Journal of The Optical Society of America A-optics Image Science and Vision最新文献

Resonances, also known as quasinormal modes (QNMs) in the non-Hermitian case, play a ubiquitous role in all domains of physics ruled by wave phenomena, notably in continuum mechanics, acoustics, electrodynamics, and quantum theory. The non-Hermiticity arises from the system losses, whether they are material (Joule losses in electromagnetism) or linked to the openness of the problem (radiation losses). In this paper, we focus on the latter delicate matter when considering bounded computational domains mandatory when using, e.g., finite elements. We address the important question of whether dispersive perfectly matched layer (PML) and high-order absorbing boundary conditions offer advantages in QNM computation and modal expansion of the optical responses compared with nondispersive PMLs.

Optical wireless communications applications are restricted by oceanic media-induced beam quality degradation. However, modulating the coherence and polarization structures of the laser beams can effectively diminish the negative influence of oceanic turbulence on the beams. The average intensity of a radially polarized Laguerre-Gaussian Schell-model vortex (RPLGSMV) beam propagating through oceanic turbulence is explored by employing the extended Huygens-Fresnel principle. We found that the average intensity of an RPLGSMV beam is greatly affected by oceanic turbulence with a large rate of dissipation of the mean-square temperature and a large relative strength of the temperature and salinity fluctuations as well as the small rate of dissipation of the turbulent kinetic energy per unit mass of fluid and small Kolmogorov microscale. It was also found that a RPLGSMV beam with a larger radial index, topological charge, initial coherent length, and beam waist has a stronger anti-turbulence ability. Our numerical findings may be of great significance for the detection and imaging of oceanic optical telecommunications links.

LiDAR camera systems are now becoming an important part of autonomous driving 3D object detection. Due to limitations in time and resources, only a few critical frames of the synchronized camera data and acquired LiDAR points may be annotated. However, there is still a large amount of unannotated data in practical applications. Therefore, we propose a LiDAR-camera-system-based unsupervised and weakly supervised (LCUW) network as a novel 3D object-detection method. When unannotated data are put into the network, we propose an independent learning mode, which is an unsupervised data preprocessing module. Meanwhile, for detection tasks with high accuracy requirements, we propose an Accompany Construction mode, which is a weakly supervised data preprocessing module that requires only a small amount of annotated data. Then, we generate high-quality training data from the remaining unlabeled data. We also propose a full aggregation bridge block in the feature-extraction part, which uses a stepwise fusion and deepening representation strategy to improve the accuracy. Our comparative, ablation, and runtime test experiments show that the proposed method performs well while advancing the application of LiDAR camera systems.

Birefringence of elliptical polarization eigenmodes can be conceptualized as a composite system comprising two distinct media: one with linear polarization eigenmodes and the other with circular polarization eigenmodes. However, the practical realization of such a system often involves the combination of two birefringent quarter-wave plates (QWPs). In this study, our objective is to characterize the variable retardation and variable elliptical polarization eigenmodes exhibited by a biplate consisting of two quarter-wave plates. Additionally, we aim to analyze the geometric properties of the transformation of one state of polarization on the Poincaré sphere, employing the emerging state's curve. This curve corresponds to the intersection between the Poincaré sphere and a cone. The outcomes of our study are presented as a function of the angle between the fast axes of the two QWPs. The findings have the potential to contribute to the configuration of q-plates and facilitate the development of quantum communication protocols.

An efficient algorithm to obtain the solutions for n-th order terms of perturbation expansions in absorption, scattering, and cross-coupling for light propagating in human tissue is presented. The proposed solution is free of any approximations and makes possible fast and efficient estimates of mammographic, optical tomographic, and fluorescent images, applying a perturbation order of 30 and more. The presented analysis sets the general limits for the applicability of the perturbation approach as a function of tumor size and optical properties of the human tissue. The convergence tests of the efficient calculations for large absorbing objects show excellent agreement with the reference data from finite element method calculations. The applicability of the theory is demonstrated in experiments on breast-like phantoms with high absorbing and low-scattering lesions.

The terahertz band is considered to be the next breakthrough point to revolutionize communication technology, attributed to its rich spectrum resources. The study of terahertz atmospheric transmission characteristics is important in guiding the terahertz communication window selection process. In this report, based on the equivalent medium theory, the scattering characteristics of terahertz Gaussian beams by moist media are discussed. Numerical results show that the extinction coefficient of particles is mainly affected by the humidity, and the scattering efficiency is affected by both temperature and humidity. When the temperature is over 273 K and the humidity is 0.5, the extinction efficiency shows a trend of increasing initially and decreasing afterwards. Hence, the appropriate temperature is beneficial to minimizing the attenuation coefficient.

Continuous orthogonal moments are widely used in various image techniques due to their simplicity and good rotational invariance and stability. In recent years, numerous excellent continuous orthogonal moments have been developed, among which polar harmonic Fourier moments (PHFMs) exhibit strong image description capabilities. However, the numerical integration error is large in the calculation, which seriously affects the calculation accuracy, especially in higher-order calculation. In this paper, a continuous orthogonal moments-fast and accurate PHFM (FAPHFM) is proposed. It utilizes the polar pixel tiling technique to reduce numerical errors in the computation; this method particularly improves the accuracy of higher-order moments of traditional PHFMs. However, as accuracy increases, calculation complexity also increases. To address this issue, an eight-way symmetric/anti-symmetric calculation of the angular and radial functions was performed using the symmetry and anti-symmetry of traditional PHFMs, and clustering of pixels was performed as a way to improve the computational speed. The experimental results show that FAPHFMs perform better in image reconstruction (including noise), with higher computational accuracy, lower time complexity, and better image description ability.

The analytical propagation formulae of spectrally combined laser beams (SCLBs) in nonlinear Kerr media are derived, and the analytical expression of the ratio of the effect of the photorefractivity to the diffraction of SCLBs propagating in nonlinear Kerr media is also obtained. The validity of the analytical propagation formulae of SCLBs in nonlinear Kerr media is confirmed, and the error of the analytical propagation formulae is also discussed. It is shown the calculation time is reduced greatly by using the analytical propagation formulae. Therefore, a useful method is presented to study the propagation of SCLBs in nonlinear Kerr media.

In this paper, we generate a type of double helico-conical beam (HCB) by binarizing the modified helico-conical phase (MHCP). The diffraction patterns of the double HCBs were analyzed theoretically and experimentally. The relative position of the double HCBs can be adjusted arbitrarily by introducing a blazed grating only. In addition, the superposition of multiple binary MHCPs can be used to generate multi-helix beams. Accordingly, the diffraction patterns of the multi-helix beams were also analyzed theoretically and experimentally. The results demonstrated that the number and relative position of multi-helix beams can be adjusted by the number of superimposed MHCP profiles and the azimuth factor θ _j, respectively. This kind of arrayed HCB will be potentially applied in the fields of optical manipulation and multiplexed holography.

The fusion of optical and infrared images is a critical task in the field of image processing. However, it is challenging to achieve optimal results when fusing images from complex environments. In this paper, we propose a deep learning network model comprising an encoding network and a decoding network based on the modified U-Net network to fuse low-quality images from complex imaging environments. As both encoding and decoding networks use similar convolutional modules, they can share similar layer structures to improve the overall fusion performance. Furthermore, an attention mechanism module is integrated into the decoding network to identify and capture the crucial features of the fused images. It can assist the deep learning network to extract more relevant image features and thus get more accurate fusion. The proposed model has been compared with some existing methods to prove its performance in view of subjective and objective evaluations.