Broadband Regime Research Articles

Self-Driven Perovskite/Organic Quasi-Tandem Photodetectors Operating in Both Narrowband and Broadband Regimes.

Dual-band photodetectors (PDs) have attracted extensive research attention due to their great potential for diverse and refreshing application scenarios in full-color imaging, optical communication, and imaging detection. Here, a self-driven dual-band PD without filters and other auxiliary equipment to achieve a narrowband response in Mode 1 and a broadband response in Mode 2 was designed based on carrier-selective transmission narrowing (CSTN). The polymer material poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), which has the appropriate energy level, was selected to be the carrier-selective transmission layer. In Mode 1, the dual-band PD exhibits a near-infrared (NIR) narrowband response in 750-900 nm, which indicates a responsivity of 360 mA/W, a full-width at half-maximum (fwhm) of 81 nm, and a specific detectivity (D*) of 7.49 × 1010 Jones at 810 nm. Simultaneously, in Mode 2, the dual-band PD exhibits a UV-visible-NIR broadband responsivity of 180 mA/W and a specific detectivity (D*) of 3.8 × 1010 Jones at 520 nm. Our study provides a reliable idea for the commercial applications of dual-function photodetectors.

Nonlocal active sound control for composite regions

In the active sound control problem, additional sound sources, known as control sources, are implemented at the perimeter of a protected domain. The control sources can generate secondary sound inside the shielded domain, which attenuates incoming noise. This leads to an inverse source problem. Such a problem becomes much more complicated if some desired sound is generated inside the protected area. The algorithm, known as nonlocal active sound control, successfully tackles this problem due to the projection property of the nonlocal operators involved. With the application of nonlocal control, noise generated outside the shielded domain is attenuated while the internal component of sound remains unaffected. In the present paper, the approach of nonlocal active sound control is significantly modified to be applicable to composite domains. In the test cases, three different sound propagation patterns are realized such as sound shielded from peers, free propagation, and selective sound cancelation. Numerical simulation is carried out in both frequency and time domains for broadband regimes. The results show that, even with a relatively small number of sensors and control sources, significant noise attenuation can still be achieved for a predetermined communication pattern among individual subdomains.

Enhancing photon generation rate with broadband room-temperature quantum memory

Photons with high generation rate is one of the essential resources for quantum communication, quantum computing and quantum metrology. Due to the naturally memory-built-in feature, the memory-based photon source is a promising route towards large-scale quantum information processing. However, such photon sources are mostly implemented in extremely low-temperature ensembles or isolated systems, limiting its physical scalability. Here we realize a single-photon source based on a far off-resonance Duan-Lukin-Cirac-Zoller quantum memory at broadband and room-temperature regime. By harnessing high-speed feedback control and repeat-until-success write process, the photon generation rate obtains considerable enhancement up to tenfold. Such a memory-enhanced single-photon source, based on the broadband room-temperature quantum memory, suggests a promising way for establishing large-scale quantum memory-enabled network at ambient condition.

Ultrasound Matrix Imaging-Part I: The Focused Reflection Matrix, the F-Factor and the Role of Multiple Scattering.

This is the first article in a series of two dealing with a matrix approach for aberration quantification and correction in ultrasound imaging. Advanced synthetic beamforming relies on a double focusing operation at transmission and reception on each point of the medium. Ultrasound matrix imaging (UMI) consists in decoupling the location of these transmitted and received focal spots. The response between those virtual transducers form the so-called focused reflection matrix that actually contains much more information than a confocal ultrasound image. In this paper, a time-frequency analysis of this matrix is performed, which highlights the single and multiple scattering contributions as well as the impact of aberrations in the monochromatic and broadband regimes. Interestingly, this analysis enables the measurement of the incoherent input-output point spread function at any pixel of this image. A fitting process enables the quantification of the single scattering, multiple scattering and noise components in the image. From the single scattering contribution, a focusing criterion is defined, and its evolution used to quantify the amount of aberration throughout the ultrasound image. In contrast to the state-of-the-art coherence factor, this new indicator is robust to multiple scattering and electronic noise, thereby providing a contrasted map of the focusing quality at a much better transverse resolution. After a validation of the proof-of-concept based on time-domain simulations, UMI is applied to the in-vivo study of a human calf. Beyond this specific example, UMI opens a new route for speed-of-sound and scattering quantification in ultrasound imaging.

Modeling a broad-band single-coordinate autocollimator with an extended mark and a detector in the form of a linear-array camera

This paper presents the results of modeling the parameters of a compact autocollimator with a single-coordinate detector in the form of a linear-array camera. The modeling was carried out by successively tracing the rays through the elements of the autocollimator’s optical system between the conjugate planes of the mark and the detector with intermediate reflection from a flat mirror. The described original shape of the mark and algorithm for processing the measured signals to be modeled make it possible to implement a broad-band operating regime in the device with high-accuracy angle measurements in the center of the range.

Direct-write nanocomposite sensor array for ultrasonic imaging of composites

To improve the ultrasonic imaging of composites, an all-printed nanocomposite sensor array (APNSA) is developed using a direct-write approach. Individual sensing elements of APNSA are inkjet printed by directly writing graphene/poly (amic acid) (PAA)-based nanocomposite ink on Kapton film substrates, with an ultra-thin thickness of ∼1 μm only. APNSA is morphologically tuned at a nano scale to be sensitive to acousto-ultrasonic waves of a broad band regime. Each sensing element features a homogenous and consolidated nanostructure, with which transient change of tunneling resistance between adjacent graphene nanoplatelets in the polyimide (PI) matrix can be triggered when the element is loaded with acousto-ultrasonic waves. The triggered quantum tunneling effect endows APNSA with capability to perceive dynamic strains in a broadband regime with high fidelity and accuracy. Compared with a conventional ultrasonic phased array which is of a low degree of compatibility with composites, APNSA can be fully integrated with the inspected composites. In conjunction with the use of the additively manufactured APNSA, ultrasonic imaging of composites can be implemented, spotlighting a nature of full integration of APNSA with composites for in situ structural health monitoring and anomaly detection, yet without degrading the original integrity of the composites.

A transgenic genetic algorithm design method that helps to increase the design freedom of metasurfaces

While the optimization of design is an effective way to increase the performance of metasurfaces, there is still much to be done to improve optimization algorithms. In this work, a transgenic genetic algorithm (TGA) proposed for metasurface design offers higher performance and more design freedom. Based on GAs, transgenic technology is introduced into metasurface design to improve both performance and flexibility. We describe the generation of a transgenic factor (TF), how it operates on metasurface design, and explain the feasibility of enhancing design freedom using a TGA. To target the broadband regime and high efficiency, an electromagnetic polarization converter and an absorber are then designed by TGA, respectively. As a result, polarization conversion of more than −1 dB and absorption of over 90% were achieved from 8.09 GHz to 24.90 GHz and 7.71 GHz to 20.01 GHz, respectively. Both simulated and measured results are highly consistent, which validates the stable performance achieved by the proposed TGA design. What is more, a performance comparison between different TFs illustrates the subtle influence of TFs, revealing that the performance is improved to some extent by an increase of surface-design freedom. Significantly, this effort provides more freedom in the design method, leading to the realization of many expected improvements.

Electromagnetic Radiation (EMR) and Human Health: A Study on the Health Effect of EMR from GSM Base Stations in North-Western Nigeria

Nigeria had maintained substantial intensification in the perspective of the mobile communication utilization, services improvement and sustainable broadband regime and this development is presumed to persist into the conceivable future with the evolution of the contemporary 6G, 5G, 4G and 3G mobile communication technologies. The current mobile communication technologies intensification had equally brought the unavoidable multiplications in the ratio of the base service stations which also had raised the public concern over the considerable health hazards of the radioactive emissions from the communication systems. Notwithstanding the assurances of the several regulatory agencies, the World Health Organization and service providers, confirming compliance and strict observance to the international exposure standards in implementation, the apprehension over the electromagnetic spectrum emission is increasing. To that effect, the International Commission on Non-Ionizing Radiation Protection (ICNIRP) had made recommendations that established the intensities of the radio frequency (RF) exposures which are considered harmless to the community of users. This paper assessed the radio frequency radiation from mobile base stations in some selected states in north western Nigeria. The methodology employed for the study is measurement and instrumentation method. Handheld spectrum analyzer (Aaronia HF 4040V3) and a wheel meter were used for the measurement of electromagnetic emissions from selected Airtel, Glo, MTN and Etisalat base stations at capital city of Kano, Jigawa and Katsina states respectively. It was found from the study that 17 to 70mW/m2 is the average electromagnetic radiation emitted in the study area, which showed total compliance of exposure limit by the GSM service providers in the selected states. The result confirmed the environmental safety level of the RF energy maintained within the general public and that are predictably low to produce any significant health hazards to human.

Broadband coherent optical memory based on electromagnetically induced transparency

Quantum memories, devices that can store and retrieve photonic quantum states on demand, are essential components for scalable quantum technologies. It is desirable to push the memory towards the broadband regime in order to increase the data rate. Here, we present a theoretical and experimental study on the broadband optical memory based on electromagnetically-induced-transparency (EIT) protocol. We first provide a theoretical analysis on the issues and requirements to achieve a broadband EIT memory. We then present our experimental efforts on EIT memory in cold atoms towards the broadband or short-pulse regime. A storage efficiency of ~ 80 % with a pulse duration of 30 ns (corresponding to a bandwidth of 14.7 MHz) is realized. Limited by the available intensity of the control beam, we could not conduct an optimal storage for the even shorter pulses but still obtain an efficiency of larger than 50 % with a pulse duration of 14 ns (31.4 MHz). The achieved time-bandwidth-product at the efficiency of 50 % is 1267.

Blind Estimation of Sparse Broadband Massive MIMO Channels With Ideal and One-bit ADCs

We study the maximum likelihood problem for the blind estimation of massive mmWave MIMO channels while taking into account their underlying sparse structure, the temporal shifts across antennas in the broadband regime, and ultimately one-bit quantization at the receiver. The sparsity in the angular domain is exploited as a key property to enable the unambiguous blind separation between user's channels. The main advantage of this approach is the fact that the overhead due to pilot sequences can be dramatically reduced especially when operating at low SNR per antenna. In addition, as sparsity is the only assumption made about the channel, the proposed method is robust with respect to the statistical properties of the channel and data and allows the channel estimation and the separation of interfering users from adjacent base stations to be performed in rapidly time-varying scenarios. For the case of one-bit receivers, a blind channel estimation is proposed that relies on the Expectation Maximization (EM) algorithm. Additionally, performance limits are derived based on the clairvoyant Cramer Rao lower bound. Simulation results demonstrate that this maximum likelihood formulation yields superior estimation accuracy in the narrowband as well as the wideband regime with reasonable computational complexity and limited model assumptions.

Finite-Difference Modeling of Broadband Huygens’ Metasurfaces Based on Generalized Sheet Transition Conditions

An explicit time-domain finite-difference technique for modeling zero-thickness Huygens’ metasurfaces based on generalized sheet transition conditions (GSTCs) is proposed and demonstrated using full-wave simulations. The Huygens’ metasurface is modeled using electric and magnetic surface susceptibilities, which are found to follow a double-Lorentz dispersion profile. To solve zero-thickness Huygens’ metasurface problems for general broadband excitations, the double-Lorentz dispersion profile is combined with GSTCs, leading to a set of first-order differential fields equations in time domain. Identifying the exact equivalence between Huygens’ metasurfaces and coupled RLC oscillator circuits, the field equations are then subsequently solved using standard circuit modeling techniques based on a finite-difference formulation. Several examples, including generalized refraction, are shown to illustrate the temporal evolution of scattered fields from the Huygens’ metasurface under plane-wave normal incidence, in both harmonic steady-state and broadband regimes. In particular, due to its inherent time-domain formulation, a significant strength of the methodology is its ability to model time-varying metasurfaces, which is demonstrated with a simple example of a pumped metasurface leading to new frequency generation and wave amplification.

Tunable continuous wave single-mode dye laser directly pumped by a diode laser

In this work, a tunable continuous wave single-mode ring dye laser (a modified version of Coherent model CR 699-21), directly optically pumped by an economy-class diode laser, has been set up. The laser was operated on Coumarin 498, and its generation profile covered part of the green spectral region not easily accessible in single-mode operation. The performance of the laser in both broad-band and single-mode operation regimes was studied. It was proved that optical pumping by diode lasers allows one to obtain single-mode operation of dye lasers that is sufficiently stable for high-resolution spectroscopy applications.

Perovskite Photodetectors Operating in Both Narrowband and Broadband Regimes

Photodetectors are designed, which operate in the broadband regime upon bottom illumination (from the indium tin oxide (ITO) side) and in the narrowband regime upon top illumination (from the air/perovskite side). The narrowband photodetectors show high external quantum efficiency of above 104 %. The operational spectrum of the photodetectors can also be tuned by adjusting the halide composition in the active material.

Oil dependency and exchange rate regimes in Arab oil economies: time to rethink the paradigm

This study examines implications of the current exchange rate regimes on the macroeconomic and growth performance of five Arab oil-producing countries: Saudi Arabia, the UAE, Sudan, Algeria and Yemen. The study evaluates alternative exchange rate regime policy options towards exploring an optimal exit strategy to ensure successful transition to more sustainable exchange rate regime, especially in the fixed regime economies of Saudi Arabia and the UAE. This study proposes the adoption of a transparent broad basket, band and crawl (BBC) regime by the Arab oil economies in order to provide a better alternative to the existing fixed pegs or dirty floats. However, it is imperative to note that, the timing of the exit from the current regime and the extent of institutional development and market sophistications are very critical to successful transition to more sustainable regime that would provide a larger scope for counter-cyclical policies and diversification in these economies.

Exploiting the dispersion of the double-negative-index fishnet metamaterial to create a broadband low-profile metallic lens.

Metamaterial lenses with close values of permittivity and permeability usually display low reflection losses at the expense of narrow single frequency operation. Here, a broadband low-profile lens is designed by exploiting the dispersion of a fishnet metamaterial together with the zoning technique. The lens operates in a broadband regime from 54 GHz to 58 GHz, representing a fractional bandwidth ~7%, and outperforms Silicon lenses between 54 and 55.5 GHz. This broadband operation is demonstrated by a systematic analysis comprising Huygens-Fresnel analytical method, full-wave numerical simulations and experimental measurements at millimeter waves. For demonstrative purposes, a detailed study of the lens operation at two frequencies is done for the most important lens parameters (focal length, depth of focus, resolution, radiation diagram). Experimental results demonstrate diffraction-limited ~0.5λ transverse resolution, in agreement with analytical and numerical calculations. In a lens antenna configuration, a directivity as high as 16.6 dBi is achieved. The different focal lengths implemented into a single lens could be potentially used for realizing the front end of a non-mechanical zoom millimeter-wave imaging system.

Anisotropy-induced broadband stress wave steering in periodic lattices

This paper investigates two-dimensional periodic lattices as a means to induce strongly directional stress wave propagation in solids in the low-frequency broadband regime. The real 2D structure of the lattice is considered as opposed to traditional truss-like approaches, allowing the characterization of the system seamlessly between the extremes of grid-like systems, porous systems, and a continuum material. Wave directionality in structural lattices is associated to their effective anisotropic mechanical properties. When the wavelength of deformation is larger than the representative unit cell, the system behaves as an equivalent medium with orthotropic properties that are correlated to the lattice skewness and void volume fraction. Polar plots of wave velocities, computed through the application of Bloch’s theorem, provide insights into the effective anisotropy and wave directionality (or “steering”) of the structure. Such directional response is also correlated to the stiffness properties of an equivalent medium by means of proper homogenization techniques. The effects of the resulting anisotropy on wave propagation are also illustrated through wave propagation simulations for problems involving both harmonic excitations and impulsive loads.

Compressive matched-field processing

Source localization by matched-field processing (MFP) generally involves solving a number of computationally intensive partial differential equations. This paper introduces a technique that mitigates this computational workload by "compressing" these computations. Drawing on key concepts from the recently developed field of compressed sensing, it shows how a low-dimensional proxy for the Green's function can be constructed by backpropagating a small set of random receiver vectors. Then the source can be located by performing a number of "short" correlations between this proxy and the projection of the recorded acoustic data in the compressed space. Numerical experiments in a Pekeris ocean waveguide are presented that demonstrate that this compressed version of MFP is as effective as traditional MFP even when the compression is significant. The results are particularly promising in the broadband regime where using as few as two random backpropagations per frequency performs almost as well as the traditional broadband MFP but with the added benefit of generic applicability. That is, the computationally intensive backpropagations may be computed offline independently from the received signals, and may be reused to locate any source within the search grid area.

Anomalous Refraction of Light Colors by a Metamaterial Prism

A prism of glass separates white light into its spectral components in such a manner that colors associated with shorter wavelengths are more refracted than the colors associated with longer wavelengths. Here, we demonstrate that this property is not universal, and that a lossless metamaterial prism with a suitable microstructure may enable a broadband regime of anomalous dispersion, where the spectral components of light are separated in an unconventional way, so that "violet light" is less refracted than "red light." This phenomenon is fundamentally different from conventional anomalous dispersion effects, which are invariably accompanied by significant loss and are typically very narrow band.

Single-Conductor Strip Leaky-Wave Antenna

This paper presents a leaky-wave antenna with only a single-conductor strip on a substrate without a practical ground plane. The full-wave integral equation method is used to investigate the EH/sub 01/ leaky mode of this single-conductor strip structure. When this single-conductor strip is on a thin substrate with a low dielectric constant, a broad-band radiation regime can exist for the EH/sub 01/ leaky mode. The balanced microstrip lines and the inverted balanced microstrip lines are used to excite this EH/sub 01/ leaky mode. This work presents both the numerically simulated and measured data. The measured bandwidth of a voltage standing-wave ratio /spl les/2 is from 6.55- 13.75 GHz (2.34:1). In this case, the normalized phase constant is very close to 1 and this results in a fixed main-beam radiation pattern in the end-fire direction. This leaky-wave antenna with only a single rectangle stripline of length 110 mm can achieve the same broad-band performance as a tapered microstrip leaky wave antenna with a length 310 mm, as previously reported by the authors.

Application of hilbert spectroscopy to pulsed far-infrared radiation

We present our results on the development and characterization of a prototype of Hilbert spectrometer, which is intended to operate with pulsed far-infrared radiation. The new prototype consists of high-T/sub c/ Josephson detector in an optical cryostat, analog electronics with the bandwidth of 14 MHz, and a DSP-based data acquisition system, controlling spectroscopic measurements. The specially developed digital data acquisition system gives a possibility to operate in two regimes - with and without integration of the pulsed signal. The tests have been carried out using pulsed 94 GHz radiation with pulse duration of 200 ns and a pulse repetition rate of 1 MHz. A measuring time of 7 ms for a data set of 512 spectral points has been realized. It has been demonstrated, that in a broadband (/spl ap/10 MHz) regime of measurements without integration the developed spectrometer has a dynamic range of external signal power of 17 dB, which can be enhanced by using integration function.