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A thin-structured light projection system with simple setup is proposed and applied to small-height measurement. In this system, the design of structured light pattern is carried out on the computer. The structure, color, geometric dimension, motion mode, projection brightness, contrast, and other attributes of the pattern can be edited easily. The optical system with zoom function is designed, which can output thin-structured-light fringe with a minimum width of 10 μm. The camera and microscope are used to construct a vision system, which is used to capture the pattern of structured light. The three-dimensional (3D) shape reconstruction is realized by analyzing the pattern of structured light. The results show that this system can project a small width of thin-structured light pattern, which is very suitable for 3D shape reconstruction of microscopic objects with the small-height of tens of microns to hundreds of microns.

Complex vector light fields have become a topic of late due to their exotic features, such as their non-homogeneous transverse polarisation distributions and the non-separable coupling between their spatial and polarisation degrees of freedom (DoF). In general, vector beams propagate in free space along straight lines, being the Airy-vector vortex beams the only known exception. Here, we introduce a new family of vector beams that exhibit novel properties that have not been observed before, such as their ability to freely accelerate along parabolic trajectories. In addition, their transverse polarisation distribution only contains polarisation states oriented at exactly the same angle but with different ellipticity. We anticipate that these novel vector beams might not only find applications in fields such as optical manipulation, microscopy or laser material processing but also extend to others.

The teaching programming mode and offline programming mode of welding robot are essential parts in today’s manufacturing industry. However, these modes can’t meet the automation requirements and adaptive ability of welding robot. To achieve 3D path acquisition of weld seam for robot autonomous programming, a fast and accurate offline 3D seam extraction method is proposed based on monocular structured light sensor. In this method, gray code and phase-shift code raster images are projected to the workpiece, and the 3D coordinates of the weld are calculated by collecting the workpiece images with raster patterns. The path fitting of robot is completed by polynomial fitting method. The novel monocular structured light sensor used by this paper has compact structure and small volume, and can adapt to a variety of welding working scenes. The combination of gray code and phase shift code makes the measurement accurate and fast, and achieves the effect of full resolution decoding. The experimental results show that the proposed method can complete the task of 3D weld extraction and path fitting, which has the characteristics of high efficiency and strong robustness.

Existing projector-camera calibration methods typically warp keypoints from a camera image to a projector image using estimated homographies and often suffer from errors in camera parameters and noises due to imperfect planarity of the calibration target. This article proposes a practical and robust projector-camera calibration system that explicitly deals with these challenges. First, a graph-theory-based correspondence algorithm is built on top of a color-coded spatial structured light (SL) pattern. Such SL correspondences are then used for a coarse projector-camera calibration. To gain more robustness against noises from an imperfect planar calibration board, we develop a bundle adjustment algorithm to jointly optimize the estimated projector-camera parameters and the correspondences’ coordinates. Moreover, our system requires only one shot of an SL pattern for each calibration board pose, which is much more practical than multishot solutions. Comprehensive experimental validation is conducted on both synthetic and real data sets, and our method clearly outperforms the existing methods in all experiments. For the benefit of the society, a practical open-source software with graphical user interface (GUI) of the developed system is publicly available at https://github.com/bingyaohuang/single-shot-pro-cam-calib . Note to Practitioners —The proposed method is motivated by two challenges in industrial structured light (SL) system calibration: 1) robustness against imperfect planarity of the calibration target and 2) the number of SL projections per pose. In many industrial SL-based 3-D reconstruction systems, the calibration accuracy greatly affects the reconstruction reliability. Our SL calibration system explicitly deals with calibration target’s imperfect planarity and thus outperforms the existing methods in terms of system accuracy. Another advantage of our SL calibration system is single-shot-per-pose, allowing fast recalibration and reducing the decoding error due to slight pattern misalignment in multishot methods [37] . In addition, we release the open-source calibration software with a graphical user interface (GUI), with which calibration and sparse 3-D reconstruction can be easily performed without any further instructions. Moreover, considering the complex calibration environment and setup, we make the camera and projector imaging parameters, such as exposure, brightness, and contrast, adjustable through widgets and preview. Finally, a limitation of our color-coded SL system is its sensitivity to environment lighting and target texture. This problem may be solved by projector photometric compensation [16] , [18] , [19] , [39] .

Dynamic control over the conduction band electrons of a semiconductor is a central technological pursuit. Beyond electronic circuitry, flexible control over the spatial and temporal character of semiconductor currents enables precise spatiotemporal structuring of magnetic fields. Despite their importance in science and technology, the control of magnetic fields at the micrometre spatial scale and femtosecond temporal scale using conventional electromagnets remains challenging. Here, we apply structured light beams to interfering photoexcitation pathways in gallium arsenide to sculpt the spatial and momentum configuration of its conduction band population. Programmable control over several hundred micrometre-scale current elements is achieved by manipulating the wavefronts of an optical beam using a spatial light modulator, enabling vast flexibility in the excited current patterns. Using this platform, we demonstrate dynamic optoelectronic interconnects, circuits for spatially tailored magnetic fields and magnetic field lattices. Structured beams of light are used to engineer conduction band populations and pattern currents. Using the approach, dynamic optoelectronic interconnects and other applications are demonstrated.

Vectorial holography has gained a lot of attention due to the promise of versatile polarization control of structured light for enhanced optical security and multi-channel optical communication. Here, we propose a bifunctional metasurface which combines both structural color printing and vectorial holography with eight polarization channels towards advanced encryption applications. The structural colour prints are observed under white light while the polarization encoded holograms are reconstructed under laser illumination. To encode multiple holographic images for different polarization states, a pixelated metasurface is adopted. As a proof-of-concept, we devise an electrically tunable optical security platform incorporated with liquid crystals. The optical security platform is doubly encrypted: an image under white light is decrypted to provide the first key and the corresponding information is used to fully unlock the encrypted information via projected vectorial holographic images. Such an electrically tunable optical security platform may enable smart labels for security and anticounterfeiting applications., The authors present a bi-functional metasurface, combining structural color printing observed under white light and polarization encoded It is appropriate. vectorial holography. A pixelated design is used encode multiple holographic images, and they demonstrate an electrically tunable optical security platform.

Mobile omnidirectional structured light vision is increasingly used in scene perception and robot navigation. A wide range of information is obtained by means of the vision system by only one image and laser image features are detected and extracted easily and quickly. In this paper a novel calibration method for mobile omnidirectional camera based on structured light is presented. Firstly, a set of parallel laser planes is emitted on the walls of corridor as auxiliary targets by structured light and intersects with wall orthogonally. Secondly, the constraint relationship is analyzed between the vanishing points in fisheye images and intrinsic parameters of imaging model. Finally, effects of the laser stripes’ interval and the angle between the wall which contains laser stripes and ground on calibration results are evaluated. Compared to Scaramuzza method, the calibration method shows its superiority in terms of both feasibility and efficiency. The method with the characteristic of self-calibration since the planar target is replaced by actively projected laser stripes. The result illustrates that our method has the advantages of simple and feasible operation, but result is effective and accurate. The calibration parameters are independent of the laser stripes’ interval and the angle between the wall and ground. Therefore, the method of the mobile omnidirectional structured light vision presented in this paper can be applied to many areas.

Image-based relighting, projector compensation and depth/normal reconstruction are three important tasks of projector-camera systems (ProCams) and spatial augmented reality (SAR). Although they share a similar pipeline of finding projector-camera image mappings, in tradition, they are addressed independently, sometimes with different prerequisites, devices and sampling images. In practice, this may be cumbersome for SAR applications to address them one-by-one. In this paper, we propose a novel end-to-end trainable model named DeProCams to explicitly learn the photometric and geometric mappings of ProCams, and once trained, DeProCams can be applied simultaneously to the three tasks. DeProCams explicitly decomposes the projector-camera image mappings into three subprocesses: shading attributes estimation, rough direct light estimation and photorealistic neural rendering. A particular challenge addressed by DeProCams is occlusion, for which we exploit epipolar constraint and propose a novel differentiable projector direct light mask. Thus, it can be learned end-to-end along with the other modules. Afterwards, to improve convergence, we apply photometric and geometric constraints such that the intermediate results are plausible. In our experiments, DeProCams shows clear advantages over previous arts with promising quality and meanwhile being fully differentiable. Moreover, by solving the three tasks in a unified model, DeProCams waives the need for additional optical devices, radiometric calibrations and structured light., Source code and supplementary material at: https://github.com/BingyaoHuang/DeProCams

For efficiency surveying fishery resource, the authors developed the scanner which measure the target shape at once time. The scanner based on the structured light method irradiated the laser patter coded on De Bruijn for high resolution the measurement under water. The evaluation experiment results showed that the scanner can measure the target shape less than 1.4 % error for the measurement range., 2021 IEEE/SICE International Symposium on System Integration (SII 2021), January 11-14, 2021, Iwaki, Fukushima, Japan (Virtual Conference)

The seam tracking method by using structured light is widely used in the automatic welding process. Most of the noise can be filtered out by a narrow-band optical filter whose center wavelength is the same as the structured light. However, it still suffers from light noise caused by sparks and fumes when the structured light is getting close to the welding pool. This limitation of the structured-light based method is inherent because light noise caused by the welding process has a wide spectrum and couldn’t filter out by the optical filter. To circumvent this problem, we proposed a seam tracking method that can modulate the intensity of the structured light at a high frequency by an acoustic-optic modulator (AOM) and extract the modulated frequency from multiple seam images by Fourier transformation. As the frequency of noises such as sparks is random and different from the modulated frequency, the proposed method can remove these noises in the frequency domain directly. We demonstrated the robustness of this method by detecting seam in noisy welding conditions.

Seam feature point acquisition is the premise of the intelligent welding process such as initial point guiding and seam tracking. However, conventional seam feature point acquisition methods based on geometric feature have shortcomings of poor flexibility and robustness. In this article, a seam feature point acquisition method based on efficient convolution operator (ECO) and particle filter (PF) is proposed, which could be applied to different weld types and could achieve fast and accurate seam feature point acquisition even under the interference of welding arc light and spatter noises. First, a structured light vision sensor is developed to acquire welding image. Second, the ECO algorithm is adopted to track the seam region and acquire seam feature point during gas metal arc welding process. Third, the state and measurement equations of the weld seam position are established, and PF is applied to improve seam feature point acquisition accuracy. Finally, a welding experiment system is built and a series of seam feature point acquisition experiments of butt joint, lap joint, and fillet joint are carried out to validate the performance of the proposed method. The experiment results demonstrate that the processing speed of the proposed method could reach up 35 Hz, and the seam feature point acquisition errors are smaller than 0.15 mm, which could meet the real-time and accuracy requirement for subsequent initial point guiding and seam tracking.

Polarization plays a key role in science; hence its versatile manipulation is crucial. Existing polarization optics, however, can only manipulate polarization in a single transverse plane. Here we demonstrate a new class of polarizers and wave plates—based on metasurfaces—that can impart an arbitrarily chosen polarization response along the propagation direction, regardless of the incident polarization. The underlying mechanism relies on transforming an incident waveform into an ensemble of pencil-like beams with different polarization states that beat along the optical axis thereby changing the resulting polarization at will, locally, as light propagates. Remarkably, using form-birefringent metasurfaces in combination with matrix-based holography enables the desired propagation-dependent polarization response to be enacted without a priori knowledge of the incident polarization—a behaviour that would require three polarization-sensitive holograms if implemented otherwise. Our work expands the use of polarization in the design of multifunctional metasurfaces and may find application in tunable structured light, optically switchable devices and versatile light–matter interactions. Using a metasurface that allows shaping of the polarization state of a light beam independently at each point of space along its propagation direction, longitudinally variable polarization optical components are demonstrated, inspiring new directions in structured light, polarization-switchable devices and light–matter interaction.

Fast optical 3D inline inspection sensors are a powerful tool to advance factory automation. Many of these visual inspection tasks require high speeds, high resolutions, and repeatability. Stereo vision, photometric stereo, light sectioning, and structured light are the most common principles for inline imaging in the several micrometers to sub-millimeter resolution range. Selecting the correct sensor principle can be challenging as manufacturers’ datasheets frequently use different values to describe their systems and do not stick to proposed characterizations defined by the “Initiative Fair Data Sheet” or the VDE/VDI standards. With the help of standardized parameters, this paper aims to compare four different measurement principles, namely AIT’s own single sensor light field camera method, a structured light pattern projector, a laser triangulation sensor, and a stereo camera system, with an approximate field of view of $100\times 100$ mm. We demonstrate simple yet meaningful experiments to determine lateral resolution, temporal noise, and calibration accuracy to enable an objective system comparison. Additionally, the reproduction of small surface structures and an overall performance on a challenging test object is evaluated. Results show that the measurement principles partly serve different application areas. The provided methods will help end users to select the correct sensor for specific applications.

Structured light depth imaging offers a high precision of 3D measurement for applications to industrial modeling, inspection, reproduction and archiving. Despite recent progress, however, structured light depth imaging has yet to settle the trade-off between the number of captured 3D points and that of unwanted outliers, in particular, when a low reflectance surface is mixed with projector and camera shades. This paper presents an approach to solving such trade-off by accurately mapping projector and camera shades under the presence of a low reflectance surface. Unlike conventional approaches relying mostly on pattern intensity for detecting shades, the proposed approach first identifies stripe boundaries legitimate in terms of the projected pattern sequence. Based on the list of legitimate boundaries identified, then, the gaps in pixel and boundary addresses are analyzed to define the respective projector and camera shades, possibly, in the presence of address juxtaposition. Experimental results show that the proposed approach shows superior performance in shade detection as well as outlier removal compared to the state-of-the-art approaches, maximizing the number of captured 3D points while minimizing that of unwanted outliers.

A method is proposed for the formation and transmission of 3D holographic images, based on forming a 2D holographic signal by subtracting the carrier spatial frequency from it and thereby compressing the holographic information for fast transmission over a standard radio channel in real time. The data on 3D structure of the holographic object is recorded using coherent and incoherent radiation, in which an equivalent of an object hologram is obtained using the structured light techniques, that can be transmitted over a distance as a 2D frame, similar to a hologram with eliminated redundancy. Such transmission of 3D holographic information is similar to the single sideband transmission used in radio engineering, with the subtraction of its carrier frequency and possible subsequent introduction of any carrier at a distance from the holographic object. It can be applied for problems of holographic TV and 3D augmented reality. The article provides examples of this technology used for creating holographic images of a real 3D portrait of a person and transmitting it over a Wi-Fi channel. 3D images formed in the IR range are shown. This technology is easily adaptable to the tasks of integrating images of different parts of the electromagnetic radiation spectrum. Possible applications of the method in 3D instrumentation are proposed.

Structured light (SL) based three-dimensional (3D) imaging technology has been widely employed in many fields of computer vision. However, currently available SL based depth sensors are sensitive to imaging noises, which severely limits the performance of subsequent advanced vision tasks. In this letter, we propose a robust and practical SL illumination pattern coding method based on epipolar geometry. The proposed pattern can effectively alleviate coding redundancy in traditional global random speckle SL patterns and make the stereo matching more robust to noise. Meanwhile, this coding strategy supplies sufficient non-local similar blocks, which inspires us to propose a uni-direction block-stacking 3D filtering algorithm to further improve the 3D imaging quality. To verify the proposed algorithms, we developed a prototype using the off-the-shelf projector and camera. Both simulation and real scene experimental results show that the proposed methods can achieve high-quality 3D imaging performance under different noisy conditions.

The possibility to achieve unprecedented multiplexing of light-matter interaction in nanoscale is of virtue importance from both fundamental science and practical application points of view. Cylindrical vector beams (CVBs) manifested as polarization vortices represent a robust and emerging degree of freedom for information multiplexing with increased capacities. Here, we propose and demonstrate massively-encoded optical data storage (ODS) by harnessing spatially variant electric fields mediated by segmented CVBs. By tight focusing polychromatic segmented CVBs to plasmonic nanoparticle aggregates, record-high multiplexing channels of ODS through different combinations of polarization states and wavelengths have been experimentally demonstrated with a low error rate. Our result not only casts new perceptions for tailoring light-matter interactions utilizing structured light but also enables a new prospective for ultra-high capacity optical memory with minimalist system complexity by combining CVB’s compatibility with fiber optics.

An omnidirectional vision system consisting of a fisheye camera and structured light projector has its own distinctive advantages toward other vision systems. A vision system provides a wide range of information by one single capture. Moreover, the laser feature is easy to detect and extract from the given image for further analysis. In order to obtain the reliable results, the vision system must be calibrated. There have been improvements toward calibration techniques for vision systems with laser illumination. However, these techniques are not suitable for an omnidirectional vision system in a particular configuration. Motivated by the abovementioned problem, this article presents a novel omnidirectional vision system with laser illumination in a flexible configuration and a method for its extrinsic calibration. Flexible configuration means that both camera and laser plane are no longer parallel to the floor. The calibrated vision system is evaluated experimentally by using simulated and real data to demonstrate that the proposed calibration method is more robust and provides a higher measurement accuracy.

In automatic non-destructive testing (NDT), weld bead tracking is usually performed outside. However, irregular weld boundaries, unconstrained illumination, and rough metal surfaces can cause noise, which increases the difficulty of seam tracking. In this paper, a method of parallel structured light (PSL) sensing based on deep learning and information fusion is proposed to detect weld lines. First, a camera is used to capture the laser stripe image projected by the PSL on the weld bead. Then, a MobileNet-SSD deep learning model is trained to extract the regions of interest (ROIs) to de-noise the laser stripe image. Finally, the weld line is obtained by fusing information from multiple weld boundaries.

The optical three-dimensional (3D) measurement technique based on the laser stripe has become increasingly important in additive manufacturing, which is necessary to extract the laser stripe accurately. In welding, the wrong laser stripe centers due to the high-brightness noise are usually extracted, which causes serious measurement error. In this paper, a laser stripe extraction algorithm based on spatiotemporal noise regularization (SNR) is proposed, which calculates the noise weight of each pixel in time dimension and suppresses the high-brightness noise in space dimension. The proposed algorithm contains four novel steps to achieve accurate and fast laser stripe extraction when the laser stripe is influenced by the high-brightness noise. Meanwhile, an online welding 3D measurement system is constructed based on double-line structured light, which can achieve online 3D measurement in additive manufacturing. Experimental analysis verifies its effectiveness and accurateness.

Modern beam shaping techniques have enabled the generation of optical fields displaying a wealth of structural features, which include three-dimensional topologies such as Möbius, ribbon strips and knots. However, unlike simpler types of structured light, the topological properties of these optical fields have hitherto remained more of a fundamental curiosity as opposed to a feature that can be applied in modern technologies. Due to their robustness against external perturbations, topological invariants in physical systems are increasingly being considered as a means to encode information. Hence, structured light with topological properties could potentially be used for such purposes. Here, we introduce the experimental realization of structures known as framed knots within optical polarization fields. We further develop a protocol in which the topological properties of framed knots are used in conjunction with prime factorization to encode information., Beam shaping methods can generate optical fields with nontrivial topologies, which are invariant against perturbations and thus interesting for information encoding. Here, the authors introduce the realization of framed optical knots to encode programs with the conjoined use of prime factorization.

This review offers the reader some of the achievements of modern optical metrology. Over the past decades, it has become possible to make a leap in the basic approaches of metrology from the nano to the femto, approaching the pico level of measurements. Control of nano (micro) particle motion by an optical field and their use for testing complex optical fields; ultra-precise determination of the optical parameters of both solid and liquid and gas-like substances by optical methods; the tiny metrology of the phase shift of orthogonally polarized beams and the determination of their degree of mutual coherence, by interference methods and many other, are proposed for consideration in this paper. Optical metrology, which is provided by three-dimensional polarization distributions of optical fields, where structured light plays a special role; by using femtosecond lasers, and much more, demonstrates the prospects of optical methods in modern measuring systems.

With the rapid development of artificial intelligence and intelligent manufacturing, the traditional teaching-playback mode and the off-line programming (OLP) mode cannot meet the flexible and fast modern manufacturing mode. Therefore, the intelligent welding robots have been widely developed and applied into the industrial production lines to improve the manufacturing efficiency. The sensing system of welding robots is one of the key technologies to realize the intelligent robot welding. Due to its unique characteristics of good robustness and high precision, the structured light sensor has been widely developed in the intelligent welding robots. To adapt to different measurement tasks of the welding robots, many researchers have designed different structured light sensors and integrated them into the intelligent welding robots. Therefore, the latest research and application work about the structured light sensors in the intelligent welding robots is analyzed and summarized, such as initial weld position identification, parameter extraction, seam tracking, monitoring of welding pool, and welding quality detection, to provide a comprehensive reference for researchers engaged in these related research work as much as possible.

This article proposes an analytical method of computing distorted laser sheet of a laser line scanner and compensating it. In this article, a distortion model of laser sheet generated from a laser line scanner with large fan angle is derived from physical principles to achieve accurate depth perception even around its edges on which significant depth estimation errors occur in existing algorithms. From a laser beam incident obliquely on a contact surface of two cylindrical lenses, a curved laser sheet is expressed in terms of the nonzero incident angle by the laws of geometrical optics. From the mathematical model of the distorted laser sheet, the incident angle is estimated through an optimization technique and then its estimate is used for depth computation. It is shown through simulations and experiments that the proposed distortion model enables a proper compensation scheme and hence the distortion-compensated depth estimation errors are reduced all over the range of interest, specially much around the both side edges of the laser sheet. Quantitatively in comparison to the compensation-free method, the depth estimation error is improved from 225 to 28 mm on average and from 1781 to 187 mm for worst-case scenarios near edges of a laser sheet.

The use of three-dimensional (3D) optical instruments to measure soft tissue facial characteristics is increasing, but systematic assessments of their reliability, practical use in research and clinics, outcome measurements, and advantages and limitations are not fully established. Therefore, a review of the current literature was performed on the reliability of facial anthropometric measurements obtained by 3D optical facial reproductions as compared to conventional anthropometry or other optical devices. The systematic literature search was conducted in electronic databases following the PRISMA guidelines (PROSPERO registration: CRD42018085473). Overall, 815 studies were identified, with 27 final papers included. Two meta-analyses were conducted. Tested devices included conventional cameras, laser scanning, stereophotogrammetry, and structured light. Studies measured living people or inanimate objects. Overall, the optical devices were considered reliable for the measurement of linear distances. Some caution is needed for surface assessments. All instruments are suitable for the analysis of inanimate objects, but fast scan devices should be preferred for living subjects to avoid motion artefacts in the orbital and nasolabial areas. Prior facial landmarking is suggested to improve measurement accuracy. Practical needs and economic means should direct the choice of the most appropriate instrument. Considering the increasing interest in surface-to-surface measurements, fast scan devices should be preferred, and dedicated protocols devised.

Structured light is a widely employed approach for profile measurement in active stereo vision. Recent methods have developed learning-based single pattern structured light systems and unstructured light stereo vision systems. However, their methods require additional cameras or a diffractive optical element. In addition, the calibration methods of the learning-based structured light systems require a large number of images, while the stereo vision method cannot detect the blocked region. Classically, a digital projector is treated as a pseudocamera, and the stripe pattern is employed to measure the depth. However, an additional pattern is employed to calibrate the camera-projector system in the stripe-based method. In this paper, 24 reliable features and a novel calibration algorithm are proposed. With the proposed calibration algorithm, the stripe patterns are calibrated without additional patterns, and with the proposed RGB features, the number of encoded columns is enlarged significantly. Experiments demonstrate that the proposed method is accurate and robust.

The uneven reflective metal surface has great influence on the high-precision measurement of the structured light 3-D shape. By analyzing the laser scattering and reflection models, a set of light stripe center’s subpixel extraction methods which has strong robustness is proposed. The method first cuts off the influence of the uneven fixed background by using the difference image method to process the bright field and the dark field. Then, the regional growth statistics method is used to eliminate the influence of random laser speckle noise, and then the gray-gravity method is used to obtain the coarse center of the laser stripe. The Sobel operator is used to obtain the gradient vector of the stripe pixel point, and then the normal direction field of the light stripe is obtained. The normal direction field vector is taken as the direction to find the $5\times5$ neighborhood of the coarse light stripe’s center, and then the gray-gravity method is reused to determine the center position of the laser stripe in the normal line direction; the pixel coordinates of the subpixel level are obtained by using bilinear interpolation. The experimental results show that the method can effectively eliminate the interference of flash point noise and has strong robustness. The detection error of the stripe is less than 0.1 pixels, which ensures the system measurement accuracy. Compared with other methods, the system’s resolution can reach 0.02 mm.

Orbital angular momentum (OAM) from lasers holds promise for compact, at-source solutions for applications ranging from imaging to communications. However, conjugate symmetry between circular spin and opposite helicity OAM states (±l) from conventional spin–orbit approaches has meant that complete control of light’s angular momentum from lasers has remained elusive. Here, we report a metasurface-enhanced laser that overcomes this limitation. We demonstrate new high-purity OAM states with quantum numbers reaching l = 100 and non-symmetric vector vortex beams that lase simultaneously on independent OAM states as much as Δl = 90 apart, an extreme violation of previous symmetric spin–orbit lasing devices. Our laser conveniently outputs in the visible, producing new OAM states of light as well as all previously reported OAM modes from lasers, offering a compact and power-scalable source that harnesses intracavity structured matter for the creation of arbitrary chiral states of structured light. A metasurface laser generates orbital angular momentum states with quantum numbers reaching l = 100. Simultaneous output vortex beams, with Δl as great as 90, are demonstrated in the visible regime.

We developed an ultracompact three-dimensional (3D) endoscopic scanner that utilizes an electromagnetic-based stereo imaging method (EBSIM) for shape measurements. The method was used to investigate the applicability of imaging fiber optics to featureless surface profiles in confined spaces. The EBSIM is combined with a coherent flexible fiber bundle for structured light pattern projection to ensure that the scanner head can achieve a final diameter of merely 3.4 mm and a baseline length of 1.4 mm. Compared with the existing methods, the scanner is designed to have a minimum focal distance of 2 mm to address the intraoperative evaluation problem. System registration and complex calibration are unnecessary before measurements, and the scanner can be operated from any position and orientation. The scanner is capable of acquiring 3D videos at 30 frames per second. The experimental results demonstrate the feasibility of using the EBSIM for 3D surface profile measurements of featureless cylindrical surfaces. A prototype scanner is presented in extensor, and the average error of a series of known depth distances is found to be equal to 0.15 mm. The implementation shows that the 3D scanner can be potentially applied for endoscopic inspections and intraoperative evaluations in minimally invasive surgeries.

Conventional pain assessment methods such as patients’ self-reporting restrict the possibility of easy pain monitoring while pain serves as an important role in clinical practice. Here we report a pain assessment method via 3D face reading camera assisted by dot pattern illumination. The face reading camera module (FRCM) consists of a stereo camera and a dot projector, which allow the quantitative measurement of facial expression changes without human subjective judgement. The rotational offset microlens arrays (roMLAs) in the dot projector form a uniform dense dot pattern on a human face. The dot projection facilitates evaluating three-dimensional change of facial expression by improving 3D reconstruction results of non-textured facial surfaces. In addition, the FRCM provides consistent pain rating from 3D data, regardless of head movement. This pain assessment method can provide a new guideline for precise, real-time, and continuous pain monitoring.

The vector optical beam with longitudinally varying polarization during propagation in free space has attracted significant attention in recent years. Compared with traditional vector optical beams with inhomogeneous distribution of polarization in the transverse plane, manipulating the longitudinal distribution of polarization provides a new dimension for the expansion of the applications of vector optical beams in volume laser machining, longitudinal detection, and in vivo micromanipulation. Two theoretical strategies for achieving this unique optical beam are presented in the way of constructing the longitudinally varying phase difference and amplitude difference. Relevant generation methods are reviewed which can be divided into the modulation of complex amplitude in real space and the filtering of the spatial spectrum. In addition, current problems and prospects for vector optical beams with longitudinally varying polarization are discussed.

Three-dimensional (3D) measurement based on structured light, as a non-contact, active, and high-precision measurement technology, is widely applied in the diverse fields of industrial detection, face recognition, reverse engineering, and so on. We adopted an adjustable grating-stripe coding as the dynamic structured-light mode, which can continuously cover the entire measured surface to guarantee high accuracy. A one-axis resonant-mode MEMS mirror combined with a linear laser was used to project the desired adjustable grating stripes, leading to a miniaturized module size. To make the scanning angle of the MEMS mirror matching the intensity distribution of the linear laser, we further introduced a single-chip microcomputer (STM32) to receive the feed-back signals from MEMS mirror, and synchronously controlled the laser power with corresponding function relationship output. Here, the MEMS mirror could provide a resonant frequency of 1.15 kHz, a scanning optical angle of ±30°, a feed-back scanning-angle resolution of 0.05°, and a reflected mirror size of 3 mm-diameter circle, respectively. Also, the laser source could generate a line width of 70 μm at a 300 mm focused distance. To decrease the error in the energy amplitude of each cycle of the structured light stripes, the empirical mode decomposition (EMD) was used to perform principal component analysis and recombination of the structured light stripes. In addition, total harmonic distortion (THD) is used to evaluate the quality of structured light stripes. Finally, the structured light based on the scanning of the MEMS mirrors exhibits a good sinusoidal stripes and high refresh rate, implying high adaptivity for the 3D reconstruction.

Intrinsic projector calibration is essential in projection mapping (PM) applications, especially in dynamic PM. However, due to the shallow depth-of-field (DOF) of a projector, more work is needed to ensure accurate calibration. We aim to estimate the intrinsic parameters of a projector while avoiding the limitation of shallow DOF. As the core of our technique, we present a practical calibration device that requires a minimal working volume directly in front of the projector lens regardless of the projector's focusing distance and aperture size. The device consists of a flat-bed scanner and pinhole-array masks. For calibration, a projector projects a series of structured light patterns in the device. The pinholes directionally decompose the structured light, and only the projected rays that pass through the pinholes hit the scanner plane. For each pinhole, we extract a ray passing through the optical center of the projector. Consequently, we regard the projector as a pinhole projector that projects the extracted rays only, and we calibrate the projector by applying the standard camera calibration technique, which assumes a pinhole camera model. Using a proof-of-concept prototype, we demonstrate that our technique can calibrate projectors with different focusing distances and aperture sizes at the same accuracy as a conventional method. Finally, we confirm that our technique can provide intrinsic parameters accurate enough for a dynamic PM application, even when a projector is placed too far from a projection target for a conventional method to calibrate the projector using a fiducial object of reasonable size.

The nonlinear errors caused by the gamma effect seriously affect the measurement accuracy of phase-measuring profilometry systems. We present a novel robust end-to-end pattern optimization technology for phase-height mapping. This method generates standard sinusoidal patterns on the reference plane on a camera image instead of on a projection image by optimizing the projection image, which can avoid phase errors due to phase conversion from projector to camera. The pixel set mapping is achieved by chessboard calibration; then the projection image is optimized with the multiscale optimization method and the dislocation optimization method based on proportional integral derivative control. The experiments show that the proposed method can effectively avoid the influence of nonlinear effect and achieve high-quality three-dimensional measurement.

Line-structured light has been widely used in the field of railway measurement, owing to its high capability of anti-interference, fast scanning speed and high accuracy. Traditional calibration methods of line-structured light sensors have the disadvantages of long calibration time and complicated calibration process, which is not suitable for railway field application. In this paper, a fast calibration method based on a self-developed calibration device was proposed. Compared with traditional methods, the calibration process is simplified and the calibration time is greatly shortened. This method does not need to extract light strips, thus, the influence of ambient light on the measurement is reduced. In addition, the calibration error resulting from the misalignment was corrected by epipolar constraint, and the calibration accuracy was improved. Calibration experiments in laboratory and field tests were conducted to verify the effectiveness of this method, and the results showed that the proposed method can achieve a better calibration accuracy compared to a traditional calibration method based on Zhang’s method.

we discuss state-of-the-art techniques to generate on-demand structured light and their application to quantum light-matter interactions, especially in the generation and control of charged-particle beams and X-ray light sources.

Nonlinear multiplexing holography emerges as a powerful tool to produce structured lights at new wavelengths. In this work, we propose and experimentally demonstrate an angle-multiplexing nonlinear holography in an angular noncritical phase-matching configuration. In experiment, various types of structured light beams, such as vortex beam, Airy beam and Airy vortex beam, are simultaneously output at second-harmonic waves along different paths. Because of the large angular acceptance bandwidth of noncritical phase-matching, one can achieve high conversion efficiency of angle-multiplexing nonlinear holography. Our method has potentially applications in high-capacity holographic storage and security encryption.

Multi-axis Laser Engraving Machine Tools (LEMT) are widely used in precision processing of parts with complex surface. The accuracy of kinematic model and parameter measurement are the key factors determining the processing quality of LEMT. In this paper, a kinematic model of multi-axis LEMT was established based on Homogeneous Transformation Matrix (HTM). Two types of unknown parameters, linkage parameters and positioning parameters, were measured in the presented model. Taking advantage of the characteristics of laser processing, this paper proposed a rapid measurement method of linkage parameters by combining the machine tool motion with the laser marking action. For positioning parameters, this study proposed a non-contact measurement method based on structured light scanner, which can obtain the translation values and the rotation values from the Workpiece Coordinate System (WCS) to the Basic Coordinate System (BCS) simultaneously. After the measurement of two kinds of parameters of a multi-axis LEMT was completed, the processing of a spatial curve was performed and the average contour error was controlled at 15.1 μm, which is sufficient to meet the project requirements.

Image thresholding is a challenging task due to its sensitivity to environmental variations and degradation in the quality of the captured image. Although many image thresholding methods have been introduced, most of them require the fine tuning of a thresholding parameter that is not suitable for single-shot structured light (SSSL) based projector-camera applications. In this paper, we introduce a locally adaptive thresholding method with automatic parameter selection based on the local statistics of the distinct image partitions. For assessing the proposed scheme, we introduce an evaluation that relies on mapping SSSL patterns between the camera and projector spaces. Experimental results demonstrate the effectiveness of the proposed technique by maintaining the thresholding accuracy of the baseline method, without the need to fine tune the obtained thresholding parameter or any noticeable change in the qualitative results.

Structured Light (SL) patterns generated based on pseudo-random arrays are widely used for single-shot 3D reconstruction using projector-camera systems. These SL images consist of a set of tags with different appearances, where these patterns will be projected on a target surface, then captured by a camera and decoded. The precision of localizing these tags from captured camera images affects the quality of the pixel-correspondences between the projector and the camera, and consequently that of the derived 3D shape. In this paper, we incorporate a quadrilateral representation for the detected SL tags that allows the construction of robust and accurate pixel-correspondences and the application of a spatial rectification module that leads to high tag classification accuracy. When applying the proposed method to single-shot 3D reconstruction, we show the effectiveness of this method over a baseline in estimating denser and more accurate 3D point-clouds.

Background: Depth sensor is an essential element in virtual and augmented reality devices to digitalize users' environment in real time. The current popular technologies include the stereo, structured light, and Time-of-Flight (ToF). The stereo and structured light method require a baseline separation between multiple sensors for depth sensing, and both suffer from a limited measurement range. The ToF depth sensors have the largest depth range but the lowest depth map resolution. To overcome these problems, we propose a co-axial depth map sensor which is potentially more compact and cost-effective than conventional structured light depth cameras. Meanwhile, it can extend the depth range while maintaining a high depth map resolution. Also, it provides a high-resolution 2D image along with the 3D depth map. Methods: This depth sensor is constructed with a projection path and an imaging path. Those two paths are combined by a beamsplitter for a co-axial design. In the projection path, a cylindrical lens is inserted to add extra power in one direction which creates an astigmatic pattern. For depth measurement, the astigmatic pattern is projected onto the test scene, and then the depth information can be calculated from the contrast change of the reflected pattern image in two orthogonal directions. To extend the depth measurement range, we use an electronically focus tunable lens at the system stop and tune the power to implement an extended depth range without compromising depth resolution. Results: In the depth measurement simulation, we project a resolution target onto a white screen which is moving along the optical axis and then tune the focus tunable lens power for three depth measurement subranges, namely, near, middle and far. In each sub-range, as the test screen moves away from the depth sensor, the horizontal contrast keeps increasing while the vertical contrast keeps decreasing in the reflected image. Therefore, the depth information can be obtained by computing the contrast ratio between features in orthogonal directions. Conclusions: The proposed depth map sensor could implement depth measurement for an extended depth range with a co-axial design. Keywords: Depth map sensor, 3D camera, Controlled aberration

In this paper, a three-dimensional (3D) shape measurement method based on structured light field imaging is proposed, which contributes to the biomedical imaging. Generally, light field imaging is challenging to accomplish the 3D shape measurement accurately, as the slope estimation method based on radiance consistency is inaccurate. Taking into consideration the special modulation of structured light field, we utilize the phase information to substitute the phase consistency for the radiance consistency in epi-polar image (EPI) at first. Therefore, the 3D coordinates are derived after light field calibration, but the results are coarse due to slope estimation error and need to be corrected. Furthermore, the 3D coordinates refinement is performed based on relationship between the structured light field image and DMD image of the projector, which allows to improve the performance of the 3D shape measurement. The necessary light field camera calibration is described to generalize its application. Subsequently, the effectiveness of the proposed method is demonstrated with a sculpture and compared to the results of a conventional PMP system.

Weld bead measurement and weld quality inspection are important parts in industrial welding. In this paper, a structured light vision sensor is developed to achieve on-line weld bead measurement and weld quality inspection. Firstly, a structured light vision sensor with a narrow-band optical filter is developed to reduce welding noises such as arc lights and splashes. Secondly, the weld bead type identification algorithm including image pre-processing, baseline extraction, and weld bead classification is proposed to classify filling weld bead and capping weld bead. Thirdly, feature extraction algorithms of filling weld bead and capping weld bead are presented to obtain corresponding feature points. Combining the image coordinates of feature points with structured light vision model, the weld bead size could be obtained and the weld quality could be evaluated. Finally, many weld bead measurement and weld quality inspection experiments are conducted. Experimental results demonstrate that the developed structured light vision sensor and proposed methods could achieve satisfactory performance for weld quality inspection.

In the article the design specifics of the diffused lighting system of premises based on LEDs is being considered, which is determined by such problems of the designing LEDs lighting systems: formation of multiple shadows using groups of open LEDs in luminaires direct light; the need for vision protection of the users from the direct light of LEDs as the high light efficiency and miniature sizes of modern LEDs lead to the significant luminous flux in one point.In the process of work it was defined that the promising solution to the problems outlined above is using the diffused lighting, which is considered to be one of the most comfortable in terms of avoidance of disability glare and discomfort glare. However, the diffused lighting has such a disadvantage as monotony. As a result, the study suggests ways to avoid the monotony of the light environment which is formed by the diffused lighting: the main one is the enrichment of the shape of the luminaires and lighting systems through the use of complex and structured light diffusing surfaces to form them; the additional one is the enriching the colour of the light due to the nuanced differences in colour temperature of separate luminaires among the variety of those, which are in the general lighting system.The theoretical position outlined above are practically applied in: the series designed shades (PU 112427, PU 130594), which construction is based on regular (hexahedron or cube, octahedron, icosahedron) and semi-regular (cuboctahedron, rhombicuboctahedron) polyhedrons; the series LED luminaires for lighting of shades (PU 128832) and for forming the systems of diffused lighting (PU 121313). Also, it was found, that contemporary design of the luminaires with diffused light have frequent use OLED on a rigid or flexible lining as light sources.

Developing of additive manufacturing and the use of additive technologies at all stages of the product life cycle entails the necessity of developing methods providing control of their characteristics. Here we consider application of the optical measurement procedures to the objects of complicated shape. Products manufactured by the methods of additive technologies may have defects such as delamination, starved joint, porosity, warp, stress-strain state, roughness, etc. We present the devices designed and developed on the principles of interference, structured light and holography at the «VNIIOFI» Federal State Unitary Enterprise to identify the defects in the products of additive technologies. The advantages and shortcomings of the interference microscope, scanner-profilometer, and shearograph are examined with regard to the control of the aforementioned types of geometric defects. The special feature of the contact-free methods is the possibility of control of different types of materials: metals and dielectrics, transparent, reflective, scattering and composite materials. The results of experimental study aimed at detection of the surface and subsurface defects are presented. Interferograms and results of phase reconstruction are presented both for reflective and transparent objects. Defects of the refractive index of the microcavity made of an optical fiber were detected. Metrological characteristics of optical devices for non-destructive testing of products are estimated. Standards for calibration and graduation of the optical devices considered in the study were manufactured and tested. The use of specially developed standards makes it possible to use these methods both for qualitative assessment of the objects of complicated shape and flaw detection and for quantitative estimation of their characteristics.

This paper studies the laser vision-based automatic trajectory planning technology for spatial intersecting joint weld. Firstly, the mathematical model of T-type off-axis non-groove intersecting joint is established, and the welding seam characteristics of the intersecting joint are analyzed. Secondly, a triangular pseudo-rotation feature pixel detection algorithm based on monocular structured light vision is proposed to realize the rapid extraction and location of spatial intersecting joint weld. Then, a laser vision-based calibration method for the workpiece coordinate system of the T-type intersecting joint is proposed, the relationship between intersecting joint workpiece coordinate system and robot base coordinate system is established, and the trajectory equation is obtained. At last, a searching discrete of chord error interpolation control algorithm is proposed to automatically discrete and plan welding torch gesture data. Experiments show that the technology can achieve higher precision location and better intersecting joint weld trajectory planning, and realize high-quality automatic weld of intersecting joint.

The development of an optical contact instrument for measuring the geometric shape of aerodynamic profiles on blades of small power wind turbines is presented. The instrument uses the triangulation principle, where a structured line laser pattern is projected onto the surface of one of the faces of the blade under test, a camera captures the image of the line and is processed to interpret the distorted form of the projected line. A linear sweep of the instrument makes it possible to measure the profile in another section of the blade. Comparison and evaluation results of two symmetric profiles of the NACA 0012 family are presented, one manufactured in a 3D printer and the other one is a metal profile AF104 of a subsonic wind tunnel. Additionally, three sections of a blade with profile FX 63‐137 of a 1.5 kW wind turbine were evaluated. An aerodynamic analysis shows a reduction in the lift coefficient and in the efficiency of the aerodynamic profile, as well as an increase in the drag coefficient. The sensitivity of the instrument is 0.1 mm on the Z‐axis.

We present a novel high-speed sensor for simultaneously measuring the three-dimensional (3D) shape and the surface temperature of fast moving objects. The 3D topography is obtained by a structured light sensor based on GOBO projection of aperiodic sinusoidal patterns in the visible range of light. At the same time, a high-speed long-wave infrared camera records the temperature distribution on the object surface. We show first promising 3D thermography measurement results of an inflating airbag, a basketball player, and the crushing of a metal tube conducted at a 3D frame rate of 1 kHz.

Fluorescence microscopy has long been a valuable tool for biological and medical imaging. Control of optical parameters such as the amplitude, phase, polarization, and propagation angle of light gives fluorescence imaging great capabilities ranging from super-resolution imaging to long-term real-time observation of living organisms. In this review, we discuss current fluorescence imaging techniques in terms of the use of tailored or structured light for the sample illumination and fluorescence detection, providing a clear overview of their working principles and capabilities.

Single-shot three-dimensional (3D) shape measurement techniques have attracted extensive researches, as they are suitable for dynamic measurement. In this study, a cost-effective single-shot structured light system (CES-SLS) is proposed for 3D shape measurement by using a color camera and a normal projector. With the aid of two planar mirrors and an isosceles right-angle mirror, a single color camera functions as a binocular vision. A single-shot color random speckle pattern (CRSP) is used to encode the object by the normal projector. The dense corresponding points (DCP) are derived by the spatial-temporal correlation of RGB image subsets instead of the spatial correlation of gray image subsets in the conventional method. An inverse compositional Gaussian Newton (IC-GN) iteration method with the second-order shape function is then introduced to find the sub-pixel corresponding points (CP). Furthermore, a geometrical 3D recovery method is presented to calculate the 3D point by minimizing the re-projection error. The experimental results demonstrate the comparative advantages of the proposed CES-SLS against the system using a single-shot random speckle pattern (RSP) and the curve fitting sub-pixel method in the aspects of measurement accuracy and noise robustness. In addition, the re-projection error of each 3D point from the geometrical method is smaller than that of the conventional mid-point.