Special section editors Sawyer D. Campbell and Matthew E.L. Jungwirth introduce the Special Section on Advances in Computational Methods for Optical System Forward- and Inverse-Design.

We provide an analysis of the existing methods for calculating parasitic illumination, methods for its analysis, and visualization. To search for and analyze the sources of stray light in optical devices, a software model of the beam propagation criterion in an optical device is proposed, which makes it possible to select beams that satisfy a given criterion. We consider the possibility of using the method of bidirectional progressive stochastic ray tracing with inverse photon maps to calculate the stray illumination of an image and analyze the causes of its occurrence. To analyze the sources of stray illumination on the radiation detector, it was proposed to use progressive photon maps, which calculated the caustic and secondary components of the illumination and fixed the image illumination on a static regular mesh attached to the surfaces of the optical device. Special visualization tools allow the display of this illumination over the image of an optical device and determination of the elements of the device that have the greatest impact on the level of stray illumination of the image. We present examples of calculation, analysis, and visualization of parasitic illumination of a number of optical systems of lenses with real mechanical structures.

Structured light illumination systems can measure a target’s two-dimensional height profile. Recent advancements in computational power and algorithms have enabled the predesign of optical systems where all experimental variables are determined prior to use in the laboratory. We present a predesign process to align the projector of a custom-structured light illumination system. The predesign method uses the native optical design file to simulate the residual aberrations and can perform a trade space analysis to tailor the alignment variables to desired preferences. The presented method can predict the experimental focus position to 1.6 μm root mean square over a broad range of physical settings.

A random walk prediction (RWP)-based channel model is founded in the underground-mining (UM) visible-light communication (VLC) network. Among the factors that influence the communication performance of the UM-VLC network, the most significant ones are the arbitrary positioning and orientation of optical transmitters and receivers, tunnels with irregular walls, shadowing by machinery or miners, and scattering from dust clouds. This analysis allows for the development of a more realistic RWP-based channel model. These factors are integrated into a single-channel model that facilitates the derivation of complex expressions. The parameters are the received power of the RWP-based channel model, channel impulse response, root mean square delay spread, signal-to-noise-ratio, and bit error rate. The simulation results show that the RWP-based channel model meets the practical requirements better than other models in the reference papers.

This paper presents a color computational ghost imaging scheme through a dynamic scattering medium based on deep learning that uses a sole single-pixel detector and is trained by a simulated data set. Due to the color distortion and noise sources being caused by the scattering medium and detector, a simulation data generation method is proposed accordingly that easily adapts to the actual environment. Adequate simulation data sets allow the trained artificial neural networks to exhibit strong reconfiguration capabilities for optical imaging results. It is worth noting that the network trained by our method can reconstruct better details of the image than the simulation data sets according to the ideal state. Its effectiveness is demonstrated in optical imaging experiments with both rotated double-sided frosted glass and a milk solution used as the dynamic scattering medium.

Nowadays, optical designers often use multiprocessor workstations for the virtual prototyping of complex optical systems. Modern workstations may have several CPUs with up to 128 virtual cores each and a non-uniform access speed to different memory areas. Effective implementation of virtual prototyping methods and algorithms requires the development of special methods for efficient algorithm parallelization and shared memory access. As a basis for the virtual prototyping, we proposed a progressive backward photon mapping method that allows for reducing the amount of data used by photon maps, speeding up the luminance calculation process, and estimating the luminance errors for the resulting image. The main algorithmic complexity of this method is the need to synchronize data when calculating and accumulating the luminance of indirect and caustic illumination. The authors propose the three-level semi-synchronous parallelization method, which consists of fully synchronous, semi-synchronous, and asynchronous levels with illumination processing effectively distributed among the computation threads. The main benefit of the developed method is that it does not require additional synchronization when accumulating luminance, thus increasing the image synthesis speed. The designed three-level method can also be used in distributed systems with good scalability. The results obtained with virtual prototypes of complex optical systems are presented.

We proposed a new and simple scheme to implement exclusive OR (XOR) and not exclusive OR (NXOR) logic operations in the optical domain enabled by a dual-parallel phase modulator (PM). Both the intensity and phase of the optical signal are utilized to represent the four different states of two binary inputs, and direct detection is used to map the four states to the corresponding binary output. Through numerical analysis, two PMs with phase offsets were adjusted to π / 2, and the phase shifter between the two PMs was controlled atπ / 2; thus, the NXOR logic gate was successfully carried out. Two PMs with phase offsets were adjusted to π / 2, and the phase shifter between the two PMs was controlled atπ; thus, the XOR logic gate was successfully carried out. Simulations were successfully carried out at the speed of 10 Gb/s.

The present paper describes a parametric design and optimization tool [Support Optimization and Design Tool (SODT)], used to evaluate passive axial support positions on circular solid meniscus mirrors. The developed tool avoids the intrinsic limitations of methodologies of the reference literature, based on analytical formulations. A parametric finite element model of the mirror is generated from the user inputs and the support distribution is optimized in terms of the root mean square of the surface error (SFE). The optimization process is based on a hybrid optimization algorithm combining genetic algorithms and a gradient-based approach. The results are compared to the ones presented in the literature, evidencing minor discrepancies that can be basically attributed to differences in methodology and structural formulation, as it is discussed in the text. Finally, the finite element and optical postprocessing results are verified against industry-grade software: MSC Nastran^® and Sigmadyne SigFit^®.

A differential ray tracing (DRT) formulation for the analysis and design of arbitrary optical systems is presented. An approach based on sequential rays is proposed to define a functional representation of the ray path, where the gradient information associated with the ray path is obtained using an automatic differentiation technique. The proposed DRT algorithm is neither constrained to a specific optical system geometry nor restricted to a set of surface types or material definition.

Application of passive terahertz imaging in concealed weapon detection has been looked at, such that the final result is the segmentation of the foreground concealed weapons from the rest of the background. For the same, a fully automatic and completely generic technique, without any learning, has been proposed. It was observed that a simple thresholding step, exploiting varied intensity bands of the tetrahertz images is not enough. Thus, an innovative method to isolate humans and thus improve the region of interest (ROI) has been proposed. Thereafter, saliency has been used to further improve ROI, as these images are quite noisy and the central focusing aspect of saliency could handle the noise around the concealed weapons. It was observed that this step could handle the noise around the concealed weapons but degraded the boundaries of the concealed weapons. To further improve boundary adherence, superpixels are used. Finally, results are evaluated both quantitatively and qualitatively and outperformed the traditional approach.

In the artificial intelligence domain, human action recognition (HAR) has evolved as one of the major active research topics as a reason of diverse applications, namely video surveillance. The extensive variation types amidst routine human activities make the recognition procedure much more intricate. As a reason for an increment in the cameras’ usage, automated systems are essential to categorize activities, such as these utilizing computationally intelligent methodologies, namely machine learning and deep learning (DL). This paper’s organization covers all the characteristics of the HAR’s general framework. This work talks about the public dataset’s characteristics utilized that are aimed at HAR. After that, it summarizes and classifies the recently published research enhancement under the common framework. The merits and demerits of dimensionality reduction, action representation, and as well as action analysis methodologies are offered. After that, the outcomes exhibit the DL methodologies’ performance via graphs. This article gives a clear vision of what we can explore in the activity recognition area. The work talks about HAR’s challenges and its future directions.

Very high-resolution space borne missions demand finer spatial sampling and larger swath coverage for several commercial and strategic applications including cartography, disaster monitoring, urban planning, and surveillance. To meet these contrasting requirements, optical sensors often employ optical butting techniques in their focal planes as this enables the usage of small format detectors instead of large format single detectors, thereby reducing fabrication costs. In the optical butting technique, small reflecting mirrors placed before the focal plane split the optical field into smaller segments, which are alternately imaged by individual small format detectors. A single continuous image is formed using the small image segments through image processing technique. This requires optimal overlaps among the image segments with adequate image quality in the common imaged region. Factors, such as the geometric alignment of detectors with the butting mirror edge, edge-vignetting effects causing modulation transfer function, and signal-to-noise ratio degradations in the overlapping regions, largely determine the achievable overlap and image quality in the optically butted focal planes. Our study presents a comprehensive framework for the optimization of overlapping pixels in the optically butted focal planes based on a quantitative multicriteria analytical approach. The proposed framework has been tested for various sensor configurations to establish its efficacy. Our study will enable the efficient design and development of high-performance focal plane assemblies for high-resolution optical sensors.

Digital adaptive optics (DAO) created using homodyne encoding can mitigate atmospheric turbulence in passive imaging systems. This work demonstrates a self-referencing homodyne interferometry technique that combines the passive imaging utility of multiframe algorithmic procedures with the single-frame correction capability of the Shack–Hartmann adaptive optics technique. This paper presents image reconstruction improvements through the addition of (1) phase diversity modulation techniques within the interferometry reconstruction algorithm and (2) temporal image processing techniques applied after the interferometry reconstruction algorithm. By imaging quick response codes through a turbulent air chamber in the laboratory, it was possible to quantify the machine-readable performance gain provided by DAO when compared with a standard imaging camera. Results from this research verify that DAO from homodyne encoding provides turbulence mitigation for single frames of data, paving the way for environmentally robust, high-speed, self-contained imaging systems.

A split-step birefringence simulation method is proposed to investigate the gating efficiency and intensity distribution of the Kerr signal field considering the evolution of the switch beam and probe beam in their path. Using this simulation method, we investigated the switch-beam power-dependent gating efficiency and conducted an experiment to prove its reliability. Furthermore, we analyzed the optical intensity distribution of the Kerr signal exiting the Kerr medium under different switch-beam powers. This study provides an effective theoretical tool for the design and optimization of optical Kerr gates.

Prior art emission spectra of light sources utilized in chromatic confocal sensors share two disadvantages: the uneven spectral power distribution (SPD) and the fixed distribution characteristic. Consequently, the detected peak signal intensity is regulated by the SPD properties of the light source and the spectrum transmittance characteristics of the dispersive lens. To achieve this, 18 types of monochromatic light-emitting diodes (LEDs) with different peak wavelengths were selected to create a wide-spectrum light source with a tunable SPD. The SPD characteristics of the light source can be modified by adjusting the luminous intensity of each LED. The tungsten halogen lamp, the “white” LED, and the designed light source were selected as the light sources for the chromatic confocal measurement system, respectively. Comparing the peak signals obtained under various light sources. The experimental results show that, in the range of 400 to 700 nm, the peak signal intensity extreme value ratio measured with the designed light source is 1.81:1, and the normalized light intensity standard deviation is 0.118. The corresponding light intensity extreme value ratio of halogen tungsten lamp and white LED is 23.3:1, 300:1, and the normalized light intensity standard deviation is 0.302, 0.228. With the help of the designed light source, a group of wave crest signals with uniform light intensity distribution can be obtained. This can reduce the influence of the SPD characteristics of the light source itself and the transmissivity characteristics of the dispersive objective lens on the measured signal, and ensure the accuracy of spectral detection.

A laser multibeam differential interferometric sensor (LAMBDIS) was developed that provides measurement of vibration fields of objects with high sensitivity, while having low sensitivity to the whole-body motion of the object, or the sensor itself. The principle of operation of the LAMBDIS is based on the interference of light reflected from different points on the object surface illuminated with a linear array of laser beams. The Doppler shift induced by the sensor motion is approximately the same for all beams and is automatically subtracted from the measurements. The performance of the sensor for laser-acoustic detection of a buried object was experimentally investigated. The ability of LAMBDIS to detect buried objects from a moving vehicle has been demonstrated in field experiments.

In the projection moiré method based on equally spaced grating projection, the moiré pattern is often nonlinear and nonuniform because of oblique-angle projection. A new measurement method based on a newly designed nonuniform grating projection is proposed. A model of the projection moiré system based on the designed nonuniform grating projection was built, and the phase-to-height relationship of the proposed system was adjusted. High-quality periodic moiré patterns were obtained in the full measurement field in this system. Experiments demonstrated the precision and validity of the projection moiré system based on the designed nonuniform grating. The measurement resolution of the proposed system was 0.006 mm in an 800 × 600 mm² area, i.e., one hundred thousandths of the measurement field of view.

Measuring the pose of non-cooperative targets in space is a critical supporting technology for cleaning up space debris and recovering items. However, most existing methods are simulation experiments conducted in good lighting environments and tend to show poor performance in dark lighting environments. A target pose measurement method based on binocular vision is proposed, which is suitable for dark lighting environments. First, the traditional features from accelerated segment test algorithm are improved to reduce the influence of illumination on the performance of feature point extraction under various postures. The point feature and line feature are combined to extract image features more easily in a dark lighting environment while retaining the high accuracy of the pose measurement algorithm based on point features. Second, the normalized cross-correlation coefficient matching method is combined with the epipolar constraint to narrow the search range of the matching points from the two-dimensional plane to the epipolar line, which substantially improves the matching efficiency and accuracy of the matching algorithm. Finally, post-processing through feature matching is performed to reduce the probability of mismatches. Simulation and physical experiment results show that our method can stably extract features and obtain high-precision target pose information in well-illuminated as well as dark lighting environments, making it suitable for high-precision target pose measurement under insufficient illumination.

An in situ simultaneous measurement of magnetic coil constants and nonorthogonal angles method is proposed using the atomic magnetometer. Based on the transient response of the atomic spin polarization under the different magnetic fields, we establish the corresponding measurement model of magnetic coil constants and nonorthogonal angles through the relationship between the Larmor precession frequency and the external magnetic field. By this model, we experimentally obtained the coil constants of x , y, and z axes are, respectively, 9.04 ± 0.10, 8.94 ± 0.07, and 4.34 ± 0.02 nT / V in our system. The nonorthogonal angles are 89.04 deg between x axis and y axis, 88.60 deg between y axis and z axis, and 91.15 deg between z axis and x axis. This method can be used to simultaneously measure magnetic coil constants and nonorthogonal angles without relying on external instruments, which provides a basic guarantee for the accurate calculation sensitivity of spin-exchange-relaxation-free atomic magnetometers, especially for miniaturized atomic magnetometers.

When using the Fourier transform method to demodulate the phase from an interferogram, the Gibbs effect often occurs at the edge of the phase picture. Fringe extrapolation is a straightforward method to suppress the Gibbs effect. Currently, many algorithms are used in fringe extrapolation, and exemplar-based methods are one such alternative. However, the traditional exemplar-based algorithm is based on the Criminisi algorithm, which is extremely time-consuming. In this study, the structure-guided image-completion method was applied to interferogram extrapolation. Simulations and experiments show that the new method reduces computer memory requirements and saves computing time. Compared with extrapolation using the Criminisi algorithm, the speed can be increased by tens or even hundreds of times.

The advent of coding metasurfaces (MSs) has established a bond between electromagnetic scattering and digital control. Given that most of the current coding MSs are based on reflection-type, we investigate a novel transmission-type MS that can achieve ultra-wideband and efficient polarization conversion. A new double diagonal split ring resonator structure is designed to mainly constitute the unit. The 1-bit and 2-bit coding arrays are constructed using the proposed polarization rotation mechanism of the MS unit combined with the dimensional transformation to achieve beam focusing, beam deflection, and beam splitting. Finally, the broadband focusing characteristic of the coding MS is also demonstrated. Numerical simulation results demonstrate that the transmission coefficient of the proposed MS is above 90% in the frequency range of 0.4 to 2 THz, with a relative bandwidth of 133.3%. Asymmetric transmission phenomenon is observed in the range of 0.4 to 2 THz, with coefficients remaining above 80% in all ranges.The proposed coding MS can be used in terahertz polarization converters and unidirectional transmission devices due to its superior polarization conversion performance.

We describe the process through which stray light analysis should be performed in optical systems involving image slicers. We detail how scattering models should be used depending on how the image slicer assembly will be fabricated. Our work describes how to determine all ray paths, compute cross-talk on the pupil mirrors due to scattering, quantify the ghost images’ intensity, and determine baffle positions. In the example given, an ABg model is applied to all mirror arrays separately, before considering their contributions altogether. We also consider diffraction due to the image slicer’s narrow slice apertures, which contribute to unwanted light in the system by causing cross-talk on the pupil mirrors. Using Fourier optics, this quantity is computed and compared with cross-talk caused by scattering. Our work represents a useful asset for optical engineers who work on image slicer-based systems and want to analyze stray light, by providing a clear and exhaustive procedure to follow to obtain accurate estimates.

The existence of the beam vector effect requires rigorous electromagnetic computational methods for the optimization of subwavelength diffractive optical elements (DOEs). To design DOEs with high performance, we proposed an optimization strategy combining a global optimization algorithm with the finite difference time domain (FDTD) method. First, scalar initial solutions are obtained by the Gerchberg–Saxton algorithm. Then, regarding the diffraction efficiency, the uniformity error and figure of merit are calculated by FDTD as evaluation functions, and the optimization of the initial solutions is implemented by improved particle swarm optimization and continues with the simulated annealing algorithm. After several numerical simulations, the analysis results confirm the robustness of the algorithm and the reduction of the computational cost. The experimental data demonstrate that the correlation of diffraction energy orders between the simulated design and fabricated sample are above 85%. This method efficiently improves the DOEs design.

We propose a novel flat panel-based head-up display (HUD) to realize a large viewing angle automotive display. The proposed flat-panel geometry is straightforward to integrate into the dashboard. We also provide a flat-panel compatible solution to eliminate the ghost image and stray-light in large field of view using space-variant polarization sheets and optimized directional filtering, respectively. The proposed system provides an image area that is about 14 times larger compared to commercial HUD, and the P-polarized virtual image is also viewable with polarized sunglasses. The virtual image distance in our experimental system is closer than in commercial HUD.

A phase compensation method (PCM) based on the long short-term memory (LSTM) network is proposed for improving the short-term stability of fiber-optic radio frequency (RF) transfer systems. The proposed LSTM-PCM can predict the phase fluctuation within the next propagation delay and realize the precompensation of the system. For verifying the feasibility of the proposed method, we transmitted the 2.4 GHz RF signal over the optical fiber links from 200 to 1000 km. The phase fluctuations obtained from the experiment were used to construct an LSTM network. We simulated the frequency stability of the LSTM-PCM, and the findings demonstrate that the short-term stability of the system is improved more significantly with the increase of the transmission distance. With a transmission distance of 1000 km, the classical PCM achieves an overlapping Allan deviation (OADEV) of 1.02 × ^{10 − 12} at 1 s, whereas the proposed method can reduce the OADEV to 6.60 × ^{10 − 13} at 1 s. The LSTM-PCM can effectively suppress the residual delay phase fluctuations and has the potential for application in long-haul fiber-optic RF transfer systems.

In the present research, amplified spontaneous emission (ASE) emerging from the lateral surface of a thin-disk laser is investigated. Through the method presented, an equation was derived to estimate the intensity of the ASE from the side surface of the disk. The equation results were compared with the findings of numerical approaches to validate the derived equation. Using this equation, the impact of the ASE on the reduction of the output power of a Yb:YAG disk laser was also explored. A comparison of the computational results with experimental findings indicated that the obtained equation could substantially enhance the estimation accuracy of the output power of the disk laser.

This paper presents a hybrid porous-core flexible photonic crystal fiber (PCF), which has the potential for low-loss guidance of broadband terahertz (THz) waves at low THz bands. Here, the cyclic olefin polymer TOPAS is used for the main material to increase the flexibility of PCF. The central hybrid porous-core area contains a circular and hexagonal design, which reduces the loss of PCF. Simulation results show that the proposed fiber has a very low confinement loss of 3.47 × 10 ^{− 6} dB / cm at 500 GHz operating frequency. The bending loss at a bending radius of 1 cm is as low as 3.2 × 10 ^{− 4} dB / cm. The negligible modal loss facilitates the flexible application to THz systems. Moreover, the fabrication of the proposed PCF design is compatible with widely used methods and technologies, including stacking and drawing, extrusion and drilling. This newly proposed hybrid design of the porous-core region can be considered as an improved version in the research of THz porous-core waveguides.

Effect of the incident light beam conditions, such as the beam profile, the beam size, and the incident angle on the beam propagation and the firing characteristics of the radial-firing optical fiber tip comprised of conically shaped air pocket was investigated by the simulation using the ray-tracing method. Regardless of the different Gaussian profiles of the incident beam, no significant difference in the maximum firing angle but a little increase in the firing power was found with the increase of the axial distance of the Gaussian profile. With the increase of the incident beam size, no significant difference in the maximum firing angle was found but the relative firing power decreased and the extent of the power decrease depended on the numerical aperture (NA) of the fiber. On the other hand, the incident beam angle (BA) dependence of the firing power was significant, decreased to 65.9% and 31.9% for the RFF tip of NA 0.12 and NA 0.22, respectively, with the increase of the incident BA from 0 deg to 12 deg but the maximum firing angles did not show much decrease, smaller than 5 deg. The present modified simulation considering the incident light beam size and angle clearly showed the very close power distribution of the firing beam with respect to the firing angle obtained by the experimental results.

Due to the need for high bandwidth, there is growing interest in distributed fiber Raman amplifiers (FRA). In addition to having wide bandwidth, FRAs have the advantages of a low noise factor and simplicity of use. However, the optimization of the wavelength and power values of the pump lasers to be used in FRAs for a broadband and flat gain region is an important problem to be solved. In this study, a distributed FRA system was set using 100 signals with a 50-km propagation distance and 8 pump signals in the opposite direction, which were gain-flattened. The attenuation coefficient of SMF-28 type optical fiber was used in the system. First, optimum pump wavelengths and power levels were found by the binary search equation based adaptive artificial bee colony algorithm. Then, the FRA boundary value problem (BVP) was solved with the MATLAB BVP solver. Finally, the analytical Jacobian matrix required for the solution of the equation was included in the system, and faster and more effective results were obtained. The results show that the gain ripple of 100 optical signals was 0.5 dB at the maximum.

We propose and study an innovative magnetic sensor of incomplete surface defect one-dimensional (1D) photonic crystal composed of magnetic fluid, SiO₂, and TiO₂ as defect layers. The magnetic fluid film covers the surface of the 1D photonic crystal, whereas the magnetic fluid penetrates into the array of circular holes with period ∧ inscribed on the dielectric layers of SiO₂ and TiO₂ to form the incomplete surface defect layer. The sensing characteristics of a 1D photonic crystal magnetic sensor (1D-PCMS) were analyzed using the theory of rigorous coupled wave analysis. The innovative use of the angular interrogation method in magnetic field detection has investigated the effect of defect layer structure parameters, optical dielectric loss on magnetic sensor sensitivity and quality factor at a fixed wavelength. This incomplete surface defect mode 1D-PCMS structure demonstrates the feasibility of scanning angular measurements of magnetic fields and provides a reference for future research on 1D-PCMS based on angular interrogation.

Fabrication of optoelectronic devices relies on expensive, energy-consuming conventional tools including chemical vapor deposition, lithography, and metal evaporation. Furthermore, the films used in these devices are usually deposited at elevated temperatures (>300 ° C) and under high vacuum, which necessitate further restrictions on the device fabrication. Developing an alternative technology would contribute to the efforts on achieving a sustainable optoelectronics technology. Keeping this in our focus, here we present a simple technique to fabricate visible photodetectors (PDs). These fully solution-processed and transparent metal-semiconductor-metal (MSM) PDs employ silver nanowires (Ag NW) as the transparent electrodes replacing the indium-tin-oxide (ITO) commonly used in optoelectronic devices. By repeatedly spin coating Ag NWs on a glass substrate followed by the coating of zinc oxide nanoparticles, we obtained a highly conductive transparent electrode reaching a sheet resistance of 95 Ω / □ as measured by the four-probe method. Optical spectroscopy revealed that the transmittance of the Ag NW-ZnO films was 84% at 450 nm while the transmittance of the ITO films was 90% at the same wavelength. Following the formation of the conductive film, we scratched it using a heated surgical blade to open a gap. The scanning electron microscope images indicate that a gap of ∼30 μm is opened forming an insulating line. As the active layer, we drop-casted red-emitting CdSe/ZnS core-shell quantum dots (QDs) onto this gap to form a MSM PD. These visible QD-based PDs exhibited responsivities and detectivities up to 8.5 mA / W and 0.95 × 10⁹ Jones, respectively at a bias voltage of 5 V and wavelength of 650 nm. These proof-of-concept PDs show that the environmentally friendly, low-cost, and energy-saving technique presented here can be an alternative to conventional, high-cost, and energy-hungry techniques while fabricating photoconductive devices.

This paper presents a patternable two-color quantum dot (QD) color conversion film based on photolithography technique. Toluene-assisted dispersion of QD powder with the best performance matching was selected from four typical dispersions by experimental comparison. On this basis, the color conversion film of QD was prepared by photolithography technique. The experimental results show that the height of the patternable QD microstructures has good consistency. At the same time, the monochromatic spectrum test shows that the spectral characteristics of QDs are not significantly affected by the photolithographic process. Therefore, the preparation methods described in this paper can provide a reference for related research.

An ultrawideband metamaterial perfect absorber based on vanadium dioxide is proposed. It achieves >95 % absorption of vertically incident electromagnetic waves in the range of 3.50 to 10 THz. The absorption intensity can be dynamically adjusted in the range of 0.2% to 99.98% by varying the conductivity of VO₂. The mechanism of ultrawideband perfect absorption is interpreted using electric field distribution analysis and impedance-matching theory. The absorption rate related to the structural parameters of the absorber is investigated by numerical simulation. Finally, its polarization angle-insensitive and incidence angle-insensitive properties are demonstrated. This proposed absorber has potential applications in optical switching, electromagnetic stealth, and sensing applications.

Future communication networks require the entire communication system to be all-optical to overcome the bandwidth constraints of electronics. All-optical devices play a vital role in supporting future networks, which demand a high speed of up to Tbps. An all-optical gray code converter operation was demonstrated numerically using a photonic crystal semiconductor optical amplifier (PhC-SOA) in a Mach–Zehnder interferometric (MZI) configuration at 1 Tbps for M-ary differential phase shift keying modulated binary and BCD inputs. The design achieved a very high extinction ratio of about 123.8 dB with a good quality factor value of about 45. The results show that PhC-SOA-based XOR and OR gates in the gray code converter design exhibits improved modulation features compared with traditional SOAs in our previous works.

Einstein–Podolsky–Rosen (EPR) steering has important practical applications in secure quantum communication because of its unique characters. Multicolor and multipartite EPR steering is an important resource for connecting different physical systems in the quantum networks with several nodes. We investigate three-color and tripartite steering properties based on the intracavity cascaded nonlinear processes of down conversion and sum frequency. Based on the criteria proposed by Kogias [Phys. Rev. Lett. 114, 060403 (2015)], the steering parameters among down-conversion fields and sum-frequency field versus the normalized frequency and the pump parameter are studied. Our research shows that the direction of steering and steerability can be manipulated flexibly. We also show that quantum secret sharing can be realized in our scheme. And the results of asymmetric quantum steering and joint quantum steering among different modes provide a technical reference for the construction of secure quantum information network.

When detecting ultrahigh speed micro targets, because the photon Doppler signal will be seriously interfered with by high-frequency noise, it is difficult to accurately extract the beat frequency information, resulting in serious speed demodulation error. Therefore, we propose a beat frequency extraction method for high-speed and high-noise Doppler signals based on double correction, which can accurately correct the beat frequency signals of high-frequency noise interference. First, the ratio correction method is used for the first spectrum correction to screen out the normalized spectrum of high-frequency noise interference; then, according to the degree of noise interference, the energy barycenter correction method or linear interpolation method is used for the second spectrum correction. Numerical simulation results show that this method can reduce the spectral error by 1.6% to 2.1%. We used this method to process the Doppler signal from the detonation small flyer experiment in Initiating explosive device testing. The results show that it can reduce the beat frequency error by 1.83 times at most under high-frequency noise interfered, equivalent to the instantaneous velocity error of 1955 m/s can be decreased after velocity demodulation. Therefore, the beat frequency extraction method based on double correction has good noise resistance and reliability. We corrected the different regions’ frequency spectrums according to the noise interference intensity, which provides an idea for the beat frequency extraction of high-speed and high-noise Doppler signals.