Aiming at the problem of camera pixel saturation caused by the high reflective area on the metal surface of a relay, we adopt speckle projection profilometry to detect the magnetic circuit drop height of the relay. The main problem is solved through a detailed analysis of characteristics according to different speckle gray values, speckle sizes, and shapes to effectively distinguish the confusion between the speckle reflection spots and background light reflection spots. The enhanced normalized cross-correlation sub-pixel algorithm is used to get a dense matching pair of points of the right and left images, and three-dimensional reconstruction is based on the triangulation parallax principle. The random sampling consensus algorithm and European clustering algorithm are used to segment the point cloud to obtain the core and yoke iron planes and measure the distance between the two planes. We measured two standard blocks with height difference of 1 mm, and the error is within 2% by the proposed method. The correctness is verified through real-time measurement for a magnetic circuit drop height of the relay assembly line.

To automatically eliminate the influence of external illumination on the acquired image, restore the true color information of the object, and provide true and stable color features for computer vision tasks, our work is based on the convolutional neural network (CNN) VGG19 for feature extraction of image information. Moreover, it proposes a model based on atom search optimization improved by chaotic-logistic maps to optimize the regularization random vector functional link (RRVFL). The optimized RRVFL replaces CNN’s regression layer to estimate the image illumination and then restore the image. First, we used chaotic-logistic maps to optimize the initial value of search agent of the atom search optimization (CASO) algorithm and then used the search agent segment mapping method proposed in our study to simultaneously optimize the number of nodes in hidden layer, regularization factors, input weight, and the bias of RRVFL hidden layer. This avoids the problem of serious fluctuation of prediction results and low accuracy caused by the randomness of the RRVFL parameters. After the predicted illumination information was obtained with the optimized RRVFL, the image was restored using the diagonal transformation method. Comparative experiments showed that the average angular errors of the illumination estimation of the V19-CASO-RRVFL algorithm proposed in our study were 1.73, 0.30, 0.3406, and 0.0976 lower than those of the gray-edge-2, GE-CASO-RRVFL, DS-Net, and color constancy on deep residual learning algorithms, respectively.

Geometrically aligning two images is a basic image process in the machine vision field. In general, the geometric transformation model is selected according to the complexity of the geometric transformation between images, and the type of camera that takes the image is ignored. However, there are essential differences in the imaging mechanism between a line-scan camera and an area array camera, so the geometric transformation model of the area array image does not conform to the geometric transformation of the line-scan image. Therefore, according to the imaging model of the line-scan camera, we established the geometric transformation model of line-scan images. A line-scan image acquisition system was built, and planar objects were imaged by different line-scan camera poses. Then, taking the proposed model as the geometric transformation model, the line-scan images collected in this paper and the line-scan images of realistic application were respectively registered. As a contrast experiment, the homography of the area array image was adopted as the geometric transformation model to align these images again. Through the comparison of registration results, the correctness of the proposed geometric transformation model of line-scan images was verified, and the accuracy of the line-scan image registration was improved.

A laser-induced forward transfer method that allows ejecting high-viscosity inks at a bubble ring pressure is presented. In this study, we clarify the transmittance and viscosity properties of donor materials that significantly affect the print quality. A nanosecond laser with a wavelength of 532 nm irradiates the donor in a ring shape. The relationship between the donor viscosity and print quality is analyzed, and optimal fluence is highly correlated with donor viscosity at a shear stress of 1000 Pa. A donor layer with a transmittance of 10% or less exhibits good droplet quality. When the transmittance of the donor layer is higher, backside fluence (BsF) will increase, resulting in mist and satellites. The BsF indicates that it is an important parameter for achieving droplet quality. These findings suggest that it is possible to develop a printing system using high-viscosity inks.

The aspheric surface testing system based on the shearing interference principle is used to better analyze how the installation and fabrication errors of linear polarizer affects the precision of the aspheric surface. The effects of the angle error of the linear polarizer and the phase-shifting error of the wave plate on the reconstruction of the aspheric surface are studied. Constructing the model of the Jones matrix with the error term system, the reconstruction surface and residual after the corresponding error system are obtained using the four-step phase-shifting and differential Zernike method. The polarizer array of an angle of θ was varied from ( θ − 1 deg ) to ( θ + 2 deg ) every 0.2 deg, and the changes of the fitting surface and the residual surface were simulated. The phase-shifting error of the simulated one-fourth wave plate was <λ / 300. Then, the change of the fitting surface and residual surface when these two errors exist at the same time were simulated. The simulation results show that the influence of the phase-shifting error of the wave plate on the fitting surface is much greater than the angle error of the polarizer array. When assembling the interference system, the phase-shifting error of the wave plate should be <λ / 300 when the light transmission angle error of the polarizer array is between −0.2 deg and 0.2 deg, which will ensure the testing precision of the aspheric surface testing system.

The majority of microscale and nanoscale mechanical systems encountered in the world are stiff. One example of such a system is a microbead trapped in an optical tweezer. For this example, the ratio of a body’s mass to the viscous damping coefficient is negligible. Apart from being stiff, this system is also stochastic meaning that the differential equations representing the system include a random variable. This type of model can be solved with existing stochastic differential equation (SDE) solvers. Addressing the stochastic nature of the model usually requires averaging the results of multiple simulations. The computational time required to run the hundreds of simulations that may be necessary to obtain a useful average can be prohibitive. This paper presents a scaling approach that significantly reduces the computational time required to obtain these averages. However, this scaling changes the model and therefore the power spectral density (PSD) of the predicted motion. This work provides a general analysis of a mass-spring-damper model, such as an optical tweezer, that clearly shows the effect of scaling on the frequency content of the stochastic system. This analysis shows that the scaling technique can be used effectively without much loss of information. An experimental dataset of a 2 μm diameter microbead falling into an optical trap is compared with the simulation for validating the scaling method.

We present experimental results for testing concave optical surfaces by the Shack–Hartmann (S–H) test, where a set of microholes is used instead of the array of lenses employed in the original (S–H) plate.

In underwater computer vision systems, the camera is usually housed in a watertight case with a glass interface between water and air, which causes the light rays to refract, affecting image formation geometrically. In this paper, we propose an approach to calibrate the housing parameters of a flat-port underwater camera for a reasonable underwater refractive camera model. Our approach is specifically designed to deal with the refraction effect caused by the light traveling in different mediums. In this camera model, the calibrated housing parameters include the distance between the camera and glass interface and the normal of the glass interface in the camera coordinate system. We employ an underwater binocular vision system to calibrate the housing parameters in two steps. First, the distance to the glass interface is estimated by capturing a checkerboard image and computing the distance from the camera center to a known flat plane. Then, the normal of the glass interface is calculated by a multiobjective optimization method using geometric constraints in the underwater binocular stereo system. Extensive experiments have been conducted on our underwater dataset and the results verify the effectiveness of the proposed scheme for underwater camera calibration and three-dimensional measurements.

To address the problems that the dehazing algorithm is prone to distortion, block artifacts, and edge pixel loss from the minimum filter in the highlighted area of an image, a dehazing algorithm with an atmospheric veil correction model under regional detection is proposed. First, the initial atmospheric light veil is obtained by using the improved dark channel, and the atmospheric light veil correction model is established for it. Then, the color distance and color distance histogram fitting curve of the haze image are used to accurately detect the region where the initial atmospheric light veil is corrected, and the correction term is established. Finally, the atmospheric light is estimated by combining the image information entropy with quad-tree subdivision algorithm. It is proved that the proposed method effectively solves the distorted problem in the highlighted region and the block artifacts produced by minimum filtering and can recover image with rich detailed information.

We show that aberration sensitivities are independent of lens scaling when the perturbation amount is kept the same. This behavior is in agreement with the results of actual calculation. Further, we point out that aberration sensitivities scale in the same way as aberration scale as a function of the lens field of view and aperture.

The simulation and analysis of a hyperentangled photon source based on polarization and transverse momentum are achieved using the MATLAB platform. The analysis includes determining the emission pattern of a spontaneous parametric down-conversion source and the opening angles of emission cones and their dependence on wavelength. The energy conservation in the generation process and the correlations between the hyperentangled states are investigated. The results show that the generated states are maximally entangled, and Bell’s inequality test is proven to satisfy the theoretical limits. The proposed model gives better insight into the generation process of hyperentangled photons. It could be integrated with simulations of any arbitrary system based on a hyperentangled source.

Synthesis of original optical designs is a challenging endeavor for novice lens designers. It is made more difficult when attempting to design a compound lens from off-the-shelf lenses. All but the simplest compound lenses resist ready analysis or understanding from a first-principles approach of geometric optics; however, many optical design packages include powerful optimization algorithms for both local and global searches. Despite the power of these tools, the initial construction of a starting lens and merit function remains crucial to the effective utilization of the optimizer. A workflow is presented for a generic starting design, construction of the merit function, and the optimization for a compound monochromatic objective lens composed only of commercial off-the-shelf lenses. A protocol is defined for the substitution of off-the-shelf lenses into a design with optical elements of arbitrary shape factor. Additionally, the theory and method for optimization of the shape factor via a macro in Zemax OpticStudio are provided to accelerate the substitution protocol and improve search results. The performance of the objective design is presented both before and after the off-the-shelf lens substitution and performance is compared to the design requirements. A tolerance analysis is performed and sensitivity and yield are discussed. The macro, lens design, merit function, and additional supporting code are provided.

All-optical synchronous and asynchronous binary up counters that employ silicon micro-ring resonator-based T flip-flops are proposed. An alternative approach to design all-optical synchronous and asynchronous binary up counters is also demonstrated using fewer optical components. The proposed design is theoretically realized in MATLAB simulation software at a very high operational speed of 260 Gbps. The performance of this design is validated through amplitude difference, contrast ratio, extinction ratio, amplitude modulation, on–off ratio, etc. The optimized values of the micro-ring resonator are achieved through numerical simulation, which will help to implement the proposed design practically.

The size and density of nanopits, generated at the surface of their top layer, strongly affect the electrical and optical properties of AlGaN-based structures. Therefore, the control of the layer quality evolution as a function of the nanopits size/density is a crucial issue to enhance the device performance. In this paper, the effects of the nanopits diameter observed at the surface of AlGaN on carrier dynamics are systematically investigated. The variation of nanopits diam-eter is achieved through thermal annealing of a set of AlGaN/GaN heterostructures at different temperatures. The samples are characterized using the scanning electron microscope (SEM), energy-dispersive x-ray, high-resolution x-ray diffraction, photoluminescence (PL), and time-resolved PL spectroscopies. SEM images have revealed an increase in the nanopits diameter with increasing annealing temperature. In addition, we observed a linear development in the yellow luminescence intensity, accompanied by a deterioration in the PL decay times due to an increase in the density of point-defect complexes that act as nonradiative recombination centers. We also performed temperature-dependent PL measurements to study the impact of the nanopits diameter on electron–phonon scattering processes. Both electron-acoustic- and electron-longitudinal optical phonon interactions enhance with increasing nanopits diameter.

Steel structures experience plastic deformation and damage during large earthquakes. The stress–strain (S–S) curve of structural steel can be used to develop a constitutive model to simulate its structural behavior. The S–S curve can be obtained by video extensometers, the efficiency of which with a telecentric lens and telecentric illumination remains unclear. The applicability of a telecentric lens and telecentric illumination system to video extensometers were investigated. Rigid-body motion and tensile testing were performed and the carrier of displacement of six gauge lengths was traced. Further, N images were obtained under a constant displacement/force and averaged to reduce the pseudo strain. Experimental results showed that the pseudo strain increases with the out-of-plane rigid displacement but remains unaffected by the in-plane rigid-body displacement. Tensile testing results showed an error difference of <10 % for the Young’s modulus obtained from the video extensometer and strain gauge.

Interferometric imagers need to measure the phase, modulus, and spatial frequency coordinates of the complex coherence factor to reconstruct images. However, these three measurement parameters are accompanied by certain measurement errors in the actual imaging process, thereby affecting the quality of the reconstructed image. Based on the checkerboard integrated optical imaging system, we simulate the influence of measurement errors of the complex coherence factor on the imaging performance of the integrated optical interferometric imager. The simulation results show that, on the premise that measurement errors follow the normal distribution, the modulus measurement error does not significantly reduce the quality of the reconstructed image, whereas the phase and spatial frequency coordinate measurement errors have a great impact. When the mean value of the phase measurement error is 0, the standard deviation must be <0.18π to ensure the high quality of the reconstructed image. For the measurement error of the spatial frequency coordinates, when the standard deviation of the lenslet position errors is <0.075 times the shortest baseline length, its influence on the quality of the reconstructed image is acceptable. The simulation results are of great help to the engineering, manufacturing, and application of integrated optical interferometric imaging technology.

To address the problem that bonding can lead to a reduction in the surface shape precision of a space-bound mirror, relationships between mirror deformation, thermal stress, and curing shrinkage stress were studied, and a bonding microstress design route was proposed. The thermal stress and thermal deformation introduced by thermal expansion mismatch were eliminated through an athermal adhesive layer thickness design. The relationship between mirror deformation and the curing shrinkage of the adhesive layer was derived completely, and structural optimization measures for releasing the curing stress of the adhesive layer are given. Bonding stress analysis was conducted based on the equivalent thermal deformation method, and an optimal structure meeting the design requirements was obtained. Finally, bonding of the mirror assembly was completed via this route, and the measured surface shape precision was stable at 0.0225λ. The theoretical analysis and experimental study demonstrate that this bonding design method can predict the bonding stress in the assembly process, making the follow-up bonding result controllable. These results should provide an excellent reference for the design and high-precision integration of large-aperture mirrors.

The prediction of infrared extinction performance is one of the indispensable factors for the research of smoke screen. So far, it is still short of an accurate numerical simulation for the infrared extinction performance after releasing smoke screen. We present a method for calculating the infrared extinction performance of smoke screen. The standard k − ε turbulence model and the concentration equation of smoke screen are combined to carry out numerical simulation research on the sedimentation and diffusion process of smoke screen in the field. The shape and mass concentration distribution of smoke screen are studied under different wind speeds and ground roughness. Lambert–Beer’s law is combined to calculate the infrared extinction area of the smoke screen under different conditions, and the influence law on the smoke screen extinction performance is analyzed under different conditions. The validity of the numerical simulation results is verified by the field test. It is a useful method for guiding the design of field experiments. This work is widely used in the evaluation of extinction performance and provided more information for use by decision makers.

Multispectral electro-optical/infrared payloads are being developed for a variety of defence and commercial system applications. Many applications depend on their ability to detect and recognize low-contrast and distant targets in a complex environment. The development of such systems necessitates the use of specialized optical filters capable of separating different spectral bands. To separate the bands from visible to mid-wave infrared (MWIR), a dichroic beam splitter is used. We have designed and simulated these two beam splitters with a 45-deg angle of incidence that will be used to separate the bands from visible to MWIR. The beam splitter in such an optical system must separate visible, short-wave infrared (SWIR), and MWIR. We present the thin-film coating design and simulation of these two beam splitters. The first beam splitter separates MWIR from visible and SWIR. The second beam splitter separates the remaining two bands: visible and SWIR.

A split doublet is more sensitive to aberration because the inner surfaces are typically strong in curvature and can independently misalign. To improve the centering of a lens element, we discuss using a strip of material inserted in the gap between the lens edge and the barrel. This technique has the benefit of relaxing the barrel inner diameter tolerance. Four examples are provided where lens centering was estimated to range between 0.025 and 0.050 mm.

High speed, wide range, and high precise beam steering technology are fundamental to free-space optical communication (FSO). Liquid crystal optical phased array (LC-OPA) is capable of achieving non-mechanical beam steering. This paper demonstrates a parallel, four-communication access beam deflection antenna based on LC-OPA, providing a large aperture, wide steering range, and high pointing precision. This antenna is composed of a coarse tracking subsystem using cascaded liquid crystal polarized grating (LCPG) and a fine tracking subsystem based on LC-OPA. The optical aperture is 80 mm × 80 mm, arranged in 2 × 2 subapertures, each serving a single wavelength beam. Besides, a cascaded control platform based on field programmable gate array is proposed to realize low-latency response. This optical antenna achieves a steering resolution of 20 μrad and covers a range of ±12 deg in two dimensions, laying the foundation for simultaneous access of multiple terminals in FSO communication network.

To improve the carrier injection efficiency and optimize the performance of the AlGaN-based deep ultraviolet laser diodes (DUV-LDs), one-way step-shaped quantum barriers (OWS-QBs), a symmetrical step-shaped electron blocking layer (SS-EBL), and a symmetrical step-shaped hole blocking layer (SS-HBL) are proposed. Crosslight software is used to simulate the DUV-LDs with a traditional structure, with OWS-QBs, and with OWS-QBs, a SS-EBL, and a SS-HBL. The simulation results and physical mechanism analysis indicate that the SS-EBL, SS-HBL, and OWS-QBs contribute to the increased carrier concentration in the quantum wells, the reduced carrier leakage in the nonactive regions, the increased stimulated emission rate, the reduced threshold current and threshold voltage, and the enhanced output power and electro-optical conversion efficiency of DUV-LDs.

In view of the limitation that the transport of intensity equation method can only be used at a single wavelength, we propose a binocular phase retrieval algorithm based on multiwavelength illumination. First, we solve for the corresponding single-phase results at different wavelengths and then calculate the surface height of the object by combining the obtained synthetic wavelengths and synthetic phases, in order to reconstruct the initial phase results at different wavelengths. To solve the problem of amplification of traditional noise and surface profile noise in the phase diagram in the phase synthesis step, we introduce a step-by-step noise reduction method that can reduce the noise in the initial phase results to the level for a single wavelength and finally obtain the corresponding high-precision phase results at different wavelengths. The intensity images collected by the proposed dual-microscope system verify the correctness and effectiveness of the algorithm.

The fluctuation–magnification effect on the peak intensity of a laser pulse caused by the nonlinear Kerr effect in the chirped volume Bragg grating (CVBG) compressor is investigated experimentally for a high-energy, thin-disk, chirped pulse amplification system. The nonlinear Kerr effect occurs at the blue end, and the accumulated nonlinear phase shift (B-integral) in the CVBG rises with the increase of laser pulse energy. Experiments show that small fluctuations in peak power of uncompressed pulses cause increasing of the temporal fluctuation and spatial fluctuation due to high Kerr-nonlinearity in the CVBG when B-integral is larger than π. Thus the initial fluctuation would be magnified by the CVBG compressor.

Optical fiber bus technology is an important research direction in communication systems of electronic devices in special vehicle platforms. According to the requirements for communication quality between devices in special vehicle platforms, an optical fiber bus based on gigabit passive optical network topology is proposed. A data cache-based predictive weighted interpolated polling dynamic bandwidth allocation method is presented and investigated for the optical fiber bus’s upstream bandwidth allocation. The network controller establishes a weighted buffer area for the communication requirements in the polling period according to the type and data volume of the network terminal (NT) data stream and dynamically allocates the bandwidth of each optical NT to better meet the communication requirements for different data within the special device platform. Verification is done by means of OPNET software simulation and the establishment of a NT simulation test system in the laboratory. This proves that the proposed dynamic bandwidth allocation algorithm can reduce the end-to-end delay of RS422 port data by more than 50% and meet the Ethernet and controller area network port data delay requirements.

Rare earth ion doping is considered to be a feasible way to improve the optical properties of glass in recent years. We investigate the luminescence characteristics of Ho^{3 +} -Er^{3 +} -Yb^{3 +} triple-doped tellurite glass (TeO₂-ZnO-WO₃-La₂O₃) at 2.0 μm. A series of characterization analyses on the prepared samples, such as x-ray diffractometer (XRD) pattern, Raman spectrum, differential scanning calorimetry (DSC) curve analyses, absorption spectrum, emission spectrum, and fluorescence decay curve, were performed. XRD pattern and DSC curve analyses indicate that the glass sample exhibits a typical amorphous structure with excellent thermodynamic stability. Through the absorption spectrum, the position and intensity of the absorption peak of the glass sample can be detected. Under an excitation of 980 nm laser, the 2.0-μm emission peak intensity of the glass sample increases by about 1500%, which is attributed to the energy level transition among Ho^{3 +} , Er^{3 +} , and Yb^{3 +} . By analyzing the energy level transition of Ho^{3 +} , Yb^{3 +} , and Er^{3 +} ions, the energy transfer mechanism and fluorescence lifetime can be obtained, and then the fluorescence enhancement phenomenon of Ho^{3 +} -Er^{3 +} -Yb^{3 +} triple-doped tellurite glass at 2.0 μm can be explained. It is demonstrated that the as-prepared Ho^{3 +} -Er^{3 +} -Yb^{3 +} triple-doped tellurite glass has potential for the application of fiber lasers and fiber amplifiers.

To stabilize the frequency difference of the two-cavity dual-frequency Nd:YAG laser at 1064 nm, a scheme of the phase modulation of the orthogonally and linearly polarized dual-frequency laser using single electro-optic phase modulator has been proposed, and a frequency-difference stabilizing system for a two-cavity dual-frequency Nd:YAG laser based on the single-modulator quadrature-demodulated Pound–Drever–Hall (SM-QD-PDH) method has been designed and established. The characteristics of phase modulation, frequency discrimination, frequency stabilization, and frequency-difference stabilization of the orthogonally and linearly polarized dual-frequency laser with a frequency difference of ∼24 GHz at 1064 nm have been investigated experimentally. The experimental results have indicated that during a period of 1 h, the laser frequency stabilities of the linear and right-angle cavities are estimated by Allan variance to be better than 1.6 × ^{10 − 11} and 2.0 × ^{10 − 11}, respectively, corresponding to a frequency-difference stability of better than 2.9 × 10 ^{− 7}. The designed SM-QD-PDH frequency-difference stabilizing system is not only simple but also has better performances than that of the double-modulator QD-PDH frequency-difference stabilizing system. Such a frequency-difference-stabilized two-cavity dual-frequency Nd:YAG laser can be used as an ideal light source for the synthetic-wave absolute-distance interferometric system.

Conventional Brillouin optical time-domain analyzer (BOTDA) requires the process of frequency scanning, which is very time-consuming. The data acquisition speed of the conventional BOTDA is too slow to realize dynamic sensing. The use of the optical frequency comb-based BOTDA can avoid the frequency scanning and speed up the measurement. But, to achieve dynamic measurement, it is also necessary to reduce the time for signal averaging to further improve the measurement speed. However, few averaging times lead to poor signal-to-noise ratio (SNR), which will limit the sensing performance of the system. Block-matching and 3D filtering (BM3D) algorithm is proposed to achieve the denoising of sensing signals in the sweep-free BOTDA using intensity-modulated direct-detection optical orthogonal frequency division multiplexing. The impact of the BM3D parameters on the denoising performance is analyzed, which is used to realize parameter optimization. To demonstrate the denoising performance of BM3D under different noise levels, white Gaussian noise with different standard deviation (STD) is added to the original sensing signal. When the STD of the added noise is 0.07 mV, the SNR after denoising using optimized BM3D is improved by 9.7 dB for the Brillouin gain spectrum (BGS) and 10.6 dB for the Brillouin phase spectrum (BPS), respectively, and the frequency uncertainty is reduced to be below 1 MHz. For a wide range of noise levels, BM3D has shown excellent denoising performance, and the average SNR after denoising is improved to be 16.8 and 15.6 dB for BGS and BPS, respectively, and the corresponding frequency uncertainty is reduced to be below 1.2 MHz.

We designed a cubic-phase gallium nitride (c-GaN) homojunction for ultraviolet-C (UVC) detection. A physical model approach was employed to design the dimensions of the detector and the doping concentrations of each layer. The calculated electrical and optoelectronic properties were employed to perform a simulation program with integrated circuit emphasis (SPICE) equivalent circuit model to integrate c-GaN photodetection capabilities into a CAD electronic simulator. The model allows estimating the transport properties in the darkness and under ultraviolet (UV) illumination conditions. Furthermore, the effect of depletion capacitance was taken into account thinking in the circuitry amplification stage. When a transient UVC flash occurs, the SPICE simulation revealed that the output signal is in the order of 300 μV, which is suitable to be amplified by a transimpedance amplifier.

In our work, the temperature sensing properties and intrinsic mechanism based on a bismuth–erbium co-doped optical fiber (BEDF) were explored. Through temperature sensing experiments, we found that when the 980-nm pump laser was used, the fluorescence intensity ratio (FIR) at 1560 and 1435 nm showed a good linear relationship at different temperatures and its sensitivity reached 0.1151 dB/°C, the accuracy was 0.2°C, and the R² of the FIR curve is about 0.9923. At the same time, we also proposed a detection algorithm to judge the working state of the sensor. By changing the BEDF coating material while the fiber is being fabricated, the temperature measurement range can be further improved. The optical fiber temperature sensor will have a broader range of applications.

Optical gas sensing based on tunable diode laser absorption spectroscopy (TDLAS) has characteristics of high sensitivity and real-time response, but interferences and distortions may result in fluctuations and errors in the precious and stable measurement of gas concentration. Therefore, it is required to monitor and analyze parameters and waveforms throughout the TDLAS process. We propose and establish a visualized architecture with real-time interfaces and modules for the complete TDLAS process. It basically includes several functional modules, i.e., multiple frequency laser driving, operating temperature control, harmonic processing, and curve fitting, allowing elaborately in-situ monitoring the overall working status. The digital error amplifier based on type II compensation network for the proportional-integral-differential feedback controller was developed. Generated first and second harmonics and dual channel digital phase-locking algorithms were also developed in the TDLAS system. In the gas sensing experiment, the driving signal of the laser includes a 5-Hz triangular wave and a 1-kHz sine wave, and results show the favorable laser operating temperature variation of below ±0.02 ° C and the concentration calibration. The overall estimated measurement errors in the experiment are about 4.55% for the 300-ppmv gas. This visualization and in-situ monitoring system are helpful and universal for the optimization, calibration, and improvement of the TDLAS-related optical gas sensing.

Based on double-layer Sb₂S₃ material, a method is proposed to realize adjustable metalens at 1.31 μm using geometric phase to regulate the incident beam. Different functions are realized by changing different states of Sb₂S₃. In design 1, the lower layer of phase change material is set as a half-wave plate in the amorphous and crystalline states, and the upper layer can be switched between half-wave plate and full-wave plate when it is in the two states so that the focal length of the metalens can be switched between F₁ and F₂. The full width at half maximum (FWHM) is close to the diffraction limit, and the focus efficiency can reach 69%. In design 2, the upper layer is always in the amorphous state with the high transmittivity. An optical switch is realized when the lower layer is used as a half-wave plate with the transmittivity close to 0 in the crystalline state. At the same time, a bifocal metalens with the focusing efficiency of 62% can be realized when the lower layer is used as a half-wave plate with the high transmittivity in the amorphous state. By adjusting the material crystallization rate, bifocal metalens with various intensities are realized. Our design has great potential in optical imaging, scanners that combine beam switches and lenses, and dual-function devices.

The state of graphene loop applied in the slotted antenna radiator is converted from non-resonant to resonant to achieve the tunable band-notch characteristics in an ultra-wideband (UWB) antenna. In the non-resonant state, the graphene loop with value of chemical potential as 0 eV acts as a parasitic element and does not contribute to radiation. Increasing the chemical potential of graphene starts converting the state of graphene loop from non-resonant to resonant. The graphene surface starts confining the localized surface plasmons with the increment in chemical potential and hence the multiple higher order resonances are formed. The higher order resonance with the destructive effect provide the band-notch characteristic in UWB response. The variation in chemical potential can tune the created notched band over frequency. Also, conversion of state of graphene loop from non-resonant to resonant deteriorates the far-field radiation parameters and radiation efficiency of antenna drastically. A trade-off can be set to find the required value of gain and radiation efficiency and frequency of the created band notch. Moreover, another technique of utilizing the double graphene loops with less surface area has also been studied, which allows one to attain the higher radiation efficiency of antenna along with the band-notch characteristics.

A higher-sensitivity optical sensor based on cascaded double-ring resonators (CDRR) for intensity interrogation has been demonstrated. By detecting the output optical power ratio between the drop port and coupling port and reducing the free spectral range for difference (ΔFSR), the intensity interrogation sensitivity of the CDRR sensor can be improved by 2.15 times.

A photonic crystal fiber (PCF) sensor is proposed for the detection of refractive index (RI), magnetic field intensity, and temperature. The large air hole in the center of the sensor is filled with a magnetic fluid (water-based Fe₃O₄) whose RI changes with the intensity of the magnetic field and temperature. The top of the sensor is polished and coated with gold film, and external sensing technology is used to detect changes in the RI of the analyte. Due to the characteristics of the structure, the lower and upper parts of the sensor can detect magnetic field intensity, temperature, and RI. The simulation results show that the proposed magnetic field, temperature, and RI sensitivities of the sensor can reach the maximum of 1.57 nm/Oe, −1 nm / ° C, and 7600 nm/RIU in the detection range of 22 to 250 Oe, 8°C to 60°C, and 1.38 to 1.42 RIs, respectively. The proposed multiparameter PCF plasmonic sensor can be used for hyperthermia monitoring, medical and chemical sample analysis, biomolecular engineering, and magnetocardiography.

We design a waveguide crossing with composite subwavelength (SW) structures, i.e., bridged SW grating (BSWG) waveguide structures and diagonally periodic holes (DPHs), on a partial parabolic single layer crossing (PPSLC) to improve its transmission. The BSWG is located before/after the input/output regions of the PPSLC and the DPHs are in the crossing region of the PPSLC. This waveguide crossing occupies a footprint of 6.2 μm × 6.2 μm upon a silicon-on-insulator wafer with 220-nm silicon device layer on 2-μm buried oxide. We successfully gain simulated results of the transmission up to 98.72% (−0.056 dB) and the crosstalk as low as −65 dB at an input wavelength of 1.55 μm.

An approach based on optical nano electro-mechanical-system (NEMS) switches is proposed in this paper to develop low-power logic circuits and processors. Based on the specific logic tasks expressed by sum-of-products (SOP) expressions, an array of switches can be appropriately arranged to implement various logic circuits. The logical output can be detected by translating the presence or absence of the light in the optical guided mode, which is controlled by the displacement of NEMS actuators under electrostatic forces. Therefore, to show the universality of the proposed method and its capability to extend processor circuits, the operation of a MUX (2:1) is analyzed. Furthermore, the presented switch’s functional characteristics and the logic circuits’ optical performance are obtained using the Finite Element Method (FEM) and Finite Difference Time Domain (FDTD) approaches. According to simulation results, the properties of the proposed switch, such as the operating voltage and the switching time, are 12 V and 2.6 μs, respectively. Consequently, the proposed fast and low-power actuator can be a promising choice for realizing low-power digital circuits, especially in the design of NEMS processors for low-power applications because of the significant reduction in its power consumption and immunity against electromagnetic radiation.

To achieve ultrahigh-density nanoplasmonic integrated circuits, low-loss conventional dielectric waveguides (CDWs) are used to transfer light into and out of the metal–dielectric–metal (MDM) plasmonic waveguides. We show that sandwiching the MDM plasmonic waveguide between two CDWs forms a Fabry–Perot cavity-like structure, which causes oscillations in the transmission coupling efficiency (TCE) into the output CDW as the length of the MDM waveguide is increased. Three types of compact air-gap couplers (AGCs) were used at the interface between those two types of waveguides to enhance the coupling efficiency between them. Our simulation results indicate that tapering CDW before it is connected to AGC not only enhances TCE into the output CDW by 9% over a wide spectrum range but also reduces the need for high-precision fabrication techniques to align AGC at the interface. Moreover, we achieved a TCE into the output CDW of 77% optimized for the optical communications wavelength of 1550 nm when the length of the MDM plasmonic waveguide is 600 nm. In addition, we showed that our proposed design has large fabrication tolerance by investigating the change in its spectrum response as various parameters of the design dimensions differ from that of the targeted optimum dimensions. We found that increasing the dimensions of AGC reduces the width of the spectrum, whereas increasing the width of CDW with its tapered part shifts the spectrum to the right by 100 nm per 40 nm increase in the width. We also found that increasing the refractive index of the MDM plasmonic waveguide with AGC controls the cutoff wavelength, in which TCE is almost zero at wavelengths shorter than the cutoff wavelength, and consequently provides a unique advantage in using our proposed design in sensing applications.

We explore the practical limits for wave optics simulations of plane-wave propagation in non-Kolmogorov turbulence using the split-step method and thin phase screens. These limits inform two simulation campaigns where the relationship between volume turbulence strength and normalized intensity variance for various non-Kolmogorov power laws is explored. We find that simulation of power-law exponents near 3 are limited to turbulence strengths with Rytov numbers of 7 when the simulation side-length sampling rate is limited to 8192. Under these same conditions, it is possible to simulate volume turbulence strength out to Rytov numbers of 12 for Kolmogorov turbulence out to a power-law exponent of 4. We also demonstrate that the peak scintillation and Rytov number where peak scintillation occurs increases approximately linearly with the power-law exponent. Also, if turbulence strength is fixed, the relationship between the scintillation index and power law depends on the operating regime. In weak turbulence, the relationship is negative, and it is positive in strong turbulence. This work also emphasizes the importance of properly scaling turbulence strength when comparing results between different mediums with different power laws and the influence and importance of defining inner and outer scales in these simulations.

Hermite–Gaussian (HG) beam has enormous potential to enhance the capacity of free-space optical (FSO) communication due to its unique orthogonal spatial modes. However, the combined influence of atmospheric turbulence and pointing error on average irradiance for a mobile FSO link have rarely been reported before. The closed form of average irradiance of an HG beam under an arbitrary magnitude pointing error in atmospheric turbulence is deduced through a statistical averaging method. The accuracy of the proposed theoretical results was verified by a phase screen simulation. We found that the average irradiance profile of an HG beam finally changes into an approximate Gaussian shape with the increase of atmospheric turbulence and pointing error, and the larger beam waist can mitigate the profile change with an increase of atmospheric turbulence and pointing error. Based on the expressions of average irradiance, the effective spot size and average received power under the pointing error in atmospheric turbulence were derived and analyzed. This research provides the fundamental theoretical expressions for performance research on an HG beam-based mobile FSO link in atmospheric turbulence.

We experimentally investigate the performance of an active and passive optical fronthaul to be employed in a cloud/centralized radio access network (C-RAN) architecture based on software-defined radio (SDR) for 4G systems, and we discuss the viability to integrate these fronthaul configurations in coexisting 4G/5G systems based on SDR by considering the reconfigurable characteristics of SDRs and the capacity and latency characteristics of the optical fronthaul. The active optical fronthaul consists of two transponders employing dense wavelength division multiplexing (DWDM), whereas the passive optical fronthaul consists of a point-to-point scheme based on DWDM only. To perform a comparative study between the active and passive optical fronthaul in the C-RAN architecture, we have measured the throughput (bit rate) generated via iPerf^® for uplink and downlink transmissions at different DWDM channels, and we analyze the losses and latency presented in both optical fronthaul schemes. We found that for different optical fronthaul lengths up to 21.76 km, the bit rate is practically the same for the passive and active fronthaul despite the higher optical losses present in the passive fronthaul in comparison to the active fronthaul. In addition, the latency among active and passive fronthaul are almost similar with an estimated increment of 20 μs in the active fronthaul. These results are independently of the number of remote radio heads (RRHs) and user equipment (UEs) considered in the C-RAN architecture. Our findings put forward the proposed DWDM passive fronthaul as a viable, less complex, and cost-sensitive solution for C-RAN systems with fronthaul lengths up to 21.76 km. These results and all the experiences reported on the C-RAN implementation provide valuable information to design and develop 4G and 5G C-RAN architectures based on SDR with the capability to operate in a DWDM optical fronthaul infrastructure.