Modulation Devices Research Articles

Vortex beam generator based on exceptional topological phase in terahertz all-dielectric metasurface

In this study, an all-dielectric metasurface with an F-shaped chiral structure in the terahertz region has been proposed. The coupling between the electric and magnetic dipole modes supported by the metasurface can be adjusted by varying the structural parameters. In the parameter space composed of l l and s, any closed path around exceptional point in the circular polarization conversion channel t rl generates a topologically protected exceptional topological phase. A vortex beam generator with a unit topological charge was proposed to provide a novel concept for designing terahertz metasurface wavefront modulation devices.

High-speed electro-optic modulation in topological interface states of a one-dimensional lattice

Electro-optic modulators are key components in data communication, microwave photonics, and quantum photonics. Modulation bandwidth, energy efficiency, and device dimension are crucial metrics of modulators. Here, we provide an important direction for the miniaturization of electro-optic modulators by reporting on ultracompact topological modulators. A topological interface state in a one-dimensional lattice is implemented on a thin-film lithium-niobate integrated platform. Due to the strong optical confinement of the interface state and the peaking enhancement of the electro-optic response, a topological cavity with a size of 1.6 × 140 μm2 enables a large modulation bandwidth of 104 GHz. The first topological modulator exhibits the most compact device size compared to reported LN modulators with bandwidths above 28 GHz, to the best of our knowledge. 100 Gb/s non-return-to-zero and 100 Gb/s four-level pulse amplitude modulation signals are generated. The switching energy is 5.4 fJ/bit, owing to the small electro-optic mode volume and low capacitance. The topological modulator accelerates the response time of topological photonic devices from the microsecond order to the picosecond order and provides an essential foundation for the implementation of large-scale lithium-niobate photonic integrated circuits.

Nanometer resolution of 2D single-shot low-coherence & comb-based profilometry based on the effect of discrete height of spatial phase modulator surface

A 2D single-shot comb-based interferometer is well known as a powerful tool for inline inspection owing to its high speed, extensive measurement range, and anti-vibration. However, nanometer resolution is still a milestone that has not been achieved in comb-based interferometers owing to the precision limitation caused by the discrete profile of the spatial phase modulator (SPM) device, typically in the range of several micrometers. Therefore, this study confirms 2D single-shot comb-based profilometry at sub-micron and nanometer-scale resolutions. The system first investigates the effect of the discrete limitation of the SPM surface profile and then verifies the submicron detection ability of the optical frequency comb-based setup. It was quantitatively shown that the highest resolution can be obtained by properly setting the step size of the spatial phase modulator and the SPM surface resolution of the imaging optics. The highest profilometry resolution was recorded at 26.4 nm in a short measurement range, while the setup using the optical comb source with millimeters measurement range for industrial application also can achieve a resolution of approximately 259.2 nm. The results demonstrate the system feasibility in overcoming the discrete limitations of the SPM profile. It also demonstrates for the first time that the so-called 2D single-shot comb-based interferometer can achieve nanometer-scale profilometry resolution covering the measurement range from tens of millimeters to sub-micrometer detection.

A switchable terahertz metamaterial absorber between ultra-broadband and dual bands

Based on the phase change properties of vanadium dioxide (VO2), we propose a terahertz metamaterial absorber that can be switched flexibly between ultra-broadband and dual bands. The absorber consists of a resonator array above a conductive ground layer separated with a dielectric spacer, which includes four square-loop VO2 resonators and a crossed gold resonator in each unit cell. By changing the conductivity of VO2 through thermal control, the absorber can achieve the switching between ultra-broadband absorption and dual-band absorption. Simulation results show that at high temperature, the absorber realizes more than 90% absorption bandwidth in the range of 3.98 to 9.06 THz, which can be elucidated by the wave-interference theory and impedance matching theory. At low temperature, up to 95% of the dual-band absorption occurs at 5.95 and 6.95 THz, which originates the dipole mode and nonlocal surface-Bloch mode of metal resonators. In addition, the absorber has the advantages of polarization-independence and wide-angle absorption. Compared with previous studies, our design can switch between two absorption modes and its absorption performance is greatly improved. The proposed absorber design scheme is expected to expand terahertz devices and enable a variety of applications in the terahertz range, such as modulation, sensing, stealth, and switching devices.

A 35 V–5 V monolithic integrated GaN-based DC–DC floating buck converter

The paper presents the development of a GaN DC–DC power converter with a pre-driver module and power device based on a monolithic integrated GaN E/D-mode metal–insulator–semiconductor high electron mobility transistors (MIS-HEMTs) platform. The pre-driver module with direct coupled field effect transistor logic circuit structure has been monolithically integrated with a GaN power transistor on a Si-based AlGaN/GaN commercial epitaxial wafer. The MIS-HEMTs structure adopts an insulated gate dielectric layer to suppress the leakage current and increase gate voltage robustness. The GaN-based floating buck converter employs a 1 mH inductor and a 9 μF capacitor to achieve 35 V–5 V power conversion. As a result, the pre-driver module is capable of delivering a 10 V driving voltage. GaN monolithic integration of the pre-driver module and power device can reduce the system area in the DC–DC application, which allows for an integrated chip size of 1.8 mm2.

Real-time lumbosacral joint loading estimation in exoskeleton-assisted lifting conditions via electromyography-driven musculoskeletal models

Lumbar joint compression forces have been linked to the development of chronic low back pain, which is specially present in occupational environments. Offline methodologies for lumbosacral joint compression force estimation are not commonly integrated in occupational or medical applications due to the highly time-consuming and complex post-processing procedures. Hence, applications such as real-time adjustment of assistive devices (i.e., back-support exoskeletons) for optimal modulation of compression forces remains unfeasible. Here, we present a real-time electromyography (EMG)-driven musculoskeletal model, capable of estimating accurate lumbosacral joint moments and plausible compression forces. Ten participants performed box-lifting tasks (5 and 15 kg) with and without the Laevo Flex back-support exoskeleton using squat and stoop lifting techniques. Lumbosacral kinematics and EMGs from abdominal and thoracolumbar muscles were used to drive, in real-time, subject-specific EMG-driven models, and estimate lumbosacral joint moments and compression forces. Real-time EMG-model derived moments showed high correlations (R2 = 0.76 - 0.83) and estimation errors below 30% with respect to reference inverse dynamic moments. Compared to unassisted lifting conditions, exoskeleton liftings showed mean lumbosacral joint moments and compression forces reductions of 11.9 - 18.7 Nm (6 - 12% of peak moment) and 300 - 450 N (5 - 10%), respectively. Our modelling framework was capable of estimating in real-time, valid lumbosacral joint moments and compression forces in line with in vivo experimental data, as well as detecting the biomechanical effects of a passive back-support exoskeleton. Our presented technology may lead to a new class of bio-protective robots in which personalized assistance profiles are provided based on subject-specific musculoskeletal variables.

Interband carrier recombination mechanism in Al-doped ZnO

Due to strong nonlinear optical effects and ultrafast response properties, transparent conductive oxides are promising candidate materials for next-generation THz modulation devices and other photonic applications. However, the mechanisms of photon-induced ultrafast carrier relaxations in those materials have yet to be fully understood. Here we investigated the interband carrier dynamics in a prototype of this family, Al-doped ZnO, with different excitation photon energies through femtosecond optical transmittance measurements. We found that the interband relaxation of the photon-induced carriers is mainly through second-order recombination, which is essentially the direct band-to-band recombination with the assistance of intraband electron relaxation. The high density of the doped electrons provides superior intraband relaxation channels through electron-phonon interaction and electron-impurity scattering, which contribute to the overall ultrafast response, especially under indirect and band tail transitions. This study provides a new insight into the ultrafast response mechanism of Al-doped ZnO and the analyzing method may also be generalized to other heavily doped semiconductors.

Beam‐Steering Metadevices for Intelligent Optical Wireless‐Broadcasting Communications

High‐performance beam‐steering devices play a crucial role for optical wireless communication (OWC), which can meet the demand for increasing number of wireless mobile devices and emerging high‐speed multimedia applications. Conventional beam‐steering optical components like spatial light modulator and digital micromirror device are limited to realize a small steering angle (typ. several degrees), thus dramatically limits the spatial scope of OWC. Herein, a beam‐steering metadevice utilizing an ultracompact metasurface assisted with a spatial light modulator is presented, which can significantly increase the beam‐steering angle without at the cost of complicated optical setup like conventionally used angle magnifier. Based on the actively tunable beam‐steering metadevice, an intelligent bidirectional optical broadcasting communication system is designed and experimentally demonstrated, which exhibits nine broadcasting areas covering a large field‐of‐view of 20° × 20°, with user‐defined dynamic beam‐steering ability in each area, and each user has a data rate of 10 Gbps for both upstream and downstream transmission. The proposed metadevices can meet the demand of intelligent optical wireless communication which requires both high‐performance and low‐cost for practical purpose, under currently available technical architectures.

Study of a solid-state transmitting device with a phase correction system, which increases the summing efficiency

Modern radar is a complex system, built on the basis of almost all the achievements of such areas as radio electronics, computer engineering and, of course, microwave devices. One of the most important units of radar, which determines the potential characteristics of the system as a whole, is the transmitting device. Nowadays the task of signal transmission with minimal losses in transmission lines and obtaining required power levels at the output of the transmitting device is relevant. However, existing methods may be insufficient to accomplish this task. In this regard, it may be necessary to improve or develop new systems and methods using the latest advances in microwave and antenna technology, radio and microelectronics, the totality of which will provide devices with these parameters. One such way to increase the stacking efficiency and output power of the transmitting device is to correct the phase of the amplification channels of the transmitting device in the range of operating frequencies. In this article the advantages of using solid-state transmitting devices in radar stations over electric-vacuum amplifying devices are considered. The most common ways of summation the power of microwave devices are described. An algorithm of the phase correction system is presented. The results of an experimental study of the system of gain channel phase correction for a transmitting device with eight gain channels, operating in a relatively wide frequency range, are presented. The proposed amplification channel phase correction system compensates the existing difference in the electrical lengths of the elements of the divider-adder path and amplifying modules in accordance with the algorithm, by means of controlled phase shifters (integrated into each amplifying module). The change in the phases of the microwave signal in (n-1) amplification channels is performed based on the calculated phase corrections obtained on the basis of successive estimates of the total output power of the reference amplifying module with each of the (n - 1) modules, where n is the total number of amplifying modules (channels amplification) in the transmitter. The output power is estimated by the ADC according to the level of the microwave power envelope at the lower, middle and upper frequencies of the operating range, taken from the adder output by a directional coupler. The performance of the phase correction algorithm is ensured by the control device of the amplifying module, the control and monitoring device of the transmitting device, the automatic monitoring and control system from the processing and indication system, as well as the appropriate interface at the operator's workplace. The proposed algorithm corrects the phases of the amplification channels according to the values obtained by the calculation method based on the data measured in the process of phase correction, which made it possible to reduce the maximum required number of phase shifter adjustments to 3 for each of n and each frequency, thereby ensuring a threefold increase in device performance. It was experimentally confirmed that the application of the proposed technical solution increases the efficiency of power summation of the considered transmitter from 70% to 94% - 99% (excluding active losses in the divider-adder and RMSD of the output powers of the amplifying modules) and an increase in the output power of the transmitter by 30% was achieved. The obtained results can be used to improve the algorithmic-software support of developed or modernized transmitting devices of radar stations.

Research on theoretical and experimental of Interference processing based on three-channel mutual injection phase-locked laser

With the advantage of obtaining multiple phase-locked laser outputs at the same time without complicated modulation devices, the multi-channel mutual injection technique provides a new idea to solve the problem of excessive use of beam splitting devices in traditional multi-beam interference processing systems. In this paper, we analyzed the phase-locking mechanism of the mutual injection technique, studied in detail the locking process of the phase difference of three lasers with time when their energy is injected into each other, and discussed the coherence characteristics of the three Gaussian beams after convergence. Accordingly, we built a three-beam interferometric processing system based on the three-channel mutual injection solid-state laser to process the surface of silicon material. The surface of the material was observed by SEM to exhibit a clear structure of regular shaped microporous arrays with a period of 3.0 µm distributed according to the regular pattern of positive hexagon, which was consistent with the interference pattern obtained from the simulation. The comprehensive theoretical and experimental results show that the laser obtained based on the three-channel mutual injection technique has good coherence characteristics and can be effectively applied in interference processing. This opens up a new idea for the development of interference processing equipment and has positive significance for the development of multi-beam interference processing.

Two types of ultrafast mode-locking operations from an Er-doped fiber laser based on germanene nanosheets

As a member of Xenes family, germanene has excellent nonlinear saturable absorption characteristics. In this work, we prepared germanene nanosheets by liquid phase exfoliation and measured their saturation intensity as 0.6 GW/cm2 with a modulation depth of 8%. Then, conventional solitons with a pulse width of 946 fs and high-energy noise-like pulses with a pulse width of 784 fs were obtained by using germanene nanosheet as a saturable absorber for a mode-locked Erbium-doped fiber laser. The characteristics of the two types of pulses were investigated experimentally. The results reveal that germanene has great potential for modulation devices in ultrafast lasers and can be used as a material for creation of excellent nonlinear optical devices to explore richer applications in ultrafast photonics.Graphical

Ultrasensitive optical modulation in hybrid metal-perovskite and metal-graphene metasurface THz devices.

Implementation of efficient terahertz (THz) wave control is essential for THz technology development for applications including sixth-generation communications and THz sensing. Therefore, realization of tunable THz devices with large-scale intensity modulation capabilities is highly desirable. By integrating perovskite and graphene with a metallic asymmetric metasurface, two ultrasensitive devices for dynamic THz wave manipulation through low-power optical excitation are demonstrated experimentally here. The perovskite-based hybrid metadevice offers ultrasensitive modulation with a maximum modulation depth for the transmission amplitude reaching 190.2% at the low optical pump power of 5.90 mW/cm2. Additionally, a maximum modulation depth of 227.11% is achieved in the graphene-based hybrid metadevice at a power density of 18.87 mW/cm2. This work paves the way toward design and development of ultrasensitive devices for optical modulation of THz waves.

Directional Activated Exciton Highway via Fractal Electric Field Modulation for Ultrasensitive Carbon Nanotube-Based Sensors.

The electrical vapor sensor based on carbon nanotubes (CNTs) has attracted wide attention due to its excellent conductivity, stable interfacial structure, and low dimensional quantum effects. However, the conductivity and contact interface activity were still limited by the random distribution of coated CNTs, which led to limited performance. We developed a new strategy to unify the CNT directions with image fractal designing of the electrode system. In such a system, directional aligned CNTs were gained under a well-modulated electric field, leading to microscale CNT exciton highways and molecule-scale host-guest site activation. The carrier mobility of the aligned CNT device is 20-fold higher than that of the random network CNT device. With excellent electrical properties, such modulated CNT devices based on fractal electrodes behave as an ultrasensitive vapor sensor for methylphenethylamine, a mimic of illicit drug methamphetamine. The detection limit reached as low as 0.998 ppq, 6 orders of magnitude sensitive than the reported 5 ppb record based on interdigital electrodes with random distributed CNTs. Since the device is easily fabricated in wafer-level and compatible with the CMOS process, such a fractal design strategy for aligned CNT preparation will be widely applied in a variety of wafer-level electrical functional devices.

Nonlinear density waves on graphene electron fluids

The hydrodynamic behavior of charged carriers leads to nonlinear phenomena such as solitary waves and shocks, among others. As an application, such waves might be exploited on plasmonic devices either for modulation or signal propagation along graphene waveguides. We study the nature of nonlinear perturbations following an approach similar to Sagdeev potential analysis and also by performing the reductive perturbation method on the hydrodynamic description of graphene electrons, taking into consideration the effect of Bohm quantum potential and odd viscosity. Thus, deriving a dissipative Kadomtsev-Petviashvili-Burgers (KPB) equation for the bidimensional flow as well as its unidimensional limit in the form of Korteweg--de Vries--Burgers (KdVB). The stability analysis of these equations unveils the existence of unstable modes that can be excited and launched through graphene plasmonic devices.

High-sensitivity strain sensor with micron-scale imitation dumbbell structure based on differential temperature self-compensation

A micron-sized dumbbell-like -MZI structure has been developed using hydroxide flame melt taper and arc fusion discharge, with the dumbbell rod region prepared by melt taper drawing and the dumbbell sheet region prepared by arc fusion discharge. This structure has a sensitive light intensity response in the sensing field due to a double-order mode-field coupled excitation region. The geometrical parameters of the dumbbell-like system are optimized theoretically, and the feasibility of the microstructure to achieve high strain sensing sensitivity is analyzed. Experimental results show that the microstructure has a high strain sensing sensitivity of ∼ 0.074 dB/µε and a consistent temperature sensing sensitivity over the entire monitoring wavelength range. Therefore, a light intensity-dependent temperature self-compensation calculation is proposed to achieve a uniform light intensity-strain response for each characteristic peak in the monitored wavelength domain. Since the device has a significant advantage in light intensity modulation and is not affected by polarization light perturbations, it can be used as an alternative light intensity modulation device in optical communication networks and laser research. It can also be used as a probe for medical diagnostic testing based on its enhanced evanescent field properties.

NET-TEN: a silicon neuromorphic network for low-latency detection of seizures in local field potentials

Objective. Therapeutic intervention in neurological disorders still relies heavily on pharmacological solutions, while the treatment of patients with drug resistance remains an unresolved issue. This is particularly true for patients with epilepsy, 30% of whom are refractory to medications. Implantable devices for chronic recording and electrical modulation of brain activity have proved a viable alternative in such cases. To operate, the device should detect the relevant electrographic biomarkers from local field potentials (LFPs) and determine the right time for stimulation. To enable timely interventions, the ideal device should attain biomarker detection with low latency while operating under low power consumption to prolong battery life. Approach. Here we introduce a fully-analog neuromorphic device implemented in CMOS technology for analyzing LFP signals in an in vitro model of acute ictogenesis. Neuromorphic networks have progressively gained a reputation as low-latency low-power computing systems, which makes them a promising candidate as processing core of next-generation implantable neural interfaces. Main results. The developed system can detect ictal and interictal events with ms-latency and with high precision, consuming on average 3.50 nW during the task. Significance. The work presented in this paper paves the way to a new generation of brain implantable devices for personalized closed-loop stimulation for epilepsy treatment.

Safety and efficacy of the p48 MW and p64 flow modulation devices: a systematic review and meta-analysis.

Flow diverters (FDs) have demonstrated increasing safety and efficacy in treating various types of intracranial aneurysms. Although the underlying mechanism of action of all FDs is similar, differences are noted in their intrinsic characteristics, materials, and deployment techniques. The p64 flow modulation device (p64) and the newer p48 movable wire flow modulation device (p48 MW) are not yet available in the US but have been increasingly used mainly in Europe, demonstrating optimistic results. The authors performed a systematic review and meta-analysis of the literature to evaluate the safety and efficacy of the p64 and p48 MW FDs. A literature review (between January 1960 and November 2022) of the PubMed, Scopus, Embase, Web of Science, and Cochrane Central Register of Controlled Trials databases was conducted. The primary efficacy outcome was the proportion of complete angiographic occlusion at last follow-up. Complete occlusion was defined as Raymond-Roy class 1 and O'Kelly-Marotta grade D. The primary safety outcomes were the composite safety rate of ischemic and hemorrhagic events (intra- and postprocedure) and the all-cause mortality rate. Data were analyzed using a random-effects proportions meta-analysis, and statistical heterogeneity was assessed. Twenty studies with 1781 patients harboring 1957 aneurysms were included in the analysis. Seventeen studies were conducted in Europe. Sixteen studies evaluated the performance of the p64 (MW). Patient ages ranged between 20 and 89 years, and most were female (78.7%). Aneurysm size ranged between 1 and 50 mm. Most aneurysms were unruptured (92.8%) and in the anterior circulation (93.1%). Single antiplatelet therapy pre- and postprocedure was used in 2 studies. Follow-up ranged from 2 to 14.5 months. For the p64 and p48 MW, complete angiographic occlusion rates were 77% (95% CI 68%-85%) and 67% (95% CI 49%-81%), adjunctive coil usage rates were 7% (95% CI 4%-12%) and 4% (95% CI 0%-24%), primary safety composite rates were 2% (95% CI 1%-4%) and 3% (95% CI 1%-11%), and mortality rates were 0.49% (95% CI 0%-1%) and 2% (95% CI 1%-6%), respectively. The p64 and p48 MW have primarily been used in Europe thus far. This analysis found that both devices have an acceptable efficacy and favorable safety profile. However, further studies are needed to evaluate the efficacy and safety of prescribing a single antiplatelet regimen after implantation of the newer-generation FDs with antithrombotic coating surface modification.

Measurement of azo dye film with large photo-induced birefringence and complex refractive index

Azo dyes are valuable functional materials due to their sensitive response to and effective modulation of polarized light. It is essential to find out not only the optical anisotropy but also the complex refractive index of azo dye materials for photonics applications. We report here such measurements of highly ordered photoaligned azo dye films. The film has an apparent dichroic ratio of about 60. We model the photoaligned azo dye film systems using the Berreman transfer matrix. By means of regression fitting of the polarization dependent transmittance and reflectance data, we were able to determine the complex refractive indices of the aligned film at the wavelength range of 400–1000 nm. This material is found to have exceptionally large optical birefringence (Δn ∼ 0.75 at 632.5 nm and Δn ∼ 0.48 at 850.6 nm). The aligned azo dye film is valuable to applications such as coatable polarizers and optical modulation devices.

Intruder Alert System

Abstract: In this paper, we present an intruder alert system that detects and classifies potential intruders in a given environment using computer vision and machine learning. A network of cameras and a central processing unit run an object detection algorithm and a machine learning classifier in the system. This project was designed and built with an Arduino mega microcontroller, system connected to a GSM module with SIM (subscriber identification module) from a network provider (LDR) sensor which is used in this project is connected to a microcontroller unit, GSM module, and other electronic devices which thus detect any intruder in a classified area, activates the alarm system, and sends text message notifications to the house owner specifying the location and time of intrusion to the house owner's programmed phone number. The design worked in real-time in an area with good network coverage, as expected, according to preliminary testing. It has a wide range of applications in surveillance, particularly in industrial and home security, where internet connectivity is unavailable. The findings demonstrate that the system is capable of accurately identifying and categorizing possible intruders with low rates of false positives.

Local super-resolution imaging of foveated areas in super-oscillating optical fields.

Herein, we propose a super-oscillation optical field foveated local super-resolution imaging method. Firstly, the post-diffraction integral equation of the foveated modulation device is constructed, the objective function and constraints are established, and the structural parameters of the amplitude modulation device are optimally solved by using genetic algorithm. Secondly, the solved data have been input into the software for point diffusion function analysis. We have studied the super-resolution performance of different ring band amplitude types, and find the 8-ring 0-1 amplitude type has the best super-resolution performance. Finally, the principle experimental device is built according to the simulation parameters, and the super-oscillatory device parameters is loaded onto the amplitude type spatial light modulator for the principle experiments, in which the super-oscillation foveated local super-resolution imaging system is able to perform high image contrast imaging in the whole field of view and super-resolution imaging in the foveated field of view area. As a result, this method achieves the 1.25 times super-resolution magnification in the foveated field of view area, which realizes the super-resolutio n imaging of local field while keeping the resolution of other fields unchanged. Experiments verify the feasibility and effectiveness of our system.