A broadband air gap polarization prism design based on Hg₂Cl₂, Hg₂Br₂, and Hg₂I₂ crystals is suggested. Spectral ranges of operation extend from visible light up to 40  μm, and strong birefringence of the materials makes it possible to optimize the crystal cut geometry. Results include a large symmetric field of view up to 20 deg wide within the entire mid- and far-infrared transparency range, as well as a power transmittance of more than 80%. The transmittance is determined by the Fresnel reflection at the entrance and exit windows. Furthermore, it can be improved by optional antireflection coatings; losses in the air gap do not exceed 1%. Due to a combination of useful properties, the suggested design significantly outperforms commonly available crystal polarizers.

Additive manufactured Ti6Al4V alloy has excellent comprehensive properties and has broad application prospects in the aerospace, biomedicine, and other fields. However, the fabricated components are too rough to use directly. So, a corresponding postprocess is needed urgently. The conventional finishing process cannot meet the requirements of green and efficient processing because of its time consumption, environmental pollution, and low productivity. Laser polishing, as a highly efficient and noncontact post-treatment technology, has attracted more and more attention in the polishing of additive manufactured Ti6Al4V alloy. The research of laser polishing of Ti6Al4V alloy in recent years has expatiated and includes laser polishing mechanisms, surface roughness and morphology, microstructure, mechanical properties, and finite element simulation analysis during laser polishing. Furthermore, the existing challenges of laser-polished Ti6Al4V alloy are summarized, and future development directions are proposed.

The ultrashort, ultrahigh intensity pulse laser has been fully developed in past three decades. Chirped pulse amplification (CPA) system plays an important role in the generation of the ultrashort, ultrahigh intensity pulse laser. Pulse compression gratings (PCGs) are the key element of CPA system and determine the performance and lifetime of the whole system. We introduce the principle of CPA system and the performance requirements of PCGs. Then the development status of PCGs, including Au-coated grating, multilayer dielectric grating (MDG), and metal MDG, is fully reviewed. Finally, the development prospect of PCGs in the future is presented. Our study is helpful for comprehensive understanding of PCGs.

Phase measuring deflectometry (PMD) is a superior technique to obtain three-dimensional (3D) shape information of specular surfaces because of its advantages of large dynamic range, noncontact operation, full-field measurement, fast acquisition, high precision, and automatic data processing. We review the recent advances on PMD. The basic principle of PMD is introduced following several PMD methods based on fringe reflection. First, a direct PMD (DPMD) method is reviewed for measuring 3D shape of specular objects having discontinuous surfaces. The DPMD method builds the direct relationship between phase and depth data, without gradient integration procedure. Second, an infrared PMD (IR-PMD) method is reviewed to measure specular objects. Because IR light is used as a light source, the IR-PMD method is insensitive to the effect of ambient light on the measured results and has high measurement accuracy. Third, a proposed method is reviewed to measure the 3D shape of partial reflective objects having discontinuous surfaces by combining fringe projection profilometry and DPMD. Then, the effects of error sources that mainly include phase error and geometric calibration error on the measurement results are analyzed, and the performance of the 3D shape measurement system is also evaluated. Finally, the future research directions of PMD are discussed.

The algorithm designing of object localization is one of the key technologies in the research field of high-voltage power transmission line inspection robot. We present an obstacle localization method based on line stereo matching to solve the problems remaining in the current obstacle localization algorithms such as the weak capacity of resisting distraction, the low localization precision, and the extra prior conditions. The proposed algorithm regards line as the element unit for stereo matching and adopts Earth mover’s distance as similarity measurement criterion. In addition, it can remove false matching points through the condition of distance constraint and the distribution information of depth. Finally, we give all sampling points on obstacle different weights according to the distance between the points and obstacle center, through which the weighted mean depth of obstacle is obtained. The experimental result shows that the mean relative localization error is 2.697% and the fluctuating range is 1.11% to 3.58%, which means the localization precision is high and the error fluctuation is small. So this algorithm can meet the demand of obstacle localization for high-voltage power transmission lines inspection robot efficiently.

We propose a 3D Hough transform (3D-HT) algorithm that can overcome the disadvantages of high complexity and large data storage space of the existing 3D-HT-based small target detection algorithms. The proposed algorithm uses two coordinates at different times and coordinate errors to construct a 3D pipeline. Subsequently, it counts the number of points in the 3D pipeline and confirms the presence of a target trajectory in the pipeline when the number of points exceeds a predefined threshold. Finally, it performs trajectory merging and filtering before outputting the target trajectory coordinates. The proposed algorithm has low complexity because the used trajectory parameters are the coordinates in the data space, and only a linear transform between the coordinates is required. Unlike the existing algorithms that use an accumulator array to represent the Hough space, the proposed algorithm uses only a single position-adaptive cumulative cell in the Hough space. Therefore, there is no limitation on data storage in the Hough space. Simulation and analysis show that the small target detection algorithm based on the proposed transform is robust to noise, requires small data storage space, and has high computational efficiency. The proposed algorithm can be used in infrared and radar small target trajectory detection systems.

We present experimental methods and results for photo-response non-uniformity correction (PRNUC) in range for a 3D flash LiDAR camera from non-optimal static-scene calibration data. Range walk is also corrected. This method breaks up the camera’s focal plane array (FPA) into 16  ×  16 windowed regions of interest that are incrementally captured and stitched together in post-processing across the entire FPA. The illumination was not uniform, thus requiring additional methods described by our paper to create an acceptable correction. We present the results from a full non-uniformity correction and range walk error correction processed for a set of independently collected validation frames; these validation frames used identical experimental conditions and the same target as was collected for the corrections. We will show that this experimental approach improves range accuracy and range precision of the corrected validation frames despite the sub-optimal conditions of the data used to compute the corrections; the single shot range precision is corrected to 33 cm, as compared to a modeled precision of 15.65 cm, while the accuracy is corrected to 252 cm. This method has implications for simplification of characterization of non-uniformity and range walk error, and its subsequent correction, in 3D flash LiDAR cameras.

The US Army Night Vision and Electronic Sensors Directorate’s Night Vision Integrated Performance Model (NVIPM) is a robust, comprehensive, and sophisticated model that calculates the performance of an infrared imager in the task of target acquisition. The inputs are specifics about the target, atmosphere, optics, detector, electronics, and display and the outputs are probabilities of target detection, recognition, and identification. NVIPM is complicated and takes a good bit of time to master obtaining correct answers based on numerous assumptions and modeling experience. For midwave infrared (MWIR) and longwave infrared (LWIR) sensors, past research has shown that imaging system performance is strongly related to Fλ  /  d, where F is the f-number, λ is the wavelength, and d is the detector pitch. Fλ  /  d provides a metric that relates how closely to diffraction-limited performance a sensor operates. We use the past Fλ  /  d work to develop a simple model that provides probability of target discrimination as a function of range that can be performed with a simple hand calculator or spreadsheet. We compare this model to the NVIPM calculations on 10 very disparate MWIR and LWIR sensors to show robust agreement. We also describe the conditions under which the simple model is valid.

It is insufficiently powerful to compute multi-view images at a high enough frame or data rate to support high quality dynamic three-dimensional displays with the current computer software and hardware. According to the correspondence between lens position and elemental image, a real-time computer-generated content generation method for integral imaging based on cross perspective is presented. A GPU-driven rendering pipeline (GDRP) with geometry instancing and instance culling technique is designed, and the number of triangles processed in the rasterization stage is reduced greatly. Several virtual dynamic scenes including various materials and millions of vertices are used to verify the performance of the GDRP method in the experiment. Experimental results show that the frame rate can reach 60 fps with 3840  ×  2160 resolution.

Plant water stress has been extensively studied using hyperspectral visible- and near-infrared systems. Thermal imaging and the recent availability of widely tunable infrared quantum cascade laser (QCL) allow us to propose an active hyperspectral imaging system operating in the mid-infrared (MIR) band, where the system output consists of a series of narrowband subimages arranged across the reflectance spectrum of the sample, forming a hypercube data acquired by “staring” acquisition technique. To evaluate more precisely the capabilities of the active hyperspectral imaging, we propose a system composed of four powerful tunable QCL covering the 3.9- to 4.7-μm and 7.5- to 11-μm wavelengths ranges. Two cameras are used for detection: an InSb cooled camera ranging from 3 to 5  μm and a bolometer from 7.5 to 13  μm range. This system is validated by applying to growing plants for early water stress detection. Finally, we present and discuss results using partial least squares discriminant analysis classification technique to characterize water status of different plants, separated in two classes: control subjects were maintained at 80% of the amount of water to soil saturation ratio and stressed subjects at 20%. Initial discrimination results have shown the efficiency of the proposed system.

Most visual trackers focus on short-term tracking. The target is always in the camera field of view or slight occlusion (OCC). Compared with short-term tracking, long-term tracking is a more challenging task. It requires the ability to capture the target in long-term sequences and undergo frequent disappearances and reappearances of target. Therefore, long-term tracking is much closer to a realistic tracking system. However, few long-term tracking algorithms have been developed and few promising performances have been shown until now. We focus on a long-term visual tracking framework based on parts correlation filters (CFs). Our long-term tracking framework is composed of a part-based short-term tracker and a re-detection module. First, multiple CFs have been applied to locate the target collaboratively and address the partial OCC issue. Second, our method updates the part adaptively based on its motion similarity and reliability score to retain its robustness. Third, a switching strategy has been designed to dynamically activate the re-detection module and interact the search mode between local and global search. In addition, our re-detector is trained by sampling positive and negative samples around the reliable tracking target to adapt to the appearance changes. To evaluate the candidates from the re-detection module, verification has been carried out, which could ensure the precision of recovery. Numerous experimental results demonstrate that our proposed tracking method performs favorably against state-of-the-art methods in terms of accuracy and robustness.

Planar laser-induced fluorescence (PLIF) techniques have been widely used for flame structure visualization in recent years. Nevertheless, most of the studies were concerned with qualitative analysis of the obtained images and the quantitative analysis were much fewer. This work presents a quantitative feature extraction method to process the ribbon structures that are captured in images and represent the radical layers in flames. The extracted features include ridge lines, curvatures, and thicknesses. This method was demonstrated by processing the images of methyl (CH₃) photofragmentation laser-induced fluorescence (PF-LIF) and formaldehyde (CH₂O) PLIF measurements in stoichiometric, premixed methane/air flames. The flames were generated by a McKenna burner under the Reynolds numbers of 1930, 3870, and 5800. The ridge lines followed well with the wrinkled layers of CH₃ and CH₂O. The CH₂O layers were thickened, but the CH₃ layers had minor change with increased Reynold numbers.

A phase correction method that utilizes fringe color-coding in phase-measuring profilometry is proposed. Original and additional fringes are encoded into the R and B channels, respectively. The R + B channel patterns are projected onto an object, captured using a camera, where the R and B channels are extracted. Then, phase shifts obtained from the R and B channels are utilized for absolute phase calculation and correction. Simulations and experiments demonstrate that this method can correct edge order errors and avoid increasing the fringe number. Experiments performed using the R + G, G + B, and R + B channels demonstrate that R + B exhibits the least color crosstalk.

Recent advances in solid-state technologies have enabled the development of light-emitting diodes (LEDs) with favorable features such as long life expectancy, low-power consumption, and reduced heat dissipation. Visible-light communication (VLC) is a short-range wireless access technology that deploys LEDs as wireless transmitters in addition to their primary task of illumination. The major limitation for the design of high-speed VLC systems is the electrical (modulation) bandwidth of the LED. In this study, we investigate the electrical characteristics of a number of off-the-shelf LEDs. Specifically, we determine their frequency responses and match them to their small-signal models. The electrical bandwidths of measured LEDs vary from 250 kHz to 20 MHz and depend on the emitted color and internal circuitry. As a verification of our measurements, we use the sample LEDs as a transmitter in a VLC system setup and determine the supported data rates. The equivalent circuit model is utilized to compare with the measured modulation characteristic of the LED. Furthermore, the bias current effect on the modulation bandwidth is presented.

A concept of noncoaxially propagating discrete data by coding/decoding orbital angular momentum (OAM) of vortex beam through multiple channels is proposed. Four independent channels along different directions (diffraction orders/angles) are established by a series of specially designed holograms. Sixteen vortex beams are used to code each sequence with the length of 4 bits into an OAM mode in each channel. The theoretical analysis (simulation) demonstrates that the proposed scheme is reliable. In addition, an experiment is also designed and performed for practically certifying the feasibility of the proposed scheme. A 16-bits-length sequence, which is coded into four OAM modes in four channels (one channel with one OAM mode), is successfully received/decoded by observing the intensity-profile arrays (OAM-mode spectrum) generated by a specially designed Dammann vortex grating. The measured results show that the proposed concept is also viable in practice. Moreover, the received/recovered images indicate that the performance of the system decreases as the atmosphere turbulence strength increases when a color image and a gray-scale image are simultaneously propagated. Besides, the measured bit error rate (BER) gradually decreases with the increase of bit rate or propagation distance. The acceptable BER under the threshold of forward error correct can be achieved for a short-distance communication network.

Analysis of spatial temperature and gas concentration distributions is of great importance for combustion research. Algebraic reconstruction technique (ART) and adaptive algebraic reconstruction technique (AART) based on tunable diode laser absorption spectroscopy are both widely used methods for temperature tomographic imaging in a flame. After being obtained the temperature tomography through iterative method, the gas concentration reconstruction could be determined from a simple division equation (direct gas concentration algorithm) or iterative algorithm (ART gas concentration algorithm or AART gas concentration algorithm) for the second time. For the latter, iterative algorithm was used twice through the whole process. A series of numerical simulations were carried out by three gas concentration reconstruction methods mentioned above. The results demonstrated that AART method had better robustness for different phantoms and stability in the case that measured projections contained different levels of noise. Experimental measurements in a flat methane/air flame on a McKenna burner under three different equivalence ratios (1.0, 0.9, and 0.8) were conducted using AART gas concentration algorithm. The reconstructed results coincide well with those results obtained by thermocouple and theoretical calculation. Both simulation and experiment demonstrate that the AART gas concentration algorithm would be reliable and suitable for simultaneous temperature and H₂O concentration tomographic imaging during combustion. As a consequence, this method has unrivalled potential for two-dimensional combustion diagnosis.

The draft is a measurement of the vertical distance between the waterline and the bottom of the ship hull. The displacement tonnage of a ship then can be calculated by the observed draft. The current draft survey is done by surveyors, which is subject to human errors. We propose to use computer vision with deep learning for draft reading from images. First, mask R-CNN is used to segment the region of interest—draft marks and water—from images. Then UNet is used to refine the waterline detection. The detection of marks is based on the computer vision methods and the content of marks is recognized by ResNet. Finally, we can infer the draft of a ship based on the extracted visual information. Experimental results on a realistic dataset have shown that the proposed method can perform the task of draft reading on a par with humans.

Digital holography is a well-established technique for tracer particle studies in a flow. Unfortunately, its great depth of focus increases the uncertainty along the Z axis. This drawback becomes very significant when the concentration of seeding particles increases. This is the case in real installations such as wind or water channel flows. In such cases, observing the whole volume, and therefore all the particles, and tracking individual particles in order to determine their motions becomes an awesome task. Getting a hologram of the whole scene is impossible with the existing photographic sensors. The solution offered by the present day technologies and academic studies is to take several holograms and synthesize the whole scene hologram. However, for getting individual particle behavior, it is necessary to make several processing steps, makes processing very complicated if the number of seeding tracer particles is relatively high, on one hand and on the other hand, the correlation between dynamic characteristics could not highly established. In such cases, the technique of one hologram is highly recommended. In order to overcome these problems, we propose here a new technique based on combining the two instantaneous orthogonal views and hologram aperture reduction (opposed to aperture synthesis). To establish the technique, we investigate a little volume with a reduced number of particles, and the development and experimental results are presented. We focus on the development and experimental application of this technique.

The Follow-up X-ray Telescope (FXT), a key payload onboard the Einstein Probe sallite (EP), is equipped with a Wolter-I x-ray focusing mirror system. We introduce the principle of such a mirror system and analyze the influence of the mirror gap in the multishell nested mirror of the FXT on the effective area, stray-light ratio, and vignetting. To ensure that no occlusion occurs within adjacent shells and minimize stray-light ratio, the size of the gap is set to a optimized value for corresponding shell. We finished a design of a 54-shell mirror system according to these results. The optical performance of the design was then simulated using a Monte Carlo algorithm and the ray-tracing principle. The simulation shows that the effective area is 414.5  ±  0.2  cm² at 1.25 keV (considering the spider), and the field of view is 64 arcmin in diameter. These parameters meet the optical requirements of the FXT.

A triple-band metamaterial absorber (MMA), which is ultrathin and polarization-insensitive, is designed and fabricated. The top layer of the MMAs consists of a square-shaped copper film with a cross cut out in the center. The calculation result demonstrates that there are three distinct absorption peaks, which are 5.86, 15.04, and 17.5 GHz, and their corresponding absorption rates are 99.76%, 99.11%, and 99.90%, respectively. Moreover, the thickness of the MMA is very thin, only 1.05% of the wavelength of the lowest absorption frequency. The MMA also shows polarization-insensitivity for normal incident wave. In addition, we analyzed the absorption characteristics of the three absorption peaks and the impact of key structure parameters on the MMA’s absorption. Through experiments and theories analysis, it can be seen there are small absorption errors and frequency deviations of three absorption peaks. The MMA is ultrathin and has simple structure and perfect absorption, and it can be widely applied in many fields, such as detection sensors, imaging, and thermal radiometer.

We propose a technique to generate etendue maintained white light. The proposed technique uses three high-power blue light emitting diodes (LEDs) with identical characteristics to pump green aluminate (GAL) green-yellow phosphor coated on the inner channel of a waveguide. The technique offers two methods of generation of white light. Standalone partial conversion of blue to green and yellow light by GAL phosphor, combined with unconverted blue light, produces white light homogenized within the light guide. Complete conversion of blue to green and yellow light with the further addition of blue and red wavelengths from additional LED sources multiplexed with the output is also possible to further increase total white light output. Following design and optical modeling to prove the concept, the proposed technique is demonstrated, which shows white light emissions from the waveguide with no increase in aperture size while the original LED etendue is maintained. The proposed technique offers an alternative to low-lifetime, low-efficiency xenon lamps for light sources in etendue critical applications such as endoscopy.

The industrial maturity of ultrashort pulsed lasers has triggered the development of a plethora of material processing strategies. Recently, the combination of these remarkable temporal pulse properties with advanced structured light concepts has led to breakthroughs in the development of laser application methods, which will now gradually reach industrial environments. We review the efficient generation of customized focus distributions from the near-infrared down to the deep ultraviolet, e.g., based on nondiffracting beams and three-dimensional-beam splitters, and demonstrate their impact for micro- and nanomachining of a wide range of materials. In the beam shaping concepts presented, special attention was paid to suitability for both high energies and high powers.

Top-Gaussian illumination generation technology has considerable application prospects in photolithography. We propose a detailed design and optimization method for the optical component that generates the top-Gaussian illumination field. This method can generate a field with a specific profile in the scan direction and a rectangular distribution in the nonscan direction. The energy density is reduced by jointly designing the first and second microlens arrays (MLAs). Thus, design freedom becomes more extensive. The requirements of the illumination field are met by the designed top-Gaussian illumination field, whose dimensions in the scan and nonscan directions are insensitive to illumination mode. Furthermore, the influences of the rectangular distribution dimension and the Gaussian distribution σ errors on the dimension of the top-Gaussian distribution are studied. The design results show that the maximum energy density in the second MLA can be reduced to 17.43% of that in the general design method. The analysis results indicate that the full-width-at-half-maximum error of the rectangular illumination field in the scan direction should be restricted within ±0.3  mm, and the σ error of the Gaussian distribution should be restricted within ±0.05  deg. The proposed method should increase the service life of the key component of the photolithography machine, and the cost of the manufacture and maintenance may be decreased.

We present an intensity-balanced dual-frequency laser (DFL) based on an Nd: GdVO₄ microchip crystal. The intensity balance ratio tuning mechanism of the DFL, which is governed by the heat sink temperature T_c of the laser crystal, is experimentally studied. The experimental results indicate that keeping a balanced intensity condition, when the pumping power of the DFL increases, the heat sink temperature T_c of the laser crystal must be lowered to rebalance the DFL signal intensities. The T_c versus pumping power slope is experimentally measured to be −17.95  °  C  /  W. By fixing the pumping power at 5.6 W, an intensity-balanced microchip DFL with output power up to 103 mW and frequency separation up to 61 GHz is achieved, whose slope efficiency is 9%.

We investigate hybrid free-space optical (FSO) link in converged baseband and 60-GHz radio-frequency signals under adverse climate conditions. In this approach, optical double-sideband with carrier method is utilized. The adoption of such an FSO system can be contributed to existing fiber-optic architecture. Managing the signal strength by erbium-doped fiber amplifier, deployment of the system serves the data rate of 2.5  Gb  /  s to fiber-optic and pico/femto-cellular users concurrently. Our paper studies the impact of rainfall, snowfall, and fog-visibility with the maximum value of 250  mm  /  h, 10  mm  /  h, and 1.5 km, respectively. System performance is relatively evaluated for an optical wireless range of 1 km and back-to-back connection. For the bit error rate (BER) of ∼10^−  9, the receiver sensitivity in range of −25.06 to −24.86  dBm for wired and −23.48 to −23.06  dBm for wireless is obtained. The BER analysis shows effective FSO transmission up to 1 km in the rainy season and up to half a kilometer in frequent fog and snow events. The investigation reports the notable power margin for deploying a hybrid optical link in areas where fog or snow impact is higher than rain.

Multiple studies have been carried out to analyze the mutual interaction of a phase-sensitive optical time-domain reflectometer (Φ-OTDR) and parallel digital data traffic. However, interactions with analog transmission, e.g., community antenna television (CATV), have not been addressed. Our study examines and presents the influence of a developed sensing system Φ-OTDR when operated simultaneously on parallel fibers with the transfer of data from an analog CATV system. Three scenarios are suggested and discussed for the measurements and optimization of the data network in the analog CATV data transfer. These scenarios are suggested to enable the verification of the mutual interactions between data networks with the analog data transfer and suggested sensing system and to determine how the data network with the analog data transfer may or may not be influenced by the sensing system. The optimization and measurements prove that the analog CATV data transfer was negatively influenced by the sensing system Φ-OTDR, and the channel bit error rate increased by nearly half. The implementation of the sensing system Φ-OTDR was realized for a data network, followed by the testing and optimization, which proved that the safe spectral distance between the CATV and the sensing system is 150 GHz and higher.

It has become an imperative reality to find an alternative for the conventional bulk semiconductor optical amplifier (SOA), which suffers from the slow dynamic response, in light of the increased need for higher speeds. In this research, the carrier reservoir SOA (CR-SOA) is employed as a suitable alternative to investigate the all-optical AND logic gate for the first time at an operating speed of 100  Gb  /  s. For the reliability of the results, the CR-SOAs- and the conventional SOAs-based Mach–Zehnder interferometer are compared in the same operating conditions that include the effects of the amplified spontaneous emission noise and the operating temperature to obtain more realistic simulation results. The results of Wolfram Mathematica proved that the considered Boolean function is executed at 100  Gb  /  s with a higher quality factor when using CR-SOAs compared to SOAs, i.e., 14 versus 4.7.

We propose and demonstrate a photonic approach to generate and transmit a quadrupling-bandwidth dual-chirp microwave waveform with anti-dispersion transmission. Commonly, dual-chirp microwave waveforms are generated by double-sideband modulation, which brings severe chromatic-dispersion-induced power fading (CDIP) over fiber transmission. In this scheme, we perform optical carrier suppression via a polarization controller based on an integrated polarization-division multiplexing Mach–Zehnder modulator (PDM-MZM) to eliminate the CDIP. Moreover, by properly adjusting two bias voltages of PDM-MZM, we find that the bandwidth of the generated dual-chirp microwave signal is quadrupled. It is worth mentioning that we just need to operate in the central office to realize the above-mentioned functions and no optical filters are needed, which significantly improves the limitation of the devices. The method is analyzed theoretically and proved experimentally, which is of great significance for improving range-Doppler resolution and the detection capability of radars for one-to-multi base stations over fiber transmission.

In vivo optogenetics provide special and powerful capabilities in regulation of neurons, research of neural circuits and even in treatment of brain diseases. However, conventional hardware for such studies tethers the experimental animals to remote light sources, power sources, or other functional modules, which imposes considerable physical constrains on natural behaviors and limits the range of the experiment. To enable flexible and convenient optogenetic manipulation of neural circuit with finite disruption of animal behavior, a wirelessly powered optoelectronic device, composing mainly of a radio frequency (RF) energy harvester and a high-performance GaN-based light-emitting diode (LED), is demonstrated and can be used to construct an implantable optrode for optogenetics. The wireless RF power signal is collected through an antenna and a two-stage voltage doubling rectifier circuit, and finally converted into high-amplitude DC voltage. Provided with 25-dBm RF power with a distance of 0.2 m, the RF energy harvesting and processing circuit can output a stable 2.81 V DC voltage and drive the designed GaN-based LED to work normally. After being successfully lit, the emission peak wavelength of the LED locates 455 nm and the output optical power density reaches 214.9  mW  /  mm², which is fully capable of activating light-sensitive ion channel channelrhodopsin-2. The total area of the device is 3  mm  ×  3.2  mm, which is suitable for subdermal implantation.

In this study, we propose a dual-band wide-range tunable terahertz absorber based on graphene and bulk Dirac semimetal (BDS), which consists of a patterned BDS array, dielectric material, continuous graphene layer, and gold mirror. Simulation results show that the absorption at 3.97 and 7.94 THz achieve almost 100%. By changing the Fermi energy of graphene and BDS, the resonance frequency can be tuned between 3.97 and 9.28 THz. In addition, we found that when the background refractive index changes, the absorption is almost the same. This feature will broaden its applications. Finally, the influence of structural parameters and incident angles on device performance is discussed. The proposed absorber may have potential applications in photoelectric sensors and other optoelectronic devices.

A selectively excited bimodal interferometer was developed for highly sensitive detection of refractive index changes. Numerical simulation revealed that multimode waveguides with tall, narrow cross-sections are suitable for realizing a highly sensitive bimodal (fundamental and lateral first-order modes) interferometer, owing to deeper penetration of the lateral first-order mode through its side surfaces into the cladding medium. A device with an optimum design was determined by simulation and fabricated by electron-beam lithography using a negative photoresist as the material for the waveguide core. The detection of glucose was demonstrated, and the sensitivity and detection limit was found to be 2547  rad  /  RIU (RIU—refractive index unit) and 9.8  ×  10^−  6  RIU, respectively.

The phenomenon of reversed radiation pressure on free electrons in a nanoparticle requires the necessary but insufficient condition that the real part of the particle’s permittivity be negative. It is shown that Rayeigh scattering theory is adequate for modeling the phenomenon by favorable comparison with Mie theory for single particles. A multiparticle Rayleigh scattering approach demonstrates that the radiation attraction of free electrons is enhanced by the interaction of closely spaced particles when the nanoparticles are in close proximity and separated along the incident wave polarization direction. However, the negative force on free carriers is reduced when the particles are aligned perpendicular to the incident electric field polarization. The accompanying increased radiation force on the material bound carriers is proposed as a step toward understanding how nanostructured materials and surfaces exhibiting reversed internal optical momentum can be designed with interacting nanoparticles for enhanced propulsion due to the ejection of hot electrons.

The optical planar waveguides were fabricated by proton implantation with an energy of 400 keV and a dose of 8  ×  10¹⁶  ions  /  cm² or 400-keV helium-ion implantation with a fluence of 6  ×  10¹⁶  ions  /  cm² in the fluoride lead silicate glass. The morphologies were studied by a Zeiss microscope to estimate the thickness of the waveguides. The annealing effects on the fluoride lead silicate glass waveguides were investigated by 60 min annealing cycles at different temperatures ranging from 260°C to 310°C in air atmosphere. The dark-mode spectra and corresponding effective refractive indices before and after the thermal treatments were measured by the prism coupling system. The Stopping and Range of Ions in Matter 2013 code was used to simulate the irradiation process and calculate the energy losses. The refractive index distributions were reconstructed by the reflectivity calculation method. The near-field light intensity profiles of the proton and helium-ion implanted fluoride lead silicate glass waveguides were measured by the end-face coupling system. The comparison of optical properties between the proton-implanted waveguide and helium-ion implanted one was carried out. The experimental results show that the helium-ion implantation is more suitable for the fabrication of the fluoride lead silicate glass optical waveguides and the He⁺-implanted waveguide has better optical propagation performances.

A low-cost laser detection system based on coherence detection has been developed and is able to detect weak, continuous laser sources even against bright background light. The system is composed of a Mach–Zehnder interferometer with one arm modified with a piezo-mounted mirror to modulate the path length. We introduce methods to determine the laser wavelength and to extend the horizontal field of view of the detector. To widen the field of view, a cone mirror is added to the system while the additional use of a camera allows the direction of the incoming laser beam to be studied. The wavelength from three different lasers is estimated with the use of the modulation amplitude of the piezo mirror. The preliminary results demonstrate that a 360-deg horizontal field of view can be achieved and that the direction of the laser beam can be determined with an estimated angular precision of ±5  deg. Moreover, the wavelength can be determined with a precision of ±10  nm. The system trades sensitivity for a larger field of view with the resultant detection sensitivity equal to 70 nW (or 1  μW  ·  cm^−  2) at 635 nm.

We report our in-house R&D efforts of designing and developing key integrated photonic devices and technologies for a chip-scale optical oscillator and/or clock. This would provide precision sources to RF-photonic systems. It could also be the basic building block for a photonic technology to provide positioning, navigation, and timing as well as 5G networks. Recently, optical frequency comb (OFC)-based timing systems have been demonstrated for ultra-precision time transfer. Our goal is to develop a semiconductor-based, integrated photonic chip to reduce the size, weight, and power consumption, and cost of these systems. Our approach is to use a self-referenced interferometric locking circuit to provide short-term stabilization to a micro-resonator-based OFC. For long-term stabilization, we use an epsilon-near-zero (ENZ) metamaterial to design an environment-insensitive cavity/resonator, thereby enabling a chip-scale optical long-holdover clock.