Multimodal Resonance Research Articles

High gain and circularly polarized substrate integrated waveguide cavity antenna array based on metasurface

Two substrate integrated waveguide (SIW) cavity antenna arrays based on metasurface are proposed in this paper. By rotating the metasurface element, circularly polarized and high gain antennas are achieved respectively. Firstly, multi-mode resonance theory is employed to broaden the bandwidth of the slot antenna. And then, an SIW cavity composed of 4 × 4 cornercut elements is added on the top of the slot antenna to achieve the circular polarization and improve the front-to-back ratio. Thirdly, the metasurface elements are sequentially rotated and a high gain antenna with 2-dBi enhancement on average in the operation band is obtained. Based on the two antenna units, two 2×2 antenna arrays are designed. The circularly polarized and high gain antenna arrays are both fabricated to verify the correctness. Furthermore, the novel wideband phase shifter is employed in the circularly polarized antenna to obtain an operating bandwidth of 38% (4.05 GHz–5.95 GHz) and AR bandwidth of 24.9% (4.4 GHz–5.65 GHz). The bandwidth of the high gain antenna can reach 42.7% (3.95 GHz–6.1 GHz) and with the gain enhancement of 2 dBi compared with that of the circularly polarized antenna. The gain remains steady in most of operating band within a variation of 1 dBi. It is remarkable that the rotating of the metasurface element has a great influence on the antenna performance, which provides a new explication for the multi-function antenna design.

Compact and high Q-factor multimode racetrack ring resonator based on transformation optics.

The ring resonator is a versatile and functional component in the silicon-based integrated optical circuit. Most of the previously reported ring resonators work in the single-mode case. With the rapid development of mode division multiplexing technology, a multimode ring resonator (MMRR) has been proposed and the usage beyond the limit of a conventional single mode ring resonator has been explored. However, the reported MMRRs are either large in size or low in quality factor. In this paper, we designed a compact silicon MMRR with a small bending radius of 15µm, in which the three lowest TE modes all have high Q-factors. For suppressing the mode loss and inter-mode crosstalk in MMRR, a multimode waveguide bend (MWB) with mode adiabatic evolution was designed based on transformation optics and waveguide shape optimization. The independent excitation of each order mode of the MMRR is realized by using bending directional coupler and asymmetric directional coupler. We successfully fabricated the device on a silicon-on-insulator (SOI) platform using simple one-step lithography. The measured loaded Q-factors of the three lowest TE modes are 5.9 × 104, 4.5 × 104, and 4.7 × 104, respectively.

Relation of sensorimotor and cognitive cerebellum functional connectivity with brain structural damage in patients with multiple sclerosis and no disability.

Background and purposeTo investigate the relationship between the functional connectivity (FC) of the sensorimotor and cognitive cerebellum and measures of structural damage in patients with multiple sclerosis (MS) and no physical disability.MethodsWe selected 144 relapsing–remitting MS patients with an Expanded Disability Status Scale score of ≤1.5 and 98 healthy controls from the Italian Neuroimaging Network Initiative database. From multimodal 3T magnetic resonance imaging (MRI), including functional MRI at rest, we calculated lesion load, cortical thickness, and white matter, cortical gray matter, and caudate, putamen, thalamic, and cerebellar volumes. Voxel‐wise FC of the sensorimotor and cognitive cerebellum was assessed with seed‐based analysis, and multiple regression analysis was used to evaluate the relationship between FC and structural damage.ResultsWhole brain, white matter, caudate, putamen, and thalamic volumes were reduced in patients compared to controls, whereas cortical gray matter was not significantly different in patients versus controls. Both the sensorimotor and cognitive cerebellum showed a widespread pattern of increased and decreased FC that were negatively associated with structural measures, indicating that the lower the FC, the greater the tissue loss. Lastly, among multiple structural measures, cortical gray matter and white matter volumes were the best predictors of cerebellar FC alterations.ConclusionsIncreased and decreased cerebellar FC with several brain areas coexist in MS patients with no disability. Our data suggest that white matter loss hampers FC, whereas, in the absence of atrophy, cortical volume represents the framework for FC to increase.

A Dual-Band Tunable Balanced Filter With Independently Tuning Bands

A dual-band tunable balanced filter based on one hybrid microstrip-cavity structure is proposed in this paper. The cavity acts as one multimode resonator, and the differential feeding networks are printed on the PCBs. According to the electromagnetic (EM) field theory, TE101 and TE011 modes are generated under differential-mode (DM) excitation, and highly suppressed under common-mode (CM) excitation. The dielectric posts in the cavity can independently shift the resonant frequencies of the two modes. Moreover, the inter-resonator coupling of each band is independently controlled by the cross-shaped coupling slot. Therefore, good filtering differential response can be realized with in a wide band. For demonstration, a dual-band tunable balanced filter is designed and measured. The measured results indicate that the center frequencies of the two bands are tuned from 7.51 GHz to 8.22 GHz and 9.34 GHz to 10.56 GHz, respectively. Over the tuning range, the insertion losses vary from 0.5 dB to 1.5 dB and the CM suppressions in both passbands are under 50 dB and 42 dB. In this way, the proposed hybrid microstrip-cavity structure is feasible to design a reconfigurable balanced filter with wide tuning range and high CM suppression.

High-Order Balanced Dual-Band HTS BPF With Flexible Frequency Ratio and Sharp Rejection Skirts

In this article, a new class of high-order balanced dual-band high-temperature superconducting (HTS) bandpass filter (BPF) based on modified multimode stub-loaded resonators (SLRs) is presented. First, a detailed theoretical analysis of the multimode SLRs is provided to obtain insight into their frequency response characteristics under the differential-mode (DM) and common-mode (CM) operations. Specifically, the SLRs under the DM operation are designed to generate their second and third resonant modes in the two specified passbands, and they are sequentially cascaded by alternate <inline-formula> <tex-math notation="LaTeX">$J$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> inverters for sharp rejection skirts. Following that, the working mechanism of the CM rejection of the resonator is investigated for achieving good CM suppression performance for this filter. Finally, for experimental validation, an eighth-order prototype filter is designed and fabricated on the MgO substrate with double-sided YBa2Cu3Oy (YBCO) thin films. Good agreement between measured and simulated results is obtained, and the filter is at the same time with low insertion loss, flexible frequency ratio, sharp rejection skirts, and good CM suppression level.

Tunable partial polarization beam splitter and optomechanically induced Faraday effect

Polarization beam splitter (PBS) is a crucial photonic element to separately extract transverse-electric (TE) and transverse-magnetic (TM) polarizations from the propagating light fields. Here, we propose a concise, continuously tunable and all-optical partial PBS in the vector optomechanical system which contains two orthogonal polarized cavity modes with degenerate frequency. The results show that one can manipulate the polarization states of different output fields by tuning the polarization angle of the pumping field and the system function as partial PBS when the pump laser polarizes vertically or horizontally. As a significant application of the tunable PBS, we propose a scheme of implementing quantum walks in resonator arrays without the aid of other auxiliary systems. Furthermore, we investigate the optomechanically induced Faraday effect in the vector optomechanical system which enables arbitrary tailoring of the input lights and the behaviors of polarization angles of the output fields in the under couple, critical couple, and over couple regimes. Our findings prove the optomechanical system is a potential platform to manipulate the polarization states in multimode resonators and boost the process of applications related to polarization modulation.

High-speed spatial light modulation based on photon dimension mapping assisted by an integrated mode multiplexer

Photon dimension mapping provides an efficient way to learn from each other's strengths to offset their own weaknesses in a variety of applications. By mapping the conventional amplitude modulation to spatial mode modulation and employing an integrated orbital angular momentum (OAM) mode multiplexer, we present an integrated approach to break the spatial light modulation speed limit and implement the high-speed silicon-chip-assisted OAM encoding information transfer. The silicon chip is formed by a multi-mode micro-ring resonator with angular grating embedded in the inner wall and two bus waveguides with different widths for OAM mode multiplexing. Using the fabricated silicon-based OAM mode multiplexer (OAM+1 and OAM-14), we demonstrate 15-Gbit/s amplitude-to-OAM modulation mapping in the experiment, which is far beyond the achievable low-speed OAM encoding information transfer with a conventional spatial light modulator (SLM). The observed optical signal-to-noise ratio (OSNR) penalties at a bit-error rate (BER) of 2 × 10−3 are about 1.0 dB, and the OSNR penalty is improved by about 1.4 dB with the balanced detection. The demonstrations with favorable performance may open up added opportunities in more spatial-mode-enabled applications by photon dimension mapping with silicon chips.

Relationship between brain iron deposition and mitochondrial dysfunction in idiopathic Parkinson\u2019s disease

BackgroundThe underlying pathophysiology of Parkinson's disease is complex, involving different molecular pathways, including brain iron deposition and mitochondrial dysfunction. At a molecular level, these disease mechanisms are likely interconnected. Therefore, they offer potential strategies for disease-modifying treatments. We aimed to investigate subcortical brain iron deposition as a potential predictor of the bioenergetic status in patients with idiopathic Parkinson’s disease.MethodsThirty patients with idiopathic Parkinson's disease underwent multimodal MR imaging (T1, susceptibility-weighted imaging, SWI) and 31phosphorus magnetic resonance spectroscopy imaging. SWI contrast-to-noise ratios served as a measure for brain iron deposition in the putamen, caudate, globus pallidus, and thalamus and were used in a multiple linear regression model to predict in-vivo energy metabolite ratios.ResultsSubcortical brain iron deposition, particularly in the putamen and globus pallidus, was highly predictive of the region-specific amount of high-energy-containing phosphorus metabolites in our subjects.ConclusionsOur study suggests that brain iron deposition but not the variability of individual volumetric measurements are highly predictive of mitochondrial impairment in vivo. These findings offer the opportunity, e.g., by using chelating therapies, to improve mitochondrial bioenergetics in patients with idiopathic Parkinson's disease.

The Automatic Design of Multimode Resonator Topology with Evolutionary Algorithms.

Microwave electromagnetic devices have been used for many applications in tropospheric communication, navigation, radar systems, and measurement. The development of the signal preprocessing units including frequency-selective devices (bandpass filters) determines the reliability and usability of such systems. In wireless sensor network nodes, filters with microstrip resonators are widely used to improve the out-of-band suppression and frequency selectivity. Filters based on multimode microstrip resonators have an order that determines their frequency-selective properties, which is a multiple of the number of resonators. That enables us to reduce the size of systems without deteriorating their selective properties. Various microstrip multimode resonator topologies can be used for both filters and microwave sensors, however, the quality criteria for them may differ. The development of every resonator topology is time consuming. We propose a technique for the automatic generation of the resonator topology with required frequency characteristics based on the use of evolutionary algorithms. The topology is encoded into a set of real valued parameters, which are varied to achieve the desired features. The differential evolution algorithm and the genetic algorithm with simulated binary crossover and polynomial mutation are applied to solve the formulated problem using the dynamic penalties method. The experimental results show that our technique enables us to find microstrip resonator topologies with desired amplitude-frequency characteristics automatically, and manufactured devices demonstrate characteristics very close to the results of the algorithm. The proposed algorithmic approach may be used for automatically exploring the new perspective topologies of resonators used in microwave filters, radar antennas or sensors, in accordance with the defined criteria and constraints.

Co-Design of Wideband Filtering Dielectric Resonator Antenna With High Gain

In this communication, a novel synthesis design method is proposed for designing a wideband filtering dielectric resonator antenna (FDRA) using multimode resonators (MMRs). To start with, the proposed FDRA composed of a tri-mode stub-loaded resonator as the feeding network and a rectangular dual-mode dielectric resonator (DR) as the radiator is introduced. Then, an exact synthesis and design procedure is proposed for facilitating to design this FDRA. Following that, an appropriate coupling topology is selected to allocate a composite quintuple-mode resonator to achieve a wideband operation for this FDRA. Finally, for an experimental verification, a prototype of the FDRA is designed, fabricated, and measured. The simulation and measurement results are in well accordance with each other, showing a good filtering performance from 2.2 to 3.1 GHz, an average gain of 9.1 dBi, and good out-of-band suppression.

The differential association between local neurotransmitter levels and whole-brain resting-state functional connectivity in two distinct cingulate cortex subregions.

We examined the association between rsFC and local neurotransmitter levels in the pregenual anterior cingulate cortex (pgACC) and the anterior mid-cingulate cortex (aMCC) by varying rsFC-strengths at the whole-brain level. Our results showed region-dependent directionality of associations in the investigated ACC subdivisions.

Low-noise Brillouin random fiber laser with Auto-tracking dynamic fiber grating based on a saturable absorption ring

A low-noise Brillouin random fiber laser (BRFL) with stabilized lasing output and narrow linewidth is proposed and demonstrated experimentally. Stimulated Brillouin scattering and Rayleigh scattering are exploited to work as the gain and random distributed feedback mechanisms, respectively. A simple unpumped Erbium-doped fiber (EDF) loop structure which consists of a section of EDF and an optical coupler is introduced into the BRFL cavity, forming a saturable absorption ring (SAR). When light with proper intensity is incident into the SAR, a dynamic fiber grating (DFG) can be built up to work as a narrow-bandwidth filter with the ability of auto-tracking the center frequency. The SAR can effectively filter out dense random longitudinal modes and suppress multi-mode resonances and frequency jitters by restricting the mode-competition-induced mode hopping within a limited frequency range of ∼ 1 MHz and auto-tracking the center frequency of light in the cavity, simultaneously. Thus, the output of BRFL with SAR is much more stabilized than existing free-running BRFLs. In the experiment, a stable lasing output with an ultra-narrow linewidth (less than2kHz) is obtained from the proposed BRFL. The measured relative intensity noise and frequency noise demonstrate that the noise level of the proposed laser is significantly lower than that of the free-running BRFLs. This proposed technique not only provides a solution to the dilemma of previously reported BRFLs with severe lasing instabilities, but also makes a step towards the development of practical and reliable BRFLs. This high-quality laser source with advantages of high stability, low cost, low threshold power, high coherence, narrow linewidth, and low noise can find useful applications in coherent optical detection, high-resolution spectrometers, microwave photonics, and optical sensing fields.

Conversion Efficiency in Kerr-Microresonator Optical Parametric Oscillators: From Three Modes to Many Modes.

Optical parametric oscillation in a Kerr nonlinear microresonator can generate coherent laser light with frequencies that are widely separated from the pump frequency, allowing, for example, visible light to be generated using a near-infrared pump. To be practically useful, the pump-to-signal conversion efficiency must be far higher than what has been demonstrated in microresonator-based oscillators with widely-separated output frequencies. To address this challenge, here we theoretically and numerically study parametric oscillations in Kerr nonlinear microresonators, revealing an intricate solution space that arises from an interplay of nonlinear processes. As a start, we use a three-mode approximation to derive an efficiency-maximizing relation between pump power and frequency mismatch. However, realistic devices, such as integrated microring resonators, support far more than three modes. Hence, a more accurate model that includes the entire modal landscape is necessary to determine potential inefficiencies arising from unwanted competing nonlinear processes. To this end, we numerically simulate the Lugiato-Lefever Equation that accounts for the full spectrum of nonlinearly-coupled resonator modes. We observe and characterize two nonlinear phenomena linked to parametric oscillations in multi-mode resonators: Mode competition and cross phase modulation-induced modulation instability. Both processes may impact conversion efficiency. Finally, we show how to increase the conversion efficiency to ≈ 25 % by tuning the microresonator loss rates. Our analysis will guide microresonator designs that aim for high conversion efficiency and output power.

Design of a polarization‐insensitive three dimensional microwave absorber for ultra‐wideband RCS reduction

AbstractA polarization‐insensitive three‐dimensional (3‐D) microwave absorber is proposed in this letter for ultra‐wideband radar section cross (RCS) reduction. The lossy layer of the designed absorber is evolved from the bent metallic strip with a center‐embedded resistor, which performs the property of absorption‐reflection‐absorption due to its multimode resonances. A short stub with a center‐embedded resistor is connected to the long‐bent strip to abolish the reflection performance, for the sake of achieving wide absorption performance. The fundamental working principle of the designed structure is explained adequately using an intuitive equivalent circuit model. Additionally, the absorber is designed, fabricated, and measured for validation, whose fractional bandwidths is 151.5% with at least 10‐dB RCS reduction.

Compact and High-Order On-Chip Wideband Bandpass Filters on Multimode Resonator in Integrated Passive Device Technology

Compact and High-Order On-Chip Wideband Bandpass Filters on Multimode Resonator in Integrated Passive Device Technology

Multistage Kondo effect in a multiterminal geometry: A modular quantum interferometer

Quantum systems characterized by an interplay between several resonance scattering channels demonstrate very rich physics. To illustrate it we consider a multistage Kondo effect in nanodevices as a paradigmatic model for a multimode resonance scattering. We show that the channel crosstalk results in a destructive interference between the modes. This interplay can be controlled by manipulating the tunneling junctions in the multilevel and multiterminal geometry. We present a full-fledged theory of the multistage Kondo effect at the strong-coupling Fermi-liquid fixed point and discuss the influence of quantum interference effects to the quantum transport observables.

Impulse control differentiates Internet gaming disorder from non-disordered but heavy Internet gaming use: Evidence from multiple behavioral and multimodal neuroimaging data

Billions of people play Internet games and some of them may develop Internet gaming disorder (IGD), yet the differences between IGD and non-disordered but heavy Internet gaming use behavior remain unclear. We used multiple behaviors and multimodal functional magnetic resonance imaging (fMRI) to examine the specificity of impulse control to differentiate IGD from non-disordered but heavy Internet gaming use. One hundred sixty subjects, including patients with IGD (PIGD), non-disordered but heavy Internet gaming participants (NIGP), and healthy controls rated Barratt Impulsiveness Scale, and 141 out of them completed delay-discounting task and resting-state during fMRI. The PIGD but not the NIGP showed altered impulsiveness and delay discounting behavior as compared to healthy controls. Moreover, the PIGD but not the NIGP showed altered activity pattern in the frontoparietal network as compared to healthy controls. The PIGD but not the NIGP showed altered functional connectivity in the frontoparietal network during delay discounting and resting-state as compared to healthy controls. Furthermore, impulse control-related behavioral and fMRI measures significantly classified PIGD from NIGP. This study provides consistent evidence supporting the specificity of impulse control for distinguishing IGD from non-disordered but heavy Internet gaming use.

Gold nanocups with multimodal plasmon resonance for quantum-dot random lasing

Reduction of symmetry in plasmonic nanostructures may lead to great opportunities in controlling their photophysics of extinction, local field, light response, and plasmonic interactions. With their strong light scattering and unique modulation of field distribution, plasmonic nanocups hold great potential for applications in random laser, three-dimensional optical nanoantenna, and optical coherence tomography imaging. Here we demonstrate a novel and robust solution-phase synthesis approach to gold nanocups, which combines templating and seeded growth techniques to precisely control the size, morphology, and composition of the nanocups. Ripening is the key strategy in this wet-chemistry process to ensure primary anisotropic growth of gold within the cup-shaped space provided by each template, consisting of a silica nanosphere and a flexible resorcinol-formaldehyde resin shell. The resulting plasmonic nanocups possess three types of plasmon resonance modes, including axial, transverse S, and transverse P modes, determined by the polarization of the incident light. This robust and scalable synthesis allows the production of gold nanocups with high quality and efficiency, opening the door to unique photophysical properties and many potential applications, as demonstrated by their excellent performance in plasmonic quantum dot random lasing.

A low resource 3D U-Net based deep learning model for medical image analysis.

The success of deep learning, a subfield of Artificial Intelligence technologies in the field of image analysis and computer can be leveraged for building better decision support systems for clinical radiological settings. Detecting and segmenting tumorous tissues in brain region using deep learning and artificial intelligence is one such scenario, where radiologists can benefit from the computer based second opinion or decision support, for detecting the severity of disease, and survival of the subject with an accurate and timely clinical diagnosis. Gliomas are the aggressive form of brain tumors having irregular shape and ambiguous boundaries, making them one of the hardest tumors to detect, and often require a combined analysis of different types of radiological scans to make an accurate detection. In this paper, we present a fully automatic deep learning method for brain tumor segmentation in multimodal multi-contrast magnetic resonance image scans. The proposed approach is based on light weight UNET architecture, consisting of a multimodal CNN encoder-decoder based computational model. Using the publicly available Brain Tumor Segmentation (BraTS) Challenge 2018 dataset, available from the Medical Image Computing and Computer Assisted Intervention (MICCAI) society, our novel approach based on proposed light-weight UNet model, with no data augmentation requirements and without use of heavy computational resources, has resulted in an improved performance, as compared to the previous models in the challenge task that used heavy computational architectures and resources and with different data augmentation approaches. This makes the model proposed in this work more suitable for remote, extreme and low resource health care settings.

Engineering multimode resonances for tunable multifrequency superscattering.

We demonstrate a rigorous multimode engineering method to achieve multifrequency superscattering with flexible controllability in a subwavelength graphene/hexagonal boron nitride (hBN) cylindrical system. Through delicately tuning the chemical potential of graphene, different resonance channels of the proposed stucture can be spectrally overlapped to construct the multiple superscattering points. Consequently, the scattering cross section is enhanced effectively and the so-called superscattering beyond the single-channel scattering limit can be attained. Numerical calculations on scattering spectra, near-field, and far-field distributions are performed to confirm the scattering enhancement. The general principles presented here may suggest an accurate and efficient approach to actively tune the light-matter interaction at the subwavelength scale.