Showing papers on "Wavefront published in 2022"
TL;DR: In this article , a wavefront-control meta-device combining specifically designed metasurfaces and globally tuned graphene layers is proposed to generate vectorial terahertz (THz) beams with continuously varying polarization distributions upon gating.
Abstract: Abstract Dynamical controls on terahertz (THz) wavefronts are crucial for many applications, but available mechanism requests tunable elements with sub-micrometer sizes that are difficult to find in the THz regime. Here, different from the local-tuning mechanism, we propose an alternative approach to construct wavefront-control meta-devices combining specifically designed metasurfaces and globally tuned graphene layers. Coupled-mode-theory (CMT) analyses reveal that graphene serves as a tunable loss to drive the whole meta-device to transit from one functional phase to another passing through an intermediate regime, exhibiting distinct far-field (FF) reflection wavefronts. As a proof of concept, we design/fabricate a graphene meta-device and experimentally demonstrate that it can reflect normally incident THz wave to pre-designed directions with different polarizations under appropriate gating voltages. We finally design a graphene meta-device and numerically demonstrate that it can generate vectorial THz beams with continuously varying polarization distributions upon gating. These findings pave the road to realizing a wide range of THz applications, such as sensing, imaging, and wireless communications.
38 citations
TL;DR: In this paper , a Fourier-based metaprocessor for analog computing on a single-layer Huygens' metasurface has been proposed, where basic mathematical operations, including differentiation and cross-correlation are performed by directly modulating complex wavefronts in spatial Fourier domain.
Abstract: Computational meta-optics brings a twist on the accelerating hardware with the benefits of ultrafast speed, ultra-low power consumption, and parallel information processing in versatile applications. Recent advent of metasurfaces have enabled the full manipulation of electromagnetic waves within subwavelength scales, promising the multifunctional, high-throughput, compact and flat optical processors. In this trend, metasurfaces with nonlocality or multi-layer structures are proposed to perform analog optical computations based on Green's function or Fourier transform, intrinsically constrained by limited operations or large footprints/volume. Here, we showcase a Fourier-based metaprocessor to impart customized highly flexible transfer functions for analog computing upon our single-layer Huygens' metasurface. Basic mathematical operations, including differentiation and cross-correlation, are performed by directly modulating complex wavefronts in spatial Fourier domain, facilitating edge detection and pattern recognition of various image processing. Our work substantiates an ultracompact and powerful kernel processor, which could find important applications for optical analog computing and image processing.
35 citations
TL;DR: In this article , the spectral and spatial degrees of freedom can be independently tuned in suitably tailored non-local metasurfaces, enabling the design and implementation of wavefrontshaping and wavefront-selective devices.
Abstract: Metasurfaces are ushering in an era of multifunctional control over optical wavefronts realized with ultrathin planarized devices. Recent advances have been enabling unprecedented control over the frequency response of these surfaces, suggesting that the future of flat optics may tailor both spectral and spatial degrees of freedom in highly multispectral and multifunctional devices. Diffractive nonlocal metasurfaces are opening new opportunities in this direction: they leverage symmetry‐protected scattering from quasi‐bound states in the continuum and, by spatially manipulating controlled geometric perturbations, they support ultrasharp optical responses with wavefront‐manipulating features. Encoded in nonlocal (i.e., spatially extended) resonant modes, the resulting response is observed exclusively within the bandwidth of the resulting Fano resonance, affording ideal features for a wide range of applications. In this perspective, this novel class of metasurfaces are discussed in the broader context of flat optics, highlighting their peculiar operation in contrast to relevant predecessors, and highlighting the opportunities for future advancement and applications. In particular, it is emphasized that nonlocality and selectivity are inherently related, but that spectral and spatial selectivity can be independently tuned in suitably tailored metasurfaces. In turn, this freedom allows the design and implementation of both wavefront‐shaping and wavefront‐selective devices. The novel optical responses, combined with the compatibility with rational design, herald new prospects for active, nonlinear and quantum metasurfaces, ultrathin devices for augmented reality, and compact tailored optical sources.
32 citations
TL;DR: A review of state-of-the-art meta-devices employed for wavefront manipulations of optical waves can be found in this paper , where the authors focus on all-dielectric metasurfaces with high refractive indices.
Abstract: In recent years, metamaterials and metasurfaces have prospered in many fields of “science and technology,” covering the entire electromagnetic spectrum. Metasurface devices constituting of a set arrangement of meta-atoms translate into modern-day miniaturized means to achieve planar, ultrathin, multifunctional electromagnetic (EM) systems. Metasurfaces are ideal candidates to develop next-generation, lightweight, and fabrication-friendly optical components as they impart local and space-variant phase changes on incident EM waves, providing more comprehensive control over EM wavefronts. This attribute has been instrumental in realizing a variety of special beams for high-capacity data transmission and superresolution imaging. Furthermore, from the perspective of efficiency, the below-par performance of previously explored plasmonic-based metasurfaces can be enhanced by employing all-dielectric metasurfaces. All-dielectric metasurfaces with high refractive indices have high resonance quality factors, low cost, and CMOS fabrication compatibility. 2D materials-based metasurface design has succeeded in further reducing the device footprints for better integration in optoelectronic devices. The conventional, time- and computation-intensive EM solvers have largely been assisted by artificial intelligence techniques, resulting in quicker metasurface designing. This review focuses on the state-of-the-art meta-devices employed for wavefront manipulations of optical waves. The design variants and applications of metasurfaces constitute a prolific field for future research to meet existing challenges and make the devices more suitable for real-time applications.
32 citations
TL;DR: In this paper , a two-plane coupled phase retrieval (TwPCPR) method is proposed for combining two in-line holograms and one off-axis hologram using a rapidly converging iterative procedure.
Abstract: Abstract Accurate depiction of waves in temporal and spatial is essential to the investigation of interactions between physical objects and waves. Digital holography (DH) can perform quantitative analysis of wave–matter interactions. Full detector-bandwidth reconstruction can be realized based on in-line DH. But the overlapping of twin images strongly prevents quantitative analysis. For off-axis DH, the object wave and the detector bandwidth need to satisfy certain conditions to perform reconstruction accurately. Here, we present a reliable approach involving a coupled configuration for combining two in-line holograms and one off-axis hologram, using a rapidly converging iterative procedure based on two-plane coupled phase retrieval (TwPCPR) method. It realizes a fast-convergence holographic calculation method. High-resolution and full-field reconstruction by exploiting the full bandwidth are demonstrated for complex-amplitude reconstruction. Off-axis optimization phase provides an effective initial guess to avoid stagnation and minimize the required measurements of multi-plane phase retrieval. The proposed strategy works well for more extended samples without any prior assumptions of the objects including support, non-negative, sparse constraints, etc. It helps to enhance and empower applications in wavefront sensing, computational microscopy and biological tissue analysis.
30 citations
TL;DR: In this article , a high-quality-factor silicon-on-lithium niobate metasurfaces with electrically driven, independent control of its constituent nanobars for full phase tunability with high tuning efficiency was investigated.
Abstract: Dynamically reconfigurable metasurfaces promise compact and lightweight spatial light modulation for many applications, including LiDAR, AR/VR, and LiFi systems. Here, we design and computationally investigate high-quality-factor silicon-on-lithium niobate metasurfaces with electrically driven, independent control of its constituent nanobars for full phase tunability with high tuning efficiency. Free-space light couples to guided modes within each nanobar via periodic perturbations, generating quality factors exceeding 30,000 while maintaining a bar spacing of <λ/1.5. We achieve nearly 2π phase variation with an applied bias not exceeding ±25 V, maintaining a reflection efficiency above 91%. Using full-field simulations, we demonstrate a high-angle (51°) switchable beamsplitter with a diffracted efficiency of 93% and an angle-tunable beamsteerer, spanning 18-31°, with up to 86% efficiency, all using the same metasurface device. Our platform provides a foundation for highly efficient wavefront-shaping devices with a wide dynamic tuning range capable of generating nearly any transfer function.
28 citations
TL;DR: In this paper , four graphene-based meta-atoms are designed to regulate polarization state of terahertz wave by changing Fermi energy level of graphene, and three dynamic metasurfaces are designed for controlling wavefront of reflected beam.
Abstract: Polarization is an important characteristic of electromagnetic wave. Due to novel optical properties, graphene-based anisotropic structure is widely used to control polarization state of electromagnetic wave. In this work, four graphene-based meta-atoms are designed to regulate polarization state of terahertz wave by changing Fermi energy level of graphene. When Fermi energy level is 0.01 eV, cross-polarized wave is emitted by four meta-atoms with phase difference of 90° at 1.18 THz, and the corresponding polarization conversion ratio reaches ∼90%. When Fermi energy level is adjusted to 0.70 eV, linear phase gradient will disappear, and cross-polarized wave almost disappears. Using four selected elements, three dynamic metasurfaces are designed for controlling wavefront of reflected beam, and they are gradient metasurface, metalens, and vortex beam generator. The designed metasurfaces successfully combine wavefront control and polarization manipulation, and greatly improve the ability to control electromagnetic wave. Our designs may have many potential applications, such as terahertz switching, imaging, and polarization beam splitter.
27 citations
TL;DR: In this paper , a two-plane coupled phase retrieval (TwPCPR) method is proposed for combining two in-line holograms and one off-axis hologram using a rapidly converging iterative procedure.
Abstract: Abstract Accurate depiction of waves in temporal and spatial is essential to the investigation of interactions between physical objects and waves. Digital holography (DH) can perform quantitative analysis of wave–matter interactions. Full detector-bandwidth reconstruction can be realized based on in-line DH. But the overlapping of twin images strongly prevents quantitative analysis. For off-axis DH, the object wave and the detector bandwidth need to satisfy certain conditions to perform reconstruction accurately. Here, we present a reliable approach involving a coupled configuration for combining two in-line holograms and one off-axis hologram, using a rapidly converging iterative procedure based on two-plane coupled phase retrieval (TwPCPR) method. It realizes a fast-convergence holographic calculation method. High-resolution and full-field reconstruction by exploiting the full bandwidth are demonstrated for complex-amplitude reconstruction. Off-axis optimization phase provides an effective initial guess to avoid stagnation and minimize the required measurements of multi-plane phase retrieval. The proposed strategy works well for more extended samples without any prior assumptions of the objects including support, non-negative, sparse constraints, etc. It helps to enhance and empower applications in wavefront sensing, computational microscopy and biological tissue analysis.
27 citations
TL;DR: In this paper , a high-efficiency full-space metasurface (MS) is demonstrated numerically, which can independently manipulate the transmitted linear polarization (LP) and the reflected circular polarization (CP) wavefront based on the transmission and geometric phase at terahertz (THz) range.
25 citations
TL;DR: In this article , the authors summarize the amazing power and fundamental limits of controlling multiple light scattering, which lay the physical foundation to harness multiply-scattered light for imaging and communication purposes.
Abstract: The main obstacle for optical imaging or for sending information through turbid media such as paint, clouds and biological tissue is the random scattering of light. Owing to its immense complexity, the process of multiple scattering has long been described by the diffusion equation, which ignores the interference of scattered light. Recent developments in optical wavefront shaping and phase recording techniques have enabled the breaking of the diffusion limit and the control of coherent light transport in complex media, including strongly scattering tissues and multimode optical fibres with random mode mixing. Great advances have been made in focusing and controlling the transmission of light through such complex systems and in performing various tasks behind them, such as optical micro-manipulation. Here, we summarize the amazing power and the fundamental limits of controlling multiple light scattering, which lay the physical foundation to harness multiply-scattered light for imaging and communication purposes. Connections to practical applications are illustrated, in particular in those areas covered in the companion articles in this issue. Multiple scattering fundamentally complicates the task of sending light through turbid media, as many applications require. This Review summarizes the theoretical framework and experimental techniques to understand and control these processes.
25 citations
TL;DR: In this article , the authors describe novel metasurfaces-based nanophotonic platforms that have shown exceptional control of electromagnetic waves at the subwavelength scale as promising candidates to overcome existing restrictions, while realizing flat optical devices.
Abstract: The holographic display, one of the most realistic ways to reconstruct optical images in three-dimensional (3D) space, has gained a lot of attention as a next-generation display platform for providing deeper immersive experiences to users. So far, diffractive optical elements (DOEs) and spatial light modulators (SLMs) have been used to generate holographic images by modulating electromagnetic waves at each pixel. However, such architectures suffer from limitations in terms of having a resolution of only a few microns and the bulkiness of the entire optical system. In this review, we describe novel metasurfaces-based nanophotonic platforms that have shown exceptional control of electromagnetic waves at the subwavelength scale as promising candidates to overcome existing restrictions, while realizing flat optical devices. After introducing the fundamentals of metasurfaces in terms of spatial and spectral wavefront modulation, we present a variety of multiplexing approaches for high-capacity and full-color metaholograms exploiting the multiple properties of light as an information carrier. We then review tunable metaholograms using active materials modulated by several external stimuli. Afterward, we discuss the integration of metasurfaces with other optical elements required for future 3D display platforms in augmented/virtual reality (AR/VR) displays such as lenses, beam splitters, diffusers, and eye-tracking sensors. Finally, we address the challenges of conventional nanofabrication methods and introduce scalable preparation techniques that can be applied to metasurface-based nanophotonic technologies towards commercially and ergonomically viable future holographic displays.
TL;DR: In this paper , a metasurface-coated two-dimensional (2D) slab waveguide enables the generation of arbitrary complex light fields by combining the extreme versatility and freedom on the wavefront control of optical metamurfaces with the compactness of photonic integrated circuits.
Abstract: We show that a metasurface-coated two-dimensional (2D) slab waveguide enables the generation of arbitrary complex light fields by combining the extreme versatility and freedom on the wavefront control of optical metasurfaces with the compactness of photonic integrated circuits. We demonstrated off-chip 2D focusing and holographic projection with our metasurface-dressed photonic integrated devices. This technology holds the potential for many other optical applications requiring 2D light field manipulation with full on-chip integration, such as solid-state LiDAR and near-eye AR/VR displays.
TL;DR: In this article , the authors proposed a two-stage supervised+unsupervised training protocol for direct synthesis of high-quality 3D phase-only holograms using a layered depth image as a data-efficient volumetric 3D input.
Abstract: Abstract Computer-generated holography (CGH) provides volumetric control of coherent wavefront and is fundamental to applications such as volumetric 3D displays, lithography, neural photostimulation, and optical/acoustic trapping. Recently, deep learning-based methods emerged as promising computational paradigms for CGH synthesis that overcome the quality-runtime tradeoff in conventional simulation/optimization-based methods. Yet, the quality of the predicted hologram is intrinsically bounded by the dataset’s quality. Here we introduce a new hologram dataset, MIT-CGH-4K-V2, that uses a layered depth image as a data-efficient volumetric 3D input and a two-stage supervised+unsupervised training protocol for direct synthesis of high-quality 3D phase-only holograms. The proposed system also corrects vision aberration, allowing customization for end-users. We experimentally show photorealistic 3D holographic projections and discuss relevant spatial light modulator calibration procedures. Our method runs in real-time on a consumer GPU and 5 FPS on an iPhone 13 Pro, promising drastically enhanced performance for the applications above.
TL;DR: In this article , nonlocal dielectric metasurfaces in the near-infrared have been used to achieve both spatial and spectral control of light, focusing light exclusively over a narrowband resonance while leaving off-resonant frequencies unaffected.
Abstract: Abstract Photonic devices rarely provide both elaborate spatial control and sharp spectral control over an incoming wavefront. In optical metasurfaces, for example, the localized modes of individual meta-units govern the wavefront shape over a broad bandwidth, while nonlocal lattice modes extended over many unit cells support high quality-factor resonances. Here, we experimentally demonstrate nonlocal dielectric metasurfaces in the near-infrared that offer both spatial and spectral control of light, realizing metalenses focusing light exclusively over a narrowband resonance while leaving off-resonant frequencies unaffected. Our devices attain this functionality by supporting a quasi-bound state in the continuum encoded with a spatially varying geometric phase. We leverage this capability to experimentally realize a versatile platform for multispectral wavefront shaping where a stack of metasurfaces, each supporting multiple independently controlled quasi-bound states in the continuum, molds the optical wavefront distinctively at multiple wavelengths and yet stay transparent over the rest of the spectrum. Such a platform is scalable to the visible for applications in augmented reality and transparent displays.
TL;DR: In this article , the authors report ultra-broadband achromatic metasurfaces that are capable of delivering arbitrary and frequency-independent wave properties by bottom-up topology optimization.
Abstract: Metasurfaces, the ultrathin media with extraordinary wavefront modulation ability, have shown versatile potential in manipulating waves. However, existing acoustic metasurfaces are limited by their narrow-band frequency-dependent capability, which severely hinders their real-world applications that usually require customized dispersion. To address this bottlenecking challenge, we report ultra-broadband achromatic metasurfaces that are capable of delivering arbitrary and frequency-independent wave properties by bottom-up topology optimization. We successively demonstrate three ultra-broadband functionalities, including acoustic beam steering, focusing and levitation, featuring record-breaking relative bandwidths of 93.3%, 120% and 118.9%, respectively. All metasurface elements show novel asymmetric geometries containing multiple scatters, curved air channels and local cavities. Moreover, we reveal that the inversely designed metasurfaces can support integrated internal resonances, bi-anisotropy and multiple scattering, which collectively form the mechanism underpinning the ultra-broadband customized dispersion. Our study opens new horizons for ultra-broadband high-efficiency achromatic functional devices on demand, with promising extension to the optical and elastic achromatic metamaterials.
TL;DR: The wavefront of the OAM beams is helical, the intensity at the center of the beam is zero, and there is a phase singularity as mentioned in this paper , which is a characteristic of OAM beam.
TL;DR: In this paper , a fingerprint-based non-invasive fluorescence imaging technique is proposed to demix the speckle patterns emitted by a fluorescent object under variable unknown random illumination, using matrix factorization and a novel fingerprintbased reconstruction.
Abstract: Non-invasive optical imaging techniques are essential diagnostic tools in many fields. Although various recent methods have been proposed to utilize and control light in multiple scattering media, non-invasive optical imaging through and inside scattering layers across a large field of view remains elusive due to the physical limits set by the optical memory effect, especially without wavefront shaping techniques. Here, we demonstrate an approach that enables non-invasive fluorescence imaging behind scattering layers with field-of-views extending well beyond the optical memory effect. The method consists in demixing the speckle patterns emitted by a fluorescent object under variable unknown random illumination, using matrix factorization and a novel fingerprint-based reconstruction. Experimental validation shows the efficiency and robustness of the method with various fluorescent samples, covering a field of view up to three times the optical memory effect range. Our non-invasive imaging technique is simple, neither requires a spatial light modulator nor a guide star, and can be generalized to a wide range of incoherent contrast mechanisms and illumination schemes.
TL;DR: In this article , an active adjustable graphene metasurface (MS) is proposed and investigated theoretically, which can control the THz circular polarization (CP) wavefront in transmission mode, and the simulation results show that the MS structure under a Fermi energy level of 1.0 eV can realize CP conversion with efficiency of about 0.9.
Abstract: Metasurfaces (MSs) have received great attention due to their wide application potentials in terahertz (THz) wavefront manipulation. Although great achievements have been obtained in MSs so far, the functionalities are almost static. The active adjustable MS-based devices are far less explored. In this paper, an efficiency adjustable MS composed of a dielectric substrate sandwiched with bi-layered complementary Z-shaped (CZS) structure graphene is proposed and investigated theoretically, which can control the THz circular polarization (CP) wavefront in transmission mode. The simulation results show that the MS structure under a Fermi energy level of 1.0 eV can realize CP conversion with efficiency of about 0.9, and the full range of a 2 π phase shift also can be achieved by changing the rotation angle of the CZS structure graphene along the wave propagation direction. More importantly, the transmission CP conversion efficiency is positively correlated with the Fermi energy levels of graphene. The anomalous refraction and planar focusing effect can be realized by the specific design of a spatial phase profile of the graphene MS, and the corresponding efficiencies can be adjusted by changing the Fermi energy level of the graphene. Adjustable graphene MSs have wide application prospects in the fields of communication, imaging, and other THz wavefront manipulation devices.
TL;DR: Wavefront shaping can be used to achieve optical focusing deep inside scattering media for biomedical imaging, sensing, stimulation, and treatment as discussed by the authors , which can also be used for noninvasive or minimally invasive optical interactions and arbitrary control inside deep tissues.
TL;DR: In this article , the authors review the recent progress in metasurface-enabled optical waveplates, which cover both basic principles and emerging applications, and provide an overview of conventional half and quarter waveplates as well as their use in wavefront shaping applications, followed by a discussion of advanced waveplates including multifunctional waveplates and all-polarization generators.
Abstract: Abstract The polarization of light is crucial for numerous optical applications ranging from quantum information processing to biomedical sensing due to the fundamental role of polarization as another intrinsic characteristic of optical waves, which is uncorrelated with the amplitude, phase, and frequency. However, conventional optical waveplates that enable polarization control are based on the accumulated retardation between two orthogonally polarized electric fields when light propagates a distance much larger than its wavelength in birefringent materials, resulting in bulky configurations and limited functionalities. Optical metasurfaces, ultrathin arrays of engineered meta-atoms, have attracted increasing attention owing to their unprecedented capabilities of manipulating light with surface-confined configurations and subwavelength spatial resolutions, thereby opening up new possibilities for revolutionizing bulky optical waveplates with ultrathin planar elements that feature compactness, integration compatibility, broadband operation bandwidths, and multiple functionalities. Herein, we review the recent progress in metasurface-enabled optical waveplates, which covers both basic principles and emerging applications. We provide an overview of metasurface-based conventional half- and quarter-waveplates as well as their use in wavefront shaping applications, followed by a discussion of advanced waveplates, including multifunctional waveplates and all-polarization generators. We also discuss dynamic waveplates based on active metasurfaces. Finally, we conclude by providing our outlook in this emerging and fast-growing research field.
TL;DR: In this paper , the authors present a high-level overview of the many coating processes and design procedures employed for thermal barrier coatings to enhance the coating's surface quality, focusing on the cultivation, processing and characteristics of engineered TBCs.
Abstract: Thermal barrier coating is critical for thermal insulation technology, making the underlying base metal capable of operating at a melting temperature of 1150 °C. By increasing the temperature of incoming gases, engineers can improve the thermal and mechanical performance of gas turbine blades and the piston cylinder arrangement. Recent developments in the field of thermal barrier coatings (TBCs) have made this material suitable for use in a variety of fields, including the aerospace and diesel engine industries. Changes in the turbine blade microstructure brought on by its operating environment determine how long and reliable it will be. In addition, the effectiveness of multi-layer, composite and functionally graded coatings depends heavily on the deposition procedures used to create them. This research aims to clarify the connection between workplace conditions, coating morphology and application methods. This article presents a high-level overview of the many coating processes and design procedures employed for TBCs to enhance the coating’s surface quality. To that end, this review is primarily concerned with the cultivation, processing and characteristics of engineered TBCs that have aided in the creation of specialized coatings for use in industrial settings.
TL;DR: In this paper , a dual-band multifunctional coding metasurface for anomalous reflection, radar cross-section reduction, and vortex beam generation was proposed and corroborated through full-wave analysis and experiment.
Abstract: Integrated metasurfaces with diversified functionalities have demonstrated promising prospects for comprehensive implementations in compact 5G/6G communication systems by flexibly manipulating electromagnetic (EM) waves. Increasingly emerged multifunctional metasurfaces have successfully revealed integrated wavefront manipulations via phase gradient arrays, coding apertures, independent polarization control, asymmetric transmission/reflection, etc. However, multifunctional metasurfaces with more degrees of freedom in terms of multi-band/broadband operation frequencies, full-space coverage, and computable array factors are still in dire demand. As a step forward in extending manipulation dimensions, we propose and corroborate a dual-band multifunctional coding metasurface for anomalous reflection, radar cross-section reduction, and vortex beam generation through full-wave analysis and experiment. Our tri-layer meta-device comprises a shared coding aperture of split-ring and cross-shaped resonators sandwiched between two layers of orthogonal wire gratings. With an approach of independent control of a reflection–transmission wavefront under orthogonal polarization states and Fabry–Perot-like constructive interference, the low-cross-talk shared coding aperture features a smooth phase shift and high efficiency for 3-bit coding in the K-band and 1-bit coding in the Ka-band. Both numerical and measured results verify that the proposed coding metasurface can effectively realize full-space EM control and improve the capacity of the information channel, which could be developed for potential applications in multifunctional devices and integrated systems.
TL;DR: In this article , the authors demonstrate a mechanical metasurface platform with controllable rotation at the meta-atom level, which can implement continuous Pancharatnam-Berry phase control of circularly polarized microwaves.
Abstract: Abstract. Metasurfaces have enabled the realization of several optical functionalities over an ultrathin platform, fostering the exciting field of flat optics. Traditional metasurfaces are achieved by arranging a layout of static meta-atoms to imprint a desired operation on the impinging wavefront, but their functionality cannot be altered. Reconfigurability and programmability of metasurfaces are the next important step to broaden their impact, adding customized on-demand functionality in which each meta-atom can be individually reprogrammed. We demonstrate a mechanical metasurface platform with controllable rotation at the meta-atom level, which can implement continuous Pancharatnam–Berry phase control of circularly polarized microwaves. As the proof-of-concept experiments, we demonstrate metalensing, focused vortex beam generation, and holographic imaging in the same metasurface template, exhibiting versatility and superior performance. Such dynamic control of electromagnetic waves using a single, low-cost metasurface paves an avenue towards practical applications, driving the field of reprogrammable intelligent metasurfaces for a variety of applications.
TL;DR: In this article, the authors focus on geometric TTL coupling and categorise it into a number of different mechanisms for which they give analytic expressions, and discuss how understanding the geometric effects allows TTL noise reduction already by smart design choices.
Abstract: Tilt-to-length (TTL) coupling is a technical term for the cross-coupling of angular or lateral jitter into an interferometric phase signal. It is an important noise source in precision interferometers and originates either from changes in the optical path lengths or from wavefront and clipping effects. Within this paper, we focus on geometric TTL coupling and categorise it into a number of different mechanisms for which we give analytic expressions. We then show that this geometric description is not always sufficient to predict the TTL coupling noise within an interferometer. We, therefore, discuss how understanding the geometric effects allows TTL noise reduction already by smart design choices. Additionally, they can be used to counteract the total measured TTL noise in a system. The presented content applies to a large variety of precision interferometers, including space gravitational wave detectors like LISA.
TL;DR: The last decade has seen the development of a wide set of tools such as wavefront shaping, computational or fundamental methods that allow us to understand and control light propagation in a complex medium, such as biological tissues or multimode fibers as discussed by the authors .
Abstract: Abstract The last decade has seen the development of a wide set of tools, such as wavefront shaping, computational or fundamental methods, that allow us to understand and control light propagation in a complex medium, such as biological tissues or multimode fibers. A vibrant and diverse community is now working in this field, which has revolutionized the prospect of diffraction-limited imaging at depth in tissues. This roadmap highlights several key aspects of this fast developing field, and some of the challenges and opportunities ahead.
TL;DR: In this article , a platform of bi-layer all-graphene meta-mirrors with spin-selective full-dimensional manipulation is proposed to simultaneously achieve giant dual-band CD response and wavefront shaping, based on the principle of the hybridization coupling.
Abstract: The ability to simultaneous achieve circular dichroism (CD) and wavefront manipulation is extremely important for many practical applications, especially for detecting and imaging. However, many of the previously observed weakness chiral features are limited to nanostructures with complex three-dimensional building configurations, single narrow-band response, and no active tunability, which are getting farther and away from the goal of integration and miniaturization. Here, a platform of bi-layer all-graphene meta-mirrors with spin-selective full-dimensional manipulation is proposed to simultaneously achieve giant dual-band CD response and wavefront shaping, based on the principle of the hybridization coupling. By simply controlling the structural variables of the meta-mirror and the characteristic parameters of graphene, that is, the combination of passive and active regulation, the proposed design can selectively manipulate the polarization, amplitude, phase, and working frequency of the incident circularly polarized wave near-independently. As a proof of concept, we used the meta-mirror to design two metasurface arrays with spin-selective properties for dynamic terahertz (THz) wavefront shaping and near-field digital imaging, both of which show a high-performance dynamic tunability. This method could provide additional options for the next-generation intelligent THz communication systems.
TL;DR: In this paper , an advanced strategy of noninterleaved multitasked metaplexer for 3D manipulation of dual-helical EM wavefronts is reported, where cascaded multiplane digital images in the propagation direction are employed as the 3D wavefront, which are encoded into the spin-decoupled meta-atoms array, making the outputting circularly polarized waves carrying different image information at different planes.
Abstract: While electromagnetic (EM) metasurfaces have been extensively studied for wavefront manipulations, the real 3-D manipulation of wavefront remains challenging. In this article, an advanced strategy of noninterleaved multitasked metaplexer for 3-D manipulation of dual-helical EM wavefronts is reported. We first develop a general method to derive the metasurface phase distribution required to form the desired 3-D electric field patterns. Then, the spin-decoupled meta-atoms are designed to achieve this goal and further increase the degrees of freedom in EM manipulation. As a proof of concept, cascaded multiplane digital images in the propagation direction are employed as the 3-D wavefronts, which are encoded into the spin-decoupled meta-atoms array, making the outputting circularly polarized waves carrying different image information at different planes. Both the simulations and experiments verify the desirable 3-D wavefront manipulation capacities of our strategy for dual-helical states. Besides, this scheme can be further extended to achieve arbitrary energy allocation in 3-D space for dual-helical EM waves. Our strategy paves an alternative route for applications such as multiple-input multiple-output (MIMO) communications, multitarget radar detection, information storage, as well as 3-D microwave imaging.
TL;DR: In this article , a semi-analytical approach to broadband metasurface design is proposed, which incorporates network analysis and genetic algorithm to determine the frequency-independent optimal circuit parameters for multi-layer transmissive meta-surface, so that targeted complex transmission coefficients can be achieved over a wide bandwidth.
Abstract: In order to harness the capabilities of terahertz waves, various metasurface-based functional devices have been developed recently. However, due to the limited usage of systematic optimization methodologies, many existing designs leave room for further bandwidth and efficiency improvement. This article provides an overview on the bandwidth limiting factors associated with metasurfaces and gives a tutorial on a semi-analytical approach to broadband design. The broadband approach incorporates network analysis and genetic algorithm to determine the frequency-independent optimal circuit parameters for multi-layer transmissive metasurfaces, so that targeted complex transmission coefficients can be achieved over a wide bandwidth. The broadband design approach is enabling the configuration and optimization of diverse metasurfaces for wavefront and polarization control of terahertz waves, including quarter- and half-waveplates.
TL;DR: In this article , the authors provide an overview of the theoretical models of the space-time digital metasurface and information-surface, the mechanisms of wavefront shaping, and the signal modulations in space and time domains during the wave-matter interactions.
Abstract: Reconfigurable intelligent surfaces (RISs) offer an entirely new route to alter the propagation properties of electromagnetic waves and thus control their reflection, refraction, and scattering features in arbitrary manners. Such physical attributes are perceived to bring about fundamental influence on the modern wireless communication system due to the possibilities to establish artificial and controllable propagation environments for radio signals, which no longer rely on the complex encoding, decoding, and other signal processing techniques. Recent studies reveal that the wave manipulation is not the only skill of the RISs. With the rapid developments of space–time digital metasurface and information metasurface, there has been increasing attention focused on the information manipulation via these artificial surfaces. In this article, we provide an overview of the theoretical models of the space–time digital metasurface and information metasurface, the mechanisms of wavefront shaping, and the signal modulations in space and time domains during the wave–matter interactions. We will also address some practical issues during implementations of the reconfigurable intelligent metasurfaces and the associated hardware architectures at microwave frequencies to realize simplified radio frequency transmitters. Several modulation schemes and the corresponding demonstration systems are introduced to illustrate the powerful abilities of the reconfigurable intelligent metasurfaces. Potential research directions of this technique are briefly discussed for their potential applications in future wireless networks.
TL;DR: A probability-based iterative algorithm combining genetic algorithm (GA) and ant colony optimization (ACO) in which the new solutions can be generated based on a probability map is proposed, able to obtain optimization results with optimal efficiency for single and multiple focuses behind scattering media.
Abstract: Iterative wavefront shaping is a powerful tool to overcome optical scattering and enable focusing of diffusive light, which has exciting potentials in many applications that desire localized light delivery at depths in tissue-like complex media. Unsatisfactory performance and efficiency, however, have been a long-standing problem, and the large discrepancy between theoretical and experimental results has hindered the wide applications of the technology. Currently, most algorithms guiding the iterative search of optimum phase compensation rely heavily on randomness to achieve solution diversity. It is similar to black-box optimization in which the mechanism of how a good solution is arrived at is unclear. The lack of clear guidance on the new solution generation process considerably affects the efficiency of optimization. Therefore, we propose a probability-based iterative algorithm combining genetic algorithm (GA) and ant colony optimization (ACO), in which the new solutions can be generated based on a probability map. Thanks to the clearer guidance provided by the probability map and the reduced involvement of randomness, we are able to obtain optimization results with optimal efficiency for single and multiple focuses behind scattering media. Besides, with the proposed algorithm, we also demonstrate higher adaptability in an unstable scattering environment and more spatially uniform optical focusing in the field of view. This study advances the state-of-the-art in the practice of iterative wavefront shaping. More importantly, the significant improvement in optimization efficiency and adaptability, if further engineered, can potentially inspire or open up wide applications that desire localized and enhanced optical delivery in situ.