Optical Transformation Research Articles

MCCA-VNet: A Vit-Based Deep Learning Approach for Micro-Expression Recognition Based on Facial Coding

In terms of facial expressions, micro-expressions are more realistic than macro-expressions and provide more valuable information, which can be widely used in psychological counseling and clinical diagnosis. In the past few years, deep learning methods based on optical flow and Transformer have achieved excellent results in this field, but most of the current algorithms are mainly concentrated on establishing a serialized token through the self-attention model, and they do not take into account the spatial relationship between facial landmarks. For the locality and changes in the micro-facial conditions themselves, we propose the deep learning model MCCA-VNET on the basis of Transformer. We effectively extract the changing features as the input of the model, fusing channel attention and spatial attention into Vision Transformer to capture correlations between features in different dimensions, which enhances the accuracy of the identification of micro-expressions. In order to verify the effectiveness of the algorithm mentioned, we conduct experimental testing in the SAMM, CAS (ME) II, and SMIC datasets and compared the results with other former best algorithms. Our algorithms can improve the UF1 score and UAR score to, respectively, 0.8676 and 0.8622 for the composite dataset, and they are better than other algorithms on multiple indicators, achieving the best comprehensive performance.

Substitution-driven structural, optical and magnetic transformation of Mn, Co co-doped BiFeO3

Substitution-driven structural, optical and magnetic transformation of Mn, Co co-doped BiFeO3

Mono-pole blocking accident analysis caused by inaccurate measurement of optical CT in ±800 kV UHVDC transmission system under lightning strike

The ultra-high voltage direct current (UHVDC) power transmission systems usually transmit a capacity of 6-8 GW, their stability and reliability are of vital importance to the large power grid. This paper analyses a mono-pole blocking accident caused by the inaccurate measurement of optical current transformer (OCT) when the pole line of Shaanbei-Wuhan ±800 kV UHVDC transmission system was struck by lightning. Combined with electromagnetic transient simulation of the UHVDC transmission system, digital simulation and in-plant testing of the optical CT, a comprehensive understanding of the factors contributing to the accident is achieved. It reveals that optical CT measurement anomalies were significant contributors to the misoperation of protective relays, which led to the mono-pole blocking accident. Based on the simulations of optical CT under high peak currents and high di/dt conditions caused by lightning strike, the importance of proper setting of demodulation algorithm parameters in optical CT to avoid inaccurate measurements is emphasized. Through in-plant testing and steady state current accuracy verification, the reasonableness of demodulation parameters is verified. Simulation results illustrate the challenges in measuring very fast transient current accurately, which are the premise and guarantee of stable operation of UHVDC transmission systems under lightning strike.

An image encryption algorithm for colour images based on a cellular neural network and the Chua's chaotic system

In the internet era, image encryption technology plays a crucial role in ensuring the security of image information. Aiming at the problem that low-dimensional chaotic encryption has a relatively small key space and is vulnerable to chosen-plain attacks, this paper proposed a novel colour image block encryption algorithm based on the cellular neural network and the Chua's chaotic system. Firstly, the plain is separated into three primary colours. And Fourier transform is applied to achieve optical transformation, generating six chaotic sequences iteratively. Secondly, the chaotic sequences were combined in pairs. And then combined with the plain to form three sequences, which were used in the diffusion process. Finally, the improved Chua's chaotic system is used to scramble the image. Both diffusion and scrambling are performed synchronously during encryption. Through the above operation, we get the final colour encrypted picture. The experimental results show that the algorithm has excellent encryption effect and can resist common attacks.

Real-time synthesis of a nonuniformly correlated, partially coherent beam using an optical coordinate transformation

We design, build, and validate an optical system for generating light beams with complex spatial coherence properties in real time. Beams of this type self-focus and are resistant to turbulence degradation, making them potentially useful in applications such as optical communications. We begin with a general theoretical analysis of our proposed design. Our approach starts by generating a Schell-model (uniformly correlated or shift-invariant) source by spatially filtering incoherent light. We then pass this light through an optical coordinate transformer, which converts the Schell-model source into a nonuniformly correlated field. After the general analysis, we discuss system engineering, including trade-offs among system parameters and expected performance. Finally, we test and validate the system by comparing experimental results to theoretical predictions. We conclude with a brief summary and a discussion of future work.

Structural, Optical, and Electrical Transformations in FexSi1−xO Thin Films: The Role of Iron and Annealing

Structural, Optical, and Electrical Transformations in FexSi1−xO Thin Films: The Role of Iron and Annealing

Evolutions of a ring Airy vortex beam and a ring Pearcey vortex beam in turbulent atmosphere and a comparative analysis of their channel efficiencies and OAM spectra

An optical vortex beam propagating through turbulent atmosphere encounters distortions in the wavefront that result in modal scattering. Abruptly autofocusing (AAF) beams with orbital angular momentum have gained significant attention due to their non-diffracting and self-healing nature. These warrant understanding of the behavior of these beams through turbulent atmosphere absolutely necessary. With this intuition, in the present work we investigate the behavior of two AAF beams, namely the ring Airy vortex beam (RAVB) and ring Pearcey vortex beam (RPVB) through the turbulent atmosphere in two cases—multiplexed and non-multiplexed. We propagate multiplexed as well as non-multiplexed RAVB and RPVB in different levels of turbulent atmosphere. In the non-multiplexed case, channel efficiency declines for both beams with increase in mode numbers. In the multiplexed case, increasing the gap between the mode sets results in a decrease in channel efficiency. We also report that in weak atmospheric turbulence RAVB outperforms RPVB in terms of channel efficiency. We use the optical transformation sorting (log-polar) method to demultiplex the optical beams at the output. Furthermore, we investigate and compare the orbital angular momentum (OAM) spectra of both beams in different levels of atmospheric turbulence and at different propagation distances. The comparison reveals that the spectra of RPVB are more dispersive as compared to those of RAVB.

Three-view cotton flower counting through multi-object tracking and RGB-D imagery

Monitoring the number of cotton flowers can provide important information for breeders to assess the flowering time and the productivity of genotypes because flowering marks the transition from vegetative growth to reproductive growth and impacts the final yield. Traditional manual counting methods are time-consuming and impractical for large-scale fields. To count cotton flowers efficiently and accurately, a multi-view multi-object tracking approach was proposed by using both RGB and depth images collected by three RGB-D cameras fixed on a ground robotic platform. The tracking-by-detection algorithm was employed to track flowers from three views simultaneously and remove duplicated counting from single views. Specifically, an object detection model (YOLOv8) was trained to detect flowers in RGB images and a deep learning-based optical flow model Recurrent All-pairs Field Transforms (RAFT) was used to estimate motion between two adjacent frames. The intersection over union and distance costs were employed to associate flowers in the tracking algorithm. Additionally, tracked flowers were segmented in RGB images and the depth of each flower was obtained from the corresponding depth image. Those flowers tracked with known depth from two side views were then projected onto the middle image coordinate using camera calibration parameters. Finally, a constrained hierarchy clustering algorithm clustered all flowers in the middle image coordinate to remove duplicated counting from three views. The results showed that the mean average precision of trained YOLOv8x was 96.4%. The counting results of the developed method were highly correlated with those counted manually with a coefficient of determination of 0.92. Besides, the mean absolute percentage error of all 25 testing videos was 6.22%. The predicted cumulative flower number of Pima cotton flowers is higher than that of Acala Maxxa, which is consistent with what breeders have observed. Furthermore, the developed method can also obtain the flower number distributions of different genotypes without laborious manual counting in the field. Overall, the three-view approach provides an efficient and effective approach to count cotton flowers from multiple views. By collecting the video data continuously, this method is beneficial for breeders to dissect genetic mechanisms of flowering time with unprecedented spatial and temporal resolution, also providing a means to discern genetic differences in fecundity, the number of flowers that result in harvestable bolls. The code and datasets used in this paper can be accessed on GitHub: https://github.com/UGA-BSAIL/Multi-view_flower_counting.

Optical Activity and Phase Transformations in γ/β Ga2O3 Bilayers Under Annealing

AbstractGallium oxide (Ga2O3) can be crystallized in several polymorphs exhibiting different physical properties. In this work, polymorphic structures consisting of the cubic defective spinel (γ) film on the top of the monoclinic (β) substrate are fabricated by disorder‐induced ordering, known to be a practical way to stack these polymorphs together. Such bilayer structures are annealed to investigate optical properties and phase transformations. Specifically, photoluminescence and diffuse reflectance spectroscopy are combined with transmission electron microscopy, Rutherford backscattering/channeling spectrometry and X‐ray diffraction to monitor the evolutions. As a result, a two‐stage annealing kinetics is observed in γ/β Ga2O3 bilayers associated with the epitaxial γ‐to‐β regrowth at the interface at temperatures below 700 °C and a non‐planar γ‐to‐β phase transformation starting at higher temperatures. Thus, the present data enhance understanding of the polymorphism in Ga2O3, interconnecting the phase transformation kinetics with the evolution of the optical properties.

Bilateral Symmetric non-Euclidean multi-frequency invisibility.

Light propagation in non-Euclidean geometry has become a hot topic in recent years, while transformation optics theory demonstrates unique advantages in this respect. A notable application of transformation optics in non-Euclidean space is non-Euclidean invisibility cloak which avoids the challenges of negative refraction and anisotropic materials. In this work, we propose another configuration for non-Euclidean invisibility, capable of achieving invisible across a wide spectrum. Using coordinate transformation, we convert this non-Euclidean invisibility into planar gradient medium and validate its effects through full wave simulations. We also discover that the corresponding gradient medium can further relax the material parameters. Our findings suggest diverse strategies for non-Euclidean invisibility and planar gradient media, potentially advancing optical invisibility and transformation optics in non-Euclidean spaces.

Photoinduced π-Bond breakage causing dynamic closing-opening shell transition of Z-type Diphenylmaleonitriles molecules

Organic molecules with dynamic covalent-bonding characteristics have attracted much attention for their important role in constructing stimulus-responsive smart materials. However, it is difficult to realize sensitive and reversible covalent bond cleavage/formation through external stimuli in the aggregated state of molecules. Herein, a series of 2,3-diphenylmaleonitriles (DPMNs) with photoinduced π-bond cleavage properties have been designed and synthesized to construct the dynamic covalent bond materials. The cis-form 2,3-diphenylmaleonitriles (Z-DPMNs) exhibit significant photochromism in both solid and solution states under ultraviolet light and visible light. The photochromism stems from the photoinduced π-bond splitting of Z-DPMNs, resulting in a transition from the closed-shell to open-shell structure. Moreover, the twisted structure and molecular stacking of Z-DPMNs, the push-pull electron effect of substituents, and the external factors including temperature and solvent polarity have important effects on the dynamic conversion of π-bonds. Based on the sensitive and reversible optical performance transformation, Z-DPMNs can be applied as safety ink in anti-counterfeiting, information encryption and storage systems. This work not only provides an approach for constructing dynamic covalent bonds but also greatly enriches stimulus-responsive materials.

Optical transformation characteristic of silicone resin matrix composite coatings under high-energy laser ablation

The easy destruction of most conventional materials by high-energy lasers is a great concern. Anti-laser coatings with ablative heat absorption capabilities are effective in preventing laser damage. However, their extremely low reflectivity implies a high energy absorption rate, which can result in rapid failure. In this study, silicone resin matrix composite coatings were designed and prepared by incorporating ceramic modification components to realize desired optical transformation characteristics. The modification effects on ZrC/SiC, ZrSi2, TiC/SiC, and TiSi2 were specifically studied with a high-energy continuous-wave laser (1080 nm). The results showed that oxidation reactions during laser ablation play a significant role in phase change and optical transformation. The element analysis proved that the composition rapidly changed from carbide and silicide to oxide, leading to the formation of oxide layer with relatively high reflectivity in laser ablation region. In particularly, oxidation and ablation of ZrSi2 facilitated the exposure, gathering, and sintering of ZrO2, which realized an increase in reflection from 6.2 % to 34.9 % during laser ablation (500 W/cm2, 60 s). The optical transformation characteristics were compared with the evolution of diffuse reflection intensity and its corresponding differential curve, which indicates that ZrSi2 exhibited the best performance.

Addition of fake imagery generated by generative adversarial networks for improving crop classification

Combining synthetic aperture radar and optical imagery can effectively improve crop type identification. However, optical remote sensing imagery is limited by cloud contamination. In this study, fake optical images were generated using seven image-to-image translation methods and their performance in improving crop classification accuracies was evaluated. Although the sensitivity analysis of the classification models showed lower similarity between real and fake images in the near-infrared band compared to the green and red bands, a significant improvement was confirmed after adding fake images created by generative adversarial networks (GANs). In this study, we generated fake optical images using GAN–based SAR–optical image transformations and evaluated whether adding these fake optical images contributes to improving the accuracy of crop identification from SAR images. This was especially true for the signed attribute vector image-to-image transformation (SAVI2I) method, which was the most effective, achieving an overall accuracy (OA) of 81.3 % with an allocation disagreement (AD) of 11.8 % and a quantity disagreement (QD) of 6.9 %. In contrast, the OA, AD, and QD were respectively 75.9 %, 18.2 %, and 5.9 % when only vertical-horizontal polarization, vertical–vertical polarization, or the polarization ratio were applied. As a result, it was demonstrated that utilizing fake images generated through GAN–based SAR–optical image transformations is effective in improving the accuracy of crop identification from SAR images.

Radiographic description phase composition of lithium niobate crystals with anomal growth of domains during soft proton exchange

The formation of periodically polarized waveguide structures in lithium niobate crystals for nonlinear optical transformations of laser radiation in the telecommunications wavelength range is an important applied problem. One of the options for forming waveguides with low switching fields can be waveguides obtained by soft proton exchange. In this work, using X-ray diffraction analysis, it is shown that anomalously low polarization switching thresholds occur in layers with so-called intermediate κ-phases when varying the time of soft proton exchange, and when varying the concentration of lithium benzoate, a transition from the metastable β-phase to the intermediate κ-phase is revealed. The results obtained support the hypothesis that the proton concentration gradient leads to a decrease in the threshold field for polarization switching. However, high-concentration metastable and intermediate crystalline phases lead to an increase in optical losses and temperature instability of waveguides.

On-demand photonic Ising machine with simplified Hamiltonian calculation by phase encoding and intensity detection

The photonic Ising machine is a new paradigm of optical computing that takes advantage of the unique properties of light wave propagation, parallel processing, and low-loss transmission. Thus, the process of solving combinatorial optimization problems can be accelerated through photonic/optoelectronic devices, but implementing photonic Ising machines that can solve arbitrary large-scale Ising problems with fast speed remains challenging. In this work, we have proposed and demonstrated the Phase Encoding and Intensity Detection Ising Annealer (PEIDIA) capable of solving arbitrary Ising problems on demand. The PEIDIA employs the heuristic algorithm and requires only one step of optical linear transformation with simplified Hamiltonian calculation by encoding the Ising spins on the phase term of the optical field and performing intensity detection during the solving process. As a proof of principle, several 20 and 30-spin Ising problems have been solved with high ground state probability (≥0.97/0.85 for the 20/30-spin Ising model).

Improved performance of a fiber-optic hydrogen sensor based on a controllable optical heating technology.

A novel, to the best of our knowledge, and compact fiber-optic hydrogen sensor based on light intensity demodulation and controllable optical heating technology is proposed and experimentally investigated. This system employs three photodetectors for optic signal transformation. The first PD is used to receive a little fraction of the amplified spontaneous emission (ASE) for calibration, and the second PD is utilized to detect optic signal reflected by a single mode fiber deposited with WO3-Pd2Pt-Pt composite film. The last PD is utilized to receive the optical power reflected by the short fiber Bragg grating (SFBG) with a central wavelength located in a steep wavelength range (the intensity decreases approximately linearly with the increase of the wavelength) of the ASE light source. A 980 nm laser and proportion integration differentiation (PID) controller were employed to ensure the hydrogen sensitive film working at an operating temperature of 60°C. This sensing system can display a quick response time of 0.4 s toward 10,000 ppm hydrogen in air. In addition, the detection limit of 5 ppm in air can be achieved with this sensing system. The stability of this sensor can be greatly enhanced with a controllable optical heating system, which can greatly promote its potential application in various fields.

Comparative analysis of geometric transformation-based sorting systems for fractional vector beams with polarization mutation angle indeterminacy

The Polarization Topological Charge (PTC) is a crucial parameter of a Cylindrical Vector Beam (CVB). Defined as the repetition number of polarization state changes along the azimuth axis, its sign indicates the polarization’s rotation direction. This paper delves into the effects of polarization mutation within Fractional Vector Beams (FVB) with angular uncertainty on PTC sorting systems. We compare three optical geometric coordinate transformation methods: Log-Polar (LP), Beam-Copying (BC), and Spiral Transformation (ST), focusing on their robustness and suitability. Our findings show that the azimuth angle of polarization mutation markedly influences the PTC sorting system’s output, leading to measurable uncertainties. Importantly, these uncertainties are not intrinsic to the FVB, but rather stem from the sorting system itself. Our study concludes that the BC method is optimal for PTC spectra analysis, whereas the ST method with carefully selected parameters is preferable for average PTC analysis.

Metasurface Empowered Compact Non‐Paraxial Optical Vortex Mode Sorter

AbstractThe optical coordinate transformation based on the ray model can flexibly and efficiently complete the manipulation of complex light fields through a pair of phase plates, and is successfully used to sort orbital angular momentum (OAM) of light. Generally, the phase modulation required by the optical coordinate transformation is derived analytically under the paraxial approximation, however, this would induce the phase modulation error, and thus worsen the quality of the transformed beam. Here, a non‐paraxial design for the spiral coordinate transformation is proposed, where the phase of the unwrapper is obtained by numerically solving the partial differential equations on the coordinate mapping and the phase corrector is obtained by the angular spectrum diffraction integral method. Due to more accurate phase modulation, the non‐paraxial spiral transformation effectively improves the beam quality, and realizes the demultiplexing of OAM modes with higher efficiency and lower cross‐talk. The proposed approach is verified with a compact metasurface‐based optical vortex mode sorter, which is extensible toward OAM‐based multi‐mode systems involving classical and quantum optical information processing.

Development of optical voltage transformer using electro-optic Pockels effect for HVDC transmission systems

Development of optical voltage transformer using electro-optic Pockels effect for HVDC transmission systems

Ensuing the formation of photocatalytic TiO2/Fe2O3 nanocomposite from heat treatment of electrophoretically deposited TiO2 films on stainless steel

In this study, thermal transformations in electrophoreticlly coated TiO2 coatings on SS-316L substrate were investigated. Such films were previously employed for antibcaterial purposes, however their heat-treatment at 900 °C resulted in an unexpected transformation in the film color. This study was designed to trace back the origin of such optical transformation in the TiO2 film that was expected to be whitish in its outlook, however it became brownish at elevated temperature, indicating an exploitable characteristics of visible light absorbance. The films were carefully transformed to particles by subsequently applying scratching/ball milling method and characterized through various materials’ characterization tools including but not limited to SEM-(EDS), XRD, alongside characteristic characterizations such as TGA, UV-Vis and EIS for elucidating thermal, optical and electrochemical behavior respectively of particles obtained from pristine (TiO2) and heat-treated films (termed as TFNC) owing to the transformation of TiO2 to TNFC (i.e. TiO2/Fe2O3) nanocomposite. TFNC exhibited decreased band gap from 3.2 eV to 2.86 eV and consequently improved photocatalytic activity. The TFNC degraded 50% Rhodamine B dye under visible light, while pure TiO2 degraded only 13%, which was credited to the formation of Fe2O3 particles inside TiO2 film. It was estimated that the Fe-element was capable to diffuse inside such TiO2 film and resulted the formation of TFNC at ≥ 900°C. The evolution of visible light dependent photocatalytic performance in TFNC was credited to the lowering of bandgap and enhanced electron-hole generation as investigated by EIS.