Active Beam Steering Research Articles

Active inference and deep generative modeling for cognitive ultrasound.

Ultrasound has the unique potential to offer access to medical imaging to anyone, everywhere. Devices have become ultra-portable and cost-effective, akin to the stethoscope. Nevertheless, and despite many advances, ultrasound image quality and diagnostic efficacy are still highly operator- and patient-dependent. In difficult-to-image patients, image quality is often insufficient for reliable diagnosis. In this paper, we put forth the idea that ultrasound imaging systems can be recast as information-seeking agents that engage in reciprocal interactions with their anatomical environment. Such agents autonomously adapt their transmit-receive sequences to fully personalize imaging and actively maximize information gain in-situ. To that end, we will show that the sequence of pulse-echo experiments that an ultrasound system performs can be interpreted as a perception-action loop: the action is the data acquisition, probing tissue with acoustic waves and recording reflections at the detection array, and perception is the inference of the anatomical and or functional state, potentially including associated diagnostic quantities. We then equip systems with a mechanism to actively reduce uncertainty and maximize diagnostic value across a sequence of experiments, treating action and perception jointly using Bayesian inference given generative models of the environment and action-conditional pulse-echo observations. Since the representation capacity of the generative models dictates both the quality of inferred anatomical states and the effectiveness of inferred sequences of future imaging actions, we will be greatly leveraging the enormous advances in deep generative modelling (generative AI), that are currently disrupting many fields and society at large. Finally, we show some examples of cognitive, closed-loop, ultrasound systems that perform active beamsteering and adaptive scanline selection, based on deep generative models that track anatomical belief states.

Nonreciprocal Terahertz Beam Steering Manipulated by Magnetic Weyl Semimetal Metasurface Based on Universal Chirality‐ Wavevector‐ Magnetic Field Relation

AbstractMagnetic Weyl semimetal shows intriguing properties in both fundamental physics and potential applications. However, the complex relationship between nonreciprocal transmission and magnetic field manipulation in magnetic Weyl semimetal systems has not been generally clarified and fully utilized. Here, a universal Chirality–Wavevector–Magnetic field (C‐K‐B) relation is established in the magnetic Weyl semimetal system, which completely describes the spin topological band and its intrinsic polarization output in full space orientation under an arbitrary magnetic vector. This relation can provide complete guidance for the device design of nonreciprocal spin manipulation. Coupling this nonreciprocal mechanism with the photonic spin Hall effect of the geometric phased metasurface, a magnetic Weyl semimetal metasurface is constructed in the terahertz (THz) range, The experiments demonstrate the flexible THz beam steerings in a broad spatial dispersion range of ±25–±55° with four different working modes by only altering the biased magnetic vectors. Moreover, all these beam steering processes are accompanied by nonreciprocal isolating transmission with the isolation ratio reaching 27 dB. This C‐K‐B relation and active nonreciprocal beam steering devices are expected to prompt magneto‐optical devices and systems combined with echo isolation function in beam scanning, wavelength division multiplexing, and spin multiplexing.

Valley-conserved topological integrated antenna for 100-Gbps THz 6G wireless.

The topological phase revolutionized wave transport, enabling integrated photonic interconnects with sharp light bending on a chip. However, the persistent challenge of momentum mismatch during intermedium topological mode transitions due to material impedance inconsistency remains. We present a 100-Gbps topological wireless communication link using integrated photonic devices that conserve valley momentum. The valley-conserved silicon topological waveguide antenna achieves a 12.2-dBi gain, constant group delay across a 30-GHz bandwidth and enables active beam steering within a 36° angular range. The complementary metal oxide semiconductor-compatible valley-conserved devices represent a major milestone in hybrid electronic-photonic-based topological wireless communications, enabling terabit-per-second backhaul communication, high throughput, and intermedium transport of information carriers, vital for the future of communication from the sixth to X generation.

Terahertz magneto-optical metadevice for active spin-selective beam steering and energy distribution with nonreciprocal isolation

Active beam steering and energy distribution have important applications for terahertz (THz) communication, radar, and imaging. However, the spin-conjugated mirror symmetry of a passive Pancharatnam–Berry (PB) metasurface limits the active energy distribution. Here, we prepared a low dispersion, low loss, and high magneto-optical coefficient La:YIG single crystal, ±45∘ Faraday rotation angle that can be actively tuned by a weak magnetic field in broadband THz range at room temperature. Based on this functional material, a THz magneto-optical (MO) spin-modulated metadevice has been demonstrated, which is integrated with a La:YIG, an anisotropic metasurface, and a PB metasurface layer. The spin-conjugated mirror symmetry is broken by the MO chirality effect and photonic spin Hall effect in this metadevice so that spin-selective beam steering within the range of ±27∘−±41∘ is dynamically manipulated by external magnetic fields and power distribution can be tuned with the max modulation depth of 91.6%. More importantly, the MO crystal introduces nonreciprocal phase shift between two spin states so that the device not only achieves active THz beam steering but also provides isolation for reflected waves with the max isolation of 23 dB. This mechanism of THz nonreciprocal spin beam steering provides multiple functions for THz point-to-point networking communication, anti-shielding, anti-interference, and power distribution.

Universal Active Metasurfaces for Ultimate Wavefront Molding by Manipulating the Reflection Singularities

AbstractOptical metasurfaces are becoming ubiquitous optical components to control light properties. However, most of these devices are passive and cannot be arbitrarily reconfigured according to the change in the surrounding environment. Here the authors propose an innovative design strategy relying on the position of topological singularities to address full phase modulation of light with almost unity efficiency. The active metasurface unit cells consist of asymmetric Gires–Tournois resonators filled with either silicon or hetero‐structured materials to leverage on the thermo‐optical or electro‐optical effects, respectively. In both cases, a full phase modulation associated with 100% reflection amplitude is observed even when dealing with extremely low refractive index change, on the order of 0.01. Improving the deflection efficiencies for each deflection angle is performed by optimizing the refractive index modulation profile in the extended unit cell using an advanced statistical learning optimization methodology. Consequently, active beam steering designs for active thermo‐optical effect with ultimate performance exceeding 90% have been optimized. Furthermore, active wavefront splitting using electro‐optics materials is optimized to reach ultimate modulation performances with nearly 92% efficiency. The realization of highly efficient active beam‐forming operating at high frequencies would open important applications in imaging microscopy, and 3D light detection and ranging (LiDAR).

Active terahertz beam steering based on mechanical deformation of liquid crystal elastomer metasurface

Active metasurfaces are emerging as the core of next-generation optical devices with their tunable optical responses and flat-compact topography. Especially for the terahertz band, active metasurfaces have been developed as fascinating devices for optical chopping and compressive sensing imaging. However, performance regulation by changing the dielectric parameters of the integrated functional materials exhibits severe limitations and parasitic losses. Here, we introduce a C-shape-split-ring-based phase discontinuity metasurface with liquid crystal elastomer as the substrate for infrared modulation of terahertz wavefront. Line-focused infrared light is applied to manipulate the deflection of the liquid crystal elastomer substrate, enabling controllable and broadband wavefront steering with a maximum output angle change of 22° at 0.68 THz. Heating as another control method is also investigated and compared with infrared control. We further demonstrate the performance of liquid crystal elastomer metasurface as a beam steerer, frequency modulator, and tunable beam splitter, which are highly desired in terahertz wireless communication and imaging systems. The proposed scheme demonstrates the promising prospects of mechanically deformable metasurfaces, thereby paving the path for the development of reconfigurable metasurfaces.

Design of Multi-Functional Transmitarray with Active Linear Polarization Conversion and Beam Steering Capabilities

This study designed a multi-functional reconfigurable transmitarray with switchable polarization and beam steering capabilities using only a PIN diode having ON/OFF switching ability. The simulation confirmed that the proposed architecture is capable of 2D beam scanning of up to ±45° for elevation and azimuth while maintaining or converting linear polarization when operating within the X-band. The performance was verified through a far-field beam pattern measurement using the near-field antenna measurement system by producing a transmitarray with an 8 × 8 unit cell arrangement. The maximum level of gain of the proposed architecture was confirmed to be 14.5 dBi, the sidelobe level was below 14.5 dBc, the polarization converting loss was below 1.28 dB, and the polarization isolation level was above 14.7 dB. It can be utilized for the design technique of a radar system demanding small size, weight, power, and cost (SWaP-C) characteristics based on a simplified composition.

High-Precision Beam Angle Expander Based on Polymeric Liquid Crystal Polarization Lenses for LiDAR Applications

A novel beam steering angle expander is demonstrated by cascading two polymeric liquid crystal polarization lenses with different diopters. The lens module performs as a planar telescope, which has features such as a light weight, low cost, and high precision. The magnifier offers wide-angle, continuous steering when integrated with an active fine-angle beam steering device. The potential application for LiDAR is emphasized.

Design of a Novel Wideband Leaf-Shaped Printed Dipole Array Antenna Using a Parasitic Loop for High-Power Jamming Applications.

This paper proposes a novel wideband leaf-shaped printed dipole antenna sensor that uses a parasitic element to improve the impedance matching bandwidth characteristics for high-power jamming applications. The proposed antenna sensor consists of leaf-shaped dipole radiators, matching posts, rectangular slots, and a parasitic loop element. The leaf-shaped dipole radiators are designed with exponential curves to obtain a high directive pattern and are printed on a TLY-5 substrate for high-power durability. The matching posts, rectangular slots, and a parasitic loop element are used to enhance the impedance matching characteristics. The proposed antenna sensor has a measured fractional bandwidth of 66.7% at a center frequency of 4.5 GHz. To confirm the array antenna sensor characteristics, such as its active reflection coefficients (ARCs) and beam steering gains, the proposed single antenna sensor is extended to an 11 × 1 uniform linear array. The average values of the simulated and measured ARCs from 4.5 to 6 GHz are −13.4 dB and −14.7 dB. In addition, the measured bore-sight array gains of the co-polarization are 13.4 dBi and 13.7 dBi at 4 GHz and 5 GHz, while those of the cross-polarizations are −4.9 dBi and −3.4 dBi, respectively. When the beam is steered at a steering angle, θ0, of 15°, the maximum measured array gains of the co-polarization are 12.2 dBi and 10.3 dBi at 4 GHz and 5 GHz, respectively.

Design of an Active Beam-Steering Array With a Perforated Wide-Angle Impedance Matching Layer

In this communication, a tapered slot antenna array with a perforated wide-angle impedance matching (WAIM) layer is studied for active beam steering. To achieve the wide-angle beam scanning characteristic, a tapered slot antenna is used in the array antenna design. For active impedance matching in a wide beam-steering angle, a thin dielectric type of WAIM is introduced, and an optimal WAIM characteristic is realized by changing the effective dielectric constant by adding an air hole to the WAIM. To verify the characteristics of the designed antenna, a 16×16 array is fabricated and measured. The fabricated array shows active S-parameter characteristics of less than -9.13 dB during E-plane scanning and -9.31 dB during H-plane scanning when the beam is steered up to 70° on both planes. It was also confirmed that when the beam is steered to 70°, no scan blindness or grating lobes occur within the operating frequency.

Monolithic Patch-Antenna THz Lasers with Extremely Low Beam Divergence and Polarization Control

Arrays of patch antennas have impacted modern telecommunications in the RF range significantly, owing to their versatility in tailoring the properties of the emitted radiation such as beam width and polarization, along with their ease of fabrication. At higher frequencies, in the terahertz (THz) range, there is a pressing need for a similar monolithic platform to realize and enable the advanced functionalities available in the RF technology. This platform would benefit a wide variety of fields such as astronomy, spectroscopy, wireless communications, and imaging. Here, we demonstrate THz lasers made of arrays of 10 × 10 patch antenna microcavities that provide up to 25 mW output power with robust single mode frequency and spatial mode. This device architecture leads to an unprecedented beam divergence, better than 2° × 2°, which depends only on the number of resonators. This allows to functionalize the device while preserving a high quality far-field pattern. By interconnecting the symmetric square microcavities with narrow plasmonic wires along one direction, we introduce an asymmetry into the originally degenerate and cross-polarized TM01 and TM10 modes, leading to a precise control of the resonant frequency detuning between the TM modes. This feature allows devices to be designed that radiate with any coherent polarization states from linear to circular. Large-scale full-wave simulations of the emission from entire arrays support our experimental results. Our platform provides a solution to finally achieve monolithic terahertz emitters with advanced integrated functionalities such as active beam steering and polarization control.

Multicolor femtosecond pump-probe system with single-electron sensitivity at low temperatures and high magnetic fields.

We present an ultrafast spectroscopy system designed for temporal and spectral resolution of transient transmission changes after excitation of single electrons in solid-state quantum structures. The system is designed for optimum long-term stability, offering the option of hands-off operation over several days. Pump and probe pulses are generated in a versatile Er:fiber laser system where visible photon energies may be tuned independently from 1.90 eV to 2.51 eV in three parallel branches. Bandwidth-limited pulse durations between 100 fs and 10 ps are available. The solid-state quantum systems under investigation are mounted in a closed-cycle superconducting magnet cryostat providing temperatures down to 1.6 K and magnetic fields of up to 9 T. The free-standing cryomagnet is coupled to the laser system by means of a high-bandwidth active beam steering unit to eliminate residual low-frequency mechanical vibrations of the pulse tube coolers. High-NA objective lenses inside the sample chamber are employed for focusing femtosecond laser pulses onto the sample and recollection of the transmission signal. The transmitted probe light is dispersed in a grating monochromator equipped with a liquid nitrogen-cooled CCD camera, enabling a frame rate of 559 Hz. In order to eliminate spurious background effects due to low-frequency changes in the thermal equilibrium of the sample, we operate with a lock-in scheme where, instead of the pump amplitude, the pump-probe timing is modulated. This feature is provided without any mechanical action by an electro-optic timing unit inside the femtosecond Er:fiber system. The performance of the instrument is tested with spectrally resolved pump-probe measurements on a single negatively charged CdSe/ZnSe quantum dot under a magnetic field of 9 T. Selective initialization and readout of charge and spin states is carried out via two different femtosecond laser pulses. High-quality results on subpicosecond intraband relaxation dynamics after single-electron excitation motivate a broad variety of future experiments in ultrafast quantum optics and few-fermion quantum dynamics.

A silicon optical bench with vertically-oriented micromirrors for active beam steering

This paper reports a Silicon Optical Bench (SiOB) integrated with two vertically-oriented tip-tilt micromirrors that can perform active beam steering. The curling of W/SiO2 bimorphs is utilized to bend microstructures out of plane. The vertical orientation is realized by using a combination of curling W/SiO2 bimorphs and stoppers. W is employed as one of the bimorph materials to increase the bimorph stiffness, attributed to its much higher Young’s modulus than other materials. At the same time, the stress of the W layer is tuned to maximize the bending angle range of the W/SiO2 bimorphs. The fabrication process of making this new SiOB platform has been developed. Particularly, two electrothermal bimorph-based MEMS mirrors are successfully fabricated and stand upright on an SiOB. The two upright micromirrors are parallel to each other and can perform 2-axis forward-view optical scanning. The mirror plate is made of a 20 μm-thick silicon layer coated with aluminum and its diameter is 0.72 mm. The mirror can rotate ±8° at 4.5 V. This MEMS scanner has potential applications in miniature LiDAR for Micro Air Vehicles (MAVs).

Tunable Beam Steering, Focusing and Generating of Orbital Angular Momentum Vortex Beams Using High-Order Patch Array

In this paper, a tunable patch array based on high-order is proposed at the frequency of 300 GHz, achieving active controllable beam steering, focusing and generation of orbital angular momentum vortex beams. It has been demonstrated that the patch array can achieve wide beam scanning angle by controlling the phase of array elements with tunable phase shifters. Meanwhile, beam focusing on the specified position can also be realized by phase modulation of array elements based on the focusing theory. In addition, we also designed a patch array to generate vortex beams with multiple topological charges by high-order modes. The performances show that the patch antenna array we designed has a good application prospect.

Active beam steering and afocal zooming by nematic liquid crystal-infiltrated graded index photonic structures

This study presents active beam steering and afocal zooming of light by incorporating liquid crystals (LCs) with graded index photonic crystals (GRIN PCs). The GRIN PC structures are composed of low refractive index polymer annular rods with holes of gradually varying radii. To actively manipulate incident light, the annular rods are infiltrated with nematic LCs. By applying an external voltage to the infiltrated LCs, the effective index profile of the low-index GRIN PC structure is modulated without introducing any mechanical movement. The incident beam deflection and corresponding focal distance modulation are tuned only by controlling the applied bias voltage. In the present work, the hyperbolic secant refractive index profile is chosen to design GRIN PC structures. To design a GRIN PC structure with annular PCs, the Maxwell–Garnett effective medium approximation is employed. We analytically express the relation between infiltrated LCs and the gradient parameter to show the physical background of the tuning ability of the proposed devices. Beam steering and afocal zooming devices are analytically investigated via geometrical optics, and numerically realized with the help of a finite-difference time-domain method. A beam deflection with an angle change of Δθout = 44° and a light magnification with maximum ×2.15 are obtained within operating frequencies of a/λ = [0.10–0.15] and a/λ = [0.15–0.25], respectively, where ‘a’ is the lattice constant and λ is the incident wavelength. The corresponding operating frequency bandwidths are calculated as 40% and 50% for the beam steering and afocal zooming applications, respectively. LCs are inexpensive materials and work under low voltage/power conditions. This feature can be used for designing an electro–optic GRIN PC device that has the potential for use in a wide variety of optical applications.

Modulating phase by metasurfaces with gated ultra-thin TiN films.

Active control over the flow of light is highly desirable because of its applicability to information processing, telecommunication, and spectroscopic imaging. In this paper, by employing the tunability of carrier density in a 1 nm titanium nitride (TiN) film, we numerically demonstrate deep phase modulation (PM) in an electrically tunable gold strip/TiN film hybrid metasurface. A 337° PM is achieved at 1.550 μm with a 3% carrier density change in the TiN film. We also demonstrate that a continuous 180° PM can be realized at 1.537 μm by applying a realistic experiment-based gate voltage bias and continuously changing the carrier density in the TiN film. The proposed design of active metasurfaces capable of deep PM near the wavelength of 1.550 μm has considerable potential in active beam steering, dynamic hologram generation, and flat photonic devices with reconfigurable functionalities.

Nanoscale Hydrogenography on Single Magnesium Nanoparticles.

Active plasmonics is enabling novel devices such as switchable metasurfaces for active beam steering or dynamic holography. Magnesium with its particle plasmon resonances in the visible spectral range is an ideal material for this technology. Upon hydrogenation, metallic magnesium switches reversibly into dielectric magnesium hydride (MgH2), turning the plasmonic resonances off and on. However, up until now, it has been unknown how exactly the hydrogenation process progresses in the individual plasmonic nanoparticles. Here, we introduce a new method, namely nanoscale hydrogenography, that combines near-field scattering microscopy, atomic force microscopy, and single-particle far-field spectroscopy to visualize the hydrogen absorption process in single Mg nanodisks. Using this method, we reveal that hydrogen progresses along individual single-crystalline nanocrystallites within the nanostructure. We are able to monitor the spatially resolved forward and backward switching of the phase transitions of several individual nanoparticles, demonstrating differences and similarities of that process. Our method lays the foundations for gaining a better understanding of hydrogen diffusion in metal nanoparticles and for improving future active nano-optical switching devices.

Dual-Gated Active Metasurface at 1550 nm with Wide (>300°) Phase Tunability.

Active metasurfaces composed of electrically reconfigurable nanoscale subwavelength antenna arrays can enable real-time control of scattered light amplitude and phase. Achievement of widely tunable phase and amplitude in chip-based active metasurfaces operating at or near 1550 nm wavelength has considerable potential for active beam steering, dynamic hologram rendition, and realization of flat optics with reconfigurable focal lengths. Previously, electrically tunable conducting oxide-based reflectarray metasurfaces have demonstrated dynamic phase control of reflected light with a maximum phase shift of 184° ( Nano Lett. 2016 , 16 , 5319 ). Here, we introduce a dual-gated reflectarray metasurface architecture that enables much wider (>300°) phase tunability. We explore light-matter interactions with dual-gated metasurface elements that incorporate two independent voltage-controlled MOS field effect channels connected in series to form a single metasurface element that enables wider phase tunability. Using indium tin oxide (ITO) as the active metasurface material and a composite hafnia/alumina gate dielectric, we demonstrate a prototype dual-gated metasurface with a continuous phase shift from 0 to 303° and a relative reflectance modulation of 89% under applied voltage bias of 6.5 V.

Spatial accumulation of phase difference in spoof plasmon based Mach–Zehnder Interferometer

An active beam steering structure comprising the spoof surface plasmon polariton (SSPP) waveguide is presented. The proposed structure consists of two stages: the two arms structure as a Mach–Zehnder interferometer (MZI), and free space propagation stage. The SSPP waveguide includes periodic grooves, which are filled with a thin layer of doped semiconductor like GaAs. By applying electric voltage at the electrodes on top of the waveguide, the depletion layer thickness and the effective refractive index of the dielectric inside the grooves can be changed. The effective refractive index of the dielectric inside the groove is derived analytically and the phase change of the propagation wave along the single sided SSPP waveguide is calculated as a function of input voltage. The relation between the input signal and the angle of maximum radiation of output beam is investigated and the linearity is improved. We have shown that the MZI beam steering section has the capability to bend the electromagnetic beam about 42 degrees. At the end, we presented an application of the proposed beam steering device as a spatially accumulated phase difference structure that can be utilized in devices such as digital-to-analog converter (DAC).

Kirigami/Origami‐Based Soft Deployable Reflector for Optical Beam Steering

The beam steering mechanism has been a key element for various applications ranging from sensing and imaging to solar tracking systems. However, conventional beam steering systems are bulky and complex and present significant challenges for scaling up. This work introduces the use of soft deployable reflectors combining a soft deployable structure with simple kirigami/origami reflective films. This structure can be used as a macroscale beam steering mechanism that is both simple and compact. This work first develops a soft deployable structure that is easily scalable by patterning of soft linear actuators. This soft deployable structure is capable of increasing its height several folds by expanding in a continuous and controllable manner, which can be used as a frame to deform the linearly stretchable kirigami/origami structures integrated into the structure. Experiments on the reflective capability of the reflectors are conducted and show a good fit to the modeling results. The proposed principles for deployment and for beam steering can be used to realize novel active beam steering devices, highlighting the use of soft robotic principles to produce scalable morphing structures.