Mid-wave infrared interference spectral imagers possess unique advantages in gas detection and identification due to their wide characteristic spectral coverage,high-throughput detection capability,and multi-channel sampling.Particularly in daily inspection and early warning of chemical gases and rapid emergency response to leakage scenarios,they can provide early warnings of disasters at the initial stage of gas leakage,preventing the situation from escalating.After a gas leak occurs,without requiring personnel to enter the site,they can quickly identify the type of leaking gas and the distribution of its diffusion concentration,providing first-hand on-site data for the evaluation of emergency response plans.However,traditional point-scan and area-scan interference spectral imaging configurations face significant limitations in enhancing lightweight,compact design,and stability.It is of great significance to research and design interference spectral imaging instruments that meet the high demands for mobility,adaptability to complex environments,field of view coverage,and lightweight compactness in specific application scenarios.Additionally,as interference spectral imagers require high precision in detector pixel intensity detection,it is necessary to study the analysis and suppression methods of infrared stray radiation in complex scenarios. This paper proposes a spectral imaging system based on static interference modulation using a stepped micro-mirror.The optical configuration of the system is shown in Figure 1.The scanning telescope imaging lens assembly achieves wide-field one-time convergence imaging onto the stepped micro-mirror for interference modulation,and the image is then relayed onto the detection focal plane through the relay imaging lens group.A cylindrical design is introduced to compensate for the high-order astigmatism introduced by the interference beam-splitting system.Achromatic broadband design and athermalization across a wide temperature range are achieved through hybrid refractive-diffractive and aspheric designs,resulting in a static Modulation Transfer Function(MTF)better than 0.7 at the cutoff frequency.To analyze infrared stray radiation,a stray radiation model for the interference spectral imaging system was constructed.The materials and surface radiation scattering characteristics of the optomechanical structure were defined,and ray tracing was performed.Based on the tracing results,a stray radiation suppression structure was designed,achieving infrared radiation suppression at the level of 10⁻⁵. The telescope imaging lens group was optimized with an image-space telecentric design,while the relay imaging lens group adopted an object-space telecentric design,achieving a perfect match in a dual-high telecentric optical system.By employing hybrid refractive-diffractive and aspheric designs,the system demonstrated excellent performance in the mid-wave infrared band of 3 μm-5 μm across a temperature range of-40℃to 60℃.The static MTF exceeded 0.7 at 17 lp/mm,distortion was controlled within 0.2%,and the RMS radius of the imaging spot was less than 5.9 μm,meeting all imaging quality requirements.A stray radiation simulation model for the interference spectral imaging optomechanical system,as illustrated in Figure 7,was constructed.Stray radiation tracing was performed for typical field light paths,and based on the analysis results,efficient suppression was achieved through blackbody extinction treatment and dedicated stray radiation suppression structures.This reduced the infrared stray radiation energy ratio from an initial level of 10⁻² to 10⁻⁵.Imaging detection experiments on long-distance target scenes using an engineering prototype demonstrated excellent image quality.The MTF test of the prototype of high-precision alignment principle shows that the actual MTF of the designed imaging system is better than 0.32 at the cut-off frequency. The infrared spectral imaging system based on static interference modulation with a stepped micro-mirror successfully achieves high-quality remote sensing imaging,identification and analysis of gases.The adoption of achromatic methods using cylindrical lenses and hybrid refractive-diffractive lenses,together with the stray radiation suppression method proposed in this paper,has all yielded the expected effects in optimizing imaging quality,which is proven to be effective and can serve as a reference for research in the same field.In addition,the instrument's volume is reduced by a quarter and its weight by approximately 60%,which also provides a valuable contribution to the miniaturization process of such imaging systems.
Intense solar activities(such as coronal mass ejections and solar flares)release a large number of high-energy charged particles.When these particles reach Earth,they interact with the magnetosphere and trigger magnetic storms through processes like particle precipitation.The duration of magnetic storms can range from several hours to days.During this period,they cause ionospheric disturbances and drastic changes in the geomagnetic field,leading to disruptions in on-orbit satellite communications and shortwave broadcasting,significant degradation or even loss of lock in the positioning accuracy of global navigation satellite systems,and an increased risk of accelerated orbital decay for low-orbit satellites due to sudden increases in atmospheric drag. During magnetic storms,precipitating particles collide with the upper atmosphere at the poles along magnetic field lines,exciting the generation of auroras.The radiation characteristics of auroras are directly related to the flux and energy of the incident particles.Therefore,detecting the morphology of auroras in specific wavelength bands has become a key method for studying solar activities.During magnetic storms,precipitating high-energy particles collide with neutral atmospheric components(such as atomic oxygen and nitrogen molecules)above Earth's poles.Through excitation and ionization processes,these collisions produce auroral radiation covering wavelengths from visible light to the far ultraviolet.Among this radiation,the emission intensity of the LBH band of nitrogen molecules(N₂)—located in the far ultraviolet range of 160～180 nm—has a direct and sensitive quantitative relationship with the energy flux of the precipitating particles. Far ultraviolet radiation is effectively absorbed by the upper atmosphere,enabling its observation even in sunlight.However,achieving high-precision imaging of N₂ LBH band auroral radiation faces two core technical challenges.Firstly,the dynamic range of auroral brightness under natural conditions is extremely wide.Imaging across a range from approximately 100 Rayleigh(R)to over 30 000 Rayleigh(30 kR)during intense activity periods requires the instrument to have an extremely high linear dynamic range.Secondly,in the far ultraviolet band,stray light interference from non-target sources(such as the Sun and geocoronal background)is extremely strong,which can easily overwhelm weak auroral signals.This places extremely stringent requirements on the system's internal stray light suppression capability. To capture the full dynamic range(100 R～30 kR)of N₂ LBH band(160～180 nm)auroral radiation and overcome the challenges of weak far ultraviolet signals and strong background interference,this study developed an optical system based on a coaxial four-reflection structure.The core of the instrument's performance lies in its large dynamic range detection capability and high stray light suppression level.Through targeted optical design,simulation,and testing,the system ultimately achieved a signal-to-noise ratio(SNR)>1.5 for extremely weak signals(100 R),ensuring the reliable extraction and detectability of weak signals.For strong signals(30 kR),the SNR reached>30,guaranteeing measurement accuracy and the upper limit of dynamic range during intense auroral activity.Meanwhile,the stray light suppression level reached 10-3 within the 160～180 nm operating band and exceeded 10-9 in the non-operating band of 200～1 000 nm,thereby effectively extracting real auroral signals from complex optical backgrounds. This instrument can continuously monitor the spatiotemporal evolution of the position,morphology,scale,and intensity distribution of the auroral oval.Through inversion and analysis of these high-quality image data,we can quantitatively obtain core parameters such as information on precipitating particles and their energy flux.This deepens the scientific understanding of magnetic storm triggering mechanisms,energy coupling processes,and evolution laws.It provides crucial data support and technical backing for accurate magnetic storm forecasting,space weather modeling,and ensuring the stable operation of on-orbit satellites and ground communication systems,boasting significant scientific value and broad application prospects.
Intraocular Lens(IOL)is a medical device implanted into the eye,commonly utilized in the treatment of ophthalmic conditions such as cataracts.In clinical practice,implanted IOLs frequently exhibit varying degrees of decentration and tilt.These positional deviations from the ideal alignment can significantly compromise the eye's optical performance.Among the widely adopted monofocal IOLs,which are primarily designed to restore distance vision,two main categories exist:spherical and aspherical monofocal IOLs.Aspherical monofocal IOLs can be further subdivided into two types:Aberration-correcting Intraocular Lens(ACIOL)and Aberration-free Intraocular Lens(AFIOL).ACIOL is specifically designed to neutralize the cornea's inherent positive spherical aberration,thereby enhancing the quality of distance vision.Under perfect centration conditions,these lenses are capable of delivering optimal optical outcomes.In contrast,AFIOL,while not altering the overall spherical aberration of the eye,demonstrate superior performance in the presence of decentration or tilt.Under such non-ideal positional conditions,they are usually superior to ACIOL.However,while numerous studies have evaluated the optical performance of misaligned IOLs,the underlying causes of performance variations among different aspherical monofocal IOL types remain inadequately explored—a challenge that persists in the field.Some investigations have focused on compensating for refractive errors resulting from IOL tilt or axial shift,whereas others have derived analytical expressions to estimate the specific aberration terms that require correction under given decentration conditions.Despite these valuable efforts,a critical gap remains:the absence of a comprehensive theoretical model capable of simultaneously characterizing the aberrations of the human eye's optical system in the presence of both decentration and tilt.This limitation ultimately hinders a systematic analysis of the factors responsible for optical performance differences among misaligned IOLs. To address these challenges,this study introduces several key improvements.First,the computational model incorporates the thickness of both the cornea and the IOL.Under realistic implantation conditions,the anterior surface of the IOL may not be perfectly aligned with the iris and can exhibit a measurable offset.This misalignment significantly increases the complexity of aberration calculations,requiring repeated application of the pupil-shift law to both optical surfaces.To enable efficient computation and analysis,the wave aberration coefficients corresponding to primary spherical aberration and primary coma in the pseudophakic eye are explicitly derived.Then,based on functional differences,different axial lengths,and functional principles,three types of ACIOL and three types of AFIOL were designed respectively.The validity of both ACIOL and AFIOL is confirmed through a comprehensive analysis of their Modulation Transfer Function(MTF),spot diagrams,simulated imaging,and aberration characteristics.The accuracy of these aberration coefficients is subsequently verified using numerical software.During the development of the misaligned pseudophakic eye model,we clarify why the primary spherical aberration field remains invariant under lateral misalignments.Subsequently,we establish the relationship between the primary coma field and the aberration field decenter vector.A mathematical formula for determining the coordinates of the primary coma field center is derived,revealing that under misaligned conditions,the pseudophakic eye possesses only one nodal point for primary coma—a position that is demonstrably influenced by lateral misalignments.Moreover,a comparison was made between the designed IOL and a commercial ACIOL,which showed similar MTF,thus demonstrating the universality of the conclusions drawn in this study. Based on the misaligned pseudophakic eye model,this study investigates the primary coma field centers of both ACIOL and AFIOL under misaligned conditions.Analytical results indicate that a larger shift in the primary coma field center is associated with a lower MTF.Under decentered conditions,the primary coma field center shift of ACIOL is significantly greater than that of AFIOL.Since the posterior surface spherical aberration is consistent between the two types of IOLs,and the absolute value of the anterior surface spherical aberration in ACIOL is significantly higher than that of the posterior surface,reducing the anterior surface spherical aberration becomes necessary to achieve zero overall spherical aberration.However,as both IOL types share the same dioptric power,their spherical contributions to anterior surface spherical aberration are comparable.Consequently,the reduction of anterior surface spherical aberration must be achieved by decreasing its aspherical contribution,specifically by reducing the conic constant of the anterior surface.This adjustment ensures that the total spherical aberration of the IOL is zero for AFIOL.Once the conic constant of the IOL anterior surface is reduced,the aspherical contribution of the primary coma coefficient of the anterior surface decreases.Given that the aspherical contribution of the posterior surface's primary coma coefficient is zero,this reduction leads to a diminished aspherical contribution to the primary coma field center under decentered conditions.Then,the accuracy of calculating the center of the aberration field is verified through numerical software.Furthermore,by discussing the differences in refractive index between corneal and intraocular structures at different wavelengths and their impact on aberration calculation,the rationality of eye model selection can be enhanced.Finally,by discussing the potential impact of a single parameter such as corneal aberration and thickness,the applicability of the conclusions drawn in this study is demonstrated. By integrating nodal aberration theory with primary aberration theory,we establish a mathematical model that systematically relates IOL misalignments to the primary aberrations of the entire eye.This analytical framework offers a clear advantage over purely numerical approaches,allowing for a principled evaluation of how IOL decentration and tilt influence overall ocular aberrations.Consequently,the model provides a theoretical basis for explaining the performance differences between the two types of aspherical monofocal IOLs under misaligned conditions.The following conclusion can be drawn:1)Decentration and tilt of an IOL cause displacement of the primary coma field center from the field center.This displacement is collectively influenced by factors such as the magnitude of IOL misalignment,geometry of lens surface,and refractive index.Moreover,the magnitude of the primary coma field center shift demonstrates a negative correlation with the system's MTF;2)In the design of aspherical monofocal IOLs,appropriately reducing the conic constant can significantly diminish the primary coma field center shift induced by decentration,thereby enhancing optical performance under misaligned conditions.When the primary coma field center shift is sufficiently minimized,the system's MTF can be maintained nearly unchanged.In summary,the misaligned pseudophakic eye model provides a comprehensive framework for understanding how decentration and tilt influence the performance of aspherical IOLs.This approach offers valuable theoretical guidance for future IOL design and evaluation criteria.
Phase unwrapping serves as a critical step in high-precision optical measurement, aiming to recover the absolute phase from its wrapped counterpart. While current deep learning-based approaches for absolute phase extraction have achieved improvements in both accuracy and computational efficiency, critical challenges persist, including excessively large network parameter counts and low accuracy in resolving discontinuous phases. To overcome these limitations, this paper introduces the Attentive Directional Encoder-Decoder Network (ADE-Net) for structured light phase unwrapping applications. The primary objective is to develop a lightweight, efficient, and robust deep learning framework that achieves consistently high unwrapping accuracy under complex conditions such as noise corruption, phase discontinuities, and aliasing artefacts, thereby providing a practical, engineering-ready solution capable for reliable development in real-world optical measurement systems. The proposed ADE-Net is built upon a concise and efficient encoder-decoder backbone architecture. The encoder consists of four feature extraction stages, each comprising a convolutional block and a Haar Wavelet Down-sampling (HWD) module. The HWD structure preserves high-frequency directional details, such as phase jump edges, during down-sampling, providing a more complete feature foundation for subsequent processing. The decoder employs a symmetric up-sampling structure based on transposed convolutions, with skip connections to fuse multi-scale features from the encoder, ensuring effective detail recovery. To enhance feature representation, two innovative modules are integrated: the Adaptive Clockwork Long Short-Term Memory (AC-LSTM) module and the Depthwise-separable-convolution Efficient Multi-Scale Attention (DEMA) module. The AC-LSTM module is designed to capture multi-scale contextual and direction-sensitive features simultaneously. It consists of two parallel branches: an Atrous Spatial Pyramid Pooling (ASPP) branch for multi-scale context aggregation, and a bidirectional LSTM (Bi-LSTM) branch enhanced with Context Anchor Attention (CAA) to model long-range dependencies along horizontal and vertical directions with spatial awareness. The outputs of both branches are fused to produce rich, direction-aware features. The DEMA module is an improved version of the Efficient Multi-Scale Attention (EMA) mechanism. It introduces depthwise separable convolution to replace standard 3 & times;3 convolutions, significantly reducing computational complexity while maintaining receptive field coverage. Additionally, Batch Matrix Multiply (BMM) is adopted for more efficient parallel processing of batch data. DEMA operates by grouping input features, performing adaptive height and width pooling, and applying depthwise separable convolution in parallel branches, followed by cross-branch fusion via BMM and element-wise multiplication with the original features. This design enhances the model's ability to focus on critical information across scales while optimizing computational efficiency. To comprehensively evaluate the performance of ADE-Net, systematic experiments were conducted using both simulated and real-world datasets. For simulation, three distinct datasets were constructed, each comprising 2 000 pairs of wrapped and absolute phase images with a size of 256 & times;256. Dataset 1 simulated noise interference by introducing Gaussian noise with signal-to-noise ratios of 0, 5, 20, 40, and 80 dB. Dataset 2 simulated phase discontinuities by randomly generating 1 to 2 rectangular jump regions with random positions, sizes, and phase values. Dataset 3 combined both noise and discontinuities to emulate aliasing effects. Additionally, the public real dataset 'Single-input dual-output 3D shape reconstruction' was adopted to assess generalization capability, which contains 1 500 real-scene samples acquired by a structured-light 3D measurement system. The evaluation was performed using three metrics: Normalized Root Mean Square Error (NRMSE), Mean Absolute Error (MAE), and Structural Similarity Index Measure (SSIM). Benchmark comparisons were carried out against mainstream models such as U-Net, Res-UNet, Perera's Net, and TNUNet. In the comparative experiments, ADE-Net achieved the best performance across all three simulated datasets. On the discontinuous dataset, it attained an NRMSE of 4.35 degrees o, an MAE of 1.094 5 rad, and an SSIM of 0.871 4. On the random-noise dataset, the results were 4.58 degrees o NRMSE, 1.216 5 rad MAE, and 0.838 9 SSIM. On the aliased dataset, ADE-Net reached 4.34 degrees o NRMSE, 1.137 7 rad MAE, and 0.834 0 SSIM. Cross-validation on the public dataset demonstrated excellent generalization ability, with a Root Mean Square Error (RMSE) of 0.505 2, an MAE of 0.180 9 rad, and an SSIM of 0.997 1. Ablation studies further confirmed the individual performance contributions of both the AC-LSTM and DEMA modules. Moreover, while maintaining the aforementioned high accuracy, ADE-Net also exhibited remarkable computational efficiency advantages. With only 2.012 M parameters and 2.655 GFLOPs, it is significantly lighter than the compared models. The inference time per single image is only 12.71 ms, meeting real-time processing requirements without compromising accuracy, thereby achieving an effective balance between model complexity and computational performance. In conclusion, ADE-Net presents a lightweight, efficient, and highly accurate deep learning framework for phase unwrapping in structured light 3D measurement. By integrating the AC-LSTM module for capturing direction-sensitive multiscale features and the DEMA module for computationally streamlined attention-driven feature refinement, the models achieve an ideal balance between performance and computational complexity. It demonstrates superior resilience in challenging conditions involving noise corruption, phase discontinuities, and aliasing artefacts, outperforming leading benchmark models in both accuracy and processing efficiency. Rigorous validation on real-world datasets confirms its robust generalization capability, while its fast inference speed and low resource footprint make it well-suited for high-precision phase reconstruction tasks. By addressing practical constrains in deployment, this work promotes the feasibility of structured light 3D measurement system for real-world, resource-aware applications.
Ionic liquids, as a new type of molten salts with high thermal stability, low vapor pressure, and strong designability, have important application value in cutting-edge fields such as electrochemistry, catalytic synthesis, and biomedicine. However, the accuracy and efficiency of ionic liquid type identification still need to be continuously explored and optimized. Traditional characterization methods, such as infrared spectroscopy and nuclear magnetic resonance, usually rely on large precision instruments, which have limitations such as complex operating procedures, high equipment costs, and long analysis cycles. At the same time, the inherent strong hygroscopicity of ionic liquids makes the control of sample purity more stringent, and existing moisture detection methods find it difficult to achieve rapid and precise measurement. Against this background, metasurfaces, as two-dimensional artificial materials that can flexibly control the amplitude, phase, and polarization of electromagnetic waves, provide a new technical path for the development of high-performance sensing technologies. This type of structure has both high sensitivity and non-contact detection advantages, and has shown significant potential in dielectric property analysis and substance identification. However, existing metasurface sensors still have certain limitations in practical applications, such as being easily affected by external electromagnetic interference or requiring direct contact with samples. These issues not only reduce measurement accuracy but may also cause sensor contamination, thereby limiting their widespread application in practical scenarios. Aiming at the technical bottlenecks of ionic liquid type identification and moisture content detection mentioned above, this paper proposes a metasurface microwave sensor based on a dielectric substrate integrated with a double-layer metal resonant structure. The sensor converts the dielectric properties of ionic liquids into significant changes in resonant frequency shift and resonance linearity through its unique electromagnetic field localization and enhancement mechanism, providing a new way to achieve rapid and precise sensing analysis. To deeply study the working mechanism of the sensor, this study adopted a multi-level research method: from the physical mechanism level, the formation and energy distribution of electromagnetic resonance were intuitively presented through surface current distribution analysis; from the model construction level, the physical structure was transformed into circuit parameters through equivalent circuit analysis, and the regulation law of resonant frequency was quantitatively revealed; from the performance prediction level, the electromagnetic response characteristics of the sensor were accurately obtained through full-wave numerical simulation, and the structure was optimized; from the final verification level, experimental tests confirmed that the sensor can not only accurately distinguish six different types of ionic liquids but also achieve high-precision detection of trace moisture content. Before conducting experimental characterization, this study first compared and analyzed the reflection characteristic changes of the sensor before and after loading ionic liquids in the 7 similar to 10 GHz frequency band based on electromagnetic simulation software. The simulation results show that the introduction of ionic liquids not only changed the original resonant mode of the sensor but also induced a stronger electromagnetic response through the dielectric regulation mechanism, thereby verifying that the metasurface sensor has excellent dielectric sensitivity and electromagnetic regulation capabilities. Subsequently, six representative ionic liquids were selected as the measured samples for actual measurement analysis. The experimental measurement results show that when the sample to be tested in the sample holder is changed from [EMIm][BF4] to [OMIm][BF4], the resonant peak position of the reflection spectrum shifts from 8.37 GHz to 8.86 GHz, resulting in a significant frequency shift of 490 MHz. Calculations show that the sensor's average sensitivity to dielectric constant changes can reach 185.42 MHz/epsilon '. In addition, this study systematically evaluated the sensor's ability to detect trace moisture content. Experimental data show that when the water content increases from 0% to 10%, the resonant peak of the reflection spectrum shows a significant frequency shift of 180 MHz (8.22 GHz -> 8.40 GHz), proving that the sensor can effectively detect moisture changes in ionic liquids at the ppm level. In summary, this paper successfully designed and verified a metasurface microwave sensor based on a double-layer metal resonant unit. By using a three-layer structure constructed with an FR4 epoxy resin substrate, combined with an open sample holder and a fully copper-plated bottom plate design, the sensor exhibits excellent detection performance in the 7 similar to 10 GHz working frequency band, achieving non-contact and high-precision detection of ionic liquid types and their moisture content. Simulation and experimental results show that the sensor has different characteristic frequency responses for six typical ionic liquids (including [EMIm][BF4], [BMIm][SCN], [BMIm][OTf], [BMIm][BF4], [HMIm][NTf2], and [OMIm][BF4]), with a maximum frequency shift of 490 MHz and a detection sensitivity of 185.42 MHz/epsilon '. In terms of moisture detection, the sensor shows a good resonant response to 0 similar to 10% moisture content changes in [EMIm][BF4] solutions, with a resonant frequency shift of 180 MHz. The metasurface sensor designed in this study has high sensitivity and good measurement repeatability, providing an effective technical means for ionic liquid purity detection and deterioration monitoring, and has important engineering application prospects in fields such as chemical process control and real-time monitoring in hazardous environments.
The structure and coloration of butterfly scales play a crucial role in regulating their biological behavior. Accurate three-dimensional imaging of these structures is essential for understanding their functional mechanisms. Traditional imaging techniques usually may suffer from limitations such as sample damage, slow imaging speed, and inaccurate three-dimensional reconstruction. To address these issues, this study employed Fourier Light Field Microscopy (FLFM) to image the three-dimensional structural details of butterfly scales. This imaging method requires no slicing or mounting of samples, thereby preserving their native structural integrity, avoiding damage during imaging, allowing repeated use of the same specimen, and significantly reducing sample consumption. In principle, it can perform the threedimension imaging in real time by taking the same advantage of single shot three-dimensional imaging and image reconstruction of light field microscopy. Moreover, compared to the conventional light field microscopy, the FLFM can increase the lateral spatial resolution thus the reconstruction quality of the three-dimensional image. We found that FLFM is particularly suitable for delicate biological samples such as butterfly wings and provides reliable technical support for studying their color and structural characteristics. Here, the representative samples including pigmentary scales, structural color scales, and scale-free areas of different kinds of butterflies were imaged under 10 & times; and 50 & times; objectives with a consistent lighting condition. After introducing the optical system and the imaging mechanism of the FLFM, the threedimensional reconstruction method based on refocusing and deconvolution algorithms is described. The experimental FLFM setup consisted of a DOIT3DMicro Fourier light-field module mounted on an Olympus IX73 inverted microscope, and the illumination was provided in both transmission and reflection modes depending on the sample type. The refocusing algorithm adopts a shift-and-sum procedure exploiting the conjugate relation between aperture stop and MLA, while the deconvolution algorithm models the system point spread function via wavefront propagation theory for high-resolution reconstruction. The method is verified by imaging with a resolution target sample and another sample of distributed beads the resolution target image demonstrates the lateral spatial resolution about 8 mu m and the beads sample image demonstrate the depth differentiation capability around 60 mu m. Finally, the imaging results for the butterfly scales demonstrate that FLFM can clearly reveal morphological characteristics, angle-dependent color variations, and spatial distribution patterns of different scale types. Imaging at 10 & times; magnification verified the feasibility of this technology for visualizing scale structures: the Papilio wing sample shows the relative wide black and white stripes with the boundary somewhat smeared, the Morpho helenor wing sample shows the fine well-organized colorful structures and the color can change from the green blue tone to the blue violet tone, and the Haetera piera wing sample shows shrunk scales and sparsely distributed cilia. Imaging at 50 & times; magnification further revealed significant differences in scale morphology, color formation mechanisms, and optical properties between Catopsilia pomona and Morpho helenor: the color of the Catopsilia pamona wing sample appears mainly due to the pigment structures and does not change when viewing from different angles, while the Morpho helenor wing sample show typical structured color and the hue change apparently by varying the incident light angles or the viewing perspectives. Therefore, this study demonstrates the advantage and potential wide application prospect of the FLFM in imaging the samples with large depth-of-field. Through careful examination and comparison analysis, we observed the various fine details of the three-dimensional structures of the butterfly wing scales which is very helpful for understanding the different color formation mechanism of the scales. We expect that the FLFM not only can find important applications for studying the structured color of the butterfly wings, but also can provide the experiment support for the further exploration and investigation of biomimetic materials.
Exciton-polaritons are hybrid quasiparticles born from the strong light-matter coupling between microcavity photons and semiconductor excitons.Their unique half-light,half-matter nature provides a compelling physical platform:the photonic fraction yields an extremely low effective mass and extended spatial coherence,while the excitonic component introduces strong Coulomb interactions and notable optical nonlinearities.Thanks to these properties,polaritons have become a premier testbed for studying macroscopic quantum states—such as Bose-Einstein condensation(BEC)and superfluidity—often up to room temperature,as well as for developing ultra-low threshold lasers.In parallel,topological photonics has fundamentally changed how we control light.By engineering topological invariants in reciprocal space,topological photonic crystals(TPCs)can host robust states that are largely immune to backscattering from fabrication defects or sharp bends.Bringing TPCs into the realm of exciton-polaritons bridges these two vibrant fields.Instead of merely serving as passive cavities,TPCs interact with the rich material properties of polaritons.This convergence not only grants polaritonic devices topological protection but also allows researchers to utilize exciton nonlinearities,magnetic responses,and non-Hermitian dynamics to actively tune topological phases—capabilities that are exceedingly difficult to achieve in conventional linear optics. This review presents a comprehensive overview of the physics,design strategies,and recent experimental progress in topological exciton-polaritons.We begin by revisiting the core topological models that have been successfully mapped onto photonic crystal platforms.Specifically,we detail the implementations of the quantum Hall-like phase,where broken time-reversal symmetry gives rise to unidirectional chiral edge states.For time-reversal-invariant systems,we discuss the quantum spin Hall-like phase,which relies on engineered photonic pseudospins for helical transport,and the quantum valley Hall-like phase,where spatial inversion asymmetry dictates valley-momentum locking.Beyond these boundary states,we explore localization mechanisms based on the Su-Schrieffer-Heeger(SSH)model.This spans from one-dimensional(1D)topological defect states to two-dimensional(2D)higher-order topological insulators that support highly localized zero-dimensional(0D)corner modes.We also dedicate significant discussion to bound states in the continuum(BICs).Characterized by topological polarization singularities in momentum space,BICs offer theoretically infinite quality factors,making them exceptionally efficient open cavities for sustaining strong coupling. Building on these theoretical frameworks,we then examine how they translate into actual polaritonic systems,with a major focus on the experimental milestones achieved across different semiconductor materials.For topologically protected transport,we review the early demonstrations of quantum Hall-like chiral routing in GaAs microcavities,driven by exciton Zeeman splitting under magnetic fields.As the field pushed toward room-temperature operation,emerging materials like transition metal dichalcogenides(TMDs)and halide perovskites have been integrated with TPCs,enabling robust helical and valley-polarized polariton flows.When it comes to spatial localization,the interplay between topology and polariton nonlinearity has yielded remarkable results.We highlight recent observations of 1D topological gap solitons and the development of actively tunable polaritonic switches.Similarly,the realization of polariton condensation in 0D higher-order corner states opens realistic pathways for binary information storage and compact,defect-immune on-chip lasers.Furthermore,the integration of BICs has driven a surge of recent breakthroughs.BIC-polaritons have not only made room-temperature BECs more accessible but also enabled the emission of topological vortex beams carrying well-defined orbital angular momentum.They also provide a rich playground for non-Hermitian physics,where the inherent driven-dissipative nature of polaritons allows for the precise,all-optical manipulation of Exceptional Points(EPs). Ultimately,the convergence of topological photonics and exciton-polaritons does more than just improve device robustness;it provides a highly tunable environment for exploring strongly correlated many-body physics and nonlinear topological optics.While the progress over the past few years has been rapid,several pressing challenges must be addressed to move these concepts from laboratory demonstrations to practical technologies.In the final section,we outline future directions and current bottlenecks.Key issues include the need to minimize insertion and propagation losses,the challenge of maintaining material homogeneity over large areas in 2D semiconductors and perovskites,and the much-anticipated transition from optical pumping to electrical injection.Addressing these engineering and physical hurdles will be essential for realizing the next generation of polaritonic devices,moving us closer to practical topological micro-nano lasers,all-optical logic gates,and scalable quantum simulation platforms operating at ambient temperatures.
Event cameras are a novel type of visual sensor inspired by the biological retina,capable of asynchronously capturing pixel brightness changes with microsecond-level temporal resolution.Unlike traditional cameras that capture frames at fixed intervals,event cameras only trigger an event when pixel brightness exceeds a preset threshold.This unique mechanism endows event cameras with an ultra-wide dynamic range of up to 140 decibels and exceptional temporal resolution,granting them significant advantages in high-speed,high-dynamic-range scenarios such as object tracking,motion detection,and Simultaneous Localization and Mapping(SLAM).These capabilities enable event cameras to capture rapid movements and subtle changes in dynamic scenes that conventional cameras might miss.However,event cameras have a significant limitation:they can not directly capture grayscale images in static scenes.This is because when a scene is stationary and light intensity remains constant,the camera detects no change in light intensity,failing to meet the conditions for event triggering.These characteristics restrict their application in scenarios requiring complete brightness information,such as static object or scene recognition and measurement in traditional image processing tasks.Consequently,despite their ultra-high dynamic range,temporal resolution,and exceptional performance in dynamic environments,event cameras still face challenges in applications demanding detailed,continuous brightness data acquisition under static conditions. To address the challenge of capturing static scenes with event cameras,this paper introduces a novel approach using mechanical shutter mapping for imaging.The core innovation lies in modulating brightness variations in static scenes through the rotation of a mechanical shutter,triggering events even in the absence of light intensity changes.By adjusting the shutter's rotation speed at varying rates,discrete events are generated,which are then reconstructed into High Dynamic Range(HDR)grayscale images.This technique overcomes a significant limitation of traditional event cameras,which struggle to capture static scenes due to the lack of natural light variations.A key aspect of this method is the calibration process,which ensures that the generated event data is accurately aligned with the actual light intensity of the scene,enabling precise and accurate grayscale image reconstruction.In this setup,the mechanical shutter acts as an active driving mechanism,inducing event generation by modulating the scene's brightness.This allows the event camera to capture dynamic information in static scenes,where traditional event cameras would otherwise fail to register changes.As a result,this method significantly enhances the imaging capabilities of event cameras,broadening their potential applications in static environments with minimal or no natural light variations. Experimental results show that the reconstructed HDR images achieve a dynamic range of up to 112 dB.This range allows the event camera to capture fine details in both dark and bright areas of the scene,overcoming the limitations of conventional cameras with fixed dynamic ranges.The calibration process further improves the accuracy of grayscale image reconstruction.Our experimental results demonstrate that shutter-based techniques successfully reconstruct grayscale images of static scenes under extreme lighting conditions.Compared to prior methods,this approach significantly improves image quality,reduces grayscale distortion,and preserves details often lost in conventional event reconstruction techniques.By generating events through controlled brightness variations,this method enhances the imaging capabilities of event cameras in static environments.Furthermore,the mechanical shutter mechanism facilitates portability,enabling adaptation to multiple event camera models and enhancing the system's versatility and practical applicability.Beyond expanding event cameras'capabilities in static scenes,this approach also provides a solution for event cameras operating under complex lighting conditions.Our shutter mapping technology offers a controlled event triggering mechanism,enabling event cameras to function in scenarios where traditional methods fail.This opensnew possibilities for event cameras in fields requiring high-quality grayscale images,such as industrial inspection. This paper proposes and validates a shutter-mapped event camera method for grayscale imaging in high-dynamic-range static scenes.The core innovation of this approach lies in introducing a mechanical shutter as an active driving mechanism,which effectively overcomes the limitation that event cameras cannot generate event streams in static scenes due to the absence of brightness changes.By modulating the scene's brightness using controlled shutter rotations,the event camera can trigger events even in stationary conditions.Experimental results demonstrate that this method successfully reconstructs grayscale images of high-dynamic-range static scenes,achieving a dynamic range of up to 112 dB under extreme illumination conditions,all using a frameless event camera.Compared to existing methods,our approach significantly improves reconstruction quality,reduces grayscale distortion,and preserves fine details.Additionally,the proposed mechanical shutter triggering mechanism offers versatility and portability,providing a controllable active refresh mechanism that is compatible with various event camera models.In summary,the shutter mapping method extends the capabilities of event cameras in static scenes,enabling high-quality HDR grayscale image reconstruction.By inducing brightness variations through mechanical shutter actuation,event cameras can generate event streams and reconstruct HDR images,even in static scenes with extreme lighting conditions.
With the rapid development of precision manufacturing, semiconductor lithography, and aerospace engineering, ultra-precision machining and metrology have placed higher demands on micro-displacement measurement systems that combine nanometer-level precision with high-bandwidth real-time performance. In dynamic, high-speed motion scenarios, such systems not only need to achieve extremely high resolution but also provide low-latency data processing at high sampling rates. As a fundamental technology in modern length metrology, laser interferometry has inherent advantages in terms of accuracy and stability. However, traditional software-based processing architectures rely on CPUs and sequential execution models, often encountering severe computational bottlenecks when processing high-speed interferometric signals. These limitations make it difficult to simultaneously meet the conflicting demands of large measurement range, high resolution, and real-time detection. To overcome these challenges, this paper proposes a single-frequency laser displacement measurement system based on FPGA, which integrates an FPGA platform and a high-performance point-by-point phase calculation algorithm. By transferring the signal processing algorithm from software to a dedicated hardware logic platform and employing parallel computing and a pipelined approach, the system significantly improves real-time performance while maintaining nanometer-level measurement accuracy. First, this paper establishes a four-channel orthogonal laser interferometry structure and develops a real-time phase demodulation method based on the phase difference between adjacent sampling points. By introducing phase jump correction and cumulative phase compensation mechanisms, the algorithm effectively solves the problems of phase unwrapping ambiguity and displacement direction discrimination under high-speed motion conditions, thereby ensuring the continuity and robustness of displacement measurement. Meanwhile, to analyze the impact of non-ideal optical elements on nonlinear errors, this paper constructs a systematic error model using Jones matrix theory. This model quantitatively analyzes the effects of waveplate angle misalignment and Polarization Beam Splitter (PBS) splitting ratio imbalance on the interference signal, revealing their roles in introducing DC offset, amplitude mismatch, and non-orthogonality between orthogonal channels. Based on this analysis, this paper designs a vector-based error compensation algorithm to correct these defects, thereby significantly improving phase linearity and overall measurement accuracy. Based on the proposed algorithm, a complete experimental test platform was established, and a host-computer-based multi-threaded displacement measurement software was developed to evaluate the system performance. Experimental results demonstrate that, within a measurement range of 200 mu m, the system achieves a statistical measurement accuracy better than 10 nm while supporting millisecond-level data update rates, thereby validating the effectiveness and practicality of the proposed method. Based on the validated theoretical and software framework, this paper further develops an FPGA hardware system integrating a high-speed multi-channel ADC to comprehensively enhance real-time processing capabilities. By employing a fully pipelined architecture and dedicated parallel processing units, key algorithms such as error compensation and phase demodulation are transformed into hardware logic. This hardware-oriented design ensures stable and predictable computational latency, which is crucial for real-time measurement. Experimental comparisons show that the results of the FPGA-based hardware processing are in high agreement with the results of the host multi-threaded software algorithm, with a Root Mean Square Error (RMSE) of only 9.16 nm and statistical accuracy consistently maintained within 10 nm. Real-time performance evaluation further validates the advantages of the proposed system. The initial processing latency is reduced to 10.4 mu s, and the displacement data update cycle reaches 100 ns. Therefore, the system can reconstruct complete micrometer-level motion trajectories in real time within 1 millisecond, representing a significant performance improvement compared to traditional CPU-based processing architectures. These performance characteristics make the system particularly suitable for applications such as high-speed motion, dynamic vibration monitoring, and real-time feedback control. In summary, this paper proposes a laser interferometric real-time displacement measurement system by deeply integrating a point-by-point phase demodulation algorithm and FPGA-based hardware acceleration technology. This system simultaneously achieves high precision, high stability, and ultra-fast real-time performance. It provides a reliable and high-performance metrology solution for closed-loop motion control, dynamic vibration analysis, and nanometer-level precision positioning in ultra-precision engineering applications, demonstrating significant practical value and broad application prospects.
High-efficiency solar cells based on nanostructures are a research hotspot in the photovoltaic field today. On the one hand, there is the research on new types of solar cells such as perovskite cells. On the other hand, silicon-based solar cells remain the most widely studied and applied type of cell. How to further improve the efficiency of silicon-based solar cells and reduce their cost still requires in-depth research. Silicon is an indirect bandgap semiconductor material, and its absorption of incident light in the near-infrared band is very weak. Only when the thickness of the absorption layer exceeds 200 mu m can the cell achieve full absorption in a wide band (300 similar to 1 100 nm). Reasonable light-trapping nanostructure design can enhance the light absorption performance of silicon thin-film solar cells. The morphology, size, material and spatial layout of these light-trapping nanostructures have a significant impact on the surface anti-reflection characteristics and light-trapping performance of silicon thin-film solar cells. In this paper, a double-layer conformal grating silicon thin-film solar cell structure was designed. The influence of different grating shapes on the light-trapping performance of silicon thin-film solar cells was systematically studied by using the concept of super-quadratic subwavelength gratings. By changing the degree of the grating's profile function, the profile shape of the grating can be adjusted. Five representative grating profile curves (n=1, 2, 4, 10, infinity) were selected. As n increases, the grating profile shape can be gradually changed from triangular (n=1), parabolic (n=2), to rectangular (n ->infinity). The silicon thin-film solar cells with the above five grating structures were optimized by using the finite-difference time-domain method. By comparing and analyzing the short-circuit current density, absorption spectrum, and light absorption enhancement spectrum of the five grating structures and the planar structure, the light-trapping effect law of the double-layer conformal grating silicon thin-film solar cell was explored. The internal light-trapping mechanism was analyzed using the electromagnetic field intensity distribution diagrams. In addition to qualitatively analyzing the light-trapping performance of each grating structure silicon thin-film solar cell, the concept of integral absorption was also introduced to quantitatively analyze their light absorption characteristics over the entire wavelength range. Moreover, the optimization calculation of the silicon thin-film solar cells with four types of bottom metal grating materials (Ag, Au, Cu, and Al) was carried out. A comparative analysis was conducted on the short-circuit current densities and absorption spectra of four types of bottom metal grating structures, and the light absorption enhancement effect of different bottom metal grating materials was explored. The mechanism was analyzed from the perspective of optical constants. The research results indicate that as n increases, the overall light-trapping performance of silicon thin-film solar cells decreases as the grating profile shape transforms from triangular (n = 1) to rectangular (n ->infinity). Among them, the parabolic (n = 2) grating structure has superior light absorption performance in both the 300 similar to 750 nm and 750 similar to 1 100 nm bands. Because the n = 2 grating structure has excellent anti-reflection performance in the visible light band, and the LSPRs mode is excited on the surface of the bottom Ag grating in the near-infrared band, while optical waveguide mode coupling is achieved in the c-Si absorption layer. The triangular (n = 1) grating structure has better light-trapping performance in the 750 similar to 1 100 nm band, but its light absorption performance in the 300 similar to 750 nm band is poor. The results also show that the J(sc) values of the silicon thin-film solar cells with the bottom metal gratings of Ag, Au, Cu and Al decrease in sequence, among which the bottom Ag grating structure has the best light-trapping performance and the bottom Al grating structure has the worst. The research results of this paper can provide theoretical guidance for the structural design of thin-film solar cells based on nano-grating structures.
Frequency-Modulated Continuous-Wave (FMCW) radar is widely used in military, autonomous driving, and other fields for its high resolution, low power consumption, and strong anti-interference. However, traditional microwave electronic radars fail to meet broadband signal generation/ processing needs, leading to the development of microwave photonic radar. By combining photonics and electronics, it overcomes the "electronic bottleneck," with optical frequency multiplication and dechirping reception architectures gaining attention for large bandwidth and simple structure. Nevertheless, in this architecture, frequency multiplication degrades phase noise (by 20 log10(n) dB for multiplication factor n), while electro-optic/optoelectronic conversion worsens it. Phase noise impairs radar accuracy, resolution, and anti-interference, limiting broadband advantages. Existing suppression technologies for microwave photonic radar often suffer from complexity, high cost, or new noise introduction, demanding more effective compensation. This paper proposes a phase noise compensation scheme for microwave photonic FMCW radar using deskew filtering. The system adopts an optical quadrupling structure (boosting distance resolution) plus reference delay and mixing branches. The baseband linear frequency-modulated (LFM) signal splits into two paths: one drives the microwave photonic quadrupling module to generate a transmitted signal (4x baseband frequency/bandwidth, 4x phase noise), whose echo is processed via a microwave photonic mixer to get an echo dechirped signal with phase jitter; the other undergoes reference delay/mixing to produce a reference dechirped signal. Deskew filtering compensates the echo dechirped signal as follows: apply Hilbert transforms to both signals for complex signals, estimate phase noise via the reference, remove phase noise's delay dependence in the echo using the deskew filter, and eliminate phase noise to mitigate radar performance impacts. An experimental setup was built to verify the feasibility of the proposed scheme. The initial frequency of the baseband linear frequency-modulated signal was 5 GHz, with a bandwidth of 100 MHz. After passing through the microwave photonic quadrupling module, a quadrupled frequency signal in the range of 20 similar to 20.4 GHz was generated, effectively expanding the bandwidth. The reference and echo dechirped signals were collected and processed using the deskew filtering algorithm. To evaluate the effectiveness of phase noise compensation in the dechirped echo signal, we analyze two key aspects: first, comparing the stability of the half-period of the dechirped echo signal before and after compensation, and second, examining its phase noise characteristics. A reference group processed using the equal phase interval sampling method was introduced for comparative analysis. The results show that before compensation, the standard deviation of the half-period was 0.54 ns. After compensation with the equal phase interval sampling method, this value decreased to approximately 0.24 ns. Further compensation using the deskew filtering method reduced the standard deviation to 0.15 ns, representing a 3.6 times improvement in stability compared to the pre-compensation state. This indicates that the phase noise compensation achieved through the deskew filtering method significantly enhances the stability of the half-period of the dechirped echo signal. Regarding phase noise characteristics, the experimental results demonstrate that within the frequency offset range of less than 10 kHz, the deskew filtering method outperforms the equal phase interval sampling method in suppressing phase noise, resulting in a lower phase noise level in the processed signal. Additionally, a time-frequency analysis was conducted on the signals before and after compensation to compare the range profiles. The results reveal that the target energy in the compensated range profile becomes more concentrated, and the deviation range of the distance measurement results is effectively suppressed. Specifically, the distance corresponding to 10 dB bandwidth decreased from 49.57 m (pre-compensation) to 41.28 m (post-compensation), while the standard deviation of distance measurement results reduced from 0.97 m (pre-compensation) to 0.78 m (post-compensation). Collectively, these findings demonstrate that the deskew filtering method effectively improves the range resolution and distance measurement stability of the radar system.
A Microwave Photonic Filter(MPF)is a device that filters microwave signals by first modulating them into the optical domain,then processing them using optoelectronic components.Compared to traditional electronic microwave filters,they exhibit advantages such as superior frequency tuning range,flexible spectrum reconfiguration,and inherent immunity to electromagnetic interference,etc.These benefits make MPFs highly promising for widespread applications in wireless communication,radar,and electronic warfare systems.With the advancement of integrated optoelectronic technologies,MPFs are progressively evolving from discrete fiber-optic devices towards integrated solutions.This transition aims to substantially reduce their size,weight,power consumption,and cost.In this review,firstly the system architectures and working principles of both incoherent and coherent integrated MPFs are presented.Subsequently,recent research advances in these two categories of MPFs are reviewed. For incoherent integrated MPFs,multi-tap configurations are typically adopted,utilizing Finite Impulse Response(FIR)digital filter architectures rooted in discrete signal processing algorithms.Some key integrated optical components enabling dispersion-delayed sampling in multi-tap MPFs are given,such as integrated high-dispersion chips,multi-wavelength light sources,and spectral shaping chips.By adopting these functional chips into microwave photonic filter links,some MPFs with good frequency tuning capabilities and out-of-band RF suppression have been reported.But the limited number of taps and unattainable complex tap coefficients resulting in insufficient spectral reconstruction capability of the achieved incoherent MPFs.To date,only aforementioned integrated chips have been integrated into microwave photonic filter links,while other critical components still rely on discrete fiber-based devices.Incoherent MPFs with higher integration levels remain unreported in the literature. For coherent integrated MPF,typically microwave signals are modulated onto a single-wavelength laser source,where various integrated optical filters are adopted to spectrally shape modulated optical signal,followed by down-conversion at a photodetector to convert optical domain filtering response into microwave domain.Various integrated optical components to construct coherent MPFs such as Micro-Ring Resonator(MRR)/Micro-Disk Resonator(MDR),nonlinear As2S3 waveguide with Stimulated Brillouin Scattering(SBS),photonic crystal cavity,microsphere,phase shifted waveguide Bragg grating,Surface Acoustic Wave(SAW)based on suspended waveguide have been reviewed.Based on these integrated optical components,various MPF link architectures to realized band-stop and band-pass MPFs have been introduced.Band-stop MPFs can be realized through optical-to-microwave mapping based on Optical Single Sideband(OSSB)modulation.Furthermore,by employing Radio Frequency(RF)cancellation techniques via Unbalanced Optical Double Sideband(UODSB)modulation,this approach can overcome the limitation imposed by optical filter's extinction ratio on RF suppression performance and enables band-stop MPF with RF rejection ratio larger than 60 dB.On the other hand,Band-pass MPFs can be realized through either by optical carrier separation and re-entry techniques enabling direct one-to-one mapping of optical band-pass responses to the microwave domain,or phase-to-intensity conversion schemes that transform optical band-stop filtering into microwave band-pass responses.In addition,some technologies to enhance MPF's frequency resolution have been introduced,such as improving quality factors of MRR/MDR with mode manipulation,incorporating on-chip narrow-band SBS gain/loss spectra,adopting SiO2 microsphere,etc.Up to date,frequency resolution down to about ten MHz have been demonstrated for band-pass and band-stop MPFs.Building on recent advances in integrated optical filters for MPF links,this work futher surveys highly integrated microwave photonic filter chips implemented on Thin-Film Lithium Niobate(TFLN),Silicon-On-Insulator(SOI),and indium phosphide(InP)platforms,providing a comparative analysis of their respective advantages and limitations. Finally,quantitative comparative analysis of key performance metrics of the reported incoherent and coherent integrated MPFs have been given.Some key technical challenges in integrated MPFs,including the trade-offs between filter's bandwidth and frequency tuning range,insufficient noise figure/out-of-band RF rejection ratio/frequency stability,immature heterogeneous integration,and broadband photonic packaging solution with low crosstalk and high RF integrity.Moreover,an outlook on the future development trends of integrated MPF is presented.
The accurate and efficient calculation of the Beam Shape Coefficients(BSCs)is one of the key issues in researching the interaction between a structured or shaped beam and the particles.For this reason,different techniques have been established,such as the quadrature method,the Localized Approximation(LA)or its variants,the Finite Series(FS)method,the Angular Spectrum Decomposition(ASD),and the others.Among these methods,the Localized approximation has been widely used due to its advantages including mainly the efficiency in numerical calculation,the conciseness of the expressions and the straightforwardness in deducing the BSCs for the beams in both the on-axis and off-axis scenarios.However,this method,just as it is named,is an approximate one.The beam remodeling takes place when the beam field is reconstructed from the BSCs,i.e.the reconstructed beam field deviates from the originally given field.Up to date,the remodeling of the beam field has not been studied systematically. In this work,the two-step indirect method is employed to study the remodeling effects of the localized approximation method for the Gaussian beams.In the first step,the expression of the BSCs is obtained,by using the localized approximation,for the Gaussian beam which is centered in the coordinate system(called beam system)and is described by using a scalar potential function(therefore the BSCs are called scalar BSCs).Subsequently,the scalar translational addition theorem is used to transform the BSCs into another coordinate system whose axes are parallel to those of the beam system.The second coordinate system in which the spherical particle is centered is called particle system.In the second step of the indirect method,the electric and magnetic(EM)fields of the Gaussian beam are described by using the scalar potential function together with a polarization parameter.Based on this relation,the BSCs of the EM field(called vector BSCs or EM BSCs)are expressed as a linear combination of the scalar BSCs.In this way,the EM BSCs for the off-axis located Gaussian beam are obtained indirectly from the scalar BSCs of the centered beam.The two-step indirect method simplifies the analytical derivation of the BSCs.The expressions of the EM BSCs which are directly deduced in the localized approximation for the off-axis located Gaussian beam are used in the numerical calculations for making a comparison.It is found that the indirect method is at least eight times faster than the direct method in numerical calculation of the BSCs. The remodeling of the localized approximation is studied,based on a comparison between the originally given field of the Gaussian beam and the fields which are reconstructed from the directly and/or indirectly calculated EM BSCs.The numerical results reveal that,in the direct LA method,the axisymmetric structure of the Gaussian beam is broken in the reconstructed beam field,exhibiting spurious-peaks in the electric field.When the off-axis distance becomes sufficiently large,a ring structure is produced in the field.The deviation of the reconstructed beam field from the given one increases gradually along the increase of the off-axis distance.However,in the indirect method,the reconstructed field is always axisymmetric and the discrepancy between the reconstructed and given fields is independent of the off-axis distance.In both the direct and indirect methods,the reconstructed beam fields deviate from the given one,showing a close dependence on the beam waist radius.Namely,the reconstructed beam fields agree much better with the given field when the beam waist radius is large,but the quality of the remodeled fields become poorer when the beam waist radius decreases,especially when the beam waist radius is close to or less than the wavelength of the light beam. It is concluded that,compared with the direct localized approximation method,the two-step indirect method has advantages in analytical derivation of the BSCs,in conciseness of the expressions,in efficiency of numerical calculation,and in quality of reconstructed beam field.Besides,the work presented here suggests a warning against the use of the direct/indirect LA methods for strongly focused Gaussian beams and the use of the direct LA for large off-axis located beams.
Electrowetting Display (EWD) , as a novel reflective display technology, offers high reflectivity, wide viewing angles, fast response, and full-color display, making them highly promising for applications in portable terminals, wearable devices, and outdoor information displays. However, as display panels evolve toward larger sizes and higher resolutions, the scale of driving circuits and refresh rates increases significantly, leading to growing power consumption issues that directly affect device battery life and application scope. Existing low-power studies rarely fully integrate the reflective imaging characteristics and optoelectronic properties of EWD, and power optimization under complex ambient lighting conditions still has considerable room for improvement. To address these challenges, this paper proposes a low-power algorithm based on ambient light compensation, designed to reduce power consumption and improve display quality by leveraging the reflective characteristics of EWD. In addition, an adaptive voltage adjustment technique is introduced, which dynamically adjusts the driving voltage according to ambient light intensity, further reducing driving power consumption. The proposed low-power algorithm consists of four main components: 1) voltage-reflective luminance curve calibration, ensuring that the luminance differences between adjacent gray levels under various ambient light conditions are closer to those under standard ambient light; 2) extraction of the original grayscale information of the image, followed by grayscale correction using a mapping table generated during the calibration process; 3) detail enhancement to improve edge and texture representation in the image after calibration, compensating for potential detail loss; and 4) calculation of the driving voltage corresponding to the highest pixel value after processing, based on the Pulse Amplitude Modulation (PAM) driving method, and setting it as the maximum driving voltage for the given ambient light condition to achieve adaptive voltage adjustment. The proposed ambient light dynamic compensation calibration method was applied to an EWD system. Test points were set at the positive and negative power supply terminals of the source driver, and an EKA1080M power consumption tester was used to measure the power consumption before and after algorithm processing. The test video sequence consisted of black screen-original image-black screen-processed image-black screen, enabling comparison of power consumption differences before and after processing. Results show that, in the source driver voltage section, the processed images consumed significantly less power than the original images. Further measurements of current and voltage at the test points under different ambient light conditions, combined with the power calculation formula, revealed that the overall power consumption under standard ambient light was 18.93 mW/in2, and decreased to 14.21 mW/in2, 12.06 mW/in2, and 11.72 mW/in2 under ambient light intensities of 483 cd/m2, 970 cd/m2, and 1 730 cd/m2, respectively-representing reductions of 24.9%, 36.3 %, and 38.1 % compared to the unoptimized case. In terms of image quality, the objective evaluation metric Average Gradient (AG) increased by 4.9 %, 3.9 %, and 2.3 degrees o under the three ambient light conditions, respectively, indicating that the processed images exhibited higher clarity, more prominent edges, and richer details. Moreover, the brightness of the processed images was closer to that of the standard ambient light display, providing a more comfortable and stable viewing experience under varying lighting conditions. In summary, the proposed method significantly reduces the power consumption of EWD while effectively maintaining and even enhancing display quality.
With the explosive growth of next-generation information technologies, such as ultra-highspeed 5G/6G wireless communication networks, ultra-wideband radar systems, and quantum information processing, the requirements for the generation, transmission, and manipulation of high-frequency microwave signals have reached unprecedented levels. Facing the escalating challenges of bandwidth, speed, and energy efficiency, Integrated Microwave Photonics (IMWP) has emerged as a transformative solution. By leveraging the ultrawideband characteristics of photons propagating within integrated circuits, IMWP achieves high-precision modulation, distribution, and processing of microwave signals through interference and multiplexing across diverse optical paths, thereby surmounting the performance bottlenecks inherent in traditional electronic systems. Furthermore, on-chip programmable photonicmicrowave signal processors provide a robust hardware foundation for next-generation high-performance microwave systems by reconfiguring their internal architectures to achieve multi-functionality and flexible configuration. Although various architectures based on interferometer arrays, such as finite impulse response filters with delay-line arms and cascaded ring resonators, have been demonstrated, a critical bottleneck hindering their engineering transition is the difficulty in balancing architectural reconfigurability with system scalability in complex application scenarios. Conventional designs often suffer from fixed interconnection topologies and a lack of directness in functional implementation, which constrains their practical deployment in diverse and dynamic environments. Addressing these limitations, this work proposes and experimentally demonstrates an adaptive programmable integrated photonic signal processor based on a hexagonal waveguide mesh topology. The processor utilizes Mach-Zehnder Interferometers (MZIs) as fundamental tuning units, featuring an optimized physical-layer design to ensure high-fidelity functional mapping across the network. The device was fabricated on a 220 nm Silicon-on-Insulator (SOI) platform, with a compact footprint of approximately 3 mm & times; 1 mm, integrating 32 tunable MZIs, 32 thermo-optic phase shifters, and 24 optical I/O ports. Comprehensive characterization of the MZI test structures reveals excellent performance, including extinction ratios exceeding 20 dB and a half-wave heating power of 4.41 mW. A central innovation of this study is the implementation of a self-adaptive control framework driven by the Crested Porcupine Optimizer (CPO) algorithm. The operational logic of the CPO-based configuration is divided into three distinct phases: initialization, closed-loop evaluation, and strategy evolution. By generating a random population within the predefined voltage range and iteratively calculating fitness values based on real-time experimental spectral feedback, the system autonomously converges to the optimal voltage configuration. During the evolution process, the algorithm dynamically toggles between exploration and exploitation modes using four distinct evolutionary strategies, ensuring both global search coverage and local refinement precision. This self-adaptive framework enables the processor to achieve immediate operational readiness with minimal control complexity, establishing a highly stable hardware-software co-design for universal signal processing. Experimentally, the fabricated processor was configured to demonstrate two representative microwave photonic functionalities : topological filtering and frequency measurement. In the topological filtering experiments, the mesh's high degree of reconfigurability was leveraged to synthesize diverse spectral responses, including both Finite Impulse Response (FIR) and Infinite Impulse Response (IIR) filters. By precisely controlling the power splitting ratios and phase shifts within the hexagonal units, we successfully realized Asymmetric MZIs (AMZIs) with tunable extinction ratios exceeding 25 dB and Free Spectral Ranges (FSR) ranging from 0.17 nm to 0.64 nm. Furthermore, Optical Ring Resonators (ORRs) with a 6-BUL (Basic Unit Length) cavity and two-stage Coupled Resonator Optical Waveguides (CROWs) were implemented, demonstrating the mesh's capability to synthesize complex recursive structures with flattened transmission spectra. For frequency measurement, a broadband frequency identification system was constructed using an Amplitude Comparison Function (ACF) based on a Carrier-Suppressed Single-Sideband (CS-SSB) modulation scheme. The system utilized the mesh's ability to switch between multi-stage frequency discrimination channels with different FSRs. By synergistically combining the results from a wideband coarse-measurement channel and a narrowband high-precision channel, the system achieved a broad frequency identification range from 0.01 GHz to 30 GHz with a significantly improved Root Mean Square Error (RMSE) of 131 MHz. This collaborative measurement scheme effectively eliminates the periodic ambiguity typical of narrowband discriminators while maintaining high resolution across the entire spectrum. In summary, this work provides a viable and scalable pathway for realizing high-performance, low-complexity integrated microwave photonic systems. The hexagonal mesh architecture demonstrates exceptional functional adaptability and structural scalability, marking a paradigm shift from Application-specific Integrated Circuits (ASPICs) to software-defined universal photonic processors. Beyond the filtering and frequency measurement demonstrations, the architecture serves as a general-purpose hardware platform capable of supporting diverse tasks, including tunable delay lines for wideband beamforming, arbitrary waveform generation, and reconfigurable optoelectronic oscillators. Theoretical analysis and experimental validation suggest that this self-adaptive framework can be extended to larger-scale networks, providing a clear evolutionary path for multi-functional, adaptive measurement systems in complex electromagnetic environments. The successful implementation of these functionalities on a single programmable chip paves the way for the future deployment of integrated photonics in advanced radar systems, 5G/6G communication infrastructures, and high-dimensional optical signal manipulation.
This study aims to design and fabricate a silica waveguide E-11-E-21/E-11-E-31 mode conversion switch based on a cascaded structure of multimode interference couplers and Mach-Zehnder interferometers. This work addresses the limitations of existing single-structure mode converters, such as limited single-mode conversion capability, poor process tolerance, and inadequate performance. By integrating multimode interference couplers and Mach-Zehnder interferometers and leveraging the thermo-optic effect of silica, controllable and selective mode conversion between the fundamental mode (E-11) and higher-order modes (E-21/E-31) is achieved. The design is intended to meet the demand for flexible mode switching in high-capacity on-chip mode-division multiplexing systems. Prior to fabrication on a silica platform, the switch was designed, simulated, and optimized via the Beam Propagation Method. The device integrates two cascaded functional modules within a 4 & micro;m-thick germanium-doped silica core. The first module is a thermo-optic selective switch, consisting of an input Y-branch (serving as a 3-dB mode splitter) and a 2 & times;2 multimode interference coupler, which regulates the selective output of the input E-11 mode at the two multimode interference coupler ports. The second module is a mode converter incorporating an asymmetric Mach-Zehnder interferometer and an asymmetric Y-branch, enabling E-11-to-E-21 or E-11-to-E-31 mode conversion. Key parameters were optimized using Beam Propagation Method, including multimode interference coupler (length: 972 & micro;m, width: 20.6 & micro;m), asymmetric Mach-Zehnder interferometer (input width: 4 & micro;m, output width: 5 & micro;m, offsets X-1/X-2: 14.2 & micro;m/29.3 & micro;m), and waveguide dimensions of the asymmetric Y-branch at the output end. The device adopts a three-layer structure: germanium-doped silica core (refractive index: 1.474 1, thickness: 4 & micro;m) and upper/lower pure silica claddings (refractive index: 1.444 7, thicknesses: 20 & micro;m/10 & micro;m). Air trenches are etched on both sides of the waveguide modulation arm to reduce the thermal crosstalk and improve the thermo-optic modulation efficiency. Fabrication employs Complementary Metal Oxide Semiconductor-compatible technology. The lower cladding was grown on the silicon substrate via thermal oxidation. The core/upper cladding were deposited by Plasma Enhanced Chemical Vapor Deposition. The waveguide patterns were defined through ultraviolet lithography and Inductively Coupled Plasma etching. E-21-E-11 and E-31-E-11 mode converters were integrated at the output for higher-order mode signal measurement. The insertion loss, extinction ratio, and crosstalk were characterized at 1 550 nm. The dynamic response time was characterized under square-wave excitation. The stability during 10-minute short-term continuous operation and 10-day cyclic tests were conducted, too. Experimental results indicate that at a central wavelength of 1 550 nm, the E-11-E-21 mode conversion exhibits an insertion loss of 3.60 dB, an extinction ratio of 12.72 dB, a crosstalk of-12.10 dB, a rise time of 1.08 ms, and a fall time of 1.36 ms. For the E-11-E-31 mode conversion, the corresponding performance are measured as follows: insertion loss of 4.12 dB, extinction ratio of 11.58 dB, crosstalk of-12.20 dB, rise time of 1. 28 ms, and fall time of 1.44 ms. Bandwidth characterization reveals that the 1-dB bandwidth of the E-11-E-21 mode conversion is 92 nm (covering the wavelength range of 1 500 nm to 1 592 nm), while that of the E-11-E-31 mode conversion is 91 nm (spanning 1 539 nm to 1 630 nm). Notably, the 3-dB bandwidths of both mode conversions exceed 130 nm. The driving powers required for E-11-E-21 and E-11-E-31 mode switching are determined to be 297.96 mW and 261.82 mW, respectively. The optimized air trench structure effectively compensates for the low thermo-optic coefficient of silica. Stability tests demonstrate that during 10-minute continuous operation, the insertion loss fluctuations of the E-11-E-21 and E-11-E-31 mode conversions are less than 0.002 dB and 0.004 dB, respectively. In 10-day repeated testing, the insertion loss fluctuations are constrained within 0.50 dB and 0.52 dB, respectively. In comparison with state-of-the-art devices, the proposed switch realizes controllable conversion between the two modes through a cascaded multimode interference coupler and Mach-Zehnder interferometer structure. It offers enhanced process tolerance compared to the cascaded multimode interference coupler and asymmetric directional coupler structure, and superior switching flexibility relative to the cascaded Mach-Zehnder interferometer and subwavelength grating structure. Furthermore, its broadband characteristic (3-dB bandwidth exceeding 130 nm) satisfies the requirements of optical communication systems. The proposed silica waveguide mode conversion switch based on the cascaded multimode interference coupler and Mach-Zehnder interferometer structure realizes selective E-11-E-21/E-11-E-31 conversion. Its broadband performance, low loss fluctuation, and flexible switching capability endow it with substantial application potential in on-chip mode-division multiplexing. Compatibility with conventional silica optical devices further enhances its practical value, offering a feasible solution for reconfigurable wavelength-mode multidimensional multiplexing networks.
This research is driven by the critical need to overcome the inherent limitations of conventional Radio Frequency (RF)-based Over-The-Horizon (OTH) communication systems. Traditional systems, which rely on the propagation of microwave signals through the atmosphere or via ionospheric reflection, face significant challenges that constrain their performance in modern, high-demand scenarios. These challenges include severely limited bandwidth capacity, which restricts data throughput; vulnerability to both intentional jamming and unintentional electromagnetic interference, compromising reliability; and a lack of operational flexibility, making real-time reconfiguration and multi-channel parallel processing difficult. Furthermore, achieving wideband, cross-frequency operation often necessitates complex, bulky, and power-intensive electronic components. The primary objective of this work is to conceptualize, design, and validate a next-generation OTH communication system architecture that fundamentally transcends these electronic bottlenecks. By strategically integrating the field of microwave photonics- which utilizes light to generate, process, and distribute microwave signals-this study aims to create a system prototype capable of delivering unprecedented levels of bandwidth, robust anti-interference performance, and dynamic reconfigurability. The ultimate goal is to establish a concrete technological foundation for future OTH platforms that can meet the escalating demands for secure, high-capacity, and resilient long-distance tactical and strategic communication links. To achieve the stated objectives, a comprehensive system design and simulation-based research methodology was employed, centered on a novel architecture that synergizes three core microwave photonic subsystems. The system's front-end is a microwave photonic phased-array antenna. This antenna comprises 64 independent elements designed to simultaneously capture weak wireless signals from free space. The received RF signals from each element are first amplified by a dedicated Low-Noise Amplifier (LNA) to mitigate front-end noise. Subsequently, each amplified RF signal is used to directly modulate the intensity of a continuous-wave optical carrier generated by a Directly Modulated Laser (DML), thereby translating the electrical signals into the optical domain. This process creates 64 parallel optical RF channels. A critical innovation lies in the beamforming network. The 64 optical signals are fed into a tunable optical delay and attenuation module. A centralized digital control unit precisely and independently adjusts the time delay and attenuation for each of the 64 optical paths. This optical True-Time-Delay (TTD) approach is frequency-independent, enabling wideband, squint-free beam steering and shaping. The individually processed optical signals are then coherently combined via a Wavelength Division Multiplexing (WDM) stage, effectively synthesizing the desired radiation pattern in the optical domain before detection. The combined optical beam is converted back into a consolidated electrical RF signal using a high-speed Photodetector (PD). This aggregated RF signal is then routed to the second core subsystem: the microwave photonic frequency conversion unit. The heart of this unit is a coherent dual Optical Frequency Comb (OFC) setup. One OFC serves as a multi-wavelength Local Oscillator (LO), while the other is used for signal modulation. Electro-Optic Modulators (EOMs) are used for precise signal imprinting and frequency shifting. A key technique implemented is Carrier-Suppressed Single-Sideband (CS-SSB) modulation, achieved by carefully biasing the EOMs, which eliminates LO leakage and provides excellent channel isolation. This setup allows for the simultaneous up-conversion or down conversion of multiple RF channels across a ultra-wide bandwidth. The final subsystem is an integrated communication terminal, which performs demodulation, decoding, and protocol processing on the recovered baseband signals. The feasibility and performance of this integrated architecture were rigorously validated through detailed theoretical modeling and extensive link-level simulations using the industry-standard Optisystem software, which models the complex interactions between optical and RF components. The simulation and analysis of the proposed microwave photonic OTH system yielded highly promising results across multiple performance dimensions, confirming the effectiveness of the chosen architectural approach. Core Communication Performance: The system successfully demonstrated stable and high-fidelity signal transmission across the entire 4 similar to 16 GHz operational bandwidth. Within this spectrum, a sustained communication data rate of 200 Mbps was achieved, representing a significant improvement over typical narrowband OTH links and validating the system's high-bandwidth capability. Reconfigurable Channelized Processing: A major accomplishment was the implementation of reconfigurable microwave photonic channelized frequency conversion. The system possesses the ability to dynamically process signals across 13 independent wavelength channels. This channelization allows for simultaneous, parallel handling of multiple communication streams or signal sub-bands within the wide RF aperture, greatly enhancing spectral efficiency and multi-user capacity. Phased Array Link Performance: For the 64-element microwave photonic phased array link, detailed simulation confirmed that multichannel parallel processing was feasible with minimal signal quality degradation. Critically, the complex beamforming and signal combining processes were achieved with a signal-to-noise ratio (SNR) degradation of less than 3 dB, indicating highly efficient optical processing and minimal noise introduction from the photonic beamforming network. Optical Frequency Comb Conversion Performance: The dual-OFC frequency conversion subsystem exhibited exceptional precision and spectral purity. Using an array of 23 finely spaced optical comb lines, the system realized the reconfigurable switching functionality for the 13 channels. Specifically, it accomplished the up-conversion of a 336 MHz Intermediate Frequency (IF) signal to the target 4 similar to 16 GHz RF band. The converted spectrum showed excellent characteristics: a well-defined channel spacing of 1 GHz, a spurious suppression ratio better than 20 dB (indicating minimal unwanted harmonic generation), and a high in-band amplitude flatness with fluctuations not exceeding 4 dB across the entire 12 GHz range. This suite of metrics confirms the system's ability to perform precise, MHz-level frequency control and management with high spectral integrity. In conclusion, this research has successfully established the technical viability and superior potential of a microwave photonic approach to revolutionizing over-the-horizon communication. The proposed and analyzed system architecture, integrating a photonic phased array, a dual-optical-frequency-comb-based channelizer, and an integrated terminal, directly addresses and overcomes the fundamental bandwidth, interference, and flexibility constraints inherent in traditional electronic OTH systems. The simulation results provide compelling evidence that such a system can deliver wideband (4 similar to 16 GHz), high-data-rate (200 Mbps), multi-channel (13 channels), and reconfigurable communication links with high spectral purity and efficient beamforming. Beyond the immediate performance metrics, this work lays a critical and substantial foundation for the future engineering and deployment of advanced OTH communication systems. It demonstrates a clear pathway toward building more secure, resilient, and high-capacity strategic communication infrastructures. Future work will naturally focus on the practical implementation of this architecture, including the development of integrated photonic chips to reduce size, weight, and power consumption (SWaP) , experimental validation in real-world propagation environments, and the exploration of advanced signal processing algorithms to further enhance performance. This study marks a significant step forward in the convergence of photonics and wireless communications for national security and civilian long-range connectivity applications.
The broad field of view inherent to remote sensing images offers significant advantages for large scale monitoring tasks, enabling comprehensive surveillance over vast geographical areas with a single acquisition. However, this advantage is often offset by the presence of complex backgrounds, such as cloud cover, shadows, and varying terrain textures, which frequently introduce channel-level noise that interferes with target features. This interference significantly compromises the robustness and reliability of detection models, particularly in adverse weather conditions or densely cluttered environments. Additionally, the substantial variation in target sizes, ranging from small objects like vehicles and helicopters to large structures such as ports and bridges, poses a significant challenge. Detection models struggle to simultaneously capture high-resolution details necessary for identifying small targets and low-resolution semantic information essential for recognizing larger objects, leading to unbalanced detection performance across different scales. To address the aforementioned challenges, this paper proposes a remote sensing image object detection algorithm based on adaptive feature weighting, built upon the Oriented R-CNN framework. The method introduces two core modules: the Adaptive Channel Weighting Module (ACWM) and the Adaptive Multi-Scale Fusion Pyramid (AMFP), aimed at tackling background interference and multi-scale target detection issues. The ACWM module is applied after the STAGE 2 and STAGE 3 phases of the feature extraction network to adaptively adjust channel weights, a critical step for enhancing feature representation. By analyzing statistical correlations between channels using the Correlation-Aware Covariance Weighting (CACW) method, it generates dynamic channel weights to enhance target-related features while suppressing background noise and redundant information, balancing the expression of different channels and thereby improving the feature extraction network's ability to extract features from rotated targets. Subsequently, the AMFP module processes the multi-scale features (C2, C3, C4, and C5) extracted by the feature extraction network, employing a hierarchical approach for feature integration. The Multi-scale Perception and Context Integration Module (MPCIM) fuses global semantic features from deep layers with edge and positional details from shallow layers, effectively addressing the issue of small targets being obscured. The Adaptive Layer Weighting Module (ALWM) optimizes the fusion quality of multi-scale features through adaptive layer-wise weighting, enhancing the model's capability to handle diverse target scales ranging from small vehicles to large ports by dynamically adjusting the contribution of each feature level, thus improving adaptability to various target scales. The optimized features (P2, P3, P4, and P5) are then fed into the Oriented RPN and Oriented RCNN head, which, based on the Oriented R-CNN framework, generates high-precision rotated bounding boxes to complete classification and localization tasks. To validate the effectiveness of the proposed algorithm, extensive experiments were conducted on the DOTA1.0 and DIOR-R datasets. Ablation studies were performed to assess the contributions of the ACWM and AMFP modules. Results indicate that the ACWM module alone improves the mean Average Precision (mAP) by 0.97 % on DOTA1.0 and 1.73 % on DIOR-R, while the AMFP module contributes an additional 1.30 % and 2.01 % improvement, respectively. When both modules are combined, the mAP reaches 78.23% on DOTA1.0 and 68.17 % on DIOR-R, representing overall enhancements of 2.36 % and 3.87 % compared to the baseline Oriented R-CNN model. Visualization comparisons further demonstrate the superiority of the proposed method, showing a significant reduction in missed detections and false positives for small targets, particularly in categories such as Small Vehicle, Swimming Pool, Helicopter, and Storage Tank. The method also exhibits improved localization accuracy and better contour fitting for rotated objects, especially in complex backgrounds with varying angles and dense distributions. The experimental results highlight the robustness and adaptability of the proposed algorithm across diverse remote sensing scenarios. Compared to state-of-the-art methods such as Faster R-CNN, RoI Transformer, and ARC, the proposed approach achieves superior performance in handling small targets and complex orientations, as evidenced by its higher mAP and enhanced visual detection outcomes. However, limitations remain, including potential performance degradation in extremely cluttered scenes or with ultra-small targets, suggesting avenues for future optimization.
Single-frequency continuous-wave lasers are critically important for advanced applications in quantum information science, high-precision metrology, and lidar systems. These applications demand laser sources that combine a narrow linewidth, low amplitude and frequency noise, and high temporal coherence. A significant challenge in the field is scaling the output power of such lasers while simultaneously preserving their superior spectral purity and high stability. Conventional techniques for achieving single-frequency operation often face limitations in power scaling due to thermal effects and nonlinearities. This research demonstrates a high-power, single-frequency Nd:YVO4 laser system utilizing the seed injection-locking technique. A stable, narrow-linewidth fiber laser operating at 1 064 nm serves as the master oscillator. The slave laser is configured as an "8"-shaped ring resonator, which is pumped by an 888 nm diode laser. A composite Nd:YVO4 crystal is used as the gain medium to mitigate thermal lensing effects. Active frequency stabilization is implemented using the Pound-Drever-Hall (PDH) method. An error signal, derived from the cavity transmission, feeds back to a piezoelectric transducer to control the slave cavity length, thus locking it to the seed laser frequency. Under optimal injection-locking conditions and at a pump power of 38.12 W, the laser delivers a maximum output power of 13.5 W in a single longitudinal mode. The linewidth of the amplified output is measured to be 7.0 kHz. This represents only a minor broadening compared to the 5.6 kHz linewidth of the original seed laser. The system exhibits excellent power stability, with a root-mean-square power instability of less than 0.18% over a continuous 60-minute period. Furthermore, the frequency stability is significantly enhanced through injection locking. The long-term wavelength drift is reduced to 132.4 MHz, a substantial improvement over the 300 MHz drift observed for the free-running seed laser. A detailed frequency noise characterization reveals effective suppression of noise at low Fourier frequencies (1 similar to 100 Hz) in the locked state compared to the free-running slave laser. A slight increase in noise is observed at higher frequency offsets, which is attributed to residual mechanical vibrations from the locking actuator. These results confirm that the seed injection-locking technique successfully amplifies the optical power while maintaining the spectral characteristics of the seed. Crucially, this high stability is achieved without the need for active frequency stabilization of the seed laser itself. This work contributes by achieving a compelling combination of high power (13.5 W), narrow linewidth (7.0 kHz), and high stability at the important 1 064 nm wavelength. A key finding is that this high stability is accomplished without requiring active stabilization of the seed laser itself. The results robustly demonstrate that the seed injection-locking technique is a highly effective method for amplifying optical power while simultaneously preserving and even enhancing the frequency stability and spectral characteristics of the original seed source. In conclusion, this research successfully realizes a high-power, narrow-linewidth, low-noise single-frequency Nd:YVO4 laser. The system exhibits outstanding power and frequency stability, making it suitable for demanding applications. The approach provides a viable and practical pathway for developing high-performance single-frequency lasers. Future work will focus on refining the feedback control system to achieve even lower frequency noise. Additionally, the integration of intracavity nonlinear frequency conversion techniques, such as second harmonic generation, could be implemented to produce high-power, single-frequency radiation at other strategically important wavelengths, further expanding the utility of this laser architecture.
To meet the demands of future high-performance radar systems with superior resolution,agility and adptability,a reconfigurable radar waveform generation method based on the period-one(P1)oscillation dynamics of optically injected semiconductor laser is comprehensively investigated.The underlying principle involves perturbing the oscillation state of semiconductor laser through the injection of external continuous wave light.This perturbation alters the intracavity photons and carrier densities of laser,thereby exciting various nonlinear dynamics.Among these,P1 oscillation state exhibits asymmetric sideband modulation,which provides a theoretical basis for microwave signal generation. Firstly,the characteristics of P1 oscillation,including the frequency tunability and fast frequency-switching capability,are numerically analysed by solving the nonlinear rate equations.Simulation results demonstrate that the transition between distinct oscillation frequencies can be achieved with a switching speed on the order of ns level,highlighting the inherent agility of the optical injection system.The evolution routing of the nonlinear dynamics is also explored through the dynamical map as a function of injection strength and detuning frequency,which provides a guide to achieve and maintain the desired P1 oscillation state.Based on this,the experimentally generation of broadband radar signals are demonstrated.To generate broadband radar signal,a dynamical control unit of injection parameters is proposed to manipulate the instantaneous frequency of generated wideband waveform.By programming the control signals,various broadband radar signals are generated successfully,including linear frequency modulated signal,triangular wave signal,stepped-frequency signal,frequency-codded signal,frequency-codded linear and frequency modulated signal.The key waveform parameters of broadband signal such as bandwidth,time period,operating band and duty cycle,can also be flexibly adjusted by tuning the injection parameters,which further validate the feasibility of the proposed system.However,the optical injection system in application falls short in performance due to a challenge induced by the intrinsic noise of semiconductor lasers.to address this,approaches for enhancing the system performance are proposed and demonstrated.For single-frequency signal generation,a dual-loop optoelectrical feedback structure incorporating balanced photodetection is employed to improve the Side-Mode Suppression Ratio(SMSR)and phase noise of generated signals. Compared with conventional optical injection system,the linewidth of generated signal based above method is significantly narrowed by three-orders of magnitude.The SMSR is enhanced by about 65.5 dB due to the Vernier effect.In addition,the system maintains excellent frequency tunability while achieving a phase noise of below-124.10 dBc/Hz at 10 kHz offset.For broadband radar waveform generation,pre-compensation of the injection intensity and Fourier Domain Mode Locking(FDML)mechanism are incorporated,through which the in-band Signal-to-Noise Ratio(SNR)and frequency accuracy of generated radar waveforms are significantly improved.In the experiment,a broadband signal with a bandwidth of 6.3 GHz is generated,of which in-band SNR is improved by about 47 dB.In addition,limited by the transient properties of semiconductor laser,when the P1 oscillation frequency is fast changed with a large frequency step,strong damping oscillation of the output frequency occurs,resulting in deterioration of the frequency stability and accuracy.The application of the FDML mechanism is shown to effectively suppress the damping oscillation,once again underscoring the advantages of the proposed signal generation method. To validate the practical utility of the proposed radar waveform generation method,both Single-Input Single-Output(SISO)radar and a Multiple-Input Single-Output(MISO)radar systems are established.Firstly,based on the proposed SISO radar system,high resolution radar ranging is successfully realized,clearly distinguishing two closely spaced targets.The measured result shows excellent agreement with the actual distance.For MISO radar system,in the transmitter,the generated signal is emitted by means of time-division multiplexing across multiple transmitter channels.In the receiver,broadband de-chirp processing is performed via IQ mixing.When detecting a drone in an experimental scenario,the target is precisely located,which verifies that the proposed radar waveform generation system is a promising solution to construct efficient and low-complexity microwave photonic radars.
