Structured Light

Metasurfaces composed of subwavelength-scale artificial meta-atoms have emerged as a powerful platform for manipulating light. By enabling strong light-matter interactions within ultrathin planar geometries, metasurfaces have opened new avenues for highly integrated photonic devices. Lithium niobate (LiNbO 3) is considered one of the most promising multifunctional integrated photonic platforms due to its outstanding properties, such as a large second-order nonlinear susceptibility, a broad transparency window, and a strong electro-optic (EO) effect. In recent years, integrated photonic devices based on lithium-niobate-on-insulator platforms have experienced rapid development. This review summarizes recent advances in LiNbO 3 metasurfaces, providing a comprehensive overview of their demonstrated applications in nonlinear frequency conversion, wavefront and phase modulation, and dynamic EO modulation. By systematically introducing the interplay between the intrinsic material properties of LiNbO 3 and the structural design principles of metasurfaces, this review offers a coherent framework for understanding their nonlinear and active optical functionalities, and serves as a valuable reference for the design and implementation of nonlinear and actively tunable micro-and nano-photonic devices.

The location, condition, and number of the Parthenon sculptures present a considerable challenge to ar- cheologists and researchers studying this monument. Although the Parthenon proudly stands on the Athe- nian Acropolis after nearly 2,500 years, many of its sculptures have been damaged or lost. Since the end of the 18th century, its surviving sculptural decorations have been scattered to museums

Sculpted light, or optical fields with specifically engineered spatial, modal, and vectorial degrees of freedom, has developed as a powerful paradigm for optical sensing, allowing for improved and multidimensional light-matter interactions that extend beyond typical Gaussian illumination. By exploiting degrees of freedom such as orbital and spin angular momentum, spatial mode, polarization, and topology, sculpted light fields provide additional channels through which physical parameters can be mapped onto measurable optical transformations. Rather than merely enhancing sensitivity, sculpted light expands the dimensionality of optical sensing. Recent studies show how tailored optical fields provide additional sensing channels for encoding physical information, enabling precise measurement of parameters such as strain, temperature, position, velocity, refractive index, and structural asymmetry. This article provides a unified viewpoint on the generation and sensing applications of sculpted light, including both fiber-based techniques that take advantage of specialty fibers supporting higher-order modes and free-space techniques. As photonic integration, quantum-state engineering, and machine learning converge with advanced beam shaping technologies, sculpted light is poised to become a foundational strategy for next-generation optical sensing.

This working paper develops a speculative but mathematically disciplined model of luminous
plasma-orb formation. The visible object is not treated as a solid craft, but as a recruited
plasma-photonic sheath assembled from local environmental material and stabilised by field
geometry. The model sequence has five stages: extraction of ions and vapour from a
ground-air-water interface; loading into a dark coherence vapour; rotational spin-binding into a
magnetically supported sphere or enclosure; direct coupling of plasma currents to the quantum
electrodynamic field through the standard current-potential interaction; and airborne drift under an
environmental coupling potential.
The deliberately withheld component is any internal intelligence or processing node. This draft
confines itself to the observable exterior: plasma extraction, sheath inflation, geometric locking, and
field-mediated motion. The goal is not identification of any observed object, but construction of a
robust mathematical language for a hypothetical plasma-field body that can change scale, colour,
geometry, and apparent mobility through coherent sheath dynamics.
Scope boundary. This is a theoretical and entertainment-framed modelling exercise. It does not claim proof
of a non-human origin. Its purpose is to ask whether a coherent mathematical language can describe
extraction, spin-binding, QED coupling, and airborne transition in one system.

Non-diffracting beams are typically confined to a limited set of specific profiles. Existing methods for diversifying these beams face challenges in achieving arbitrarily complex intensity distributions. In this paper, we present a phase engineering approach based on local spatial frequency mapping to construct novel non-diffracting beams. The proposed method facilitates the creation of customized intensity profiles by tailoring and splicing phase modulations in the Fourier domain, enabling the generation of intricate non-diffracting beams, such as those with a Tai Chi shape. We experimentally demonstrate the robust propagation invariance and self-healing capabilities of these novel non-diffracting beams. This approach provides a versatile means for designing structured non-diffracting fields, with potential applications in areas such as precision laser machining, optical trapping, free-space communication, and structured-light imaging.

Spatiotemporal optical vortices (STOVs) possess helical phase singularities distributed jointly in space and time, enabling light to carry transverse orbital angular momentum and offering a fundamentally new degree of freedom for structured light. However, the precise detection of STOVs with fractional topological charges remains highly challenging, as conventional interferometric and diffraction-based techniques suffer from limited resolution and experimental complexity. Here we demonstrate a scattering-assisted detection scheme that enables ultra-high-precision measurement of STOVs with fractional topological charges. By exploiting the sensitivity of random scattering media to the spatiotemporal phase structure of broadband optical fields, we establish a robust mapping between scattered intensity patterns and fractional STOV states. This approach achieves reliable discrimination of fractional topological charges with step sizes down to 0.01, significantly surpassing the resolution of existing methods. Furthermore, we leverage this capability to realize a multi-level free-space optical communication scheme encoded by fractional STOV states, demonstrating enhanced channel capacity within a compact experimental configuration. This work introduces scattering media as a powerful platform for probing spatiotemporal phase singularities, and opens new opportunities for high-dimensional spatiotemporal photonics and optical communications.

Knots and links play a fundamental role across a wide range of physical fields, from classical to quantum physics. In optics, structured light fields with multiple controllable degrees of freedom provide a versatile experimental platform for investigating topological properties. Knot theory underpins the topological control of high-dimensional structured light, thereby giving rise to fundamental physical effects and applications. Furthermore, topologically structured light has attracted significant attention for light-matter interaction. Here we review the recent advances in topologically structured light from the perspective of knot theory. Starting from the basics of knots and related braids, we introduce the generation and manipulation of topologically structured light from the purely spatial domain across to the spatiotemporal domain. Moreover, we demonstrate that the particle-like structured light, such as photonic skyrmions and hopfions, can host the topologies of high dimensional space, followed by brief discussions on potential applications as well as an outlook and future trends and challenges in this field.

Optical vortices, characterized by their central singularities and spiral phase wavefront, have gained widespread attention in light manipulation and diverse applications. With their topological order being extended from integer to fraction, more unique properties have sprung out, such as continuous topological charges, fractional spiral-phase, expanded orbital angular momentum spectrum, and slit openings. These features have facilitated applications in areas such as optical tweezers, direction-selective edge enhancement imaging, robust rotational Doppler metrology, free-space communication, displacement sensing, and high-dimensional quantum entanglement. In recent years, advances in metasurface-based optical control, spatiotemporal pulse shaping, holographic imaging, and deep learning have spurred rapid innovation in the modeling, generation, and measurement of fractional vortex beams. This review begins with the fundamental theory of fractional vortex beams and surveys the latest developments in this rapidly evolving field. The scope of research has also expanded beyond optical vortices to include acoustic vortices. The growing interest in fractional vortex beams, coupled with ongoing technological innovations, is expected to pave the way for further advancements in this promising area of research.

Twisted photonic lattices have recently emerged as a promising platform for opto-twistronics, enabling the exploration of moiré-induced photonic phenomena. Despite significant progress, the implications of non-Hermitian effects within these systems remain largely unexplored. In this work, we theoretically propose and experimentally demonstrate a non-Hermitian twisted photonic lattice with dynamically tunable gain-loss modulation, realized in a four-level atomic medium through the twisted superposition of two stripe fields. By adjusting the frequency detuning, a local flat band is introduced into the photonic band structure, leading to the directional localization of light in momentum space. The degree of localization can be further controlled by varying the laser power, while the direction of localization is reconfigured in real time by tuning the twist angle. Our work uncovers an intriguing interplay between non-Hermitian band reconstruction and geometric twisting by means of reconfigurable photonic lattice, and it provides a versatile platform for studying light manipulation in twisted configurations.

Structured light fields are engineered through precise control of their amplitude, phase, polarization, and spatiotemporal properties, which are extensively studied for both scientific and applied purposes, and can offer novel pathways for information processing, quantum communication, and precision measurement. Although the linear manipulation of structured light is already very mature with the help of liquid crystal devices and planar optical elements, nonlinear manipulation remains nascent, despite demonstrating unique potential for critical functionalities such as optical field information exchange. Hence, critical challenges now lie in harnessing nonlinear interactions, between light fields themselves and between light and matter, to achieve on-demand multidimensional control of target optical fields, particularly for spatial modes of light. The advancing nonlinear optics theory, guided by structured light, reveals novel physical phenomena in various nonlinear interactions, and promotes the development of novel applications based on nonlinear light field control technologies. Accordingly, this review systematically summarizes recent advances across key areas, including the nonlinear manipulation of spatial structured light fields, optical information transfer, full-dimensional manipulation theory, field modulation and nonlinear topological frontiers, and three-dimensional (3D) light field manipulation theory, thereby providing a comprehensive perspective on the current state and the emerging trends in this rapidly evolving field.

Additively manufactured parts are fabricated by generating complex shapes, allowing almost infinite freedom of design. Such parts present significant measurement challenges related to the accessibility and the quality of the measurement results, due to the presence of hollow features, and freeform geometries. Optical measuring instruments are being increasingly applied for complex form measurement, because, compared to contact measurements, they feature higher speeds, higher point densities and often better capabilities to access recessed regions. In this paper, a novel set of indicators is presented that can be used to investigate the performance of measurement solutions based on high-density point-based sampling when applied to form measurement of complex parts. The indicators address surface coverage, sampling density and measurement error as a function of local geometric properties. The indicators are applied to an example comparative analysis involving structured light scanning and photogrammetry measurements of a complex freeform additively manufactured automotive part.

The SYDDARTA project is an on-going European Commission funded initiative under the 7th Framework Programme. Its main objective is the development of a pre-industrial prototype for diagnosing the deterioration of movable art assets. The device combines two different optical techniques for the acquisition of data. On one hand, hyperspectral imaging is implemented by means of electronically tunable filters. On the other, 3D scanning, using structured light projection and capturing is developed. These techniques are integrated in a single piece of equipment, allowing the recording of two optical information streams. Together with multi-sensor data merging and information processing, estimates of artwork deterioration and degradation can be made. In particular, the resulting system will implement two optical channels (3D scanning and short wave infrared (SWIR) hyperspectral imaging) featuring a structured light projector and electronically tunable spectral separators. The system will work in the VIS-NIR range (400-1000nm), and SWIR range (900-2500nm). It will be also portable and user-friendly. Among all possible art work under consideration, Baroque paintings on canvas and wooden panels were selected as the project case studies.

When photometric stereo technique is used to recover shape and 3D information of an object from multiple images, it is common to assume that the light sources being used are collimated. When the light sources that are being used are actually point light sources, as in robot applications for weld seam inspection or underwater imaging, such an assumption causes significant error. The error increases further when the imaging system is deployed in an attenuating and scattering media. In such situations, a purely analytical solution is not possible. Current work proposes a novel iterative algorithm for recovering shape and 3D information in such situations.

In the field of industrial metrology, there is a rising need for 3D information at a very high resolution for micro -measurements and quality control of transparent objects such as glass bottles (beer, wine, cola, cosmetics, etc.). However, such objects are particularly challenging for optical-based 3D reconstruction methods and systems such as photogrammetry, photometric stereo, structured light scanning, laser scanning, typically resulting in poor metrological performances. Indeed, these methods require the surface of the object to diffusely reflect the incoming light, which is not the case with the glass material where refraction and absorption phenomena do not permit their use. Over the years, various methods have been investigated and developed to avoid the coating (or powdering) treatment often used to make transparent objects opaque and diffusely reflecting. Most of the approaches require either some a priori knowledge of the transparent object or assumptions about how light interacts with the surface. This paper provides a general overview of state-ofthe-art 3D digitization methods for optically non-cooperative surfaces featuring absorption, scattering, and refraction. The paper reviews research works summarizing them into four categories including shape-from-X, direct ray measurements, hybrid, and learningbased approaches. Moreover, we provided some 3D results to better highlight the advantages and disadvantages of each method in practice when dealing with transparent objects.

Our ability to generate new distributions of light has been remarkably enhanced in recent years. At the most fundamental level, these light patterns are obtained by ingeniously combining different electromagnetic modes. Interestingly, the modal superposition occurs in the spatial, temporal as well as spatio-temporal domain. This generalized concept of structured light is being applied across the entire spectrum of optics: generating classical and quantum states of light, harnessing linear and nonlinear light-matter interactions, and advancing applications in microscopy, spectroscopy, holography, communication, and synchronization. This Roadmap highlights the common roots of these different techniques and thus establishes links between research areas that complement each other seamlessly. We provide an overview of all these areas, their backgrounds, current research, and future developments. We highlight the power of multimodal light manipulation and want to inspire new eclectic appr...

Structured illumination increases the spatial bandwidth of optical microscopes. We demonstrate bandwidth extension using a physical grating placed close to the sample. This comprises an array of elongated nanoparticles, whose localized surface plasmon resonance is polarization dependent. By arranging the particle orientation to vary with position the grating can be moved by changing the input polarization. A projected optical grating provides an additional independent mechanism for bandwidth extension. Experimental results showing bandwidth improvement in one direction are presented, and the measures necessary to extend the technique for routine imaging are discussed.

This paper presents the early developments of a recently started research project, aimed at studying from a multidisciplinary perspective an exceptionally well preserved ancient pan flute. A brief discussion of the history and iconography of pan flutes is provided, with a focus on Classical Greece. Then a set of non-invasive analyses are presented, which are based on 3D scanning and materials chemistry, and are the starting point to inspect the geometry, construction, age and geographical origin of the instrument. Based on the available measurements, a preliminary analysis of the instrument tuning is provided, which is also informed with elements of theory of ancient Greek music. Finally, the paper presents current work aimed at realizing an interactive museum installation that recreates a virtual flute and allows intuitive access to all these research facets.

The characterization of commercial 3D scanners allows acquiring precise and useful data. The accuracy of range and, more recently, color for 3D scanners is usually studied separately, but when the 3D scanner is based on structured light with a color coding pattern, color influence on range accuracy should be investigated. The commercial product that we have tested has the particularity that it can acquire data under ambient light instead of a controlled environment as it is with most available scanners. Therefore, based on related work in the literature and on experiments we have done on a variety of standard illuminants, we have designed an interesting setup to control illuminant interference. Basically, the setup consists of acquiring the well-known Macbeth ColorChecker under a controlled environment and also ambient daylight. The results have shown variations with respect to the color. We have performed several statistical studies to show how the range results evolve with respect to the RGB and the HSV channels. In addition, a systematic noise error has also been identified. This noise depends on the object color. A subset of colors shows strong noise errors while other colors have minimal or even no systematic error under the same illuminant.

PurposeInvestigate the use of two imaging‐based methods – coded pattern projection and laser‐based triangulation – to generate 3D models as input to a rapid prototyping pipeline.Design/methodology/approachDiscusses structured lighting technologies as suitable imaging‐based methods. Two approaches, coded‐pattern projection and laser‐based triangulation, are specifically identified and discussed in detail. Two commercial systems are used to generate experimental results. These systems include the Genex Technologies 3D FaceCam and the Integrated Vision Products Ranger System.FindingsPresents 3D reconstructions of objects from each of the commercial systems.Research limitations/implicationsProvides background in imaging‐based methods for 3D data collection and model generation. A practical limitation is that imaging‐based systems do not currently meet accuracy requirements, but continued improvements in imaging systems will minimize this limitation.Practical implicationsImaging‐based ap...

Under a nonparallel illumination condition, fringe patterns projected on an object have unequal fringe spacing that would introduce a nonlinear carrier phase component. This Letter describes a nonlinear carrier removal technique based on a least-squares approach. In contrast with conventional methods, the proposed algorithm would not magnify phase measurement uncertainty, nor does it require direct estimation of system geometrical parameters. The theoretical expression of the carrier phase function on the reference is derived and expanded in a power series. The unknown coefficients in the series are determined by a leastsquares method. By subtracting the calculated carrier phase function from the unwrapped phase map, the phase distribution of the object profile is obtained.

We present a new dense depth acquisition method using 2-D De Bruijn structured light, which is robust to various textures and is able to reconstruct dense depth maps of moving and deforming objects. A 2-D binary De Bruijn pattern is emitted to the target object by an off-the-shelf projector. Fast dynamic programming based stereo matching is performed on images taken from two different views. The depth is obtained by robust least square triangulation. The advantages include that we do not need to take image sequences with different illumination patterns and do not assume that the surface for reconstruction has uniform texture. Experimental results show that shapes can be efficiently obtained in good quality by the proposed approach. We believe that our approach is a good choice in applications of acquiring depth maps for moving scenes with inexpensive equipments.

This paper proposes a method for extracting realistic textures from real-world reference spheres. The BRDF parameters of fundamental materials, as well as a material weight map for the sphere are obtained through a non-linear optimization process. The material weight map can be used as a conventional texture for relighting. With the BRDF models recovered, the real and natural appearances of 3D objects can be reproduced under novel lighting and viewing directions.

We present a new dense depth acquisition method using 2-D De Bruijn structured light, which is robust to various textures and is able to reconstruct dense depth maps of moving and deforming objects. A 2-D binary De Bruijn pattern is emitted to the target object by an off-the-shelf projector. Fast dynamic programming based stereo matching is performed on images taken from two different views. The depth is obtained by robust least square triangulation. The advantages include that we do not need to take image sequences with different illumination patterns and do not assume that the surface for reconstruction has uniform texture. Experimental results show that shapes can be efficiently obtained in good quality by the proposed approach. We believe that our approach is a good choice in applications of acquiring depth maps for moving scenes with inexpensive equipments.

A real-time arc welding robot visual control system based on a local network with a multi-level hierarchy is developed in this paper. It consists of an intelligence and human-machine interface level, a motion planning level, a motion control level and a servo control level. The last three levels form a local real-time open robot controller, which realizes motion planning and motion control of a robot. A camera calibration method based on the relative movement of the end-effector connected to a robot is proposed and a method for tracking weld seam based on the structured light stereovision is provided. Combining the parameters of the cameras and laser plane, three groups of position values in Cartesian space are obtained for each feature point in a stripe projected on the weld seam. The accurate three-dimensional position of the edge points in the weld seam can be calculated from the obtained parameters with an information fusion algorithm. By calculating the weld seam parameter from position and image data, the movement parameters of the robot used for tracking can be determined. A swing welding experiment of type V groove weld is successfully conducted, the results of which show that the system has high resolution seam tracking in real-time, and works stably and efficiently.

This comprehensive report, constituting the second volume in our investigation into Volumetric Photonic Carriers (VPCs), rigorously expands upon the theoretical and architectural frameworks established to overcome the bandwidth and robustness limitations of planar integrated photonics. We propose a paradigm shift where optical signals are modeled not as zero-thickness rays or confined scalar modes, but as "volumetric wave-bodies"-finite-thickness Space-Time Wave Packets (STWPs) with a defined boundary layer (L_u) and field thickness (D). This volumetric model facilitates the design of advanced carrier chips capable of encoding, routing, and processing information across three orthogonal spatial degrees of freedom: radial profile (r), envelope thickness (D), and internal phase structure. Drawing upon the advanced physics of STWPs, where propagation invariance is secured via precise spatio-temporal spectral correlations satisfying \omega = c \sqrt{k_x^2 + k_y^2 + k_z^2} with tailored group velocities (v_g), this study articulates a mechanism for diffraction-resilient on-chip propagation. Furthermore, we integrate volumetric scattering models-specifically Mie theory and the Radiative Transfer Equation (RTE)-to transition scattering from a parasitic loss mechanism into a computational resource for non-linear logic and robust multiplexing. We detail the physical realization of these carriers via multilevel indirect photonic transitions in multimode waveguides, analyze their transport in inhomogeneous media, and propose a novel logic family based on Multimode Interference (MMI) and scattering-mediated reservoir computing. The report concludes with a material and fabrication roadmap, identifying Silicon-Lithium Niobate (Si-LiNbO$_3$) hybrids as the optimal platform for realizing this high-dimensional computing substrate.

Results of researches testify about influence of the grain sizes on resistance to dynamic fracture of metals and alloys. It is noticed that values of spall strength of some ultrafine-grained aluminium alloys, titanium alloys, and copper exceed values of corresponding coarse grained samples. In this work we present results of researches of deformation and fracture of aluminium and magnesium alloys with the nanostructured surface layers at a quasistatic and dynamic loading. The nanostructured surface layers on the specimens were created by surface mechanical attrition treatment. It was revealed that the structured surface layer influences evolution of shear bands in the volume of metal specimens at high velocity tension. The flow stress increasing of the aluminium and magnesium alloys after surface mechanical attrition treatment is connected with a formation delay on mesoscale levels of meso-shear bands and mesoscale damages. Failure of the alloys occurs by shear failure under approxi...