The multi-pass cell (MPC) is an effective approach to extend the interaction path between laser radiation and gas molecules, thereby improving the detection sensitivity of laser-based gas sensors. However, an inaccurate determination of the MPC optical path length can introduce significant errors in direct absorption spectroscopy. In this work, we proposed a fast and precise technique—optical frequency domain interferometry (OFDI)—for measuring the MPC length, particularly suitable for configurations where the laser entrance and exit share the same window. Both the conventional absorption-based method and the proposed OFDI method were implemented and compared. Experimental results show that for a 295.4 m-long MPC, the absorption method yielded an uncertainty of approximately 1 m, while the OFDI approach reduced this to about 5 cm. Using the corrected MPC length, a carbon dioxide sensor was developed, achieving a detection sensitivity of 1.2 ppm with an integration time of 60 s. The proposed OFDI method provides a simple and highly effective solution for accurately measuring the optical path length of multi-pass cells and other optical systems.
In the context of digital holographic microscopic quantitative phase imaging, a microscope is employed in the experimental setup to magnify both the object light and the reference light beam. The three-dimensional phase information within the hologram is influenced by the curvature of the microscope, resulting in significant distortion of the object phase. Additionally, off-axis tilting introduces further phase distortions. In this study, we propose a two-wavelength phase subtraction method to mitigate such distortions in digital holographic microscopy. The procedure involves capturing phase images at distinct wavelengths using filters that are highly transparent to the 671 nm band and highly reflective to the 532 nm band. By subtracting the phase image containing both object information and distortion from the phase image containing only distortion, a distortion-compensated phase image is obtained. Through both theoretical analysis and experimental validation, we demonstrate that the proposed method offers substantial potential for effectively compensating distortions in digital holographic microscopy.
Billions of people worldwide suffer from sleep disorders and it is important to investigate how the lack of sleep or poor sleep quality affects the visual system. The primary aim of this study was to evaluate the influence of 1 night without sleep on the near point of convergence (NPC) and accommodation parameters in young adults. Twenty three young (mean age: 23.3 +/- 1.68 years) adult subjects were recruited. NPC, accommodative facility, and amplitude of accommodation were measured after normal habitual sleep and after 1 night of sleep deprivation. Both the mean amplitude of accommodation and accommodative facility were significantly reduced after one night of sleep deprivation. With respect to NPC, both the break and recovery points of fusion were significantly receded after a sleep-deprived night. Our results showed that even 1 night without sleep may affect visual function associated with near vision tasks. Our findings suggest that sleep habits should be considered during optometric/ophthalmic examinations, especially when convergence and/or accommodation disorders are observed.
This work introduces a novel iterative reconstruction algorithm that enhances low-resolution optical spectrum. The proposed method effectively recovers spectral features that are otherwise undetectable using low-to moderate-resolution interrogators. An adaptive low-pass filter is integrated into error feedback to effectively suppress noise while selectively preserving high-frequency spectral components during iterative reconstruction process. The algorithm's performance was validated using fiber grating Fabry-Perot interferometer (FPI) sensor spectrum with varying cavity lengths (4, 19, and 25 mm). Using high-resolution spectrum as references, the reconstructed spectrum demonstrated notable improvements, with reductions in Delta MAE (4 mm: -2.42%, 19 mm: -9.37%, and 25 mm: -32.51%) and Delta MSE (4 mm: -4.23%, 19 mm: -17.96%, and 25 mm: -61.22%) compared to the original low-resolution spectrum. Amongst filter methods, an "equiripple" low-pass filter is effective in enhancing the reconstructed spectrum by suppressing noise, resulting in reduced spectral errors (Delta MAE = -6.49%; Delta MSE = -12.97%). The proposed algorithm offers aprac-tical and computationally efficient solution for recovering lost spectral details, particularly in the high-frequency region with minimal error. This capability is especially valuable for enhancing the performance of low-resolution interrogators, allowing their reconstructed spectrum to exhibit characteristics comparable to those obtained with high-resolution systems.
To enhance the early warning rate of pipeline leak events and reduce the false alarm rate in Phi-OTDR -based DAS systems, this paper proposes a new method based on FMD. The introduced vibration event types include not only pipeline leaks but also hammer strikes, steel pipe hits, and noise. A 160-meter pipeline setup was constructed, and the sensing optical fiber wound around it was monitored to collect 2 240 samples. The results after denoising demonstrate the effectiveness of the proposed denoising method. Subsequently, features were extracted using overlapping frames, dimensionality reduction was performed with t-SNE, and after training with NRBO-XGBoost, the leak event recognition rate reached 99.74%, the average classification accuracy reached 98.71%, and the false alarm rate was reduced to 0.19%.
In order to solve the problem that traditional microscopes cannot directly obtain the focus phase map from defocusing micrographs under incoherent illumination, a non-paired self-focusing quantitative phase imaging method based on Cycle-GAN is proposed. It only needs to obtain the bright field image of the cell by using an ordinary optical bright field microscope, and obtain the focused quantitative phase image by using the optimal weight model trained by the Cycle-GAN network. This method can directly reconstruct the phase image from an incoherent intensity map while achieving self-focusing. The quantitative analysis of the network-output phase images and holographically captured intensity images proves that the Cycle-GAN method can realize the self-focusing and quantitative phase image reconstruction of biological samples.
The article proves the possibility of using polarization-division multiplexing to power-supply temperature and strain fiber-optic polarization sensors, along with maintaining their high sensitivity to measured quantities. The main advantages of sensors are their light weight, reliability, wide field of sensing and absence of electricity, which make them suitable for use in environments with a high possibility of an explosion. Polarization-division multiplexing increases the capacity of already existing single-mode routes and allows simultaneous power supplying of the sensor and data transmission on one wavelength. The article describes the development of a bidirectional sensor utilizing a polarization beam splitter, which is independent of the polarization state, thereby increasing its reliability and sensitivity to measured quantities. The high sensitivity and stability of the bidirectional sensor in measuring temperature and strain changes are confirmed by mathematical descriptions of the ongoing phenomena. The two-way, one-fiber sensor, which is based on a polarization beam splitter, represents an ideal solution due to its polarization independence. This type of sensor was tested for changes in temperature, pressure, tension, and deformation.
Based on the two-plane representation model of the light field, light field cameras can synchronously record positional and directional information of the rays by sacrificing spatial resolution. To improve the spatial resolution of light field images, this paper presents a light field super-resolution network built upon the mechanism of multi-dimensional disparities mining. In the shallow layers of the network, a multi-scale self-attention module is designed, which works in conjunction with a residual atrous spatial pyramid pooling module to extract features from sub-aperture images. For the deep feature extraction, a multi-dimensional feature separator-mixer is developed to mine disparities from different forms of light field subspace, and an iterative structure is employed to extract deep fused disparity among different sub-aperture images. At the end of the network, a global-local feature refine module is added to further improve the quality of the output images. By adopting the mechanism of disparity iterative separation-fusion and re-enhancement, the proposed network achieves high-quality super-resolution reconstruction of sub-aperture images with a relatively compact architecture. Experimental results verify the superiority of the proposed network. In particular, with only 3.83 M parameters, the network achieves 4 times super-resolved images with an average PSNR of 32.27 dB in 5 public datasets.
The self-heating effect of multi-junction vertical cavity surface emitting lasers (MJ VCSELs) under continuous current injection seriously affects their output performance and durability. In this study, we designed and simulated a multi-junction bottom-emitting VCSEL structure. By adopting the n-type oxide layers and the component gradient spacer layers, the optical output performance of the device under continuous current injection was effectively improved. Compared with the traditional MJ VCSEL structure, the designed device can achieve a peak power increase of more than 30 mW and an 18% improvement in electro-optical power conversion efficiency (PCE) without changing the oxidation aperture. Meanwhile, this new type of MJ VCSEL shows good adaptability to the increase of environmental temperature. Even at an ambient temperature of 80 degrees C, it can still achieve comparable performance to the traditional structure of MJ VCSEL at room temperature. The results of this study indicate that the structure we designed is promising for the achievement of high-performance MJ VCSELs.
In this work, a reflectance polarimetry imaging system based on liquid crystal polarization rotator is proposed for the assessment of ripening process of mangoes. A low-cost voltage-controlled liquid crystal polarization rotator and a wire-grid polarizer were integrated into input ray path of a digital camera, enabling selective acquisition of horizontally or vertically polarized (0 degrees and 90 degrees) input images. Unripe Chokanan mango samples were subjected to the illumination of linearly polarized LED light at different wavelength. Digital images at two polarization states were recorded daily until the mangoes were fully ripened on the eighth day. Average reflectance intensity and Degree of Linear Polarization (DoLP) and the findings indicate the dynamic correlation between the varying reflectance intensity, illumination wavelength and the associated dominant pigments (e.g. carotenoids, anthocyanins and chlorophylls) in the fruit epidermis during the ripening process. In addition, the DoLP at different wavelengths have shown different variation characteristics with ripening. Notably, DoLPs at 593 and 660 nm decrease with ripening, due to decreasing moisture content in the fruit epidermis that promises light scattering and depolarization in the epidermis tissues. The study demonstrates the potential of reflectance polarimetry as a non-invasive method for assessing the ripeness and storage condition of fruits.
The propagation characteristics of Hermite non-uniformly correlated (HNUC) beams in axisymmetric gradient-index (GRIN) fibers were investigated, revealing the existence of dual focal points along the direction of optical transmission (z-axis) near 0.25L and 0.75L. To exploit this bifocal property, tandem GRIN fibers were employed, with the dual foci positioned within the interstitial gap between the serially connected fibers. Through systematic analysis of the intensity distribution within the gap and the resulting radiation forces on Rayleigh particles, it was demonstrated that the HNUC beam establishes two stable equilibrium points along the z-axis within the gap region, both capable of three-dimensional optical trapping of Rayleigh particles. These findings suggest potential applications in fiber-optic tweezers systems for creating longitudinally distributed multiple optical potential wells.
Digital holographic microscopy is widely applied in the study of the dynamic morphology of microscopic objects due to its characteristics of non-contact measurement, high-resolution three dimensional morphology detection, and real-time observation. This paper introduces a novel off-axis digital holographic signal spectrum extraction method based on deep learning, named DL-SEDH. The DL-SEDH algorithm is trained using approximately 1000 signal spectra from a USAF 1951 resolution test target, successfully achieving adaptive extraction of signal spectra and effective suppression of interference components. To validate its effectiveness, experiments are conducted using the USAF 1951 resolution test target and onion epidermal cells as research subjects. The experimental results demonstrate that DL-SEDH not only rapidly and accurately selects signal spectra while suppressing interference frequency components, especially coherent noise distributed near the signal spectra, but also exhibits higher accuracy, robustness, and applicability compared to traditional methods. Validation on holograms not used during training confirms the effectiveness of DL-SEDH in phase reconstruction quality. The proposed DL-SEDH method introduces innovation to the off-axis digital holography field, holding significant practical value and providing an efficient and precise solution for phase reconstruction in digital holographic microscopy.
To address the main challenge of limited vision zone and deteriorated visual clarity caused by residual astigmatism in progressive addition lenses, the study on large-anastigmatic-vision-zone progressive addition lens is conducted. By exploring the influence of optical power along the meridian on the growth rate of astigmatism, the design method for the meridian with tunable optical power is investigated. Subsequently, by extending the tunable optical power from the meridian to the entire lens surface along different shapes of contour lines, the effect of surface tunable optical power on the astigmatism and the vision zone is explored. This leads to the development of a design method for progressive addition lenses with low residual astigmatism, large vision zone, and surface tunable optical power. Based on this design method, progressive addition lens with a usable vision zone area exceeding 84% of the total lens area is optimized, while maintaining a maximum residual astigmatism of only 1.65 D. This holds significant value for the advancement of progressive addition lenses.
In this paper, we propose a robust asymmetric image encryption algorithm that integrates integer wavelet transformation (IWT) with elliptic curve cryptography (ECC). The scheme first applies the IWT to decompose the input image into sub-bands, effectively capturing both spatial and frequency domain features. Subsequently, the significant coefficients are selectively encrypted using ECC to achieve high security and efficient key management. The proposed algorithm leverages the inherent advantages of IWT for effective image representation and the robust security features of ECC, which provides smaller key sizes compared to traditional RSA-based systems while ensuring comparable security. Extensive experimental results, including statistical analyses such as histogram uniformity, correlation coefficients, and entropy metrics, demonstrate the algorithm's resilience against various attacks, including differential and brute-force attacks. The proposed method thus ensures secure image transmission while maintaining computational efficiency, making it suitable for real-time multimedia security applications.
This research introduces a photonic sensor designed to detect gamma-ray radiation, utilizing a one-dimensional regular ternary annular photonic crystal (1D APhC) structure. The sensor consists of alternating layers of porous silicon, silicon dioxide, and polyvinyl alcohol (PVA) polymer, which is doped with crystal violet and carbol fuchsine dyes. Exposure to varying levels of gamma-ray radiation alters the refractive index of the doped polymer, resulting in a shift in the photonic band-gap (PBG). The analysis of this dosimeter emphasizes how the intensity and position of the left band edge of the PBG are affected. Theoretical investigations are performed using Bruggeman's effective medium equation and the transfer matrix method (TMM). The study examines the impact of gamma-ray radiation intensity, ranging from 0 to 70 Gy, on the refractive index of the polymer. Furthermore, it explores how critical parameters, such as the movement of the left and right band edges, PBG width, and sensor sensitivity, are influenced by structural modifications. Under optimized conditions, the sensor achieves a sensitivity of 200.8351 nm/RIU in detecting gamma-ray radiation exposure from 0 to 70 Gy. This highly sensitive dosimeter design holds significant potential for various scientific applications, facilitating accurate detection of gamma-ray radiation.
Optical vortices are beams with spiral phase wave fronts capable of carrying different topological charges. This paper presents the expression for Gaussian vortex light and simulates vortices with topological charges of 0, 1, and 2, revealing a "hollow" extinction phenomenon. We derive the relationship between the radius of Gaussian vortex beams and their topological charges, express the extinction ratio of hollow vortices, and calculate the beam radius. The study demonstrates a linear relationship between the extinction ratio and topological charge (from 1 to 20). The fitting accuracy between the simulated hollow radius and the Gaussian vortex approximated radius reaches 85.93%, with an error margin of 17%. In laboratory experiments using a liquid crystal spatial light modulator, we constructed a vortex light system employing a 532.0 nm laser to generate 10 interference fringes of hollow vortex light with topological charges ranging from 10 to 100 on a CCD detector. Pixel measurements were taken for both inner and outer radii corresponding to these charge patterns, enabling precise calculation of extinction ratio. The experimental results show a similar trend to the theoretical predictions, demonstrating that hollow vortex light with extinction properties holds potential applications in signal encryption.
Using vector diffraction theory, we analyze how heterogeneous phase modulation affects the focusing behavior and propagation of Bessel-Gaussian beams. We systematically analyze the influence of beam parameters, topological charge L, phase factor n, and focusing angle phase parameter B on the normalized intensity distribution. The results reveal that the topological charge L can precisely control the opening degree of the spiral-shaped curve on the focal plane: as L increases, the ring opening widens, and a second ring emerges. Increasing the phase factor n concentrates beam energy toward the central spot. The focusing angle phase parameter B strongly affects peak intensity locations: larger B shifts energy toward bilateral regions, and further increase displaces the highest -intensity spot outward along the y = x direction. Increasing beam parameters causes focal plane intensity peaks to separate, expanding the overall focal pattern outward. We also examine how negwise. These findings have potential applications in optical trapping, particle manipulation, and modern medical technologies.
The quantum image encryption and authentication algorithm are proposed based on quantum affine transformation and quantum Haar wavelet transform. This algorithm is divided into two main steps: encryption and embedding. During the encryption phase, affine transform and H & eacute;non map are combined to carry out scrambling-diffusion processing on the plaintext image. In the phase of embedding, the color carrier image undergoes decomposition using the quantum Haar wavelet transform. Then the ciphertext image information and identity information are hidden into the wavelet domain of the color carrier image, and the final transmitted image has visual significance. The suggested algorithm significantly minimizes the risk of image data compromise during transmission and realizes the dual security of encryption and authentication. The security and the robustness of the algorithm are analyzed by using the evaluation indexes of image encryption and information hiding. The findings indicate that the introduced algorithm offers superior security compared to alternative methods, ensuring a more dependable and safeguarded transmission of image data.
To develop a hyperchaotic laser generator, we designed and investigated a novel tri-ring Er-doped fiber laser system. The system was assembled from three single-ring Er-doped fiber lasers with two couplers, and a mathematical model was established using a set of six-dimensional nonlinear coupling equations. We mathematically deduced the function of the stable field of each single-ring laser as the pump varied, and presented distributions of the lasers' stable outputs. We theoretically analyzed the instability of the system using three sets of cubic relation expressions, which were verified by nonlinear function curves. It demonstrated the possible existence of a twin-scroll strange attractor in each laser ring and a hyper-scroll strange attractor in the assembled tri-ring laser system, which was consistent with our numerical result. We found that, as a subsystem, each single -ring laser could maintain its nonlinear dynamics, while the assembled tri-ring system exhibited rich nonlinear dynamic behaviors, such as quasi-periodicity, bifurcation, chaos, and hyperchaos. Lyapunov exponents were used to characterize the system's dynamic behavior, while fractal dimensions were used to investigate the spatial construction of the dynamics within the system. In the numerical analysis, we evaluated the evolution of the system, starting at a stable state, passing from a quasi-period state, and developing into chaos. This revealed a path to chaos and hyperchaos through a bifurcation scenario by shifting one parameter of the system. Chaotic, stable, and double -periodic bifurcation regions were found after exploring a path to chaos after bifurcation by adjusting the pump level of each laser ring. Two chaotic regions and double-periodic regions were observed when exploring a path toward or away from chaos by adding the coupling level of two rings. Chaotic, stable, and double-periodic bifurcation regions were found after exploring a path toward or away from chaos by varying the gain coefficient and decay rate, respectively. We also found that hyperchaotic waves were accompanied by hyperchaotic moving orbits in the dynamic phase. The strange attractor was characterized by ergodicity, the real-time wave by both complexity and randomness, and the hyperchaotic signal by the wide-band spectrum. The power spectrum clearly revealed the hyperchaotic response, exhibiting numerous frequency peaks that were randomly distributed with varying amplitudes. The assembled tri-ring laser system demonstrated extensive application potential and significant research value in the fields of fiber laser technology, laser chaos, optical secure communication, optical random signal generator, and laser radar.
This paper introduces a novel statistical model for the performance analysis of hybrid RF/FSO (radio frequency/free-space optics) communication systems. The RF channel is modeled using the Nakagami-m fading distribution, while the FSO channel is characterized by a Chi-square-inverse Gamma distribution to account for atmospheric turbulence and pointing errors. A closed-form expression for the cumulative distribution function (CDF) of a one-hop hybrid RF/FSO system is derived under a selective combining scheme, formulated as a function of the average signal-to-noise ratio (SNR). The resulting CDF is expressed in terms of the extended generalized bivariate Meijer-G function (EGBMGF). Furthermore, new analytical expressions for the average bit error rate (ABER) are obtained for both the hybrid RF/FSO system and its FSO-only counterpart under coherent binary phase-shift keying (CBPSK) modulation. A detailed comparative analysis is performed across varying channel parameters and turbulence conditions. Numerical results, presented graphically, demonstrate the superior robustness of the proposed hybrid scheme under severe turbulence and misalignment effects.
