Ground-based telescopes are susceptible to seeing, an atmospheric blur that reduces the resolving power of large observatories to only a few arcseconds. Compensating these effects is critical to realizing the potential of both existing and upcoming extremely large telescopes, a challenging task that requires precise wavefront control. Ultimately, this precision is limited by the wavefront sensor (WFS) design and its inherent capacity to accurately encode phase and amplitude aberrations. In this work, we employ statistical estimation theory to derive fundamental limits to phase and amplitude reconstruction, providing a closed-form expression for the minimum-achievable residual error. For circular apertures, we find that this bound can be saturated by an instrument we refer to as the piston-adapted WFS (PAWS). The PAWS uses a Zernike mode sorter built from spatially varying half-waveplates to isolate the Zernike piston mode, apply a controllable phase shift to it, and then reconstitute the pupil as a pair of irradiance patterns that are nearly linear in incident aberrations. For arbitrary apertures, one can use a single-mode converter to reshape the pupil's native piston mode into Zernike piston and apply the same procedure. We expect our results to improve the residual wavefront errors in future closed-loop adaptive optics systems, while simultaneously finding applications in free-space communication and microscopy.
We present optical design concepts for a miniaturized multimodal endoscopic imaging system capable of targeting the same sample plane across widely separated wavelength ranges. The system uses a scanning-fiber approach and exploits the wavelength-selective imaging properties of diffractive optical elements (DOEs), allowing different diffraction orders to form images for distinct spectral bands and partially decoupling the optical design for each range. The system is designed to achieve high first-order diffraction efficiency in the UV/short visible region while simultaneously operating in the zeroth order for 1300-1700 nm. Angular emission variations of the scanning fiber are compensated, enabling a compact layout and low-loss beam delivery. Both three- and two-element designs with strongly aspheric surfaces are analyzed. Backward light propagation to the scanning fiber is evaluated theoretically, highlighting efficient collection via the fiber cladding and its potential enhancement by introducing ring-shaped lenses and reflective surfaces.
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.
We train a neural network using diffraction patterns to reproduce experimental diffraction patterns for a half-plane, a single slit, and a circular aperture. The training is done over theoretical data calculated under the Fresnel diffraction framework and applied to both calculated and experimental diffraction patterns. Experiments were designed to predict diffraction patterns from given obstacles and propagation distances and, conversely, to predict diffraction distances from known profiles. The second part was successfully carried out for theoretically calculated profiles and experimental data. The results show that the trained neural networks have outstanding performance as they reconstruct diffraction patterns with an error comparable to background noise of a standard experimental setup and recover propagation distances with millimeter precision from collected data.
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.
We propose an aspherical surface representation based on extended Jacobi polynomials to mitigate high-order oscillations and limited edge-fitting capability encountered in conventional polynomial descriptions of large-aperture annular optical systems. By extending the orthogonal interval and introducing adjustable weighting parameters, independent control of the aperture range and fitting weights is achieved, improving numerical stability. Effective suppression of oscillations and enhanced edge-fitting accuracy are demonstrated for large and small apertures. The proposed method, applied to a refractive-reflective panoramic imaging system with a field of view of (36-98∘)×360∘, achieved a modulation transfer function above 0.5 at 60 lp/mm.
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.
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.
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.
Speckle correlation imaging based on the optical memory effect provides a valuable approach for non-invasive imaging through scattering media, yet its practical implementation faces significant challenges in reconstruction speed. To overcome these challenges, a fast speckle correlation imaging (FSCI) algorithm that incorporates three key technical innovations is presented in this paper. The method commences with the intelligent sub-speckle quality control and initialization adaptation (ISQIA) module, which integrates two core functional sub-modules: one is sub-speckle screening (SS), which eliminates low-information sub-speckles based on the entropy-contrast criteria; the other is adaptive initialization (AI), which selects optimal sub-speckles to accelerate the convergence of subsequent calculations. The reconstruction accuracy is further enhanced through weighted coherent averaging (WCA), which utilizes cross-correlation peaks as weighting coefficients. Finally, dynamic iteration termination (DIT) automatically halts computation when reconstruction changes become negligible, thus optimizing computational efficiency. Experimental results show that the FSCI algorithm is 40.9% faster than traditional speckle correlation imaging methods, taking only 3.13 s for reconstruction in darkrooms. It also improves imaging quality significantly: PSNR reaches 27.04 dB, and SSIM is improved to 0.87. Notably, FSCI performs stably in weak to extremely strong noise (SNR 1.79 to -5.78dB), excels at recovering complex structures like Chinese characters, and thus has high application potential in fields such as biomedical imaging and industrial non-destructive testing.
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.
We revisit the expression for the contrast of spatiotemporal speckle encountered in optical lithography, in a manner different from previous studies, by exploiting the statistical properties of speckle integrated over both space and time. The necessary conditions under which this framework applies are stated explicitly, and it is emphasized that the required spatiotemporal separability is invoked at the level of the correlation function rather than the optical field. To gain physical insight into the derived expression, we present a numerical method for simulating such speckle, enabling direct evaluation of its contrast. The simulation results agree well with theoretical predictions, validating both the formulation and our interpretation of speckle behavior. We also discuss the practical significance of this type of simulation.
To overcome the conventional diffraction limit in optical systems, we propose a class of hybrid Airy-superimposed vector beams (HASVBs) and investigate their tightly-focusing properties. These HASVBs are formed by orthogonally superposing an inverse circular Airy beam and a circular Airy beam. Using the Richards-Wolf vector diffraction theory, we numerically demonstrate that HASVBs can generate a symmetric sub-diffraction focal spot, breaking the classical diffraction limit in both transverse dimensions. By adjusting the initial phase difference between two components, the focal-spot shape can be tuned periodically from elliptical to circular symmetry. Furthermore, the influence of key beam parameters-the main-ring radius, scaling factor, and decay factor-on the focal-spot size is systematically analyzed. For a given optical system with a certain numerical aperture, optimal sub-diffraction focal spots can be achieved by appropriately choosing the main-ring radius and scaling factor. Moreover, the longitudinal intensity patterns reveal that our design produces a needle-like profile near the focal region. The result has promising potential for applications in super-resolution imaging, direct laser writing, and optical manipulation.
The crosstalk of orbital angular momentum (OAM) modes induced by random light fields poses a significant challenge in free-space optical communication. Analyzing the influence of such fields on the OAM spectrum is therefore essential. Based on the coherence-orbital angular momentum (COAM) matrix, we derive analytical expressions for the OAM spectrum of partially coherent vortex beams (PCVBs) with three distinct correlation functions. Our results show that both the global coherence and the form of the correlation function significantly affect the OAM spectrum. We explain the underlying physical mechanism and support our findings with numerical simulations that closely align with the analytical predictions. This work advances the study of partially coherent light with tailored correlation structures.
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.
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.
Complex light can evolve radically as a function of propagation simply as a consequence of linear diffraction. Here, we characterize beam profiles in terms of their Dirichlet energy U~D, which scales with the asymptotic rate of diffraction, i.e., the rate of expansion of the beam mode field radius. This metric is translation-invariant, structure-informed, and constant as a beam propagates through vacuum. The diffraction length of structured light scales as Ldf∝βs=U~D. We provide examples with Laguerre-Gaussian vortex beams and fractal multi-beams using non-dimensional units, which are vital for self-consistent analyses of complex light.
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.
Computational ghost imaging (CGI) for edge detection, particularly speckle-shifting ghost imaging (SSGI), faces a severe trade-off between sampling cost and edge quality. We propose energy-descending ordered compressed ghost edge imaging (EDO-CGEI), an adaptive edge detection method that reorders binary illumination patterns in descending order of energy. Simulations and experiments show that EDO-CGEI outperforms existing schemes at low sampling rates, achieving a satisfactory 256×256 edge image with a sampling rate of only 15%. This approach effectively pushes forward the trade-off between efficiency and clarity in ghost imaging edge detection under resource constraints.
We present a reconstruction algorithm for recovering rough surface profiles from phaseless total field data measured at a single receiver as the surface undergoes controlled lateral motion. The algorithm is based on the parabolic wave equation, which offers a computationally efficient framework for forward and inverse scattering, and applies to both Dirichlet (TE polarization) and Neumann (TM polarization) boundary conditions. It operates in a marching fashion, recovering surface points sequentially along the profile. Numerical experiments demonstrate that the method yields accurate reconstructions and remains robust under measurement noise and variations in key problem parameters. The proposed approach provides a reliable and efficient tool for surface characterization in engineering applications such as non-destructive testing and remote sensing.
