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

The problem of diffraction by snake gratings is presented and formulated as an eigenvalue eigenvector problem. A numerical solution is obtained thanks to the method of moments where a tensor product of pseudo-periodic functions and Legendre polynomials is used as expansion and test functions. The method is validated by comparison with the usual Fourier modal method (FMM) as applied to crossed gratings. Our method is shown to be more efficient than the FMM in the case of metallic gratings.

We present a multiple-scattering model for the effective refractive index of an arbitrarily dense suspension of forward-scattering particles. The model provides a very simple formula for the effective refractive index of such a suspension and reproduces with high accuracy available experimental results. Furthermore, the derivation we present herein is mathematically transparent and enables us to obtain information on the underlying physical processes rather than obscuring them. We also provide insight into the extent of the model's validity and a simple way to determine whether or not it will be valid for an arbitrary suspension. Due to its simplicity, analytical closedness, and wide range of applicability, we believe the model can be used as a diagnostic tool for complex materials of vastly different natures.

We present a monolayer patterned black phosphorus (BP) metamaterial for generating a tunable dual plasmon-induced transparency (PIT). We have derived the expression for the theoretical transmittance by introducing the coupled mode theory (CMT), and the calculated results of the expression highly overlap with the simulation results. The quarterly frequency synchronous switch with two different operating bands is designed by the carrier density and scattering rate on the dual PIT modulation effect. Two parameters were selected as important markers to show the performance of the optical switch: the modulation depth (MD) and the insertion loss (IL). The theoretical analysis of this structure shows that the higher modulation depth (5.45d B<M D<12.06d B) and lower insertion loss (0.60d B<I L<0.22d B) of these switches are of good application. In addition, we found the slow light properties of the structure were excellent with a group index of up to 219. This work provides a theoretical basis to prepare multifrequency optical switch and optical buffer devices.

Computing locations and extent of images, except in the most trivial configurations or special cases, is a complex task. Even rays emanating from a point source and passing through an optical system generally fail to converge at a single image point, highlighting the care needed to establish image locations. We use three approaches to study image formation in a simple configuration, that of a point source following reflection from a spherical concave mirror. We calculate the caustic surfaces, compute cross sections of flux densities on image surfaces, and compare the results with experimentally generated light intensity fields. One of the two caustic surfaces is one dimensional while the other forms a surface. The latter undergoes a metamorphosis from a distorted cone to an open surface as the source is moved away from the axis. Cross sections of the caustic surfaces with an image plane are found to coincide with peaks in the flux density. Experimental studies validate these conclusions.

The dynamics of fluence noise of an optical pulse at free-space (e.g., vacuum) propagation has been studied. It has been shown that the fluence noise with high spatial frequency is effectively cleaned out from the primary smooth pulse either by spatial walk-off or by temporal delay at a relatively small propagation distance. This effect can be referred to as spatial and temporal self-filtering and is of major interest in ultra-high-power and ultra-short-pulse applications. The study comprises a rigorous theory and a few relevant numerical simulation examples.

We identify situations where optical phase modulation can be induced by intensity variations in the linear domain. In particular, for scalar two-beam in and two-beam out spatial unitary systems (beam splitters), we find that the phase difference between the output beams can be altered by changing the intensity ratio of the input beams. Utilizing this principle, we show that in linear optics (even in a very low-intensity regime), it is possible to introduce a two-dimensional spatial phase profile by spatial intensity modulation, thus affecting the propagation and far-field distribution of the ensuing beam.

In challenging scenarios characterized by low-photon conditions or the presence of scattering effects caused by rain, fog, or smoke, conventional silicon-based cameras face limitations in capturing visible images. This often leads to reduced visibility and image contrast. However, using near-infrared (NIR) light within the range of 850-1550 nm offers the advantage of reduced scattering by microparticles, making it an attractive option for imaging in such conditions. Despite NIR's advantages, NIR cameras can be prohibitively expensive. To address this issue, we propose a vision system that leverages NIR active illumination single-pixel imaging (SPI) operating at 1550 nm combined with time of flight operating at 850 nm for 2D image reconstruction, specifically targeting rainy conditions. We incorporate diffusion models into the proposed system to enhance the quality of NIR-SPI images. By simulating various conditions of background illumination and droplet size in an outdoor laboratory scenario, we assess the feasibility of utilizing NIR-SPI as a vision sensor in challenging outdoor environments.

In this paper, we propose a type of anisotropic elliptical-ring-shaped Talbot effect occurring in uniaxial crystals. The effect is realized by propagating a phase-only periodic elliptical-ring structure in the uniaxial crystal, orthogonal to the optical axis. Both phenomena of self-imaging at the Talbot distance and N-rings to one-ring convergence at the fractional Talbot distance were discussed. Numerical simulations were performed to demonstrate the correctness of theoretical derivation and the existence of the elliptical-ring-shaped Talbot effect. With the specific phase distribution, the N series of periodic elliptical rings of the incident plane will converge to one series of elliptical rings equally spaced at the fractional Talbot distance, where N is an even integer.

This paper describes the use of a weighted principal component analysis (PCA) method for camera spectral sensitivity estimation. A comprehensive set of spectral sensitivities of 111 cameras was collected from four publicly available databases. It was proposed to weight the spectral sensitivities in the database according to the similarities with those of the test camera. The similarity was evaluated by the reciprocal predicted errors of camera responses. Thus, a set of dynamic principal components was generated from the weighted spectral sensitivity database and served as the basis functions to estimate spectral sensitivities. The test stimuli included self-luminous colors from a multi-channel LED system and reflective colors from a color chart. The proposed method was tested in both the simulated and practical experiments, and the results were compared with the classical PCA method, three commonly used basis function methods (Fourier, polynomial, and radial bases), and a regularization method. It was demonstrated that the proposed method significantly improved the accuracy of spectral sensitivity estimation.

We introduce an approach to calculating three-dimensional freeform reflectors with a scattering surface. Our method is based on optimal transport and utilizes a Fredholm integral equation to express scattering. By solving this integral equation through a process analogous to deconvolution, we can recover a typical specular design problem. Consequently, we consider freeform reflector design with a scattering surface as a two-step process wherein the target distribution is first altered to account for scattering, and then the resulting specular problem is solved. We verify our approach using a custom raytracer that implements the surface scattering model we used to derive the Fredholm integral.