Optical Review最新文献

We present a method for single-shot blind deconvolution in coherent diffraction imaging. Coherent diffraction imaging is a technique for non-interferometric quantitative phase imaging without reference light. In our method based on coherent diffraction imaging, a complex amplitude object is illuminated with coherent light, and light from the object is captured through unknown aberrating media and a coded aperture located on the pupil plane to reduce estimated variables on the aberrated pupil function. Both the amplitude and the phase of the object are recovered from the single captured intensity image by a phase retrieval algorithm in which the coded aperture is utilized as a support to estimate the sparse aberrated pupil function. We numerically and experimentally demonstrate the proposed method with complex amplitude objects under severe aberrating conditions. In the experiment, we quantitatively evaluate its performance with ptychography, which is a method for multi-shot coherent diffraction imaging. Our method enables quantitative phase imaging through turbulence by using simple and reference-free optical hardware without any invasive process.

Unsharp masking is a common method of image sharpening. If unsharp masking is applied to each RGB component of a color image, the hue of the output image is changed from that of the input image. A hue-preserving unsharp masking method has been proposed thus far. However, the effect of image sharpening is slightly small. In this paper, we propose a new hue-preserving unsharp masking method that sharpens the image effectively. In the proposed method, componentwise unsharp masking is approximated by linear transformation satisfying Naik’s hue-preserving condition, and the gamut problem is solved by processing in an equi-hue plane in an RGB color space. In the experiments, the effectiveness of the proposed method is verified by qualitative and quantitative evaluations.

In this letter, we propose a new edge-preserving smoothing filter, the cuboid filter. Since many applications for image processing and computer vision are based on the idea of denoising and extracting edges, the edge-preserving smoothing filter can be utilized in many applications, such as high dynamic range image compression, unsharp masking, stylization, and more. For this reason, various edge-preserving smoothing filters, such as the bilateral filter, the guided filter, and the domain transform, have been proposed. In general, these filters face a trade-off relationship between denoising performance and computational speed. The cuboid filter calculates only the mean of 3-dimensional neighboring pixels. The cuboid filter performs satisfactorily in reducing small-amplitude noise and fast filtering. On the basis of qualitative and quantitative evaluations, the effectiveness and the validity of the cuboid filter are shown.

This study aimed to examine the effect of selective wavelength range-cutting lenses at the following three wavelengths: less than 420 nm, approximately 460 nm, and approximately 585 nm. Contrast sensitivity when wearing a selective three-wavelength range-cutting lens was higher than that of clear lenses; further, contrast sensitivity was improved in both non-glare and glare conditions in the testing room with an illuminance of approximately 500 lx. Selective three-wavelength range-cutting lenses could improve contrast sensitivity while reducing lens color. Therefore, multiple wavelength-controlled lenses can contribute to the improvement of the quality of vision in daily life.

Inspection systems with a machine vision camera have been extensively applied in factory automation detecting unclear defects. In this automatic inspection, optical engineering technology needs to emphasize the contrast of defects in order to quickly find them in a camera image and improve image recognition accuracy. Using the phase-shift illumination method with striped structured illumination, we develop optical engineering and image processing technology to enhance defects in transparent materials. Our challenge has been to distinguish actual defects from dark fringes due to artificial three-dimensional texture on a target sample. We proposed theoretically that an innovative method providing an illumination pattern with finite-width dark regions would make the gentler slope of artificial texture less visible than actual defects. We extended our theoretical model in the case of a square wave as the typical illumination pattern and established an inspection method distinguishing defects from artificial texture. We confirmed with simulations and experiments that the square-wave illumination enables us to distinguish between defects and artificial texture.

Surface-plasmon-enhanced circular dichroism (CD) spectroscopy is a powerful analytical technique used for detecting chiral molecules, with great potential in biomedical diagnosis and pathogen detection. This work focuses on understanding the physical mechanisms of CD production and developing high-sensitivity CD detection substrates. Numerical simulation of the finite difference time domain (FDTD) method is utilized to design and study half-roll plasmonic nanostructures. The scattering spectra of the structure and the corresponding CD spectra show two resonance peaks, λ₁ = 691 nm and λ₂ = 903 nm, where the charge distribution of the upper surface and the lower surface shows a quadrupole distribution and a dipole distribution, and both of them are in antibonding mode. The structure’s sensitivity is demonstrated by varying the structure parameters and surrounding medium environment, which provides valuable insights for designing optical devices.

A novel design for an efficient coupling configuration, which consists of a L-shaped dielectric loaded surface plasmon polaritons (DLSPPs) waveguide and L-shaped nanoantenna, is proposed and investigated numerically in this paper. We carried out the theoretical analysis for the coupling characteristics by utilizing the finite-difference time-domain (FDTD) method. The factors affecting the coupling efficiency of light from free space to the proposed structure were studied in detail, including the structural parameters and incident light source. The simulation results reveal that the coupling performance of proposed structure with optimized geometric parameters is at least three times enhanced compared to that of a single straight DLSPPs waveguide when the incident light is polarized perpendicular to DLSPPs waveguide at a wavelength of λ?=?532?nm. The proposed configuration, which is simple and easy to fabricate, can not only achieve the subwavelength mode confinement but also possesses a relatively high coupling efficiency, thus may potentially be used in nano-photonic coupling circuits and nano-optical manipulation.

A novel scheme that generates terahertz optical frequency comb (THz OFC) based on optimized cascaded difference frequency generation (OCDFG) with an aperiodically poled lithium niobate (APPLN) crystal is proposed. Two pump lasers initially generate cascaded optical waves by cascaded difference frequency generation (CDFG), the n multiple-frequency THz waves are generated by mixing cascaded optical waves, and finally THz OFC is formed by optimizing phase mismatches of CDFG along the APPLN crystal length. High-performance THz OFC with characteristics of high repetition rate, tunable repetition rate, high flatness and tunable spectral distribution range is exhibited by providing a theoretical calculation. We argue that the scheme based on OCDFG is promising for achieving high-performance THz OFC.

Temporal phase unwrapping based on phase-encoding is a technique widely used in 3D measurement for its high-speed advantage. However, eliminating fringe order jump error induced by the system’s luminance nonlinearity is still a key challenge. We propose a fringe order jump error self-correction method to address this issue. First, we encode the shifting phase and stair phase separately and combine them into the same pattern based on four-step phase shifting. This allows us to calculate the fringe order and wrapped phase simultaneously and avoid the overlapping of two set phases. Then, we add auxiliary patterns to obtain information on the order-located period’s odd-evenness characteristic. Theoretically, we demonstrate that under the influence of the nonlinear effect, the order calculation value for a particular period fluctuates between the ideal values of two adjacent orders. Thus, the correct order value can be directly determined by acquiring the period characteristic information, without the need for complex error compensation. Simulations demonstrate that the method performs good robustness where random noise and luminance saturation exist simultaneously in addition to system nonlinearity. Our experiments confirm the effectiveness of this method for high-accurate and fast fringe order determination.

Using a combination of the finite element method (FEM) applied in COMSOL Multiphysics and the machine learning (ML)-based classification models, a computational tool has been developed to predict the appropriate amount of power flow in a plasmonic structure. As a plasmonic coupler, a proposed structure formed of an annular configuration with teeth-shaped internal corrugations and a center nanowire is presented. The following representative data mining techniques: standalone J48 decision tree, support vector machine (SVM), Hoeffding tree, and Naïve Bayes are systematically used. First, a FEM is used to obtain power flow data by taking into consideration a geometrical dimensions, involving a nanowire radius, tooth profile, and nanoslit width. Then, we use them as inputs to learn about machine how to predicate the appropriate power flow without needing FEM of COMSOL, this will reduce financial consumption, time and effort. Therefore, we will determine the optimum approach for predicting the power flow of the proposed structure in this work based on the confusion matrix. It is envisaged that these predictions’ results will be important for future optoelectronic devices for extraordinary optical transmission (EOT).