Generation Of Structured Light Research Articles

Broadband multifunctional metasurfaces enabling polarization multiplexed focused vortex array generation

Metasurfaces are ultrathin artificially engineered structures exquisitely designed to tailor the wavefront, polarization, and amplitude of incident light, offering a versatile platform for implementing compact and integrated photonics devices. Metasurface-based structured light generation has gained considerable attention in the scientific community for its various exotic applications, including optical communication, particle manipulation, and high-resolution lithography. State-of-the-art design techniques include polarization multiplexing, multiple vortices beam generation, and vortex arrays. However, there needs to be more techniques for generating polarization switchable vortex arrays, despite the apparent advantages in significant application fields, necessitating a simple design technique. Here, we present a straightforward design technique utilizing computer-generated holography (CGH) and photonic spin Hall effect (PHSE) to realize a metadevice platform capable of generating broadband multiple optical vortex arrays with switchable polarization output. Our approach involves designing phase masks for the vortex arrays using CGH, which are then encoded onto the metasurface. By leveraging PSHE, the designed metasurfaces produce the desired optical response depending on the input polarization state. Using the proposed design technique as proof of concept, different all-dielectric metasurfaces capable of generating optical vortex arrays of different dimensions are demonstrated. The results verify the effectiveness of the proposed methodology. The design has potential applications in data communications, storage, quantum computation, nanoscale physical manipulation, and microscopy.

Single-stripe-enhanced spacetime stereo reconstruction for concrete defect identification

Few studies explored the 3D reconstruction of concrete defects, and existing methods often suffer from noise interference or impracticality in real-world applications. This study proposes a novel single-stripe-enhanced spacetime stereo reconstruction method that combines a laser liner for structured light generation and a stereo vision camera. This method analyses the morphology and intensity variation of laser stripes from images captured from single scans, achieving accurate defect reconstructions. It is designed for handheld scenarios with image re-alignment eliminating the vibration caused by handheld operation. The morphology of laser stripes at crack sections is analysed for robust fine crack reconstruction. Active frame searching is introduced to improve the calculation efficiency, enabling spacetime stereo to operate over hundreds of frames. A comparative study of the proposed method and two commonly-used stereo matching methods demonstrates its ability to mitigate the impact of handheld operation and generate 3D reconstructions that highlight potential crack regions.

AdaptiveStereo: Depth estimation from adaptive structured light

Recovering depth with active stereo methods has become an important approach to three-dimensional perception. However, when the properties of the measurement scene change, projecting predesigned structured light can cause improper exposure and defocus blur on some object surfaces. To address these problems, we propose an active stereo depth perception method called AdaptiveStereo, based on adaptive structured light (ASL). The core idea is to use prior depth information to generate optimal structured light for different measurement scenes, ensuring even illumination of the object’s surface and thereby improving depth perception results. To this end, firstly, a novel ASL encoding scheme based on speckle pattern is designed. Then, we construct an adaptive structured light generation model (ASL-GM) to automatically generate the optimal structured light. Finally, depth perception is realized by using the active stereo matching network with adaptive guidance (AGS-Net). Compared with mainstream depth perception methods, the evaluation results show that our method has higher accuracy, and can obtain better depth perception results.

Low-cost printed holography for the generation ofstructured light.

Recently, the study of structured light fields has attracted great interest, which includes their generation and characterization techniques, as well as their application. Most of these techniques rely on the use of expensive devices, such as liquid crystal spatial light modulators or digital micromirror devices that also require specialized knowledge and software. In this work, we present a scheme for producing low-cost amplitude holograms for the generation of structured light fields. We demonstrate the feasibility of this technique by creating a variety of paraxial modes, such as the well-known Laguerre-Gaussian and Hermite-Gaussian beams. We also demonstrate the potential of our technique in solving the phase retrieval problem to generate 2D and 3D holographic images of objects. Finally, we compare our proposal with the typical generation techniques using digital micromirror devices. Our proposal will pave the path for the generation of structured light beams in more affordable ways for the application in undergrad laboratories.

Directionally duplexed all-dielectric metalens for multifunctional structured light generation.

Directionally duplexed metalenses manipulated by the geometric phase of a silicon nano-bar are theoretically designed to generate multifunctional structured light. It is numerically demonstrated that incident light with different linear and circular polarization states, along forward and backward propagation directions, can be differentially converted into multiple focusing structured beams of arbitrary topological charges, either of vector light with azimuthally variant polarizations or of vortex light with helical phases. Due to the all-silicon and nonresonant metastructural design, the resultant high working efficiencies of our proposed metalens are promising for applications such as optical communication, nanoparticle manipulation, and other direction-duplexed multifunctional optical meta-devices.

Advancing broadband light structuring through single-size nanostructured all-dielectric meta-devices

Traditional optical components and most artificially engineered structures (metamaterials) used for light manipulation are usually designed for narrow bandwidth and limited functionalities. Furthermore, bulkiness and inefficiency limit their application for integrated devices. Metasurfaces, the ultracompact counterpart of bulky metamaterials, exhibit an unprecedented ability to manipulate incident electromagnetic waves at a micron scale. Metasurfaces have emerged as promising candidates for light structuring and its potential applications, ranging from high-capacity data communication to particle manipulation. Despite significant advancement in metasurfaces, realizing high-performance metadevices exhibiting a broadband light manipulation capability is still challenging due to the material's intrinsic nature and lack of a more straightforward design methodology. Here, we demonstrated a broadband single-cell driven all-dielectric metadevice platform to realize high-performance phase modulation for light structuring over the broad visible spectrum475−650nm. The building block consists of an intelligently optimized nanoantenna made of unique zinc sulfide material that employs the PB phase to realize single-layered broadband metadevices for structured light generation, ensuring a decent average transmission efficiency ηavg=79.9% over the intended band. To prove the concept, we designed numerous metadevices for structured light generation and numerically investigated each under the illumination of selected visible wavelengths. We envisioned that the presented work could accelerate real-life applications such as high-resolution color imaging, optical communication and sensing, quantum information processing, and micromanipulation.

Advanced Optical Imaging Based on Metasurfaces

AbstractRecently, metasurfaces have arisen as next‐generation optics with various merits, such as being ultrathin and lightweight with multi‐function integration. Numerous applications of metasurfaces have been demonstrated up to now, including wavefront shaping, optical imaging, hologram display, structured light generation, polarization detection, and so on. Among them, optical imaging components and techniques have been substantially promoted with the advent of metasurfaces due to their superior spatial modulation properties over electromagnetic waves. Here, the forward and reverse design approaches of metasurface and recent advances in various imaging applications based on them are reviewed. Due to the ability of arbitrary wavefront encoding, metasurfaces have been widely applied to numerous imaging applications, including diffraction‐limited imaging with aberration correction, polarization‐related imaging, high‐resolution spectral imaging, three‐dimentional (3D) imaging, and even algorithm‐assisted imaging, etc. Optical imaging applications combined with novel metasurfaces can make breakthroughs with the development of nanofabrication technologies and the improvement of computer algorithms.

Compact structured light generation based on meta-hologram PCSEL integration

Metasurfaces, a catalog of optical components, offer numerous novel functions on demand. They have been integrated with vertical cavity surface-emitting lasers (VCSELs) in previous studies. However, the performance has been limited by the features of the VCSELs such as low output power and large divergence angle. Although the solution of the module of VCSEL array could solve these issues, the practical application is limited by extra lens and large size. In this study, we experimentally demonstrate reconstruction of a holographic images using a compact integration of a photonic crystal surface-emitting laser and metasurface holograms designed for structured light generation. This research showcases the flexible design capabilities of metasurfaces, high output power (on the order of milliwatts), and the ability to produce well-uniformed images with a wide field of view without the need for a collection lens, making it suitable for 3D imaging and sensing.

Reconfigurable structured light generation and its coupling to air–core fiber

Recently, structured light beams have attracted substantial attention in many applications, including optical communications, imaging, optical tweezers, and quantum optics. We propose and experimentally demonstrate a reconfigurable structured light beam generator in order to generate diverse structured light beams with adjustable beam types, beam orders, and beam sizes. By controlling the sizes of generated free-space structured light beams, free-space orbital angular momentum (OAM) beams and vector beams are coupled into an air–core fiber. To verify that our structured light generator enables generating structured light with high beam quality, polarization distributions and mode purity of generated OAM beams and vector beams in both free space and air–core fiber are characterized. Such a structured light generator may pave the way for future applications based on higher-order structured light beams.

Structured Light Generation Using Angle‐Multiplexed Metasurfaces

AbstractOn the basis of the Jones matrix, independent control over the amplitude and phase of light has been demonstrated by combining several meta‐atoms into the supercell of a metasurface. However, due to the intrinsic limitation of a planar achiral structure, the maximum number of independent, complex elements in one Jones matrix is three, giving rise to up to three‐channel amplitude and phase control. In this work, more Jones matrices corresponding to different angles of incidence are proposed to add, so that the degrees of freedom in the amplitude and phase control can be further increased. The supercell of the designed metasurfaces consists of three dielectric nanoblocks with predefined rotation angles and displacements in the 2D space, which can be inversely determined with the help of the genetic algorithm. Empowered by the ability to realize four‐ or even eight‐channel amplitude and phase control, the generation of multiple structured light, including two independent perfect Poincaré beams, two double‐ring perfect Poincaré beams, two perfect Poincaré beam arrays, and four vector vortex beam arrays, is numerically demonstrated. Such novel designs are expected to benefit the development of modern optical applications, including but not limited to optical communications, quantum information, and signal encryption.

Generating superposed terahertz perfect vortices via a spin-multiplexed all-dielectric metasurface

Perfect optical vortices (POVs), characterized as a ring radius independent of topological charge (TC), possess extensive application in particle manipulation and optical communication. At present, the complex and bulky optical device for generating POVs has been miniaturized by leveraging the metasurface, and either spin-dependent or spin-independent POV conversions have been further accomplished. Nevertheless, it is still challenging to generate superposed POVs for incidences with orthogonal circular polarization. Here, a spin-multiplexed all-dielectric metasurface method for generating superposed POVs in the terahertz frequency range is proposed and demonstrated. By using the multiple meta-atom comprised structure as the basic unit, the complex amplitude of two superposed POVs is modulated, decoupled, and subsequently encoded to left- and right-handed circular polarization incidences. Furthermore, two kinds of metasurfaces are fabricated and characterized to validate this controlling method. It is demonstrated that the measured intensity and phase distributions match well with the calculation of the Rayleigh–Sommerfeld diffraction integral, and the radius of superposed POVs is independent of TCs. This work provides promising opportunities for developing ultracompact terahertz functional devices applied to complex structured light generation and terahertz communication, and exploring sophisticated spin angular momentum and orbital angular momentum interactions like the photonic spin-Hall effect.

Polarization-Encoded Structured Light Generation Based on Holographic Metasurface

In view of large information capacity of holographic metasurface and wide applications of structured light, the polarization-encoded structured light generation is proposed based on holographic metasurface. The polarization-encoded structured light generators consist of rotated L-shaped nanoholes, and they work under linearly polarized light illumination. The rotated L-shaped nanoholes simultaneously manipulate the intensity, phase, and polarization of light field and generate the structured light composed by multiple perfect vortices with polarization-encoded orbital angular momentum (OAM) modes. The generated polarization-encoded structured lights also behave the incident polarization dependence. The polarization multiplexing performance of holographic metasurface is embodied in both incident and output fields, and it is also verified by the numerical simulations. The designed method can be expanded to construct any transmission or reflection holographic metasurfaces, and the generated structured lights provide more switchable OAM channels. The polarization-encoded structured light and the compact holographic metasurface are benefit to broadening the wide applications of structured lights.

Inverse design in flat optics

Due to the sub-wavelength resolution, compact size, and ease of integration, flat optics has emerged as a pivotal player for applications in diffractive metalens, structured-light generation, holograms, nonlocal metasurfaces, etc. In the design of flat optics devices, the traditional forward design method demonstrates insurmountable limitations while inverse design has developed into an indispensable approach to focus designers only on high-level optical functionalities while handing over the task of finding conforming structures to machines. Here, we outline a cross-section of main advances of inverse design in flat optics: moving from basic theories and algorithms to further developments and diversified applications.

Flexible THz Carrier‐Envelope Phase Shifter Based on Metamaterials

AbstractThe ability to manipulate terahertz (THz) waveform is important for its applications. Despite rapid progress in metamaterials (MMs), the carrier‐envelope phase (CEP) control for THz pulse is still challenging due to its broadband feature. THz scanning tunneling microscope (THz‐STM), as an emerging technique combining both high temporal and spatial resolution, imposes additional requirements. Here, an ultra‐thin and flexible THz CEP shifter with five groups of different MM arrays is proposed. The CEP shifter is based on a specified split‐ring resonator with a pair of cross‐oriented gratings to enhance transmission efficiency. Simulation and experimental results show that the CEP of the THz pulse is modulated by passing through different MM arrays in turn, which can be shifted as high as 2π. The CEP shifter has good tolerance to wide‐angle oblique incidence and structural bending, which is expected to be used as a key component for THz‐STM. The structure of the CEP shifter has many potential applications, including THz wave focusing, beam‐steering, spatial phase modulation, and structured light generation.

Use of Digital Twins-Based Intelligent Navigation Visual Sensing Technology in Environmental Art Design of Scenic Spots

The study expects to solve the bottleneck problem in the field of intelligent navigation visual sensing and build a network system of information physics, to achieve a visual sensor which can correspond the depth and color of a scene. It aims to improve the robustness and accuracy of color recognition of color structured light in a complex environment. Based on the digital twins (DTs) technology, the effective transformation of logistics process and physical entity to quasi-real-time digital image is realized. The omnidirectional vision sensing technology of a single viewpoint and the panoramic color volume structured light generation technology of a single emission point are integrated. The new active 3D panoramic vision sensor is achieved for which makes the current visual sensing technology developed into the visual perception of body structure. This technology is adopted in the preliminary design of environmental art in the scenic spot, and it can predict the design feasibility of environmental art in the scenic spot, avoid mistakes in decision-making to a great extent and save human and material resources. And also it can analyze and predict some possible dangerous situations, which can greatly improve the environmental safety factor of the scenic spot. In the improvement stage of environmental art design in the scenic spot, using active 3D vision sensing technology can obtain more comprehensive information and is more conducive to the selection of design schemes.

Broadband spatial polarization processing of light via a photopatterned dichroic medium

Vector beams, featured by a specific space-variant distribution of polarization, have attracted intensive attention. Arbitrary and broadband spatial polarization processing is a key pursuit for vector beam generation, modulation, and detection. Here, we introduce black dye into liquid crystals to form a dichroic medium and imprint high-resolution patterns into the medium via photopatterning. Continuous cylindrical and binary vector beams are freely generated. Switching between a vector beam generator and a high-transmittance homeotropic state can be realized due to the electro-optical tunability of liquid crystals. On the basis of a radial vector beam generator array, the polarization distribution is characterized by calculating the darkest line of each generator. This strategy provides a platform for arbitrary spatial polarization processing and may bring more possibilities for polarization imaging, structured light generation, and materials characterization.

High‐Efficiency Phase and Polarization Modulation Metasurfaces

Use of metasurfaces to control the characteristics of electromagnetic waves is an emerging trend at present. Multifunctional metasurfaces, which can modulate multiple wave parameters, greatly reduce the complexity and enrich the functionality of optical systems. Herein, a high‐efficiency multifunctional metasurface for operation in the terahertz band is proposed and demonstrated. Use of a trilayer structure allows the working efficiency to reach 85% at the designed operating frequency. The phase and polarization states of the transmitted waves are modulated individually via subtle adjustment of the geometric parameters of each layer. Two terahertz‐band vector beam generators are demonstrated based on the proposed metasurface. The two devices individually generate radial and azimuthal terahertz vortex beams that can carry arbitrary orbital angular momentum. The experimental results demonstrate the validity of the proposed approach. This method represents a route toward easy fabrication of high‐performance phase and polarization modulation metasurfaces that can improve the information‐carrying capabilities of terahertz systems and offers benefits for structured light generation, optical information security, and optical communication applications.

The Use of Digital Image Art under Visual Sensing Technology for Art Education

The traditional art education model often cannot achieve good teaching results due to the development of digital technology. Art is integrated with technology based on three-dimensional (3D) panoramic vision sensing technology, so as to study the application of the combination of visual sensing technology and digital image art in the field of art education. With the application of projection virtual game “Whac-A-Mole” as an example, the integration of panoramic color volume structured light generation technology with single emission point and omnidirectional visual imaging technology with single view is proposed; the mathematical model of the active vision system is established, and the camera model, projector model, object surface illumination model, and their relationship are studied. On this basis, the mathematical relationship between the color of the projected light source and the color of the corresponding imaging point is proposed; a light source color correction algorithm based on the two-color reflection model is proposed. The object surface color is corrected by three-channel reflectance after the light source color correction algorithm is used for correction. The results suggest that the 3D panoramic vision sensing technology makes the current active stereo vision develop from the visual perception of surface structure to the visual perception of volume structure and reduces the error rate of recognition from 44% to 11%. Moreover, the algorithm does not need to know the coding method of the projected light source and the surface material of the object in advance. The scene teaching combined with technology overcomes the limitations of the teaching site and brings students into a completely realistic teaching situation. The presentation of digital image art using visual sensing technology can inspire children’s imagination, combine education and games, and perform edutainment. Thereby, the application research of digital image art based on 3D panoramic visual sensing technology has an irreplaceable development prospect in the field of art education.

Nonlinear wavefront engineering with metasurface decorated quartz crystal

Abstract In linear optical processes, compact and effective wavefront shaping techniques have been developed with the artificially engineered materials and devices in the past decades. Recently, wavefront shaping of light at newly generated frequencies was also demonstrated using nonlinear photonic crystals and metasurfaces. However, the nonlinear wave-shaping devices with both high nonlinear optical efficiency and high wave shaping efficiency are difficult to realize. To circumvent this constraint, we propose the idea of metasurface decorated optical crystal to take the best aspects of both traditional nonlinear crystals and photonic metasurfaces. In the proof-of-concept experiment, we show that a silicon nitride metasurface decorated quartz crystal can be used for the wavefront shaping of the second harmonic waves generated in quartz. With this crystal-metasurface hybrid platform, the nonlinear vortex beam generation and nonlinear holography were successfully demonstrated. The proposed methodology may have important applications in nonlinear structured light generation, super-resolution imaging, and optical information processing, etc.

Spontaneous and stimulated electron\u2013photon interactions in nanoscale plasmonic near fields

The interplay between free electrons, light, and matter offers unique prospects for space, time, and energy resolved optical material characterization, structured light generation, and quantum information processing. Here, we study the nanoscale features of spontaneous and stimulated electron–photon interactions mediated by localized surface plasmon resonances at the tips of a gold nanostar using electron energy-loss spectroscopy (EELS), cathodoluminescence spectroscopy (CL), and photon-induced near-field electron microscopy (PINEM). Supported by numerical electromagnetic boundary-element method (BEM) calculations, we show that the different coupling mechanisms probed by EELS, CL, and PINEM feature the same spatial dependence on the electric field distribution of the tip modes. However, the electron–photon interaction strength is found to vary with the incident electron velocity, as determined by the spatial Fourier transform of the electric near-field component parallel to the electron trajectory. For the tightly confined plasmonic tip resonances, our calculations suggest an optimum coupling velocity at electron energies as low as a few keV. Our results are discussed in the context of more complex geometries supporting multiple modes with spatial and spectral overlap. We provide fundamental insights into spontaneous and stimulated electron-light-matter interactions with key implications for research on (quantum) coherent optical phenomena at the nanoscale.