搜索结果：Journal of the Optical Society of America. A, Optics, image science, and vision

Structured light propagation experiments were carried out in a Rayleigh-Bénard (RB) convective water tank in order to evaluate beam characteristics and susceptibility of several topological charges to optical turbulence conditions spanning several fluid turbulence levels set by the system Rayleigh number. Structured light fields were generated using a spatial light modulator, which imparts a phase change to create light that carries optical orbital angular momentum (OAM). Beams were propagated over a 1.2 m path under weak, moderate, and strong optical turbulence conditions. The flow dynamics, relative to the OAM beam dynamics, are such that a "frozen" state is realized in the R-B tank for set flow conditions. This ensures consistent turbulence across all tested beams, enabling reliable comparisons of beam performance under identical scenarios. The study focuses on observing turbulence dynamics within the structured beam's profile using intensity fluctuation analysis in the temporal and spatial domains, correlations with dynamic masking between consecutive realizations of the beam's intensity, and power spectral densities and histograms. The scintillation index (SI) was evaluated using three methods: (1) at the point of maximum intensity within the annulus, (2) at the centroid within the vortex, and (3) averaged over the region of interest containing all non-zero beam intensities. It was found that a reduction in the SI for OAM-carrying beams with increasing topological charge was independent of the optical turbulence conditions. Since SI represents a normalized variance, this reduction is not simply a result of intensity redistribution associated with higher topological charge; rather it demonstrates that the SI systematically decreases with increasing topological charge under all experimental conditions. In addition, to gain deeper insight into the optical turbulence dynamics, histograms of the annular maximum intensity fluctuations, spectra of the correlation coefficients, and maximum intensity measurements are presented.

The atmospheric coherence length is a key parameter for quantifying the intensity of atmospheric motion, and understanding its variation characteristics is of considerable practical importance. In this paper, phase-based moiré deflectometry is employed to investigate the influence of heat disturbance on the temporal and spatial distributions of the atmospheric coherence length. First, the theoretical relationship among phase, deflection angle, and atmospheric coherence length is refined. Next, numerical simulations indicate that the average relative error of the theoretical model is 2.8% in both the temporal and spatial distributions, which validates the feasibility and reliability of our proposed approach. Then, two sets of experiments are implemented without and with heat disturbance, respectively. Each set lasts for one hour, during which 3600 frames of moiré fringes are acquired. Finally, the temporal and spatial distributions of atmospheric coherence length are characterized by the optimized theoretical model. The comparison of results reveals that the atmospheric coherence length exhibits a strong negative correlation with temperature fluctuation, decreasing by 95.2% as the temperature rises by 42.8°C. In a word, our work further extends the application of moiré deflectometry and provides some valuable insights for future atmospheric turbulence research.

BACKGROUND: The purpose of low-vision rehabilitation is to allow people to resume or to continue to perform daily living tasks, with reading being one of the most important. This is achieved by providing appropriate optical devices and special training in the use of residual-vision and low-vision aids, which range from simple optical magnifiers to high-magnification video magnifiers. OBJECTIVES: To assess the effects of different visual reading aids for adults with low vision. SEARCH METHODS: We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (which contains the Cochrane Eyes and Vision Trials Register) (2017, Issue 12); MEDLINE Ovid; Embase Ovid; BIREME LILACS, OpenGrey, the ISRCTN registry; ClinicalTrials.gov and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP). The date of the search was 17 January 2018. SELECTION CRITERIA: This review includes randomised and quasi-randomised trials that compared any device or aid used for reading to another device or aid in people aged 16 or over with low vision as defined by the study investigators. We did not compare low-vision aids with no low-vision aid since it is obviously not possible to measure reading speed, our primary outcome, in people that cannot read ordinary print. We considered reading aids that maximise the person's visual reading capacity, for example by increasing image magnification (optical and electronic magnifiers), augmenting text contrast (coloured filters) or trying to optimise the viewing angle or gaze position (such as prisms). We have not included studies investigating reading aids that allow reading through hearing, such as talking books or screen readers, or through touch, such as Braille-based devices and we did not consider rehabilitation strategies or complex low-vision interventions. DATA COLLECTION AND ANALYSIS: We used standard methods expected by Cochrane. At least two authors independently assessed trial quality and extracted data. The primary outcome of the review was reading speed in words per minute. Secondary outcomes included reading duration and acuity, ease and frequency of use, quality of life and adverse outcomes. We graded the certainty of the evidence using GRADE. MAIN RESULTS: We included 11 small studies with a cross-over design (435 people overall), one study with two parallel arms (37 participants) and one study with three parallel arms (243 participants). These studies took place in the USA (7 studies), the UK (5 studies) and Canada (1 study). Age-related macular degeneration (AMD) was the most frequent cause of low vision, with 10 studies reporting 50% or more participants with the condition. Participants were aged 9 to 97 years in these studies, but most were older (the median average age across studies was 71 years). None of the studies were masked; otherwise we largely judged the studies to be at low risk of bias. All studies reported the primary outcome: results for reading speed. None of the studies measured or reported adverse outcomes.Reading speed may be higher with stand-mounted closed circuit television (CCTV) than with optical devices (stand or hand magnifiers) (low-certainty evidence, 2 studies, 92 participants). There was moderate-certainty evidence that reading duration was longer with the electronic devices and that they were easier to use. Similar results were seen for electronic devices with the camera mounted in a 'mouse'. Mixed results were seen for head-mounted devices with one study of 70 participants finding a mouse-based head-mounted device to be better than an optical device and another study of 20 participants finding optical devices better (low-certainty evidence). Low-certainty evidence from three studies (93 participants) suggested no important differences in reading speed, acuity or ease of use between stand-mounted and head-mounted electronic devices. Similarly, low-certainty evidence from one study of 100 participants suggested no important differences between a 9.7'' tablet computer and stand-mounted CCTV in reading speed, with imprecise estimates (other outcomes not reported).Low-certainty evidence showed little difference in reading speed in one study with 100 participants that added electronic portable devices to preferred optical devices. One parallel-arm study in 37 participants found low-certainty evidence of higher reading speed at one month if participants received a CCTV at the initial rehabilitation consultation instead of a standard low-vision aids prescription alone.A parallel-arm study including 243 participants with AMD found no important differences in reading speed, reading acuity and quality of life between prism spectacles and conventional spectacles. One study in 10 people with AMD found that reading speed with several overlay coloured filters was no better and possibly worse than with a clear filter (low-certainty evidence, other outcomes not reported). AUTHORS' CONCLUSIONS: There is insufficient evidence supporting the use of a specific type of electronic or optical device for the most common profiles of low-vision aid users. However, there is some evidence that stand-mounted electronic devices may improve reading speeds compared with optical devices. There is less evidence to support the use of head-mounted or portable electronic devices; however, the technology of electronic devices may have improved since the studies included in this review took place, and modern portable electronic devices have desirable properties such as flexible use of magnification. There is no good evidence to support the use of filters or prism spectacles. Future research should focus on assessing sustained long-term use of each device and the effect of different training programmes on its use, combined with investigation of which patient characteristics predict performance with different devices, including some of the more costly electronic devices.

As a rule, transitions between the optical current singularities in vortex beams with a general astigmatism are associated with changes in featured orbital angular momentum (OAM) states (zeros and extremes). However, we have brought to light significant differences in transforming optical current singularities and the OAM in vortex and vortex-free astigmatic Gaussian beams. First of all, this is manifested in the sequential conversion of optical current singularities in a Gaussian beam with a simple astigmatism, whose OAM is always zero. Besides, in the case of general astigmatism, the conversion of optical current singularities does not coincide with the OAM transformations, but has a wide range of propagation of the astigmatic Gaussian beam. Such a mismatching indicates the competing processes in optical currents during the beam propagation. We evaluated the competing processes based on the mechanical model of optical currents and the OAM. We found that a combined contribution of the local OAMs leads to the effect of matching the total OAM with a physically measurable cross-intensity moment. This effect enabled us to develop and implement a technique for measuring small and large OAM in astigmatic Gaussian beams.

In this paper, we study the backward scattering of light in a composite system consisting of a rough surface and anisotropic scatterers. Based on the theories of Kirchhoff's rough surface scattering and particle backscattering, we develop a theoretical framework applicable to modeling backscattering from rough surfaces in turbid media. We then give theoretical and simulation results of this model in the quasi-ballistic regime under the single scattering approximation. For the turbid media conditions and surface roughness parameters considered in this study, it is found that the albedo distribution of the system in the small exit angle interval is mainly determined by rough surface scattering, and particle scattering makes a major contribution in the large exit angle interval. The different proportions of scattered light intensity between rough surfaces and particles in different intervals lead to the inflection points of the albedo distribution. Additionally, the anisotropy factor, scattering mean free path, and roughness of rough surfaces affect the albedo distribution. The theoretical results of the proposed model are in good agreement with the Monte Carlo simulation results.

The minimum equivalent Abbe number can be used to describe the maximum axial dispersion achievable by a hyperchromatic doublet lens. In this study, the axial dispersion limit of such a doublet is investigated under the constraints of lens surface shapes. The paraxial formula with respect to lens curvature is organized to find the relationship between the equivalent Abbe number and the parameters of the glass material. Using data from an optical glass database, the minimum equivalent Abbe number is computed for different types of glass combinations. Ray tracing is then employed to simulate non-paraxial systems for validation purposes. The result reveals that the doublet exhibits an average minimum equivalent Abbe number of 10.5 when surface shape constraints are considered. The preferred glass combination tends toward H-ZPK2A for the first element and H-ZF73 for the second. Furthermore, this study presents the design of a chromatic confocal optical probe, which satisfies dispersion specifications and achieves an energy utilization efficiency 1.2 to 2.9 times that of the reference commercial probe across the measurement range. This research provides guidance for selecting suitable initial structures based on different dispersion requirements in hyperchromatic optical systems, thereby reducing the difficulty of subsequent optimization.

Solution-processed multilayer dielectric stacks can act as scalable and effective light-managing optoelectronic devices with low input cost but are less efficient than their vacuum-deposited counterparts due to layer thickness inconsistency and scattering caused by defects. To further the understanding of how solution-processed thin-film devices can be more accurately modeled and ultimately become viable in real applications, this work developed an experimentally based approach for measuring and modeling nonidealities in spin-coated one-dimensional photonic crystals. This was done by synthesizing these structures using the promising TiO2-PMMA material system and directly quantifying the thickness variability, film roughness values, and macroscopic scattering defects via atomic force microscopy. The resulting experimental parameters were then directly incorporated into ideal transfer matrix method calculations to more accurately model the real design space for spin-coated one-dimensional photonic crystals. This exercise revealed that the layer thickness variability remains the greatest limitation for these structures as compared to scattering. Despite these challenges, strong agreement with ideal transfer matrix method curves and large reflectance peaks (R≥0.9) were achieved across the visible light domain with strong color purity. To simplify the fabrication, different iterations of the key TiO2 sol-gel film heating steps were performed. This demonstrated a new degree of reduced processing burden: 7-layer 1D PCs were able to recover the reflectance spectra of equivalent stacks that underwent multiple interstitial heating cycles through a single, long heating step after complete synthesis. Finally, to investigate the system's readiness in more complex applications, the quantified thickness variability was simulated for three aperiodic structures with many layers. This revealed that the spin-coated TiO2-PMMA material system has high potential in longpass filtering roles, but reducing the degree of thickness deviation is needed for high performance in shortpass filter and microcavity applications.

Underwater wireless optical communication (UWOC) has emerged as a promising solution for short-range high-speed underwater data transmission in recent years. For what is believed to be the first time, this work presents a comprehensive secrecy performance analysis of a downlink non-orthogonal multiple access (NOMA)-UWOC system over the composite vertically stratified Weibull-generalized gamma (WGG) oceanic fading channel, in which the impacts of path loss, underwater turbulence, pointing errors, and angle-of-arrival fluctuations are considered. Specifically, the closed-form expressions for the probability density function (PDF) and cumulative distribution function (CDF) of the vertically stratified WGG fading channel coefficient are derived analytically. Then, on the basis of these derivations, analytical frameworks for the key secrecy performance metrics, including secrecy outage probability, strictly positive secrecy capacity, and effective secrecy throughput, are obtained, taking into account the residual interference from successive interference cancellation (SIC), which are validated through Monte Carlo simulations. Finally, the effects of the number of layers, the thermohaline gradient and air bubbles, the residual power factor of imperfect SIC, the transceiver misalignment, and the angle-of-arrival deviation are investigated on this UWOC system. The presented results give valuable insights into the practical aspects of deployment of UWOC networks.

The propagation dynamics and autofocusing behaviors of the Bessel-modulated circular Airy beam (BMCAB) and the Bessel-modulated circular Airyprime beam (BMCAPB) in free space are investigated. The results demonstrate that the number (one or two) of focal points of these two beams could be manipulated by the initial beam width w0, the primary ring radius r0, and the exponential decay factor a. The BMCAPB possesses stronger focusing ability and wider dual-focus adjustable range than the BMCAB, whereas the BMCAB can be flexibly switched between single-focus and dual-focus modes. The focusing positions and the peak intensity can be precisely controlled by the focal length f. Interestingly, a needle-like optical field with controllable needle length could be formed by changing the focal length f of the BMCAB. Furthermore, the BMCAPB provides stronger optical trapping at the front focus, while the BMCAB offers more stable forces at the rear focus.

Modulating electromagnetic fields is a key issue in modern optics. In this study, a depolarizer is considered for modulating electromagnetic fields. The depolarizer under investigation is a polarizer array in which the transmission axis of each cell is randomly oriented in a spatially correlated manner. This arrangement whose correlation can be tailored differs from both ordered and completely disordered structures. The optical properties-such as the degree of polarization (DOP) and the degree of coherence (DOC)-of electromagnetic fields behind the depolarizer are rigorously calculated using the probability density method. We find that the depolarizer induces changes in the statistical properties of the incident beam. In particular, the correlation among the random transmission axis of polarizer cells influences both the DOC and the DOP behind the depolarizer. Furthermore, the depolarizer is simulated using the Monte Carlo method, and the simulation results are in good agreement with the analytical findings. Our results may have applications in the design of devices for modulating electromagnetic fields.

Quantitative phase imaging enables label-free visualization of transparent and weakly absorbing cells with the transport of intensity equation, derived from the paraxial wave equation widely used for its simple and non-interferometric approach. However, it struggles with noise and high-frequency details, which are strongly influenced by the choice of defocus distance. In this study, we enhance the feature of retrieved phase through the recursive transport of intensity and phase equations using frequency-domain filtering. The filter identifies the frequency range where the phase transfer functions of transport of intensity and the contrast transfer function converge, enabling accurate and feature-enhanced phase reconstruction while mitigating diffraction and noise artifacts. The study establishes the upper limit of allowable frequency information in the phase image, with particular relevance to weak-phase samples. The proposed concept has been verified through numerical simulations, considering the initial (ground-truth) phase as a weak-phase sample. For experimental validation, the method is first tested using a resolution chart and subsequently applied to onion peels.

Employing the Richards-Wolf formalism that adequately describes an electromagnetic field near the sharp focus of an ideal spherical lens, we demonstrate that certain light fields (linearly polarized optical vortex, cylindrical vector fields of an arbitrary order) have a reverse canonical energy flow in the focus plane. When the numerical aperture is 0.95, maximal magnitude of the reverse energy flow amounts to nearly 0.7% of the maximal magnitude of the direct energy flow. The distribution of the reverse canonical flow in the focus plane can have the shape of concentric rings or only arcs of the concentric rings. For certain light fields, for instance, for an azimuthally polarized light field, the longitudinal component of the canonical energy flow vector coincides with the longitudinal component of the Poynting vector. It is shown that a circularly polarized optical vortex does not have the reverse flow at the focus.

In this research, a comprehensive method by which to create array-focus beams using diffractive optical elements is presented. The main purpose of the paper is to shape a Gaussian laser beam into specific array beams with controllable parameters while keeping costs low and requiring minimal equipment. This is achieved by using a single diffractive optical element for each pattern. By applying integrated structure techniques and Fourier optics, diffractive optical elements are designed and simulated prior to fabrication using the laser lithography method. A verification setup was devised to evaluate the optical performance of the diffractive optical element. The outcomes of the research demonstrate the effectiveness of diffractive optical elements in independently forming array-focus patterns for various types of beams, such as Gaussian beams, high-order twisted vortex beams, and circular beams, with minimal expense, a compact size, and good durability. The applications of these patterns extend across various fields, including glass cutting, modified Hartmann mask design, and surface scanning. These patterns are particularly beneficial in non-light wavelength scenarios, such as X-rays, gamma rays, and ultraviolet light, where traditional lenses are challenging to manufacture due to material limitations.

We present a solution to the problem of branch points in wavefront sensing by circumventing the problem altogether and reconstructing the full complex optical field instead of the phase. Traditional wavefront reconstruction algorithms are based on least-squares fitting of phase gradients and fail in the presence of strong scintillation due to the formation of branch point singularities in the phase. However, these points are simply zeros (and not singularities) of the optical field-thus, reconstruction of the full optical field is a well-posed problem. Using the intensity and gradient data of a Shack-Hartmann wavefront sensor, our method poses a linear least-squares problem for the full optical field rather than the phase, which can be solved efficiently using standard techniques. Crucially, the algorithm is efficient and readily implementable in real-time adaptive optics applications. Numerical results show the accuracy of our algorithm and its robustness to noise in nontrivial examples of highly scintillated fields with numerous branch points.

Poincaré beams can be mapped on the hybrid-order Poincaré sphere using longitude and latitude coordinates. Mapping on a geometrical sphere is crucial in the study of the topological aspects and applications of singular beams. Currently, there is a dearth of methods that enable the mapping of Poincaré beams on these spheres. This paper presents a simple and robust detection method to determine the coordinates of Poincaré beams on a hybrid-order Poincaré sphere (HyOPS). The method requires only a single intensity measurement obtained through a fixed linear polarizer. The transmitted intensity pattern contains unique null points whose positions encode both longitude and latitude coordinates of the beam. This approach eliminates the need for polarizer rotation or multiple projections, thereby reducing experimental errors and improving reproducibility. The method is applicable to beams belonging to all three types of HyOPS, where the beams are formed by linear/circular state superpositions. Experimental results demonstrate accurate mapping of beam coordinates, consistent with theoretical predictions.

The spectral modulation of polychromatic light waves with a Gaussian spectral profile upon scattering from a semi-soft anisotropic hollow deterministic medium is theoretically and numerically investigated. By deriving analytical expressions for the far-zone spectral density, we systematically analyze the critical conditions inducing spectral anomalies, specifically redshift, blueshift, and spectral switches. Numerical simulations reveal that these spectral switches exhibit robust azimuthal selectivity, strictly governed by the medium's three-dimensional anisotropy. A pivotal finding is that the structural dimensions parallel to the observation plane dominate the primary spectral response, whereas the inner hollow core and longitudinal structure uniquely modulate higher-order spectral features at large scattering angles. Crucially, we demonstrate that this specific hollow configuration enables the effective decoupling of inner and outer structural information. These insights provide a rigid theoretical framework for the non-invasive characterization of complex multi-layered particles, offering new degrees of freedom for the precise control of far-field spectral properties.

In optical coherence tomography (OCT) images, sidelobe artifacts are weaker signals that emanate from regions adjacent to high-intensity sample signals. These artifacts do not correspond to actual tissue structures and can be easily misinterpreted as low-intensity sample signals, which affects the clarity of OCT images. Current methods for sidelobe suppression are limited in effectiveness or in their ability to handle complex samples. In this paper, we propose an OCT sidelobe suppression method based on dual-path phase sinusoidal modulation and minimum value fusion. In the two operation paths, the Hilbert transform and the inverse Hilbert transform are used to extract the phase angle, respectively. The sine value of the phase angle is used to modulate the axial intensity distribution. Finally, the minimum value of the two modulated curves is extracted using minimum-value fusion to achieve sidelobe suppression. The processing results of OCT images of coverslip, tape, and fingertip skin samples show that the proposed method can achieve a maximum sidelobe suppression effect of 50.1 dB, and the full width at half-maximum of the point spread function is reduced to 53% of that of the traditional methods, thereby achieving an improvement in image clarity.

Based on vector diffraction theory and the inverse Faraday effect (IFE), this study employs complex phase filters (CPFs) to modulate azimuthally polarized hyperbolic-sine-Gaussian vortex beams, achieving simultaneous optimization of the depth of focus and aspect ratio of magnetic needles, and generating magnetization chains with remarkable length and uniform magnetic spots. Specific results include the following: in a single lens system, a single-channel magnetization needle with a longitudinal full width at half-maximum (FWHM) of 87λ (aspect ratio of 249), and a dual-channel magnetization needle with a longitudinal FWHM of 87λ (aspect ratio of 322) were obtained; in a 4π system, single- and dual-channel magnetization chains with lengths exceeding 85λ were realized, with both transverse and longitudinal dimensions of the magnetic spots in the dual-channel chain measuring 0.27λ. Furthermore, by adjusting the parameter m (m is the order of the sine-hyperbolic-Gaussian beam), the axial intensity distribution of the structures can be effectively modulated. This work provides a new, to our knowledge, approach for applications such as multiple atoms trapping and transport, as well as ultrahigh-density magnetic storage.

Optical wave propagation in the ocean constitutes a challenging random-medium problem due to the combined effects of depth-dependent absorption, scattering, and refractive-index fluctuations induced by oceanic turbulence. In this work, we develop a depth-dependent statistical propagation model for vortex beams along slant paths by coupling realistic chlorophyll-induced attenuation profiles with an inclined-path oceanic turbulence spectrum. Based on this framework, the evolution of spatial coherence radius, beam attenuation, and orbital-angular-momentum (OAM) modal crosstalk of Bessel-Gaussian vortex beams is systematically investigated as functions of ocean depth, propagation distance, and turbulence parameters. The results reveal a pronounced depth dependence of beam attenuation governed by the vertical distribution of chlorophyll, as well as significant turbulence-induced degradation of spatial coherence leading to enhanced intermodal coupling among OAM states. As an illustrative application, the proposed model provides a quantitative prediction of the optical power required to sustain long-range underwater propagation, and demonstrates that appropriate optimization of beam parameters can effectively mitigate OAM crosstalk in inhomogeneous oceanic turbulence. These results provide a unified statistical framework for analyzing the propagation and modal evolution of structured optical fields in depth-varying oceanic random media.