To address the inefficiency and errors caused by manual polarizer rotation in traditional underwater polarization imaging, this paper proposes an active polarization-based enhancement method. It directly generates optimal polarized image pairs via Stokes vector analysis, reducing acquisition time. An adaptive threshold low-pass filtering algorithm is designed to accurately estimate and suppress backscattered light without requiring prior knowledge of the background. Furthermore, a polarization-weighted fusion strategy, guided by a novel Image Quality Evaluation Unit (IQEU) that integrates SSIM, VIF, and contrast weight, is employed to optimize fusion and significantly improve detail clarity and global contrast. Experimental results demonstrate excellent performance across a range of turbidity levels and target types. Compared to existing methods, the proposed approach shows marked advantages in detail recovery, backscatter suppression, and contrast enhancement, highlighting its strong versatility and robustness for underwater detection and high-quality imaging.
In this paper, self-stabilized recordings in the reflection geometry were carried out in an undoped titanosillenite Bi12TiO20 photorefractive crystal for characterization purposes. In this two-wave mixing experiment with the light of a 532 nm wavelength laser, the evolution of the diffraction efficiency was measured during the recording of the gratings with different light intensities and the Debye screening length, the quantum efficiency, and the holographic sensitivity parameters were determined.
With the demand for flexible, high-resolution, low-cost, and fast smartphone-based microscopy, image quality is degraded by severe distortions from both the microscope and smartphone lens. This paper builds a distortion model and designs a grid-like micro-structure calibration target. A multi-resolution feature point extraction method using 2D discrete Fourier transform is developed, and the distortion center is estimated via linear fitting. Distortion parameters are then computed, achieving a root mean square error of 4.68 pixels in re-projection. The method successfully corrects distorted microscopic images of an USAF 1951 resolution board, oleander stem, pine stem, and roundworm cross-sections. Notably, the calibration assumes strict parallelism between the calibration target and image sensor planes-a condition naturally met in microscopy, eliminating the need for complex extrinsic parameter estimation.
Radio over Fibre (RoF) technology is an emerging solution with growing demand for higher data speed, greater bandwidth, and large channel capacities. This manuscript presents a comprehensive design and analysis of an RoF communication system based on Dense Wavelength Division Multiplexing (DWDM), employing Dual Port Dual Drive Mach-Zehnder Modulator (DPDD-MZM). To overcome the dispersion effect challenge, a linearly chirped Fibre Bragg Grating (FBG) is incorporated as a dispersion compensation technique. A 64-channel DWDM-based RoF communication system provides an overall data rate of 512 Gbps. The system performance is analysed using OptiSystem Simulator 16.0 for transmission distances of 120 and 60 km, with channel spacing of 50 and 100 GHz. It was observed that the optimal performance is achieved at a signal input power of -2.5 dBm. Under these conditions, the obtained Quality Factors (Q-factors) are 20.55 for a 120 km link and 21.97 for a 60 km link at channel spacing of 50 and 100 GHz, respectively. Furthermore, the received power levels before and after the FBG are 21.56 and 69.67 dBm, respectively, confirming the effectiveness of the dispersion compensation. The results confirm that the integration of DWDM technology with advanced modulation techniques and dispersion compensation significantly enhances the performance of RoF systems. This architecture enables high-capacity, long-distance transmission while maintaining excellent signal quality, making it a strong candidate for supporting 5G and future high-speed communication networks.
Estimating Newton's ring parameters using the Concise Fractional Fourier Transform (CFRFT) faces accuracy and complexity challenges due to its nonlinear quadratic phase term. This paper proposes the Linear Concise Fractional Fourier Transform (LCFRFT), which linearizes the quadratic phase-term coefficients to decouple the fringe coefficients and the lens's curvature radius. Simulations and experimental validations confirm LCFRFT's superiority in various noise environments. In real-world tests on 23 images with a 1.443 m curvature radius, LCFRFT reduced the average estimation error from 2.98% (CFRFT) to 1.71% at a step length of 50. Notably, LCFRFT processed these interferograms in just 29.161 s. To achieve a comparable error level, CFRFT required a step length of 300, extending processing time to 165.956 s. Overall, LCFRFT provides a robust, high-precision and efficient metrology solution for scenarios involving large curvature radii and complex noise environments.
This study presents a theoretical investigation on performance enhancement of fibre Bragg grating (FBG) temperature sensors using a frequency-shifted interferometry fibre loop ring-down (FSI-FLRD) technique. A bare FBG is employed as the temperature sensing probe, and the temperature variations are detected via changes in ring-down distance. Within the temperature range of 10-40 degrees C, the proposed sensor achieved the sensitivities of 0.3680 km-1 & centerdot;degrees C-1 and -0.3657 km-1 & centerdot;degrees C-1 in the sub-ranges of 10-21 degrees C and 27-38 degrees C, respectively. The system exhibits a ring-down baseline stability of 0.47% and a temperature resolution as low as 0.026 degrees C. This resolution represents a 76-fold improvement over conventional spectrum-analysis-based and edge-filter-based FBG sensors, and a 7-fold enhancement compared to traditional FLRD-based FBG sensors. Furthermore, it is theoretically shown that by optimizing the laser operating wavelength, the sensitivity, resolution, and measurement range can be improved by a factor of 2-3 compared to previously reported experimental results of the FSI-FLRD FBG sensor.
In this paper, the security of a cryptosystem based on DRPE and a phase mask generation process relying on hash function and chaos theory is analyzed. The cryptosystem under investigation uses two deterministic phase masks generated by the SHA-512 hash function and two-dimensional coupled logistic chaotic map. a. In this study we demonstarte the vulnerability of cryptosystem towards modified chosen-plaintext attack (mCPA) and modified known-plaintext attack (mKPA) using different type and size of images. . The robustness of proposed attack algorithm is also analysized through contimined ciphertext. The results vildate that proposed attack algorithm retirve the images successfully. The results are validated using various statistical metrics and visual metrics. The results validate the proposed attack algorithms, mKPA and mCPA, which also retrieve the plaintext from compressed ciphertext. Results validate the effectiveness and robustness of the proposed attack algorithms towards the cryptosystem under investigation.
Conventional fibre Bragg grating (FBG) strain sensors are limited by silica fibre's elastic tolerance (<0.5 % strain). To overcome this, we propose a curvature-release mechanism converting external tensile strain into bending curvature variation of a seven-core fibre Bragg grating (SCFBG). The SCFBG is selectively inscribed by a femtosecond laser phase-mask method with photo-fluorescence imaging and arc-encapsulated in PDMS. When stretched, the embedded SCFBG experiences curvature changes instead of axial strain. Curvature is reconstructed from differential wavelength shifts of six outer cores using vectorial bending theory, while the central core compensates for temperature and residual strain. The sensor achieves an ultra-large strain range of 0 similar to 300 m epsilon (30 % deformation), two orders beyond conventional FBGs, with a maximum sensitivity of 127.15 m(-1)/epsilon. Performance can be tailored by adjusting initial curvature, grating offset and PDMS thickness. This work provides a new paradigm for flexible optical fibre sensing under extreme deformation.
This paper presents a novel image encryption algorithm that combines a four-dimensional chaotic system, a dynamic S-box, and XOR bitwise operations. Firstly, the color image is subjected to pixel confusion processing through Arnold perturbation to make the positions of image pixels become chaotic. Then, a chaotic sequence is generated by the chaotic system, which is used to construct the dynamic S-box to encrypt the image data for the first time. Finally, the classic XOR algorithm is used to generate the key stream for the second encryption of the image and obtain the final encrypted image. The dynamic S-box and XOR bitwise operations can significantly confuse the image and enhance the encryption security.
This study numerically proposed and analyzed a wide-range surface plasmon resonance refractive index sensor based on a dual D-shaped photonic crystal fiber. The design employs an external sensing mechanism, with a gold film deposited as the plasmonic material on the outer surface of the elliptical groove, ensuring feasible fabrication. The proposed sensor is capable of detecting analytes within a refractive index range of 1.20-1.36, achieving a maximum spectral sensitivity of 14,000 nm/RIU. Additionally, it supports amplitude-based detection, offering a maximum amplitude sensitivity of -101.99 RIU-1. The study systematically examines the effects of key design parameters, including the air hole diameter, spacing between air holes, and gold film thickness, among others. With its wide detection range, high sensitivity, ease of fabrication, and user-friendly design, the proposed sensor demonstrates significant application potential in detecting fluorinated organic compounds, medical anaesthetics, liquid carbon dioxide, and other analytes.
This article examines the exact wave patterns and chaotic dynamical behaviours of the dispersive concatenation model with spatio-temporal dispersion, Hamiltonian perturbation terms and multiplicative white noise. The higher-order dispersion terms of this model have important applications in nonlinear fibre optics. First, an integrating factor equation of the higher-order nonlinear amplitude equation is given by using the trial equation method. Then, combined with bifurcation theory and the complete discrimination system for polynomial method, the topological structure of the dynamical system is analysed, proving the existence of soliton solutions and periodic solutions, and obtaining a series of rich exact solutions, including new solutions. Finally, it is found that the system exhibits chaotic behaviours under appropriate perturbations. In particular, the numerical simulation results show that the non-averaged solutions still preserve the characteristics of solitons and periodic modes. To our knowledge, these results are new for this model and can provide new insights into the study of optical transmission under random perturbations.
In this paper, we have realized the synchronic spiral beam with a square array by the interference of 12 plane waves. The interference of the outer eight quasi-symmetrical plane waves can form the vortices with a square array. The interference of four central symmetrical plane waves can form spots with a square array. The superposition of the vortex and spot arrays formed the synchronized spiral beam array. This type of spiral beam with a square array can be applied in the fields of chiral material processing, micro-particle manipulation, etc. The simulation and experimental results demonstrate the feasibility of this method.
We address the problem of constructing a stable T-matrix formulation for electromagnetic scattering by smooth dielectric particles, with particular emphasis on axisymmetric geometries. The proposed approach is based on an asymptotic analysis of the matrix elements using the saddle-point method, which helps identify the dominant contributions at high multipole orders. A key feature of the work is the LOT scheme, which combines Tikhonov regularization with a parity-based decomposition of the basis functions. This strategy improves the numerical stability of the resulting linear systems and reduces the effective dimensionality of the problem. Benchmark tests show quantitatively reasonable agreement with the reference Mie theory: the relative errors are typically of order 5- $ 10\% $ 10% over the tested benchmark range, with the best cases below $ 1\% $ 1% and a minimum error as low as $ 0.3\% $ 0.3%.
Natural gas is a low-carbon energy, but it carries solid particles and liquid droplets during long-distance transportation, causing pipeline wear, corrosion and potential safety hazards. Existing detection methods fail to effectively differentiate solid and liquid impurities, leading to low detection accuracy. This work proposes a polarization-based particle discrimination method. Micro-nano solid and liquid particles show different light polarization scattering characteristics. The T-matrix method is adopted to calculate scattering polarization features of differently shaped particles, and the optimal scattering angle for particle classification is determined. Combined with vector Monte Carlo algorithm, a coupled multi-scattering model for mixed particle groups is established and verified. The effects of liquid proportion, particle morphology and incident polarization state on scattering properties are analyzed. This study lays a theoretical foundation for high-precision online optical monitoring of impurities in natural gas pipelines.
Multispectral imaging systems capture spatial and spectral data simultaneously. Aperture segmentation reduces system size versus multi-lens designs, but lowers spatial resolution. Wide working band requires different lens counts per channel to correct chromatic aberration, increasing complexity. We propose a local high spatial resolution imaging method for segmented wide-spectral systems, using a main image plane and a spatial light modulator (SLM) that dynamically adjusts local aberration, enabling high spatial resolution observation of regions of interest. The system operates at 500-1600 nm (visible and near-infrared groups, each with four channels, total eight channels), with a 20 degrees field of view. Each exposure captures all four channels of either group. With SLM, the RMS radius of the selected field drops, up to about 50%. MTF differences between tangential and sagittal planes reduce, as does wave aberration. This design enables simultaneous overall and local target observation for complex environments.
In this paper, the two-photon blockade effect in an atom-cavity system, by two-photon Jaynes-Cummings coupling, has been studied. In this hybrid system, that is, a three-wave-mixing system with an atom, by means of analytical calculations and numerical simulations, we show that the two-photon blockade effect can be realized. The presence of an atom by two-photon Jaynes-Cummings coupling could make the blockade effect much stronger than that in a three-wave-mixing system. Furthermore, the increase in two-photon Jaynes-Cummings coupling strength could further enhance the blockade effect. All of these may provide useful references for future experimental or application studies of two-photon sources or devices.
We present a theoretical study of nonclassical light generation in Nondegenerate Triple-Photon Down-Conversion (NTPDC), using a first-order interaction Hamiltonian within the short-time approximation. The analysis reveals quadrature squeezing and both bipartite and tripartite entanglement, indicating strong multimode quantum correlations. We show that increasing the coherent input amplitude and the nonlinear coupling enhances the degree of two-mode squeezing, while the squeezing depth is strongly controlled by the relative phase, enabling suppression of quantum noise. Bipartite entanglement is stronger and persists over a wider parameter range than tripartite entanglement, which occurs only under symmetric excitation and precise phase matching. The presence of bipartite entanglement is quantitatively verified using the Hillery-Zubairy (HZ) criteria (HZ-1 and HZ-2), with HZ-1 exhibiting higher sensitivity in high-coherence regimes. The results demonstrate that NTPDC is a promising scheme for generating scalable quantum resources for applications in quantum information and integrated photonics.
