at an additive phase angle, and hence create greater relative motion between the two dominating resonance frequencies, which realizes the wideband generator. Each resonator system consists of a distinctive cantilever beam, one attached with four magnets and steel keepers, the other attached with a copper coil and stainless steel holder as the free end mass. Both cantilevers are clamped and fitted to a common base that is subjected to a vibration source. Basic analytical models are derived and a numerical model is implemented in MATLAB-Simulink. Electromagnetic, structural modal and static mechanical analysis for the design of the prototype are completed using ANSYS finite element tools. For a 0.8ms−2 acceleration, the open-loop voltage obtained from the experiment shows a good correlation with those from the simulation. Peak induced voltage is measured to be 259.5Vrms as compared to 240.9Vrms from the simulator at 21.3Hz, which implies an error range of 7.7%. The results also indicate that there is a maximum of 58.22% improvement in the induced voltage within the intermediate region which occurs at the intersection point between the output response plots of two single resonator generators.

Wideband generation of pulses in dual-pump optical parametric amplifier: theory and experiment

The generation of pulses in dual-pump fiber optical parametric amplifier is investigated. Theoretically, it is shown that in an analogical manner to pulse generation in single-pump fiber optical parametric amplifiers, the generated pulse shape depends on the linear phase mismatch between the interacting waves. However the dual-pump architecture allows for the bounding of the phase mismatch over a wide bandwidth. This feature permits the generation of uniform pulses over a wide bandwidth, contrary to the single-pump architecture. Using the developed theory, a pulse source with uniform pulses at 5 GHz repetition rate and duty cycle of 0.265 over 40 nm is demonstrated.