Editor-in-Chief Mike Eismann writes about supplemental materials in scientific journals.

Although several optical techniques have been developed to overcome the resolution limit in microscopy, the optical imaging of subwavelength features is still a real challenge (difficulty to build, or risks of phototoxicity). Microsphere-assisted microscopy has recently made super-resolution imaging accessible to scientists. An easy-to-implement optical setup to perform full-field and contactless super-resolution measurements using transparent microspheres is presented. We show that this rather simple imaging system (in comparison with the usual optical nanoscopes) makes it possible to achieve a lateral resolution of 200 nm in air and, thus, to visualize nanostructured media and biological elements.

This guest editorial introduces the Special Section on Situation Awareness in Degraded Visual Environments.

Research, development, test, and evaluation of flight deck interface technologies is being conducted by NASA to proactively identify, develop, and mature tools, methods, and technologies for improving aviation safety of new and legacy vehicles operating in the Next Generation Air Transportation System (NextGen). One specific area of research was the use of small head-worn displays (HWDs) to serve as a possible equivalent to a head-up display (HUD) for commercial aircraft. A simulation experiment was conducted to evaluate if the HWD can provide an equivalent level of performance to a HUD. Airline flight crews conducted simulated approach and landing operations during low visibility operations. The results showed that there were no statistical differences in flight crews’ performance in terms of flight technical error suggesting that the HWD may serve as an equivalent display to the HUD. Further, the HWD may have several advantages over a HUD making its adoption an attractive alternative for commercial flight deck implementation. Technical hurdles remain to be overcome for complete display equivalence including, most notably, the end-to-end latency of the HWD system. The results and conclusions taken from the results of the high fidelity simulation experiment are described and offer future research directions.

High on the list of desired capabilities for warfighters noted at the 2008 Fort Benning “Lab Day” was the development of combat protective eyewear with lenses that would instantly change the amount of light they transmit, based on incident lighting conditions. We reviewed the investigation regarding the effect of four different protective spectacle lens designs [clear, standard sunglass, step filter (SF), and electro-optical (EO)] on a soldier’s ability to rapidly transition from bright to dim environments. The dependent measures were selected to specifically permit the findings to be evaluated in both clinical and operational terms. A multifactorial analysis of variance revealed global statistically significant interactive effects regarding the viewing lenses, subject marksmanship, and subject visual acuity. The subjective preference ratings indicated a clear preference for the SF and the EO eyewear over no eyewear, the Authorized Protective Eyewear List (APEL) clear eyewear, and the APEL sun eyewear. Operational performance results while wearing either of these two optical devices (the SF eyewear and the electronic eyewear) are equally effective. Consequently, the fielding of either transition strategy provides equal acceptance and utility by the soldiers using this transitional gear.

In military aviation helmet-mounted displays (HMDs) or head-up displays, light from the ambient scene is added to the symbology to create a complex mixture of colors, textures, and luminances. In the case of color mixing, the color of the transparent symbology symbols shifts toward the colors of the ambient background that the symbology overlays. The magnitude of the shift depends on the contrast of the symbology against the background. Against a darkened background, there is negligible shifting of symbology color. However, during daylight conditions, symbology colors shift toward the background hue. Using CIELAB distances between symbology colors as a measure of color discrimination, confusion contrast thresholds are calculated for each of seven symbology colors mixed with fourteen different background colors over a wide range of luminance contrasts. Confusion contrast thresholds are calculated for color normal and color vision deficient (CVD) observers. For CVD observers, colors are filtered using the RGB coefficients developed by Machado. Using the color discrimination data presented here as well as previous assessments of HMD luminance requirements based on observer ratings of the quality of symbology, luminance guidelines for see-through displays are presented, which correct for a calculation error made previously.

The macular pigment (MP) is an accumulation of the carotenoids lutein, zeaxanthin, and mesozeaxanthin in the central retina. These are derived from dietary sources. MP absorbs light in the 400- to 520-nm range. Consequently, the MP is a spectral filter over the photoreceptors, reducing the effects of internally scattered light and attenuating the short wavelength component of natural sunlight. The average MP optical density (OD) is about 0.2 to 0.6 log units depending on the sample population, whereas the range of MPOD is reportedly 0 to 1.5 log units. Some people can increase their MPOD by increasing their consumption of lutein, zeaxanthin, and mesozeaxanthin, and this may be important for vision in degraded visual environments (DVE). Specifically, nutritional interventions and dietary supplements have produced statistically significant enhancements under laboratory conditions in visual tasks, such as visibility through haze, low contrast target detection, contrast sensitivity, glare resistance and recovery, photostress recovery, dark adaptation, mesopic sensitivity, and enhanced reaction times. The question is whether these enhancements are operationally meaningful or not. The present paper begins to address the question by modeling MPOD effects on the visibility to low contrast photopic and scotopic targets seen under a range of DVE over realistic distances that incorporate atmospheric filtering. Specific model parameters include luminance, target contrast, spectral content, and distance. The model can be extended to estimate the efficacy of MPOD effects on target detection, discrimination, and standoff distances.

The scattering of light in fog is a complex problem that affects imaging in many ways. Typically, imaging device performance in fog is attributed solely to reduced visibility measured as light extinction from scattering events. We present a quantitative analysis of resolution degradation in the long-wave infrared regime. Our analysis is based on the calculation of the modulation transfer function from the edge response of a slant edge blackbody target in known fog conditions. We show higher spatial frequencies attenuate more than low spatial frequencies with increasing fog thickness. These results demonstrate that image blurring, in addition to extinction, contributes to degraded performance of imaging devices in fog environments.

Increasing the pilot’s situational awareness is a major goal for the design of next-generation aircraft cockpits. A fundamental problem is posed by the pilot’s out-the-window view, which is often degraded due to adverse weather, darkness, or the aircraft structure itself. A common approach to this problem is to generate an enhanced model of the surroundings via aircraft-mounted sensors and databases containing terrain and obstacle information. In the helicopter domain, the resulting picture of the environment is then presented to the pilot either via a panel-mounted display or via a see-through head-worn display. We investigate a third method for information display. The concept—called Virtual Cockpit—applies a nonsee-through head-worn display. With such a virtual reality display, advantages of established synthetic and enhanced vision systems can be combined while existing limitations can be overcome. In addition to a theoretical discussion of advantages and drawbacks, two practical implementation examples of this concept are shown for helicopter offshore operations. Two human factors studies were conducted in a simulation environment based on the game engine Unity. They prove the general potential of the Virtual Cockpit to become a candidate for a future cockpit in the long term.

A method of improving situation awareness in a degraded environment based on a distributed array made up of quantum hyperentangled sensors is considered. This approach greatly reduces the effect of interference, noise, and signal loss mechanisms. It offers significant increases in the performance range for sensor or communications applications. It simultaneously improves resolution, signal-to-interference ratio (SIR), diminishes time-on-target (TOT), information transfer rates, etc. Each hyperentangled system consists of a single hyperentangled signal and single ancilla photon. The effect of noise in every single photon state as well as loss is included. The signal photon will experience classical loss and each ancilla photon will suffer a low level of loss. Forming an array offers further advantage of an increased reduction in measurement time. Let d be the number of single photon states, i.e., the dimensionality of the underlying Hilbert space resulting from hyperentanglement. It is shown mathematically that in the large d limit, that different members of the array do not interfere with each other, implying they can be put close together. This permits an enormous reduction in the measurement time, i.e., the TOT. Each hyperentangled system making up the array receives a factor of d improvement in the signal-to-noise ratio, SIR, and a factor of d reduction in measurement time.

Color-coded symbology has the potential to enhance the performance of people using head-up and head-mounted displays, as well as head-worn, optical see-through, augmented-reality displays. The distinguishing feature of these displays is the optical combiner that presents symbology overlaid upon the forward natural scene. The presence of high-ambient daylight can desaturate the symbol colors, making them difficult to identify. This is especially true for blue symbols that become faint and colorless in even moderate daylight. We defined a set of colors for testing based on color coding conventions, color symbology research, and results from our previous testing. Included in this set was blue-prime, a color that lies between blue and cyan. We then conducted an experiment to test the visibility of color symbols, the naming of symbol colors, and the legibility of color text mixed with daylight. Results were statistically analyzed and modeled using color-difference formulae. Additional experiments were conducted to test the effects of increasing the luminance of blue symbols and shifting primary colors to increase the luminance. Specific attention was given to the symbol color blue, where the alternative color blue-prime was shown to always outperform the color blue while retaining the color name blue.

The increasing number of microunmanned aerial vehicles (MUAVs) is a rising risk for personal privacy and security of sensitive areas. Owing to the highly agile maneuverability and small cross section of the MUAV, effective countermeasures (CMs) are hard to deploy, especially when a certain temporal delay occurs between the localization and the CM effect. Here, a reliable prediction of the MUAV flight behavior can increase the effectiveness of CMs. We propose a pose estimation approach to derive the three-dimensional (3-D) flight path from a stream of two-dimensional intensity images. The pose estimation in a single image results in an estimation of the current position and orientation of the quadcopter in 3-D space. Combined with flight behavior model, this information is used to reconstruct the flight path and to predict the flight behavior of the MUAV. In our laboratory experiments, we obtained a standard deviation between 1 and 24 cm in a five-frame prediction of the 3-D position, depending in the actual flight behavior.

In a gene sequencing system, ensquared energy is an important parameter for base-calling software. Nevertheless, the displacement between wafer and camera, which is caused by vibration and position error of the wafer stage while photographing, will decrease the image quality and further influence the ensquared energy. Our study established the relationship model between the dynamic factors and ensquared energy. Several experiments were carried out on the sequencing platform. The results revealed that the ensquared energy has a linear relationship with the location standard deviation of dynamic errors. In the sequencing platform described, if the ensquared energy value required is larger than 65%, the location standard deviation should be controlled below 140 nm. Furthermore, the ensquared energy calculated by a DNA nanoballs image is accordant with the conclusion in the meantime. The performance parameters of the wafer stage and vibration suppression could be drawn up reasonably.

Electron-multiplying charge-coupled device (EMCCD) has the characteristic of single photon response under a low-light environment. It is proposed that the reconstruction algorithm of low-light integral imaging by EMCCD reconstruct the details of the target under a low-light environment. First, the algorithm acquires a series of element images by EMCCD integral imaging system. Second, as grayscale values of different element images of the same target meet Poisson distribution, the algorithm introduces a local self-adaptive factor and derives the posterior probability distribution of grayscale value of the target. Finally, it calculates the new element images by posterior probability distribution and reconstructs the target image by updated element images. Experimental results show that the peak signal-to-noise ratio of the reconstructed image by the proposed method is 4.3 dB higher than that of conventional Bayesian estimation. Considering the reconstructed image quality and computational complexity, the overall quality of the reconstructed image is the best when using the 7  ×  7 neighborhood range to calculate the local self-adaptive factor in the algorithm. Experimental results show that the proposed algorithm greatly improves the quality of the reconstructed image of the target under low-light environment.

In underwater wireless optical communications (UWOC), low signal-to-noise ratio (SNR) and baseline drift problems caused by the attenuation of seawater channels and limited bandwidth of the transceiver system deteriorate the quality of the received signal and result in a higher bit error rate (BER). The transmission characteristics of underwater optical communication systems are analyzed, and a scheme combining length-limited coding and improved energy detection is proposed to improve the detection performance under low SNR and baseline drift. Experiments show that the scheme can improve the performance of the intensity-modulated direct-detection nonreturn-to-zero UWOC system. The BER performance of 3  ×  ^{10  −  4} can be achieved at SNR  =  5.14  dB, which lays the foundation for long-distance UWOC.

We propose an optimized initial weight scheme in a quantum-inspired neural network for compressing computer-generated holograms (CGHs). An optimized initial weight generation strategy is applied to accelerate the compression process. The pixel blocks’ complexity distribution of CGH is analyzed, and the parallel quantum neural network structure is used to compress the image pixel blocks. A deep convolutional neural network with residual learning is also adopted for improving the quality of the reconstructed image. The experimental results have shown that the compression iterations are reduced by using the optimized initial weight, and the reconstructed image quality of the compressed CGH is improved using the parallel quantum-inspired neural network structure and the deep convolutional neural network with residual learning.

Visual tracking plays a significant role in computer vision. Although numerous tracking algorithms have shown promising results, target tracking remains a challenging task due to appearance changes caused by deformation, scale variation, and partial occlusion. Part-based methods have great potential in addressing the deformation and partial occlusion issues. Owing to the addition of multiple part trackers, most of these part-based trackers cannot run in real time. Correlation filters have been used in target tracking owing to their high efficiency. However, the correlation filter-based trackers face great problems dealing with occlusion, deformation, and scale variation. To better address the above-mentioned issues, we present a scale adaptive part-based tracking method using multiple correlation filters. Our proposed method utilizes the scale-adaptive tracker for both root and parts. The target location is determined by the responses of root tracker and part trackers collaboratively. To estimate the target scale more precisely, the root scale and each part scale are predicted with the sequential Monte Carlo framework. An adaptive weight joint confidence map is acquired by assigning proper weights to independent confidence maps. Experimental results on the publicly available OTB100 dataset demonstrate that our approach outperforms other state-of-the-art trackers.

An infrared (IR) sensor model is validated using experimentally derived peak pixel signal-to-noise ratio (SNR) versus range for detection of either an unresolved or a resolved unmanned aerial vehicle (UAV) target. The model provided estimates the time-averaged peak SNR values for the ranges used in the field collection. A mid-wave infrared (MWIR) camera and a long-wave infrared (LWIR) camera provided the measured data. Commercially available UAVs are flown along a line from the cameras to a clear sky region for background. A laser range finder measures the range at seven stopping points along the path. The data result in five ranges of unresolved target information for the MWIR camera and in four ranges for the LWIR camera. We provide details for using the data collected from the model to match the cameras used in the field collection. Also, the processing used to extract peak SNR versus range from imagery is presented.

Display technology is the main source for humans to obtain information and entertainment. Increased display screen size is a trend, whether on mobile phone or television, and projection display has become increasingly popular in achieving large screen displays. Previous projection display systems have used a traditional light bulb which cannot be modulated, so the power of the display device is constant and the contrast of the display device can only be improved by controlling the size of the aperture in the light path. With the appearance of solid-state light sources, i.e., lasers, the luminance of the light source can be modulated according to the image content so that the power of the light source can be reduced and the dynamic contrast can be improved simultaneously. A method to modulate the power of the laser light source on a frame-to-frame basis in response to the input image data is shown. An ultrahigh contrast is achieved with the laser display. A dynamic contrast of greater than 100,000:1 can be achieved, and the average power consumption of the laser TV can be reduced by about 20% with typical video source material.

Iris center estimation is widely used in various computer vision applications, such as driving monitoring and eye tracking. However, accurately locating iris centers in low-resolution images remains a significant challenge. We propose a robust, accurate, and real-time iris center localization method based on cascaded regression, weighted averaging, and weighted snakuscule. In the proposed scheme, a powerful cascaded regressor is trained to detect the eye contours and iris centers, which is further refined by the inverse-intensity weighted averaging method. Further, an improved weighted snakuscule is proposed to fine-tune the detected iris centers. The performance of the proposed method is tested on publicly available databases, namely BioID, GI4E, and Talking Face Video. Accuracies of 96.58%, 98.30%, and 96.12%, respectively, are achieved at a normalized error <0.05. Compared with the state-of-the-art methods, the proposed scheme increases the overall accuracy by 3.72% at a normalized error <0.025 and achieves the highest accuracy on the BioID and Talking Face Video databases. The total execution speed is 33 fps. The superior performance of the proposed method proves its usefulness for real-time application with improved robustness and accuracy.

Direct-detection Doppler LIDAR has been demonstrated for its high temporal and spatial resolution in atmosphere wind detection from troposphere to stratosphere. As Doppler frequency is a relative value, the zero point drift would lead to wind velocity error. So the zero Doppler correction was necessary for high-accuracy wind measurement. We analyzed the reasons that would cause zero point drift and demonstrated a designed Fabry–Pérot interferometer and front optics to measure Rayleigh scatter laser and emitted laser frequency in the meantime. Wind observation experiments were demonstrated in XinJiang, China, and the measured wind profile coincided well with radiosonde results.

A computational method is proposed to measure the aberration of a lens using an extended ptychographic iterative engine. By reconstructing the entering wavefront φ_in and exiting wavefront φ_ex of the lens under detection from two sets of diffraction patterns iteratively, the lens aberration can be easily extracted by subtracting the phase of φ_in and theoretical lens phase from the phase of φ_ex. Since it needs no extra reference beam and high quality optics, this suggested method has advantages of simplicity in structure, high accuracy, and low requirement on working environment, and it is free of the aberration of other optical elements in the experimental system, indicating it can find lots of applications in lens evaluation.

The phase obtained in the interferogram is generally not continuous real phase information. Therefore, a phase larger than 2π will have a phase jump called wrapped phase. The traditional phase unwrapping algorithm usually requires a large amount of computation, and in reality, phase unwrapping is often a complex and morbid inverse problem due to factors such as speckle noise, random perturbations, low modulation, and phase discontinuity, and the processes of unwrapping of some algorithms depend on the path chosen. Therefore, it is difficult to obtain an accurate absolute phase under actual conditions. To improve the accuracy of the absolute phase, a phase unwrapping algorithm based on the transport-of-intensity equation with two-wavelength illumination is proposed. The experimental results illustrate that the proposed method not only improves the accuracy of absolute phase but also holds a good antinoise performance.

We describe the design and ground-based performance of the two-color calibration lamp for the Michelson Interferometer for Global High-Resolution Thermospheric Imaging (MIGHTI) instrument on the NASA Ionospheric Connection (ICON) satellite. The calibration lamp assembly contains radio frequency excited krypton and neon lamps, which generate emission lines at 557 and 630 nm, respectively, and which are used to monitor thermal drifts in the two MIGHTI Doppler asymmetric spatial heterodyne interferometers. The lamps are coupled to two mixed optical fiber bundles that deliver the calibration signals to the two MIGHTI optical units. The assembly starts reliably, consumes <8  W, and has passed environmental testing for the ICON satellite. The total mass of the lamp assembly is 1.8 kg. Special features of the assembly and its implementation are described along with results of life tests.

Because the sensitivity of shearography is determined by its shearing direction, aeolotropic defects could be difficult to detect in nondestructive testing (NDT) using a digital shearography system with a single shearing direction. We report an adjustable aperture multiplexing spatial phase-shift digital shearography system for simultaneous measurement of displacement derivatives in three directions. By setting the aperture parameters properly, three spatial carrier frequencies are produced within the speckle pattern, and the information of three interferograms can be separated in the frequency domain. Phase maps of the three shearograms can be obtained by applying a windowed inverse Fourier transform, which enables simultaneous measurement of the displacement derivative. The system is suitable for NDT with a dynamic load. The capability of the triple-directional spatial phase-shift digital shearography system is described by theoretical discussions as well as experiments.

Robot-guided laser ablation for surgical applications potentially offers many advantages compared to by-hand mechanical tissue cutting. However, given that tissue can be rough and/or uneven, ablation quality can be compromised if the beam waist deviates significantly from the target tissue surface. Therefore, we present a method that uses optical coherence tomography (OCT) for dynamic refocusing of robot-guided surgical laser ablation. A 7-DOF robotic manipulator with an OCT-equipped optical payload was used to simulate robotic guided laser osteotomy. M-mode OCT feedback is used for continuous surface detection to correct for axial deviations along the ablation path due to surface nonuniformity. We were able to show that such a correction scheme could maintain the beam waist within the depth of focus for surface variation as aggressive as 45 deg with feed rates up to 1  mm  /  s. Strategies for implementation in surgical and nonsurgical applications are examined.

We propose a noncontact method for measuring the cone angle of an axicon. A microscanning stage moves the axicon being tested while a Fizeau interferometer is recording the scanning interferograms. The cone angle is measured accurately with the axial moving distance and the phase change calculated from interference fringe counting. Numerical analysis discusses the influence of standard deviation of the interference fringe count and the standard deviation of the scanning distance. Three methods for systematic error calibration are also proposed. This approach can measure both concave and convex axicons with a cone angle in the range of 96.4 deg to 170 deg. The measurable diameter of the axicon exceeds 100 mm. The spatial distribution of cone angle can be obtained with a resolution from 300  μm to 1 mm. The theoretical measurement accuracy is better than 10″ when the scanning distance is 1000  μm, and the positioning error is <10  nm. Experiments have been carried out to prove the feasibility of the proposed method, a 140-deg convex axicon is measured, and the measurement repeatability is ∼6^″.

The accuracy of the visible light positioning (VLP) system is improved by using regression-based and interpolation-based approaches. These approaches are mixed with the received signal strength in both linear and nonlinear least squares techniques. The simplicity of the model is the key point, where a highly accurate VLP system with only one equation “interpolation” is used instead of many complex equations. Gaussian noise and reflections up to three bounces with high reflectivity are the source of noise. In addition, the strength of the methods is studied by changing some affecting parameters. In a previous work, we introduced the regression-based approach in VLP-based systems with one reflection. Here, we extend the work with three reflections, leading to an increase in noise to examine system robustness. The approaches are compared to the traditional ones, and show a remarkable enhancement, e.g., the average error has been improved by 67%.

Magnetorheological finishing (MRF) is usually used to remove subsurface defects (SSD) of workpieces to improve the laser-induced damage threshold due to its low stress. Although MRF has been widely used to remove surface defects and SSD, the evolution and removal mechanism of surface scratches under MRF have not been fully elucidated. A systematic study is conducted on the scratch removal process and removal ability of MRF. First, an experimental study on the removal of scratches with different depths is carried out, and the effect of the scratch depth on the removal efficiency is analyzed. Second, when the scratches are removed, the processing is performed in two directions: parallel and perpendicular to the scratch. Thereby, the relationship between the scratch removal efficiency (SRE) and the processing direction is analyzed. Finally, based on the scratch removal process and mechanism, an innovative method for efficient scratch removal using a sacrificial layer is proposed. The effectiveness of this method is verified by experiments. This method can significantly improve the SRE of MRF.

We present a numerical investigation of the study of the Michelson interferometer by exploring the potential of such a device to act as an all-optical logic gate when excited with ultrashort pulses of 100 fs. The input pulse is controlled by a pulse-position modulation (PPM) modulator, which has the role of controlling the value and direction of the temporal displacement from the variation of the PPM modulating factor. We present the study on the signal-to-noise ratio (SNR), which served as the basis for constructing a merit figure of the studied logic gates in order to verify their performance. We considered pulse propagation under the influence of dispersive effects, as well as the nonlinear effects in the propagation regime with no loss for the input pulses. It was possible to implement the OR logic operation in at least one interval of the modulation adjustment parameter in each of the distinct pumping power regimes, thus obtaining a total of nine intervals of OR logic gate. The situation with the best SNR  =  29.36  dB, for the suggested logic gate operation, was found at the power of 150 kW with the modulation adjustment parameter ε  =  43  fs. Numerical studies were done from the coupled–coupled equations solved using the fourth-order Runge–Kutta method. The implementation of fully optical logic gates tends to revolutionize digital systems in the field of data storage, such as optical memory, “replacement” of electronic circuits among other applications.

For an indoor localization system based on visible light communication (VLC) by using received signal strength technique, visible light signals used for estimating the distances between each localization target and reference nodes suffer from non-line-of-sight (NLoS) signal propagation, which could introduce large errors in estimating their locations. Both line-of-sight (LoS) link and NLoS link are taken into account in a noisy VLC channel, and thus the NLoS signal and ambient noise are the sources of localization error. Ricean K factor is introduced to evaluate the relation between the value of NLoS signal and the quality of localization in the proposed system. Analytical expressions for the distance measurement error and the upper bound of localization error are derived by using the least squares method. The simulation results show that the estimation of localization error matches the distribution of Ricean K factor in the noisy overall link. The environmental parameters that can be used to decrease the value of Ricean K factor are also discussed in the simulations, which provide the reference of parameters for building an experimental demonstration of a VLC indoor localization system. A comparison is conducted with the previous works to demonstrate the good performance of our scheme.

Ultrawideband (UWB) signals have low allowable transmission powers. To enhance the coverage and capacity of UWB signals, a cost-efficient solution for the access network has been proposed and simulated. The access network is based on gamma–gamma free-space optical channel model, which is employed between the central unit and the four different carrier-free radio access units (RAUs). All-optical generation and transmission of UWB signals at a rate of 1.5 Gbps to each RAU are demonstrated. Bit error rate results are obtained to observe the performance of the UWB signals received at the mobile stations. The proposed architecture requires minimum deployment cost and gives acceptable bit error rate results.

At present, most of the research work aims to optimize the technological parameters of laser derusting under the condition of without damaging the metal substrate. The surface microstructure and corrosion resistance of the 35# carbon steel metal substrate were investigated by selecting an appropriate laser power density without affecting laser derusting effect. The surface microstructure and topography were characterized by scanning electron microscope, metallographic microscope, and white light interferometer. X-ray diffraction method was used to determine the surface structure of original new samples and derusting samples. The microhardness of the cross-section of the metal substrate after laser derusting was measured by Vickers microhardness tester with the load of 0.098 N. The polarization curves and galvanic corrosion measurement curves were used to characterize the corrosion resistance of laser derusting samples and original new samples. It is found that a heat-affected layer (HAL) of about 25-μm depth was formed on the surface of the metal substrate after laser derusting, which was composed of ferrite and pearlite-like. And the hardness of the HAL was increased. Comparing with the original new samples, the corrosion resistance of the derusting samples was significantly improved due to the change of the surface microstructure. As a common structural steel, 35# carbon steel is easily corroded. It really has great significance if its corrosion resistance could be improved while the rust layer on the surface is removed by the laser derusting technology.

In strong oceanic turbulence, we investigate the bit error rate (BER) performance of underwater wireless optical communication links by employing phase shift keying subcarrier intensity modulated Gaussian laser beam at the transmitter and positive-intrinsic-negative photodetector having finite sized aperture at the receiver. Using the extended Huygens–Fresnel principle, which is conventionally used to analyze the optical beam propagation through turbulence, we evaluate the optical intensity and corresponding signal power over the receiver aperture. Gamma–gamma statistical model for the received intensity is adopted due to strong oceanic turbulence and the required aperture averaged scintillation for this model is obtained by the use of asymptotic Rytov theory. In our performance investigation, we consider the effects of various oceanic turbulences, modulation, receiver noise type, and the photodetector parameters on the BER performance.

An integrated approach by combining finite-element analysis (FEA), Kriging model, and nondominated sorting genetic algorithm-II (NSGA-II) is utilized to realize modeling and optimization in mask-assisted laser transmission microjoining thermoplastic urethane and polyamide 6 (PA6). First, a three-dimensional FEA model is developed for obtaining the simulation data of the temperature field distribution that can determine the molten pool geometry. Then based on the initial training points generated by the optimal Latin hypercube sampling, the relationships between input parameters (laser power P, scanning speed V, and clamping force F) and weld quality [weld width (WW) and shear strength (SS)] are approximated through the Kriging model. Meanwhile, the main effects and contribution rates of various input parameters on the joint performance are discussed. Finally, the optimal weld quality is characterized as maximum SS and WW with a desired value, the NSGA-II is carried out to solve the multiobjective optimization problem for searching the Pareto-optimal front. The results of validation experiments under the optimal parameters indicate that the corresponding welding joint quality is significantly superior to that under other parameters.

Spatial domain multiplexing (SDM) offers a degree of photon freedom to optical fibers. One variant of SDM utilizes ring-like output profiles, created through specific oblique input angles, and shows high-performance gains. Conventional modeling of this system utilizes Laguerre–Gaussian based models; however, these models are more suitable for free-space environments as opposed to fiber propagation. Therefore, a diffraction-based approach to deriving a Bessel–Gaussian beam solution is presented that adheres well to experimental data while maintaining continuity requirements. The derived model shows an input angle to azimuthal index relationship proportional to the transverse wave number of the carrier optical fiber region of SDM architectures.

To eliminate the serious detrimental effects caused by frequency drifts of acousto-optic frequency shifters (AOFSs) in conventional all-fiber-optic heterodyne Doppler measurement systems, a differential all-fiber-optic heterodyne configuration is proposed. By delicate arrangement of the fiber-optic path and using only one AOFS, zero drift, which commonly occurs in conventional systems, is eliminated. Based on the proposed configuration, a differential all-fiber-optic heterodyne Doppler measurement system has been built. Using a piezoelectric ceramic oscillator as the moving object, it has been verified that the proposed system is able to eliminate zero drift, and the displacement and velocity measurement accuracies reach 0.775  μm and 0.009  mm  /  s, respectively. It has been shown that the differential all-fiber-optic heterodyne Doppler measurement system can achieve good performance in both displacement and velocity measurements, even in a harsh environment with drastic temperature variation.

To achieve the minimum cladding diameter (CD) at fixed cladding thickness (35  μm) in the trench-assisted (TA) homogeneous multicore fibers (MCFs), five different core structures have been proposed under the single-mode propagation condition. The high-core counts, up to 37 cores with dense hexagonal closed packing arrangement of homogeneous cores have been considered for the analysis. The expression for cross talk (XT) under bending and twisting conditions has been derived using conventional method. The influence of core pitch, fiber length, fiber bending, twisting, and trench depth has also been exhibited on the XT performance for fundamental (LP₀₁) mode propagation. The optimal CD based on specific values of cladding thickness and core pitch has been estimated in all the respective core structures for the target XT value of   <    −  50  dB  /  100  km. The dispersion properties have also been investigated for all the proposed core structure, which is obtained nearly as −6  ps  /  nm-km at operating wavelength of 1550 nm. Further, in anticipation of high transmission capacity, the 61-core TA MCF has been analyzed for the XT performance under the limited CD of 300  μm.

For satellite-to-ground downlink optical communication systems, it is desirable to reduce the size, weight, and power profiles of the space terminals by employing high sensitivity and large collection area ground terminals. Multiaperture coherent receivers utilizing spatial diversity techniques can satisfy this requirement and have many advantages over the single large aperture coherent receivers. The influence of both atmospheric turbulence and weather conditions on the bit error rate performance of multiaperture coherent receivers utilizing maximum ratio combining, equal gain combining, and selection combining techniques is systematically investigated and compared for the satellite-to-ground downlink communication system. The results are useful for the design and adaptive optimization of the multiaperture coherent receiver-based downlink communication systems.

Microseismic wave detection is important to avoid major disaster in coal mines. Here, a scheme of differential power measurement is proposed that can detect microseismic waves by converting minimal wavelength shift detected by a fiber Bragg grating interrogation system into corresponding variation in optical power. The Bragg-reflected signals are phase modulated by 500-MHz RF signal and detected by differential arrangement circuit consisting of photodetectors (PDs). The differential power at the PD is calculated theoretically and verified through simulation experiment. The variation of differential power with applied strain is nonlinear with the threshold at 100  με. The sensitivity of the present system is 0.041  dB  /  με below the threshold and increases to 0.598  dB  /  με above the threshold with the system resolution of 16.72  nε.

We present a theoretical perspective on the notion of a highly sensitive multimode fiber optic evanescent wave absorption-based sensor by exploiting a zero-order Bessel–Gauss beam to determine the concentration of sodium chloride (NaCl) from its aqueous solution. The phenomenon of excited waveguide modes inside the sensor structure has been assessed by using a classical wave-optic model. By harnessing the advantages of the Bessel–Gauss beam, the difference in transmitted output power is evaluated for various concentrations of NaCl, ranging from 0 to 360 g/L. To corroborate our theoretical predictions, the computer-aided simulation in Mode Solutions software has been performed on the proposed sensing configuration. In contrast to the conventional concentration sensor using Gaussian beam, the projected scheme yields a maximum 14.40-fold superior sensitivity of 0.072  dB  /  gL^−  1 with a commendable sensing resolution of ∼0.013  g  /  L. Also, attention has been paid to the Bessel–Gauss beam shined U-bent fiber-optic absorption-based concentration sensor, where the sensor response has been numerically investigated for different bending radii, and it is concluded that the sensitivity can be enhanced appreciably by gently reducing the bending radius. Due to ultrahigh sensitivity, the present paradigm is very much alluring and evocative, establishing pivotal implication in chemical and biological sensing fields.

A dumbbell-shaped fiber laser with dual-functional pulsed outputs is demonstrated using a filmy polyvinyl alcohol-based gold nanorods (GNRs) saturable absorber (SA), which can deliver mode-locked soliton and multiwavelength Q-switched pulse. The GNRs-SA is fabricated by seed-mediated method with a modulation depth of 4.1% and nonsaturable loss of 32.9%. When the fiber laser operates in mode-locked regime, stable fundamental solitons with a temporal width of 910 fs and repetition rate of 2.88 MHz are directly generated from the laser cavity. The corresponding spectrum is located at 1560.1 nm with a 3-dB bandwidth of 3.08 nm. When the laser operates in Q-switched regime, more than 5-wavelength oscillation is achieved. The repetition rate of Q-switched monotonically increases from 13.4 to 31.7 kHz and the pulse duration can be significantly narrowed from 6.07 to 3.12  μs by varying the pump power from 128 to 154 mW. The results further expand the applications of GNRs-SA to obtain versatile pulse sources in ultrafast laser field.

Phase-sensitive optical time-domain reflectometry (ϕ-OTDR) has been widely used to interrogate multipoint vibration events in the health monitoring of large-scale infrastructures. Since high signal-to-noise ratio (SNR) is the core parameter for evaluating the performance of ϕ-OTDR, many researchers have presented digital signal processing (DSP) methods for SNR enhancement. However, the DSP methods using fixed parameters cannot achieve the optimum SNR for different vibration events. In addition, although transform domain analysis methods such as wavelet transform could provide multiscale observation for target events, a large amount of computation would be required simultaneously. Matched filtering is a commonly used technique to extract noisy signals in traditional wireless radar systems. Mathematical theory has indicated that matched filtering is also suitable for signal extraction in ϕ-OTDR. The optimization of system performance could be realized when the filter scale matches the length of vibration events. For different lengths of disturbance region, a multiscale matching filtering method has been proposed, which makes it possible to choose appropriate filter scale and finally obtain the optimal SNR. Experimental results have shown that the proposed multiscale matching filtering method could improve the SNR by over 6 dB even under strong noise influence and reach the lowest locating uncertainty of 0.49 m with low time consumption, compared to conventional methods.

A simple, efficient, and low-cost method is proposed to reduce the timing jitter in passively Q-switched microchip lasers by self-injection seeding. A portion of the output pulse of the microchip laser was incident into the fiber delay line, and then, the backward reflection light induced the formation of the pulse. With different lengths of fiber, it was found that the timing jitter of the microchip laser could be reduced effectively when the repetition rate of the microchip laser was about 0.8 times the reciprocal of the delay time. The standard deviation of the microchip laser was reduced from several hundred nanoseconds to less than 181 ps.

A time–frequency-varying multicarrier generation scheme based on dynamic single-sideband recirculating frequency shifter is proposed and experimentally demonstrated. Through the use of two time-domain sinusoidal signals with stationary phase shift provided by a phase control module, multicarriers with flexible frequency intervals are obtained without carrier-to-noise ratio and flatness loss. We have experimentally attained multicarriers with 10-/12.5-/15-GHz carrier intervals in 3-nm bandwidth, and carriers with arbitrary intervals can be achieved when using the proposed scheme combined with a flexible wavelength selective switch.

We propose a flexible method for multiple feature frequencies-based bridge T hardware pre-equalizer that can better match the channel of an LED-based visible light communication (VLC) system and dramatically increase the system capacity. Based on this method, three kinds of equalizers are fabricated with the same maximum attenuation but different envelopes of frequency response. The performance of the three equalizers is experimentally compared in an underwater VLC system. The results show that the different shapes of the pre-equalizer can significantly impact the system SNR as well as the system capacity. By utilizing one of the optimally designed equalizers, an overall data rate of 3.075 Gb/s underwater VLC system can be achieved based on 64 QAM discrete multitone modulation over 1.2-m water channel. The measured bit error rate is under the hard decision-forward error correction threshold of 3.8  ×  10^−  3.

We fabricated a cost-effective and tractable near-infrared nanowire grid polarizer array with six different directional grating elements on a Borofloat 33 glass substrate at once using a soft nanoimprint and metal thermal evaporation process. Each element consists of a 200-nm period bilayer Al grating with an area of 1.3  ×  1.3  mm². Scanning electron microscopy images reveal that each unit of the polarizer array has an intact nanostructure without large-area damage. Meanwhile, the TM transmittance of each element exceeds 65% in the wavelength range of 1 to 2.5  μm, and of particular note, it is >70  %   in the wavelength range of 1.2 to 2.5  μm. The extinction ratio is more than 20 dB in 1.38- to 2.5-μm wavelength range, proving that the polarizer array has good polarization characteristics. Such a polarizer array has low costs and better compatibility with microfabrication processes, which can be used as an element of near-infrared polarization image detection equipment.

An optical fiber sensor for simultaneous measurement of refractive index (RI) and temperature is achieved by using an optical fiber Mach–Zehnder interferometer (MZI) with two core-offset trapezoid cone structures, in which part of the core mode light will be coupled into cladding modes when passing through the first trapezoid cone and the two parts of light will combine in the second one and interfere with each other over there. The transmission spectrum would vary with the RI and the temperature. The experimental data show that the RI sensitivities of the two interference valleys are −35.93 and −51.14  nm  /  RIU, respectively. The temperature sensitivities of them are 0.05 and 0.04  nm  /    °  C, respectively. Therefore, it can be realized to gauge the RI and the temperature simultaneously. The proposed sensor can also be applied to chemistry and biology which has broad application prospects.

We have proposed and experimentally demonstrated a compact temperature sensor based on cascaded fiber Sagnac interferometer (FSI) and fiber Fabry–Perot interferometer (FFPI) with Vernier effect. The FSI is composed of a certain length of panda polarization-maintaining fiber and a 3-dB four-port coupler, whereas FFPI consists of two collimators and a wave plate. Both are used for temperature sensing, but where FSI is more sensitive to temperature than FFPI, the free spectral ranges of the two interferometers differ by 0.12 nm. The experimental results show that the temperature sensitivity is increased from −1.7  nm  /    °  C (single FSI) and 0.008 nm/°C (single FPI) to 10.28 nm/°C (cascade configuration), which is basically consistent with the theoretical analysis (10.82 nm/°C).

An infrared wire-grid polarizer consisting of a 400-nm pitch Au grating on a photocuring film with ∼30  μm thickness was fabricated using photoimprinting, thermal evaporation, and peeling off the imprinted film from the substrate in a high humidity environment. This element exhibited a transverse magnetic transmittance greater than 75% in the 4- to 5.5-μm wavelength range because of thin film and an extinction ratio typically greater than 20 dB in the 2.5- to 7.5-μm wavelength range. The maximum extinction ratio of this element exceeded 28 dB at 6.5  μm wavelength. This film polarizer with high TM transmittance can be fabricated at lower costs and simpler fabrication processes compared to conventional infrared polarizers.

Sensitivity is of particular importance in developing liquid-core Bragg fiber sensors for refractometry instrumentations. We study the factors that influence the sensitivity of such sensors and propose to enhance it by optimizing the Bragg fiber geometry. Both theoretical analysis and experimental demonstrations have been performed to verify the feasibility. By designing and fabricating Bragg fibers with optimized bilayer thicknesses, we have enhanced the sensitivity. Furthermore, we studied the influence of fiber length on the sensitivity. Finally, we propose one possible portable sensing configuration on smartphones.

Graphene-based transistors were investigated as simple photodetectors for a broad range of wavelengths. Graphene transistors were prepared using p-doped silicon (Si) substrates with a SiO₂ layer, and source and drain electrodes. Monolayer graphene was fabricated by chemical vapor deposition and transferred onto the substrates, and the graphene channel region was then formed. The photoresponse was measured in the broadband wavelength range from the visible, near-infrared (NIR), and mid- to long-wavelength IR (MWIR to LWIR) regions. The photoresponse was enhanced by the photogating induced by the Si substrate at visible wavelengths. Enhancement by the thermal effect of the insulator layer became dominant in the LWIR region, which indicates that the photoresponse of graphene-based transistors can be controlled by the surrounding materials, depending on the operation wavelength. These results are expected to contribute to provide the key mechanism of high-performance graphene-based photodetectors.

We report on the fabrication of a ridge waveguide in the Tb^3  +-doped aluminum borosilicate glass by combining the 550-keV proton implantation and the precise diamond blade dicing with a rotating speed of 20,000 rpm. The relative atom displacement of the original structure induced by the proton implantation is simulated by Stopping and Range of Ions in Matter 2013 in the Tb^3  +-doped aluminum borosilicate glass. The morphology of the ridge waveguide is acquired by scanning electron microscopy. The near-field intensity distribution of the waveguide is recorded by the end-face coupling system, which indicates that the light can be well confined in the ridge waveguide region.

The effect of gamma radiation dose (∼1  MGy) on the performance of negative-index fiber Bragg grating (FBG) formed by prolong UV laser exposure (type-IIa grating) and prolong thermal exposure (thermally regenerated grating) is presented for the first time. It is observed that for both negative-index gratings, the radiation-induced shift in Bragg wavelength and temperature sensitivity were less than 37 pm and 0.06  pm  /    °  C, respectively. The performance of negative-index grating is also compared with that of positive-index grating (type-I) under the same gamma irradiation conditions. It is observed that variation in Bragg wavelength, reflection intensity, and temperature sensitivity was lower in negative-index gratings compared to that of positive-index grating. The effect of radiation is analyzed in terms of “radiation-optic coefficient” for all FBGs. The different behavior of the FBG is linked with a different mechanism responsible for the formation of negative- and positive-index FBGs.

We design and experimentally demonstrate micron- and submicron-sized color filters in the visible region using metal–dielectric–metal (MDM) Fabry–Pérot cavity arrays. Large-area MDM filters (150  μm  ×  150  μm) of varying dielectric thicknesses show polarization-independent bandpass filtering of primary and secondary colors. The lateral dimensions of each cavity and the spacing between adjacent cavities are systematically reduced to study the possibility of using these color filters as Bayer filter arrays for color cameras. Up to micron-sized dimensions with micron-sized spacing between the adjacent MDM cavities, it is observed that the dominant mechanism for color filtering is Fabry–Pérot effect. However, as the size and the pitch of the arrays of MDM are reduced further to the submicron length scale, polarization-dependent transmission is observed, and the dominant effect for color filtering is observed to be the leaked radiation from the grating-coupled plasmons. By keeping the pitch and lateral dimensions of MDM arrays fixed for plasmon resonance, the dielectric spacer thickness is systematically varied. Our electromagnetic simulations and microscopy-based imaging reveal that there exists a critical dielectric thickness for a specific cavity period, where the Fabry–Pérot resonance and the Plasmons couple to each other and exhibit a high transmittivity. However, at other dielectric thicknesses, two weaker transmission peaks corresponding to decoupled modes; one corresponding to Fabry–Pérot effect and the other corresponding to the signature of grating-coupled plasmons are present. Such MDM filter arrays can act as polarization-insensitive Bayer filters, as well as current-drawing contacts of multispectral imaging sensors with pixel sizes and separations, each up to a micron. With the pixel sizes in submicron regime, the integrated color filters with photodiodes may be useful for polarization-sensitive color imaging and surface sensors.