Calibration of optical metrology stereophotogrammetric systems is vital to obtain accurate and precise three-dimensional (3-D) measurements. Despite its importance, the work pipeline of intrinsic and extrinsic camera calibration still remains manually laborious with high technical complexity. The use of a multilayer perceptron neural network to calibrate an optical metrology stereophotogrammetric system utilizing a statistical band-limited pattern projection system is demonstrated. Highly accurate, highly precise, and highly dense 3-D surface reconstructions are obtained solely from homologous corresponding pairs without the need for intrinsic and extrinsic camera calibration. Measurement performance in the typical optical metrology sense, where 3-D measurements were evaluated with respect to length and surface gauges, is shown.

This paper presents a pose estimation method for planar mirror based on a one-dimensional (1-D) target. First, a 1-D target is maneuvered in front of a camera so as to allow the camera to capture several images of both the original and virtual feature points on the target. Next, the normal vector of the mirror and the distance between the mirror and the camera are calculated by a closed-form method. Last, a nonlinear optimization is used to refine the closed-form solution by minimizing the reprojection error of reflection projection. Synthetic data and real experiments show that the proposed method is accurate and reliable. The proposed method is simple and flexible. No prior information about the target motion and camera pose is assumed. A minimum of two nonparallel target positions are required. It is suitable for the pose estimation of planar mirrors, especially when they are in fixed positions. We can find the posture of the fixed camera according to the normal vector of the plane mirror.

Optical sectioning through the numerical reconstruction of digital holographic data with low diffraction noise is the key process for understanding the structure of a recorded three-dimensional object. Recently, this has been enabled by compressive holography, by virtue of sparse signal processing. However, interpretation of the object signal domain has been limited to predefined domains, such as spatial, discrete cosine transform, and wavelet transform domains. We propose a reconstruction technique of compressive Fresnel holographic data using an overcomplete dictionary learned from natural images to enhance the axial resolution of the sectional images. The redundant (overcomplete) dictionary gives sparser and more flexible solutions for representing the two-dimensional images compared to predefined transforms. We provide simulation results to verify the feasibility of our proposed method.

When the interval between transmitted pulses is shorter than the time of flight, it is not straightforward for a lidar to determine the distance uniquely. We present a method that uses varying pulse intervals, constructs a set of tentative point positions for each received pulse, and exploits the clustering of such tentative points to determine the correct distance with high probability. The clustering of true points also helps suppress noise pulses, even in a regime where the number of noise pulses is far greater than the number of true return pulses. It is then possible to use a detection threshold close to the noise level.

A visual localization approach for unmanned aerial vehicles (UAVs) based on the hybrid real-time stereo visual odometry (VO) is presented. The hybrid VO initializes the semidirect visual odometry (SVO) with depth obtained from the stereo camera, which runs with the monocular scheme at 30 Hz. Meanwhile, a feature-based stereo VO runs in a parallel thread to improve the reliability. Considering the robustness of the feature-based VO, we not only are able to estimate the pose of the UAV with the same rate of the incoming images but also to recover the pose of the UAV when the SVO fails. We demonstrate the accuracy and the reliability of the hybrid VO based on a public benchmark dataset and a dataset recorded on our experimental platform. In addition, the autonomous hovering experiment verifies that the estimated result is fast and accurate enough to control the position of the UAV.

Multitarget tracking in video surveillance is challenging because the appearance features of the target are often unreliable in complicated scenes. To solve the problem, we propose a multitarget tracking method using multifeature model with acceleration feature. First, an acceleration feature descriptor is derived from the histograms of the optical flow features according to the background difference. Our approach filters and normalizes the descriptors of consecutive frames to establish acceleration feature models. Then, the multifeature models of target templates are initialized by combining acceleration and multiple spatial feature models. Second, we implement data association based on the tracklet confidence by integrating the acceleration and multiple spatial feature affinities. As a result, the optimal associated pairs between target tracklets and detections are solved by the Hungarian algorithm. Finally, our tracking system updates the multifeature models of target templates online depending on the reliability of the tracklets, and the trajectories of multiple targets are output. Experiments conducted on the challenging multiple object tracking benchmark confirm the effectiveness and superiority of the proposed method.

An analysis is presented of the error introduced into estimates of avalanche photodiode (APD) laser-rangefinder performance by assuming Gaussian distribution of the APD multiplication gain. The amplitude of current pulses emitted by an APD obeys the McIntyre distribution, the tails of which diverge from the Gaussian distribution having the same mean and variance. Because extinction of false alarms requires setting a discrimination threshold far into the tail of an analog photoreceiver’s output distribution, the threshold level required to achieve a specified false alarm rate (FAR) using an APD-based photoreceiver is often not accurately predicted by the standard FAR model of Rice. Characteristics of APD-based photoreceivers are calculated using the McIntyre distribution and are compared with characteristics calculated using the Gaussian approximation.

Three-phase segmentation of solid oxide fuel cell (SOFC) anode image is essential for its microstructure quantitative analysis. A quantum-inspired mixture clustering model is developed for Ni/YSZ anode optical microscopy (OM) images. The proposed mixture clustering model focuses on combining Markov random field (MRF)-based fuzzy logic model with Gaussian mixture model (GMM). In the premise part of fuzzy if-then rules, the clique potential MRF function is defined by multiplication of both prior distributions and fuzzy membership functions with a quantum-inspired adaptive fuzzy degree, which takes prior statistics properties and spatial contextual information of SOFC anode OM image into consideration. In addition, GMM is introduced into the consequent part to design a negative log-prior function as the pixel distance metric. The proposed method has been compared to other state-of-the-art segmentation algorithms on both simulated images and real SOFC anode OM images. The experimental results demonstrate that the proposed method is able to achieve a higher segmentation accuracy with a faster convergence speed, which lays firm foundation for microstructural parameters extraction from SOFC electrodes image datasets.

X-ray framing camera (XFC) is usually used as the principal diagnostic tool in inertial confinement fusion research. The methods on how to precisely calibrate the temporal resolution are important topics for XFC with several picoseconds gate time. A method to measure the temporal resolution of XFCs is proposed based on a high-power subpicosecond ultraviolet laser facility called LLG-ultimate. In our method, series of duraluminium alloy stepped reflective surfaces are used to separate the incident laser beam into sequentially delayed beams with equal size, spacing, and time interval. The temporal resolution of XFC can be measured if the sequentially delayed beams irradiate a gold photocathode microstrip line while the high-voltage pulse transferring along the same area simultaneously. A Fabry–Perot etalon is placed in the light path, improving the probability of synchronization of the voltage pulse and laser pulse. The accuracy of this measurement method can be very high by reducing the time interval of the sequentially delayed beams.

This paper presents the use of the high-speed digital image correlation (DIC) method for measurement of the head injury of a pedestrian in a vehicle–pedestrian collision experiment. Two simultaneous high-speed cameras captured the images of the impact process between the head-simulator and the car hood. The DIC method can achieve comprehensive analysis of the impact and help to reconstruct the impact process, from which not only the velocity, acceleration of the headform impactor, and the head injury criterion (HIC) but also the angular velocity and acceleration can be calculated. The possibility of using DIC to calculate of the neck injury criterion (NIC) is also discussed in this paper. Furthermore, the quantitative calculation of the full-field deformation of the car hood during the collision can also be achieved with the DIC method, which is of great practical value in optimizing automobile design and collision protection. A vehicle–pedestrian collision experiment is carried out, and the comprehensive results show that the DIC method can obtain accurate and comprehensive data in the calculation of human and vehicle collision.

High-power laser devices have stringent requirements for the surface accuracy of optical elements. Continuous polishing is an effective technique for polishing high-precision optical elements. To overcome the problem of poor real-time capability and low accuracy in traditional surface shape monitoring and controlling methods used in continuous polishing, an online monitoring device is developed to monitor the surface shape of the polishing pad. The experimental results of the online measurement are highly consistent with the offline results obtained using an interferometer. The correctness and feasibility of the online monitoring scheme are well validated. Based on the online monitoring device for the surface shape of the polishing pad, we propose a method of automatic control for the surface shape of the polishing pad. This method maintains the flatness of the polishing pad to 0.05λ (λ = 632.8 nm), peak to valley, as measured on a 100-mm monitoring element through computer control.

To achieve nonscanning three-dimensional measurement of microstructures, the optically sectioning mechanism has been used based on the structured illumination microscopy. The key point is to implement nonscanning measurement within a limited axial range according to the measured one-sided linear response curve. One-dimensional transmission grating pattern was projected onto the sample, and optically sectioned images were extracted from three-step phase-shifting manipulation. Compared with the basic and differential confocal microscopy, the described method does not need time-consuming axial scanning, so it greatly improves the measurement efficiency. The results show that the described method is useful in the fields of micromechanics, microelectronics, and biomedicine.

Interferometers using computer-generated holograms (CGHs) have become the industry standard to accurately measure aspheric optics. The CGH is a diffractive optical element that can create a phase or amplitude distribution and can be manufactured with low uncertainty using modern lithographic techniques. However, these CGHs have conventionally been used with visible light and piezo-shifting interferometers. Testing the performance of transmissive optics in the infrared requires infrared CGHs and an infrared interferometer. Such an instrument is used in this investigation, which introduces its phase shift via wavelength-tuning. A procedure on how to design and manufacture infrared CGHs and how these were successfully used to model and measure the Wide-Field Infrared Survey Telescope grism elements is provided. Additionally, the paper provides a parametric model, simulation results, and calculations of the errors and measurements that come about when interferometers introduce a phase variation via wavelength-tuning interferometry to measure precision aspheres.

For large space telescopes, the design of lightweight primary mirrors with an acceptable level of optical performance is a challenge. A parametric optimization method based on topology optimization of the basic configuration of the mirror is proposed. A finite-element model of the mirror is generated with linear shell elements, and the optimal distribution of the material is obtained using the continuum topology optimization technique. The lightweight ribs are grouped according to the results of topology optimization results. The design of experiment method is used to pick out the key factors for parametric optimization. The RMS value of the surface shape error of the mirror and the total mass of the mirror are treated as the objective merit functions, and the first-order natural frequency of the mirror is taken as a constraint for parametric optimization. Results show that the local stiffness of the mirror is significantly affected by the thicknesses of the ribs at the corresponding positions. The optimum mirror design obtained using our optimization method is compared with the initial design, and the comparison shows superior optical performance for the optimized mirror.

We have developed an 8K4K liquid-crystal display (LCD) with diagonal size of 55 inch with the backplane based on an amorphous silicon (a-Si) technology. The 8K4K-LCD has high frame frequency at 120 Hz, which is enabled by a unique technology to compensate the charging voltage of pixels. The achievement of a high resolution of 8K4K including high frame frequency of 120 Hz with a-Si backplanes is ground-breaking for LCDs. Furthermore, a backlight system with laser diode as light source expands the color gamut dramatically. This backlight system enables covering 99% of color space recommended in BT.2020. What is more, the 8K4K-LCD has evolved into a three-dimensional (3-D) display device by attaching a 3-D polarizing film. The vertical viewing angle of the 8K-3D LCD prototype is 8.6 deg at its optimal viewing position set to 1.2 m.

A silicon photonic crystal (PhC)-based structure is proposed to efficiently couple power from two different wavelengths, targeted to the application of an integrable Raman amplifier. The coupler uses two asymmetrical PhC waveguides as input ports which are joined together and the coupled power is directed to a slotted photonic crystal waveguide-based output port. Coupling efficiency and the other performance metrics are evaluated using a three-dimensional full-vector finite-difference time domain simulation method, which is tested for accuracy using some existing experimental structures and corresponding results. The heuristic approach has been adopted to optimize the design for maximizing the coupling efficiency. Dependence of the coupling performance on different design parameters has also been investigated. Simulations exhibit ∼3-dB coupling losses for both arms in a small footprint as small as ∼54  μm2.

The use of visible light communication (VLC) in vehicular communication systems for vehicle safety applications is proposed. The system aims to ensure the communication between a LED-based VLC emitter and an on-vehicle VLC receiver. A traffic scenario is established. Vehicle-to-vehicle (V2V) and infrastructure-to-vehicle (I2V) communications are analyzed. For the V2V communication study, the emitter was developed based on the vehicle headlights, whereas for the study of I2V communication system, the emitter was built based on streetlights. The VLC receiver is based on amorphous SiC technology and enhances the conditioning of the signal enabling to decode the transmitted information. Receivers are located at the rooftop of the vehicle, for I2V communications, and at the tails for V2V reception. Clusters of emitters, in a square topology, are used in the I2V transmission. The information and the ID code of each emitter in the network are sent simultaneously by modulating the individual chips of the trichromatic white LED. Free space is the transmission medium. An on–off code is used to transmit data. An algorithm to decode the information at the receivers is set. The proposed system was tested. The experimental results confirmed that the proposed cooperative VLC architecture is suitable for the intended applications.

This paper investigates the transmission performance of a 1.55-Tb/s Nyquist-wavelength division multiplexing superchannel along with a mixed line rate approach using 4  ×  111  Gb  /  s polarization-multiplexed quadrature phase shift keying (PM-QPSK) and 5  ×  222  Gb  /  s polarization-multiplexed quadrature amplitude modulation (PM-16QAM) formats. The system transmission performance with acceptable bit error rate of 4  ×  10  −  3 is analyzed over standard single mode fiber (SSMF), large effective area fiber (LEAF), and pure silica core fiber (PSCF). It is observed that SSMF increases 45% reach over LEAF, whereas PSCF increases 66% to 84% reach over LEAF for 4.5 b/s/Hz spectral efficiency of the system. Also, spectral efficiency × distance product of 24,750 and 10,350 b/s/Hz.km are obtained for PM-QPSK and PM-16QAM, respectively, which is, to the best of our knowledge, better in comparison with the other existing literatures for single core channel investigations.

Flexible Cu2ZnSn(S,Se)4 (CZTSSe) thin film solar cells are fabricated on titanium substrate by magnetron sputtering with a composition gradient precursor followed by selenization. By varying polishing time with diluted HNO3 and HF from 0 to 90 s, an atomic force microscope shows that the substrate with the minimal surface roughness of 8.6 nm is obtained with the polishing time of 60 s. X-ray diffraction and Raman spectroscopy reveal a highly crystalline structure for the prepared CZTSSe thin films. The gradual grown up grain size of CZTSSe thin film is observed with the increasing polishing time of the substrate. Compared with the CZTSSe solar cells on untreated titanium substrates, a maximum power conversion efficiency enhancement of 56% is achieved for solar cells on polished substrates, which can be attributed to the reduction of recombination at the interface and isolated defects in devices. External quantum efficiency curves show an enhancement in the visible and near-infrared region after optimizing substrate roughness. On the basis of Ti substrate with a minimum roughness, the percentage reduction of efficiency is found to exhibit the minimum value of 5% after bending for five times.

A flexible optical filter based on tunable arrayed waveguide grating (AWG) with triangular-like model electrodes is designed on lithium niobate-on-insulator. Using the electro-optic effect of lithium niobate, the 10  −  3 increase of the waveguides refractive index could be achieved with a 4.348-V effective external voltage. The tunable range of the central wavelength of AWG can reach 3.8 nm and the 3-dB bandwidth is about 0.43 nm.