Modulation Speed Research Articles

Microemitter-Based IR Spectroscopy and Imaging with Multilayer Graphene Thermal Emission.

IR analyses such as Fourier transform infrared spectroscopy (FTIR) are widely used in many fields; however, the performance of FTIR is limited by the slow speed (∼10 Hz), large footprint (∼ millimeter), and glass bulb structure of IR light sources. Herein, we present IR spectroscopy and imaging based on multilayer-graphene microemitters, which have distinct features: a planar structure, bright intensity, a small footprint (sub-μm2), and high modulation speed of >50 kHz. We developed an IR analysis system based on the multilayer-graphene microemitter and performed IR absorption spectroscopy. We show two-dimensional IR chemical imaging that visualizes the distribution of the chemical information. In addition, we present high-spatial-resolution IR imaging with a spatial resolution of ∼1 μm, far higher than the diffraction limit. The graphene-based IR spectroscopy and imaging can open new routes for IR applications in chemistry, material science, medicine, biology, electronics, and physics.

Positive Effect of Kinesiotape on 1 km Run Performance in University-Level Males: A Cross-Sectional Study.

Introduction: The kinesiotape (KT) method is used to exert a positive effect on muscular, nervous, and organ systems, recognizing the importance of muscle movement. It is widely applied in runners for performance enhancement. However, there is no scientific background to use it as a running speed modulator. Objectives: The purpose of this study was to verify the KT effect on running performance in university-level students while speed is considered. The 1 km run and 40 m shuttle run were investigated. Participants were highly motivated to run as fast as possible since the research was part of the graded fitness test. Students wanted to perform as well as possible to get good marks. Methods: A total of 150 students aged 19.93 ± 0.85 with BMIs of 26.93 ± 0.98 were randomly distributed to the experimental (EG), placebo (PG), and control group (CG). In the EG, 50 students were measured pre-test (no KT) and post-test (KT applied). In the PG, 50 students were measured the same way using the placebo application post-test. In the CG, 50 students were measured without any intervention pre-test or post-test. The application area was the triceps surae muscle bilaterally with KT tension of 75%. The Kruskal–Wallis test and repeated measures ANOVA were used for analysis with a 0.05 level of significance. Results: A statistically significant group effect was reported in the EG (<0.05) in the 1 km run discipline. The time results obtained were significantly shorter than in the PG and the CG. There was no statistically significant difference (0.717) reported in the 40 m shuttle run discipline between the groups. Conclusions: Applying KT with a tension of 75% on the triceps surae muscle bilaterally might be useful to increase the performance of medium or longer distance runs but may not be effective in improving sprinting ability. We recommend applying the KT in the overall muscle and tendon area with a tension of 75% if there is a focus on performance enhancement.

Experimental elastic wave control in a piezoelectric phononic crystal with spatio-temporal modulation of electrical conditions

This work concerns the propagation of elastic waves in a piezoelectric phononic crystal made of several identical piezoelectric elements separated by electrodes. In such a structure, electrical conditions prescribed to the electrodes can be modulated in space and in time and therefore can strongly modify the dispersion curves of the phononic crystal. For example, a periodic grounding of the electrodes introduces a Bragg band gap which does not exist when the electrodes have a floating potential condition [Degraeve et al., J. Appl. Phys. 115, (2014)]. When the electrical conditions of the electrodes are modulated in space and in time, dispersion curves are tilted with respect to the configuration in the reference medium and nonreciprocal wave propagation may occur at some modulation speeds in specific frequency bands [Croënne et al., Appl. Phys. Lett.110, (2017)]. The experimental set-up is based on a stack of 113 piezoelectric rings and 114 electrodes. The spatio-temporal modulation of the electrical conditions is performed using a digital signal processor (DSP) in order to reach high modulation speeds. This modulation is performed by shifting the position of the periodic ground conditions of the electrodes versus time. The experimental dispersion curves are obtained using measurements of the normal displacement of the piezoelectric rings with a scanning laser vibrometer. The evolution of dispersion curves as a function of modulation speed is analyzed and compared to finite element simulation results.

Knifefish turning control and hydrodynamics during forward swimming.

Rapid turning and swimming contribute to ecologically important behaviors in fishes such as predator avoidance, prey capture, mating and the navigation of complex environments. For riverine species, such as knifefishes, turning behaviors may also be important for navigating locomotive perturbations caused by turbulent flows. Most research on fish maneuvering focuses on fish with traditional fin and body morphologies, which primarily use body bending and the pectoral fins during turning. However, it is uncertain how fishes with uncommon morphologies are able to achieve sudden and controllable turns. Here, we studied the turning performance and the turning hydrodynamics of the black ghost knifefish (Apteronotus albifrons, N=6) which has an atypical elongated ribbon fin. Fish were filmed while swimming forward at ∼2 body lengthss-1 and feeding from a fixed feeder (control) and an oscillating feeder (75 Hz) at two different amplitudes. 3D kinematic analysis of the body revealed the highest pitch angles and lowest body bending coefficients during steady swimming. Low pitch angle, high maximum yaw angles and large body bending coefficients were characteristic of small and large turns. Asynchrony in pectoral fin use was low during turning; however, ribbon fin wavelength, frequency and wave speed were greatest during large turns. Digital particle image velocimetry (DPIV) showed larger counter-rotating vortex pairs produced during turning by the ribbon fin in comparison to vortices rotating in the same direction during steady swimming. Our results highlight the ribbon fin's role in controlled rapid turning through modulation of wavelength, frequency and wave speed.

Programmable Terahertz Metamaterials with Non‐Volatile Memory (Laser Photonics Rev. 16(4)/2022)

Programmable Memory Metamaterials In article number 2100472, Benwen Chen, Jingbo Wu, Biaobing Jin, and colleagues present a programmable terahertz metamaterial with memory function. Each pixel is electrically addressable by suppressing the thermal crosstalk, and modulation speed of 1 kHz is obtained. Its state enables being written, read, and erased with an electrical pulse; thus, the non-volatile storage of multi-state terahertz images is demonstrated.

Pulsatility hemodynamics during speed modulation of continuous-flow total artificial heart in a chronic in vivo model.

BackgroundThe evaluation of pulsatile flow created by the new Cleveland Clinic continuous‐flow total artificial heart (CFTAH100), which has a re‐designed right impeller and motor, had not been tested in vivo. The purpose of this study was to evaluate the feasibility of pulsatility with the CFTAH100 during the application of pump speed modulation protocols in a chronic animal model.MethodsA 30‐day chronic animal experiment was conducted with a calf. Five pulsatile studies were performed on the alert animal. The mean pump speed was set at 2800 rpm, and modulated sinusoidally within a range of 0 to ± 35% of mean speed, in increments of 5% at 80 beats per minute (bpm). The pressures and pump flow were collected and a pulsatility index (PI) was calculated.ResultsThe calf was supported with the CFTAH100 without any major complications. The maximum and minimum pump flows changed significantly from baseline in all conditions, while the mean pump flow did not change. All flow pulsatility (FP) readings in all conditions significantly increased from baseline, and the percent modulation (%S) and FP had a strong positive correlation (r = 0.99, p < 0.01). The PI also increased significantly in all conditions (maximum at %S of 35%, 2.2 ± 0.05, p < 0.01), and a positive correlation between %S and PI (r = 0.99, p < 0.01) was observed.ConclusionThe CFTAH100 showed the feasibility of creating pulsatile circulation with sinusoidal pump speed 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.

Effects of Pulsatility on Arterial Endothelial and Smooth Muscle Cells

Continuous flow ventricular assist device (CFVAD) support in advanced heart failure patients causes diminished pulsatility, which has been associated with adverse events including gastrointestinal bleeding, end organ failure, and arteriovenous malformation. Recently, pulsatility augmentation by pump speed modulation has been proposed as a means to minimize adverse events. Pulsatility primarily affects endothelial and smooth muscle cells in the vasculature. To study the effects of pulsatility and pulse modulation using CFVADs, we have developed a microfluidic co-culture model with human aortic endothelial (ECs) and smooth muscle cells (SMCs) that can replicate physiologic pressures, flows, shear stresses, and cyclical stretch. The effects of pulsatility and pulse frequency on ECs and SMCs were evaluated during (1) normal pulsatile flow (120/80 mmHg, 60 bpm), (2) diminished pulsatility (98/92 mmHg, 60 bpm), and (3) low cyclical frequency (115/80 mmHg, 30 bpm). Shear stresses were estimated using computational fluid dynamics (CFD) simulations. While average shear stresses (4.2 dynes/cm²) and flows (10.1 mL/min) were similar, the peak shear stresses for normal pulsatile flow (16.9 dynes/cm²) and low cyclic frequency (19.5 dynes/cm²) were higher compared to diminished pulsatility (6.45 dynes/cm²). ECs and SMCs demonstrated significantly lower cell size with diminished pulsatility compared to normal pulsatile flow. Low cyclical frequency resulted in normalization of EC cell size but not SMCs. SMCs size was higher with low frequency condition compared to diminished pulsatility but did not normalize to normal pulsatility condition. These results may suggest that pressure amplitude augmentation may have a greater effect in normalizing ECs, while both pressure amplitude and frequency may be required to normalize SMCs morphology. The co-culture model may be an ideal platform to study flow modulation strategies.

EML Based on Identical Epitaxial Layer, Side-Wall Grating and HSQ Planarization

We present an electroabsorption modulated laser based on an identical epitaxial scheme, side-wall grating, on- chip microwave probe interface, and a new low-permittivity planarization method. The modulation speed is significantly increased by reducing the electrode capacitance by planarizing with a 5-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula>-thick HSQ layer. Furthermore, implementing the electrode with a direct ground-signal-ground probe interface provides a straightforward interconnection that obviates the need for an external circuit and bonding wires. The device operates at 1565 nm wavelength with stable single-mode lasing, no mode-hopping, and a side mode suppression ratio above 35 dB. An extinction ratio of 19.5 dB was recorded at the maximum modulator bias of &#x2212;4 V. The electrical to optical power response of the modulated signal at&#x2013;3-dBo demonstrated a 19 GHz bandwidth at an extinction ratio of 7 dB, which supports error-free data transmission up to 27 Gbit/s.

Peak wind speed modulation by large-scale motions in neutrally stratified atmospheric surface layer

Peak wind speed modulation by large-scale motions in neutrally stratified atmospheric surface layer

Modelling, characterization, and applications of silicon on insulator loop terminated asymmetric Mach Zehnder interferometer

This work presents a loop terminated asymmetric Mach–Zehnder interferometer (LT-aMZI) structure based on the widespread silicon-on-insulator (SOI) platform. Four different path length differences of the LT-aMZI, which correspond to free spectral ranges (FSR) from 0.8 to 6.4 nm, are designed. These designs are compared to the common asymmetric Mach–Zehnder interferometer (C-aMZI) and are shown to be more compact. These devices are suitable for optical filtering as well as wavelength demultiplexing (WDM) applications. A compact analytical model is derived that accurately describe the operation of the LT-MZI devices. The designs are then fabricated using Electron Beam Lithography (EBL) and characterized. The experimental data show good agreement when compared to the simulation results. To our knowledge, this is the first time LT-aMZI fabrication and characterization. Moreover, the LT-MZI spectrum can be tuned not only by the interferometer arms phase difference like C-MZI, but also by using its directional couplers coefficients, forming a spectral tunable filter. Finally, we determine the performance parameters of optical sensors and modulators and show that our proposed LT-MZI structure will enhance the sensor figure of merit (FOM) and modulator speed, power consumption and Vπ × L compared to C-MZI. A comparison between symmetric and asymmetric MZI sensors and the advantage of the latter is also mentioned.

Compact electro-optic modulator on lithium niobate

Fast electro-optic modulators with an ultracompact footprint and low power consumption are always highly desired for optical interconnects. Here we propose and demonstrate a high-performance lithium niobate electro-optic modulator based on a new 2 × 2 Fabry–Perot cavity. In this structure, the input and reflected beams are separated by introducing asymmetric multimode-waveguide gratings, enabling TE 0 − TE 1 mode conversion. The measured results indicate that the fabricated modulator features a low excess loss of ∼ 0.9 dB , a high extinction ratio of ∼ 21 dB , a compact footprint of ∼ 2120 μm 2 , and high modulation speeds of 40 Gbps OOK and 80 Gbps PAM4 signals. The demonstrated modulator is promising for high-speed data transmission and signal processing.

High-Speed and On-Chip Optical Switch Based on a Graphene Microheater.

Graphene is a promising material for producing optical devices because of its optical, electronic, thermal, and mechanical properties. Here, we demonstrated on-chip optical switches equipped with a graphene heater, which exhibited high modulation speed and efficiency. We designed the optimal structure of the optical switch with an add/drop-type racetrack resonator and two output waveguides (the through and drop ports) by the electromagnetic field calculation. We fabricated the optical switch in which the graphene microheater was directly placed on the resonator and directly observed its operation utilizing a near-infrared camera. As observed from the transmission spectra, this device exhibited high wavelength tuning efficiency of 0.24 nm/mW and high heating efficiency of 7.66 K·μm3/mW. Further, we measured the real-time high-speed operation at 100 kHz and verified that the graphene-based optical switch achieved high-speed modulation with 10%-90% rise and fall response times, 1.2 and 3.6 μs, respectively, thus confirming that they are significantly faster than typical optical switches that are based on racetrack resonators and metal heaters with response times of ∼100 μs. These graphene-based optical switches on silicon chips with high efficiency and speed are expected to enable high-performance silicon photonics and integrated optoelectronic applications.

Integrated early fault diagnosis method based on direct fast iterative filtering decomposition and effective weighted sparseness kurtosis to rolling bearings

The fault vibration signal of rolling bearing is typical non-stationary and non-linear signals. It usually exhibits the characteristics of amplitude modulation and frequency modulation (AM-FM) due to the interaction between the various components within the bearing and modulation of the rotor speed. In addition, the incipient weak fault feature information is inevitably masked by the strong background noise and other vibration interference because of the influence of the working environment of mechanical equipment. Therefore, new high efficiency and effective processing methods are indispensable for feature extraction of bearing fault diagnosis signals. Direct fast iterative filtering (dFIF) is a new kind of adaptive mode decomposition method proposed by Antonio Cicone based on iterative filtering (IF) and fast iterative filtering (FIF). dFIF is used to quickly decompose multi-component signals into a set of intrinsic mode functions (IMFs) by means of fast Fourier transform (FFT). In order to study the decomposition performance and examine the feature extraction ability of the dFIF method, a group of harmonic signals with simple linear superposition, multi-components AM-FM signals with different data length and different signal-to-noise ratio (SNR) are simulated and analyzed. For comparison, other mode decomposition methods were also applied to the simulated signals, such as adaptive local iterative filtering (ALIF), local mean decomposition (LMD), and empirical mode decomposition (EMD). The results show that dFIF decomposition methods have faster decomposition speed and better accuracy than other methods. Furthermore, the results also demonstrate excellent performance in AM-FM feature extraction and anti-mode mixing. On the other hand, the effective weighted sparseness kurtosis (EWSK) index integrates the periodicity and intensity of impact in each mode, which can effectively identify the effective mode. Therefore, considering the above merits, EWSK is integrated on the dFIF to effectively accomplish the fault diagnosis for rolling bearing under strong background noise. Firstly, the raw vibration signals of rolling bearing fault are decomposed into a set of IMFs by using dFIF. The EWSK indicator is then utilized to select IMFs with rich bearing fault impulse information for reconstruction. Finally, the Hilbert envelope demodulation analysis is used to analyze the reconstructed signal, extract the bearing fault feature and then judge the fault type. This proposed method is applied to analyze the simulated and field measured vibration signals of rolling bearing faults. Simultaneously, the other above-mentioned adaptive TFA methods are also adopted to analyze the signals. The results compared show that the proposed method has excellent performance in the aspects of decomposition speed and accuracy under the influence of strong background noise. It demonstrates the effectiveness and applicability of the proposed method for signal processing and fault pattern recognition of rolling bearings.

Čerenkov radiation in vacuum from a superluminal grating

Nothing can physically travel faster than light in vacuum. This is why it has been considered that there is no \v{C}erenkov radiation (\v{C}R) without an effective refractive index due to some background field. In this Letter, we theoretically predict \v{C}R in vacuum from a spatiotemporally modulated boundary. We consider the modulation of traveling wave type and apply a uniform electrostatic field on the boundary to generate electric dipoles. Since the induced dipoles stick to the interface, they travel at the modulation speed. When the grating travels faster than light, it emits \v{C}R. In order to quantitatively examine this argument, we need to calculate the field scattered at the boundary. We utilise a dynamical differential method, which we developed in the previous paper, to quantitatively evaluate the field distribution in such a situation. We can confirm that all scattered fields are evanescent if the modulation speed is slower than light while some become propagating if the modulation is faster than light.

Controllable Electrodeposition Adjusts the Electrochromic Properties of Co and Mo Co-Modified WO3 Films

Metal ion modification is considered to be an effective way to construct metal oxides with specific physical and chemical properties. In this paper, we prepare a tungsten oxide (WO3) film co-modified by Co-ion and Mo-ion to serve as the electrochromic material through a one-step electrodeposition method. The effect of electrodeposition time on film thickness, surface morphology and electrochromic properties is systematically studied as well. The results show that, compared with pure WO3 film, the surface morphology of the tungsten oxide film modified by Co-ion and Mo-ion (WO3: Co, Mo) is significantly different. The Co and Mo co-modified film possesses a higher transmission modulation (58.5% at 600 nm) and rapid switching speed (coloring and bleaching time are 2.7 s and 5.6 s, respectively), low impedance value and excellent cycle stability. The performance enhancement is mainly attributed to the coral-like structure of the membrane, which provides a larger specific surface area, more ion adsorption sites and faster ion diffusion. Therefore, this work provides a fast and low-cost method to prepare tungsten oxide electrochromic films co-modified with cobalt and molybdenum ions. At the same time, it also provides an idea to obtain films with different electrochromic properties by adjusting the film thickness.

Optical phase modulation by natural eye movements: application to time-domain FF-OCT image retrieval.

Eye movements are commonly seen as an obstacle to high-resolution ophthalmic imaging. In this context we study the natural axial movements of the in vivo human eye and show that they can be used to modulate the optical phase and retrieve tomographic images via time-domain full-field optical coherence tomography (TD-FF-OCT). This approach opens a path to a simplified ophthalmic TD-FF-OCT device, operating without the usual piezo motor-camera synchronization. The device demonstrates in vivo human corneal images under the different image retrieval schemes (2-phase and 4-phase) and different exposure times (3.5 ms, 10 ms, 20 ms). Data on eye movements, acquired with a spectral-domain OCT with axial eye tracking (180 B-scans/s), are used to study the influence of ocular motion on the probability of capturing high-signal tomographic images without phase washout. The optimal combinations of camera acquisition speed and amplitude of piezo modulation are proposed and discussed.

Nanosecond-scale all-optical Ti3C2T x -MXene modulator

Inspired by recent advancements of graphene-based ultrafast photonic devices, Ti3C2T x -MXene, as a graphene-like two-dimensional layer-structure material, has gained extensive interest in nonlinear optical applications, especially in all-optical intensity modulation. Herein, we successfully fabricated an all-optical modulator based on Ti3C2T x -Mxene/polyvinyl-alcohol film with nanosecond-scale response time, modulation speed of 100 kHz, and modulation depth of 10%. Furthermore, the variation of fall edges of modulated signal pulse caused by thermo-optic effect under different pump power was also observed. Considering the ease of fabrication, low cost, and ease of integration, the proposed modulator may open the door for high-speed all-optical communications and signal processing.

Low Risk for Persistent Back Pain Disability Is Characterized by Lower Pain Sensitivity and Higher Physical Performance.

The STarT Back Tool (SBT) predicts risk for persistent low back pain (LBP)-related disability based on psychological distress levels. Other non-psychological factors associated with LBP, such as pain sensitivity and physical performance, may further characterize SBT-risk subgroups. The purpose of this study was to determine whether a low-risk SBT subgroup demonstrated lower pain sensitivity and/or higher physical performance compared with a medium-/high-risk SBT subgroup. In this cross-sectional, secondary analysis, adults with LBP (N = 76) completed SBT and demographics (age, sex, race, chronicity) questionnaires. Participants underwent pain sensitivity (local and remote pressure pain thresholds, temporal summation, conditioned pain modulation) and physical performance (Back Performance Scale, walking speed, obstacle negotiation, Timed "Up & Go" [TUG], TUG Cognitive) testing. Independent samples t tests determined low- versus medium-/high-risk SBT subgroup differences. A follow-up discriminant function analysis was also conducted. The medium-/high-risk subgroup demonstrated a lower proportion of participants with acute pain. The low-risk subgroup demonstrated lower pain sensitivity (higher local pressure pain thresholds and higher conditioned pain modulation) and higher physical performance (superior Back Performance Scale scores, faster walking speeds, faster obstacle approach and crossing speeds, and faster TUG completion). Discriminant function analysis results supported the 2-subgroup classification and indicated strong to moderate relationships with obstacle crossing speed, chronicity, and conditioned pain modulation. Lower pain sensitivity and higher physical performance characterized the low-risk SBT subgroup and may represent additional LBP prognostic factors associated with persistent disability. Longitudinal studies are needed to confirm whether these factors can enhance SBT prediction accuracy and further direct treatment priorities. Sensory and physical factors contribute to SBT risk classification, suggesting additional, non-psychological factors are indicative of favorable LBP outcomes. Findings highlight the need for assessment of multiple factors to improve LBP clinical prediction. People at low risk for back pain disability have less sensitivity to pain and better physical performance. By measuring these factors, physical therapists could guide treatment and improve outcomes for people with back pain.

Carrier transport effect on the high speed modulation performance of integrated optoelectronic transceiving chip

Carrier transport effect on the high speed modulation performance of integrated optoelectronic transceiving chip