Search

Fourier ptychography (FP) is a high resolution wide‐field imaging method based on the extended aperture in the Fourier space, which is synthesized from raw images with varying illumination angles. If FP is extended to coherent nonlinear optical imaging, the resolution could be further improved due to the increase of the cutoff frequency of the synthesized coherent optical transfer function (C‐OTF) with respect to the order of nonlinear optical processes. However, there is a fundamental conflict between wide‐field FP and nonlinear optical imaging, whereby the nonlinear optical imaging typically requires a focused excitation laser beam with high power density. To tackle the problem, in this work, a unique point‐scanning FP (PS‐FP) method is presented for super‐resolution nonlinear optical imaging, in which the nonlinear optical signal is obtained by using focused laser beam, while the conventional FP algorithm can still be used to retrieve the super‐resolution image. PS‐FP coherent anti‐Stokes Raman scattering (PS‐FP‐CARS) imaging on a variety of samples, where a 1.8‐fold expansion of the OTF is achieved experimentally for enhancing vibrational imaging. Further theoretical calculation shows that the C‐OTF of PS‐FP higher‐order CARS (PS‐FP‐HO‐CARS) can be expanded up to ≈4.9‐fold, thereby improving the spatial resolution by ≈3‐fold in comparison with conventional point‐scanning CARS with under tightly focused beams. The generality of PS‐FP method developed in this work can be adapted to other coherent nonlinear optical imaging modalities for super‐resolution imaging in tissue and cells. [ABSTRACT FROM AUTHOR]

Determining the flame transfer function plays a crucial role during the development phase of lean-burn injectors to predict the overall stability of the combustion system. This study develops an enhanced acoustic post-processing strategy using acoustic network modeling and compressible large-eddy simulation for a lean-burn aero-engine injector in a realistic test rig. Results show that optical flame transfer functions experimentally obtained align with those derived from large-eddy simulation based on heat release rate. However, discrepancies, especially in gain, are observed when using the standard acoustic post-processing method. By employing an acoustic network model, it is shown that comparable flame transfer functions can be achieved through refined post-processing strategies. This study highlights the limitations of conventional acoustic post-processing and underscores the necessity of explicit acoustic modeling in complex setups to accurately obtain the flame response. A generalized formulation applicable to a broader range of setups, extending beyond simple configurations, is presented as an alternative to the conventional acoustic post-processing method. [ABSTRACT FROM AUTHOR]

Polarization plays a crucial role in understanding the interaction of fluorescent molecules in a light field. We report the study on the effect of a field–dipole interaction under polarization light-sheet fluorescence microscopy using the vectorial theory of light. The molecule is suitably modeled as a radiating electric dipole in a polarized electric field (both linear and random), and the system point spread function (PSF) is determined for different orientations of the dipole (both fixed and random). PSF analysis and contour plots suggest distinct nature of a field distribution in each case, indicating the importance of a field–dipole interaction for high-quality fluorescence imaging. The analysis suggests that the field spreads gradually along the polarization axis at a high numerical aperture (NA) of the objective lens, whereas it is more isotropic and homogeneous at low NA. Moreover, fast changes are not observed at low NA (i.e., far from the central lobe in the field contour plots), suggesting the absence of high-frequency components. However, sidelobes are prominent for linear polarized (along x) light. On the other hand, rapid variations are evident for randomly polarized light, depicting the presence of high spatial frequencies in the system optical transfer function. The other significant observation is the distinct frequency spectrum (both k x and k y) for random and fixed dipoles, indicating the significance of dipole orientation in a light-sheet field. Compared to the point-illumination-based fluorescence microscopy, sheet based polarization technique provides a high signal-to-noise ratio, a uniform field, an order large field of view, and critical information (related to the micro-environment of a dipole and its short-range interactions). The study is expected to facilitate polarization-sensitive investigation of large biological specimens (both fixed and live). [ABSTRACT FROM AUTHOR]

The segmented mirror co-phase error identification technique based on supervised learning methods has the advantages of simple application conditions, no dependence on custom sensors, a fast calculation speed, and low computing power requirements compared with other methods. However, it is often difficult to obtain a high accuracy in practical application situations with this method because of the difference between the training model and the actual model. The reinforcement learning algorithm does not need to model the real system when operating the system. However, it still retains the advantages of supervised learning. Thus, in this paper, we placed a mask on the pupil plane of the segmented telescope optical system. Moreover, based on the wide spectrum, point spread function, and modulation transfer function of the optical system and deep reinforcement learning—without modeling the optical system—a large-range and high-precision piston error automatic co-phase method with multiple-submirror parallelization was proposed. Finally, we carried out relevant simulation experiments, and the results indicate that the method is effective. [ABSTRACT FROM AUTHOR]

Purpose: Any new intraocular lens (IOL) on the market claims to outperform competitors. We aimed to estimate the modulation transfer function (MTF) for different defocus of a novel refractive enhanced depth of focus (EDoF) IOL and the simulated visual acuity over this range of vision. Further, we analyzed the wavefront pattern produced by this IOL to reveal the function of the IOL's optics. Methods: For the novel TECNIS® PureSee® (ZEN00V) IOL, through frequency and through focus MTF were recorded on the optical bench (ISO-2 Cornea 0.28 μm, 546 nm). MTFa and the simulated visual acuity were calculated for different defocus. Apertures of 3 mm and 4.5 mm were applied. Higher order aberrations of the IOLs' optics were recorded and analyzed. Results: PureSee® IOL demonstrated a considerable depth of focus of about 1.7 D at the spectacle plane and a continuous simulated visual acuity over this range of defocus. For the 4.5 mm aperture, near focus depth was reduced, yet far distance MTF was even better. Higher order aberrations revealed increased primary and secondary spherical aberrations. Conclusion: Optical bench results suggest that the new ZEN00V matches the clinical criteria of an EDoF IOL by an increased range of vision and is far distance dominant for an enlarged pupil. This behaviour seems to be due to subtle power changes in the central optics that produce a complex modification of wavefront. [ABSTRACT FROM AUTHOR]

Localization of light spots in a given image is a common task in digital processing but is challenging in analog. Herein, a periodic nonlocal metasurface that has an optical transfer function defined in reciprocal space is proposed to resolve this issue. Assuming an ideal optical transfer function that encodes that of a local lens, the selective spot size reduction of incident Gaussian beams and sharpening of a patterned incidence with a Gaussian line shape are demonstrated. A realistic nonlocal metasurface comprising a trilayer structure with air grating on top that operates as a 2D analog light localizer under unpolarized incidence is presented. Nonlocal metasurfaces, combined with conventional optics, are expected to improve the resolution by sharpening the spatial features and find applications in diverse scientific fields such as medical, materials, and life science. [ABSTRACT FROM AUTHOR]

We compute the optical transfer function and corresponding satellite image estimate in order to test validity of our modulation transfer function (MTF) extraction algorithms. The test targets allow MTF computation by using slanted edge and sine wave star patterns. Comparison of extracted MTFs with the input ones yields 0.013% mean squared error for the slanted edge method and less error for the sine wave star method. Various factors affect the extracted MTF results such as slanted edge angle, noise level, image restoration level, region of interest selection and oversampling factor. We investigated effect of each factor on the MTF extraction performance.

Parallel compressive super-resolution imaging has attracted increasing attention in recent years. However, the super-resolution quality depends on modulation masks and reconstruction algorithms. A deep-learning method provides an efficient solution, but in wide field-of-view (FOV) scenarios, the differences between optical transfer functions (OTFs) of each pixel increase the system complexity and limit its practical application. This study proposed a wide FOV parallel compressive super-resolution imaging approach based on a physics-enhanced network. First, the network and modulation masks of an arbitrary 128 × 128-pixel region were trained; then, the trained network was fine-tuned for the rest of the 128 × 128-pixel regions in the entire wide FOV, which effectively eliminated the OTF variability. Numerical simulations and practical experiments demonstrated that through the proposed approach, super-resolution images of 1020 × 1500 pixels can be reconstructed from 272 × 400-pixel low-resolution measurements using only three designed masks, with the resolution enhanced 3.75 × 3.75 times and the peak signal-to-noise ratio improved by 89.4% compared to the results of the previous compressed sensing algorithm. Besides, the training time was dramatically reduced by 95.5-fold compared with the traditional training strategy for each region alone. This approach decreases the imaging complexity of wide FOV and achieves the high-quality super-resolution reconstruction under few trained masks, thus we believe it can promote rapid imaging for super-resolution and a wide FOV ranging from infrared to terahertz. [ABSTRACT FROM AUTHOR]

As an important method of image processing, image differentiation enables edge detection of targets to achieve recognition of object features and information compression and the computation speed can be boosted by optical information techniques. Traditional optical image differentiation methods mainly rely on spatial spectrum filtering by using classical 4f system, while some work focus on 1D or single‐direction differentiation. It is only in recent years that the rapid development of metasurfaces has facilitated image differentiation methods. In this work, a Laplace operation device is demonstrated based on a silicon hollow brick dielectric resonant metasurface for incident light field. The optical transfer function (OTF) required by the optical Laplace operation can be obtained by exciting an angularly selective toroidal dipole (TD) resonance supported by the metasurface. This hollow silicon brick differentiator not only realizes 2D second‐order edge detection but also has a numerical aperture close to 0.4 and a broad working wavelength range >100 nm and can be directly integrated with imaging systems. Such metadevice may be potentially applied in the fields of optical sensing, microscopy, machine vision, biomedical imaging, etc. [ABSTRACT FROM AUTHOR]

This paper presents findings from a spaceborne Earth observation experiment utilizing a novel, ultra-compact hyperspectral imaging camera aboard a 3U CubeSat. Leveraging the Offner optical scheme, the camera's hyperspectrometer captures hyperspectral images of terrestrial regions with a 200 m spatial resolution and 12 nanometer spectral resolution across a 400 to 1000 nanometer wavelength range, covering 150 channels in the visible and near-infrared spectrums. The hyperspectrometer is specifically designed for deployment on a 3U CubeSat nanosatellite platform, featuring a robust all-metal cylindrical body of the hyperspectrometer, and a coaxial arrangement of the optical elements ensures optimal compactness and vibration stability. The performance of the imaging hyperspectrometer was rigorously evaluated through numerical simulations prior to construction. Analysis of hyperspectral data acquired over a year-long orbital operation demonstrates the 3U CubeSat's ability to produce various vegetation indices, including the normalized difference vegetation index (NDVI). A comparative study with the European Space Agency's Sentinel-2 L2A data shows a strong agreement at critical points, confirming the 3U CubeSat's suitability for hyperspectral imaging in the visible and near-infrared spectrums. Notably, the ISOI 3U CubeSat can generate unique index images beyond the reach of Sentinel-2 L2A, underscoring its potential for advancing remote sensing applications. [ABSTRACT FROM AUTHOR]

In recent years, optical systems near the diffraction limit have been widely used in high-end applications. Evidently, an analytical solution of the point spread function (PSF) will help to enhance both understanding and dealing with the imaging process. This paper analyzes the Fresnel diffraction of diffraction-limited optical systems in defocused conditions. For this work, an analytical solution of the defocused PSF was obtained using the series expansion of the confluent hypergeometric functions. The analytical expression of the defocused optical transfer function is also presented herein for comparison with the PSF. Additionally, some characteristic parameters for the PSF are provided, such as the equivalent bandwidth and the Strehl ratio. Comparing the PSF obtained using the fast Fourier transform algorithm of an optical system with known, detailed parameters to the analytical solution derived in this paper using only the typical parameters, the root mean square errors of the two methods were found to be less than 3% in the weak and medium defocus range. The attractive advantages of the universal model, which is independent of design details, objective types, and applications, are discussed. [ABSTRACT FROM AUTHOR]

This article is an interview with optical scientist and engineer Joseph Braat, who discusses his career and contributions to the field of optics. He talks about his experiences at the Institut d'Optique in Paris and his work on holography using spatially incoherent light. Braat also discusses his role in designing the light path for recording and reading optical discs, including CD, DVD, and Blu-ray technology. The article explores the development of optical data storage and lithography technology, noting the challenges faced and advancements made. It concludes with Braat's reflections on his career and advice for students and researchers in the field of optics and photonics. [Extracted from the article]

Structured illumination microscopy (SIM) achieves super-resolution (SR) by modulating the high-frequency information of the sample into the passband of the optical system and subsequent image reconstruction. The traditional Wiener-filtering-based reconstruction algorithm operates in the Fourier domain, it requires prior knowledge of the sinusoidal illumination patterns which makes the time-consuming procedure of parameter estimation to raw datasets necessary, besides, the parameter estimation is sensitive to noise or aberration-induced pattern distortion which leads to reconstruction artifacts. Here, we propose a spatial-domain image reconstruction method that does not require parameter estimation but calculates patterns from raw datasets, and a reconstructed image can be obtained just by calculating the spatial covariance of differential calculated patterns and differential filtered datasets (the notch filtering operation is performed to the raw datasets for attenuating and compensating the optical transfer function (OTF)). Experiments on reconstructing raw datasets including nonbiological, biological, and simulated samples demonstrate that our method has SR capability, high reconstruction speed, and high robustness to aberration and noise. [ABSTRACT FROM AUTHOR]

The problem of monitoring space debris (SD) of anthropogenic origin is discussed to ensure the safety of near-Earth space environment exploration. For dynamic low-orbit SD fragments, acquisition and processing technologies of short-exposure image series, obtained in a non-redundant aperture synthesis array, are proposed and investigated. Specific features of the optical transfer function (OTF) of the non-redundant array, namely, its "insular" character, lead to difficulties in restoring the spatial spectrum of the control object, undistorted by the atmosphere, in the whole spatial-frequency domain of the array. It is shown that to restore the object's spatial spectrum module, undistorted by the atmosphere, in the whole spatial frequency domain of the array, it is necessary to use algorithm of the Labeyrie method, modified by the authors of the present work. To restore the phase of the spatial spectrum, it is necessary to use the algorithms of unfolding the closed phase equations of the triple correlations method. By physical modeling of the formation and registration processes of analog images in the atmosphere-array system and subsequent statistical processing of digitized images, experimental evidence is given of the effectiveness of the proposed restoring technologies to achieve high resolution of SD fragments in the array, aimed at their subsequent identification and removal. Recommendations are given for practical implementation of the considered promising construction and application technologies of optical systems to control SD fragments. • The problem of space debris (SD) control is investigated to ensure the safety of space flights. • Technologies for short-exposure images of control objects in a non-redundant aperture synthesis array for SD were proposed. • Algorithms of digital processing and restoration of the diffraction images of control objects in the array were developed. • Restoring technologies of SD image processing in non-redundant aperture synthesis array were studied by PC simulation methods. • High resolution of the observed SD fragments for their subsequent identification and removal were experimentally shown. [ABSTRACT FROM AUTHOR]

We compute the optical transfer function and corresponding satellite image estimate in order to test validity of our modulation transfer function (MTF) extraction algorithms. The test targets allow MTF computation by using slanted edge and sine wave star patterns. Comparison of extracted MTFs with the input ones yields 0.013% mean squared error for the slanted edge method and less error for the sine wave star method. Various factors affect the extracted MTF results such as slanted edge angle, noise level, image restoration level, region of interest selection and oversampling factor. We investigated effect of each factor on the MTF extraction performance. [ABSTRACT FROM AUTHOR]

The article considers a mathematical model of an incoherent optical system, into which defocusing is introduced as an aberration. When modeling, it is assumed that if non-coherent lighting is used to illuminate an object, then the transforming optical system should be considered as linear with respect to the intensity of the light. An analysis of the optical system of a general form was carried out, and relations were obtained for a system with a circular pupil, who allowed obtaining defocused images at the output of the optical system, and the defocusing value was rather simply adjustable. The proposed model can be used either as a low-pass filter for preprocessing of interferograms, or as a method for extracting informative image fragments, using which it is possible to synthesize the original image. [ABSTRACT FROM AUTHOR]

We present estimated images of a hypothetical satellite system in the presence of Seidel aberrations. We exemplified the effects of defocus, spherical, coma, astigmatism, field curvature, and distortion aberrations. Our analysis methods allow the investigation of aberration effects individually and in any combined form. Thereby, we introduce a potentially rich analysis dimension for the imaging chain, image processing, and image quality analyses. For a number of degrees of aberrations, we provide image estimates, show and quantify how individual (field‐dependent) aberrations would introduce degradations on the satellite images. We got correlation coefficient values for defocus, spherical, coma, astigmatism, field curvature, and distortion aberrations as 0.69, 0.71, 0.66, 0.79, 0.76, and 0.60, respectively. Thereby, we identfied the significance order of Seidel aberrations for this system by using image simulations and image similarity measures. [ABSTRACT FROM AUTHOR]

This study presents the image quality estimates of a hypothetical earth observation satellite (EOS) equipped with metaxel-based image sensors for the oblique viewing angle of the pitch manoeuvre scenario. Oblique-view image estimation methods are proposed and demonstrated for the optical and detector images. Owing to the small detector period (p) of the metaxel supercells ( $ p=1.32\, \mu {}{\rm m} $ p = 1.32 μ m ), the optical system image is optics limited. For oblique angle of $ \theta _{p}=15^{\circ },30^{\circ },45^{\circ },60^{\circ } $ θ p = 15 ∘ , 30 ∘ , 45 ∘ , 60 ∘ , image quality degradation owing to the aberration remained minor and average signal to noise ratio (SNR) for nadir view was SNR = 64 because of the local field enhancement of the metaxels. However, changes in the viewing angle reduced the image quality. Correlation coefficient between synthetic ground truth and oblique viewing cases was corr = 0.833, 0.818, 0.793 and 0.745 for the viewing angles of interest listed above. [ABSTRACT FROM AUTHOR]

This paper addresses the issue of reduced image quality due to annular turning marks formed by single-point diamond turning (SPDT) during the processing of metal-based mirrors and infrared lenses. An ideal single-point diamond turning marks diffraction action model to quantitatively analyze the impact of turning marks diffraction on imaging quality degradation is proposed. Based on this model, a fast estimation algorithm for the optical modulation transfer function of the system under turning marks diffraction (TMTF) is proposed. The results show that the TMTF algorithm achieves high computational accuracy, with a relative error of only 3% in diffraction efficiency, while being hundreds of times faster than rigorous coupled wave analysis (RCWA). This method is significant for reducing manufacturing costs and improving production efficiency, as it avoids the problem of being unable to compute large-size optical systems due to computational resource and time constraints. [ABSTRACT FROM AUTHOR]

Introduction: Despite the known associations between near work and myopia, and retinal image quality and eye growth, accommodation‐induced changes in higher order aberrations (HOA's) and retinal image quality in children with different refractive errors are poorly understood. Methods: Ocular HOA's were measured using a Hartmann‐Shack wavefront sensor (COAS‐HD, Wavefront Sciences) in 18 myopic and 18 age‐ and sex‐matched non‐myopic children during short‐term accommodation tasks (four demands of 0, 3, 6 and 9 D) presented using a Badal optometer. Eighth order Zernike polynomials were fitted across a 2.3 mm pupil diameter to determine refractive power vectors (M, J180 and J45) and the accommodation error, and a 4 mm pupil was used for HOA analyses. Retinal image quality was examined using the visual Strehl ratio based on the optical transfer function (VSOTF) for third to eighth radial orders only. Results: Most refractive error group differences were observed for the 6 and 9 D demands. Myopic children underwent greater changes in with‐the‐rule astigmatism (J180), higher order and third order RMS values, primary vertical (C3−1) and horizontal coma (C31), and several other individual Zernike coefficients compared with non‐myopic children (all refractive error group by demand interaction p‐values of ≤0.02). Non‐myopic children exhibited a greater negative shift in primary (C40) and positive shift in secondary spherical aberration (C60) (both refractive error group by demand interaction p‐values of ≤0.002). The VSOTF degraded for the 6 and 9 D demands in both groups, but the myopic children underwent a greater mean (SE) reduction from 0 D of −0.274 (0.048) for the 9 D demand, compared with −0.131 (0.052) for the non‐myopic children (p = 0.001). Conclusion: These results may have implications for the association between near work, accommodation and myopia development, particularly related to the use of short working distances during near tasks. [ABSTRACT FROM AUTHOR]

The Vertical Cavity Surface-Emitting Laser (VCSEL) has led to the rapid development of advanced fields such as communication, optical sensing, smart cars, and more. The accurate testing of VCSEL beam quality is an important prerequisite for its effective application. In this paper, a method for measuring the divergence angle of the VCSEL far field spot based on transmissive Fourier ptychography is proposed. First, a single CCD multi-angle VCSEL far-field spot acquisition system is designed. Second, based on the proposed Fourier ptychographic algorithm with synchronous optimization of embedded optical transfer function, a resolution-enhanced phase image of the spot is reconstructed and the boundary extracted by the Sobel operator of the phase image is defined as the boundary position of the beam waist. In this way, the beam waist radius of the laser beam is calculated. Finally, the divergence angle of the laser beam is measured via the radius of the beam waist. Compared with the traditional Gaussian beam definition method, the method proposed in this paper has higher accuracy in divergence angle measurement. The experimental results show that this method can improve the divergence angle measurement accuracy by up to 9.7%. [ABSTRACT FROM AUTHOR]

As spectroscopic detection technology rapidly advances, back-illuminated InGaAs detectors with a wider spectral range have emerged. Compared to traditional detectors such as HgCdTe, CCD, and CMOS, InGaAs detectors offer a working range of 400–1800 nm and exhibit a quantum efficiency of over 60% in both the visible and near-infrared bands. This is leading to the demand for innovative designs of imaging spectrometers with wider spectral ranges. However, the widening of the spectral range has led to the presence of significant axial chromatic aberration and secondary spectrum in imaging spectrometers. Additionally, there is difficulty in aligning the system optical axis perpendicular to the detector image plane, resulting in increased challenges during post-installation adjustment. Based on chromatic aberration correction theory, this paper presents the design of a wide spectral range transmission prism-grating imaging spectrometer with a working range of 400–1750 nm using Code V. The spectral range of this spectrometer covers both the visible and near-infrared regions, which is beyond the capability of traditional PG spectrometers. In the past, the working spectral range of transmission-type PG imaging spectrometers has been limited to 400–1000 nm. This study's proposed chromatic aberration correction process involves selecting optical glass materials that match the design requirements and correcting the axial chromatic aberration and secondary spectrum, ensuring that the system axis is perpendicular to the detector plane and easy to adjust during installation. The results show that the spectrometer has a spectral resolution of 5 nm, a root-mean-square spot diagram less than 8 μm over the full field of view, and an optical transfer function MTF greater than 0.6 at a Nyquist frequency of 30 lp/mm. The system size is less than 90 mm. Spherical lenses are employed in the system design to reduce manufacturing costs and complexity while meeting the requirements of wide spectral range, miniaturization, and easy installation. [ABSTRACT FROM AUTHOR]

Purpose: To quantify the amount of myopic defocus, contrast modulation and other optical characteristics of two novel spectacle lenses (MiYOSMART by Hoya and Stellest by Essilor) with the inclusion of lenslets in their designs were investigated computationally and experimentally. This paper examined the hypothesis that despite the non‐coaxial nature of the optics, image degradation will exist due to the fragmented nature of the base optic when imaging through the lens regions populated by lenslets. Methods: Optical power was evaluated by computing wavefront vergence and curvature from wavefront slope measured with the Optocraft aberrometer within 1.0 and 6.0 mm apertures across MiYOSMART hexagons and Stellest rings. Point‐spread functions (PSFs) were computed using physical (wave) optics and geometrical ray optics principles, and compared with experimental measurements using a 4f optical system. Simulated retinal images and modulation transfer functions (MTFs) were computed from PSF‐derived optical transfer functions (OTFs). Results: Mean lenslet power in MiYOSMART was +3.95 ± 0.10 D through the hexagons and +6.00 ± 0.15 D in Stellest in rings 1–5 and decreased by 0.42 D/ring reaching 3.50 D in the final one. Stellest lenslets included up to −0.015 microns of primary spherical aberration. PSFs and retinal images revealed simultaneous contributions of the base optic and lenslets. MTFs showed a decrease in contrast at low (1–10 c/deg) spatial frequencies (SFs) comparable to 0.25 D of defocus, and retention of diminished levels of contrast at higher SFs. Conclusions: Varying sagittal power and consistent curvature power across the lenslets is an identifying signature of the novel non‐coaxial lens design included in both spectacle lenses. Lenslet array structure itself plays a significant role in determining image characteristics. For both lenses, the blur created by the fragmented base optic contributes to the image quality. The reduced MTFs over a wide range of spatial frequencies result in lowered image contrast. [ABSTRACT FROM AUTHOR]

Optical diffraction tomography is a powerful technique to produce 3D volumetric images of biological samples using contrast produced by variations in the index of refraction in an unlabeled specimen. While this is typically performed with coherent illumination from a variety of angles, interest has grown in partially coherent methods due to the simplicity of the illumination and the computation-free axial sectioning provided by the coherence window of the source. However, such methods rely on the symmetry or discretization of a source to facilitate quantitative analysis and are unable to efficiently handle arbitrary illumination that may vary asymmetrically in angle and continuously in the spectrum, such as diffusely scattered or thermal sources. A general broadband theory may expand the scope of illumination methods available for quantitative analysis, as partially coherent sources are commonly available and may benefit from the effects of spatial and temporal incoherence. In this work, we investigate partially coherent tomographic phase microscopy from arbitrary sources regardless of angular distribution and spectrum by unifying the effects of spatial and temporal coherence into a single formulation. This approach further yields a method for efficient computation of the overall systems' optical transfer function, which scales with O(n3), down from O(mn4) for existing convolutional methods, where n3 is the number of spatial voxels in 3D space and m is the number of discrete wavelengths in the illumination spectrum. This work has important implications for enabling partially coherent 3D quantitative phase microscopy and refractive index tomography in virtually any transmission or epi-illumination microscope. [ABSTRACT FROM AUTHOR]

It is shown that anomalous boundary conditions at the surface of a negative‐refractive‐index metamaterial planar lens severely diminishes the resolution of the lens when its relative permittivity and permeability are both −1. Anomalous boundary conditions arise in practical microwave metamaterials that are typically a periodic array of identical unit cells comprising dielectric and conducting elements. For a unit‐cell size much smaller than the wavelength, homogenised permittivity and permeability are the constituent parameters of the average fields. Average fields vary on a scale larger than the unit cell size compared to localised fields associated with the constituent elements. Unlike the tangential components of the localised field, tangential components of the average fields are discontinuous across the surface of such materials. This anomalous boundary condition at the lens surface must be described by generalised sheet transition conditions. This study develops expressions for the negative‐refractive‐index lens optical transfer functions, as a function of spatial frequency, for transverse‐electric waves, that account for anomalous surface boundary conditions. Both the simulations and experimental data are used to verify the expressions at a frequency of 3 GHz. [ABSTRACT FROM AUTHOR]

Remarkably, the proposed algorithms outperformed other stitching algorithms currently available in the literature in the four selected test cases in [[3]] (i.e., polymer abrasion, mirror polished copper, arm skin replica, and titanium alloy abrasion). Materials characterization is a basic field of science and engineering. For this reason, Abdelhamid et al. [[5]] developed Cu- and/or Zr-modified TiO SB 2 sb nanoparticles, characterizing them with photo-thermal beam deflection spectrometry (BDS), UV-Vis spectro-photometry, X-ray diffraction (XRD), and energy-dispersive X-rays (EDXs) to determine their thermo-optical and transport parameters. [Extracted from the article]

Applying the optical transfer matrix method and the drift-diffusion equations, the efficient light absorption, exciton generation, and recombination rate in bulk heterojunction (BHJ) organic solar cells (OSCs) with conventional and inverted configurations are studied. Analysing the influence of the electric field component of the electromagnetic radiation propagating through the layered structure of BHJ OSCs and using contour plots of normalized modulus squared of the electric field, the constructive interference points (CIPs) which represent the positions of maximum absorption of photons and hence generation of excitons within the active layer are investigated for both the conventional and inverted OSCs. Also, the influence of the thicknesses of other layers in both the inverted and conventional structures is investigated. It is found that except the thickness of MoO3 in the inverted structure the thicknesses of other layers do not have any significant influence on CIPs. The maximum CIP occurs at an active layer thickness of 190 nm, regardless of the thickness of the second layer, which is MoO3, Ag, or ITO in the inverted structure and PEDOT:PSS, Al, or ITO in the conventional structure. The results of 3D plots of the normalized modulus squared of the electric field reveal that the absorption of photons at the end of the active layer in the inverted structure is higher than that in the conventional structure for all the effective wavelengths and different active layer thicknesses. It is expected that this study provides a deeper understanding of exciton generation within the two structures. [ABSTRACT FROM AUTHOR]

The article presents a study which developed a simulation model to probe the fundamental governing principles in optics, chemical kinetics, and mass transport in the three-dimensional (3D) printing process. Topics discussed include contrast-based focusing mechanism to optimize the focal plane and print resolution, high-resolution continuous liquid interface production (CLIP) modeling of optics, momentum, and mass transport, and analytical solution for oxygen concentration profile.

The energy resolution in hyperspectral imaging techniques has always been an important matter in data interpretation. In many cases, spectral information is distorted by elements such as instruments' broad optical transfer function, and electronic high frequency noises. In the past decades, advances in artificial intelligence methods have provided robust tools to better study sophisticated system artifacts in spectral data and take steps towards removing these artifacts from the experimentally obtained data. This study evaluates the capability of a recently developed deep convolutional neural network script, EELSpecNet, in restoring the reality of a spectral data. The particular strength of the deep neural networks is to remove multiple instrumental artifacts such as random energy jitters of the source, signal convolution by the optical transfer function and high frequency noise at once using a single training data set. Here, EELSpecNet performance in reducing noise, and restoring the original reality of the spectra is evaluated for near zero-loss electron energy loss spectroscopy signals in Scanning Transmission Electron Microscopy. EELSpecNet demonstrates to be more efficient and more robust than the currently widely used Bayesian statistical method, even in harsh conditions (e.g. high signal broadening, intense high frequency noise). [ABSTRACT FROM AUTHOR]

A double-layer metal superlens was rigorously analyzed and systematically designed to improve subwavelength imaging ability. It was revealed that transmission properties of the imaging system could be accurately interpreted by the five-layer waveguide mode theory—each amplification peak among the spatial frequency range of evanescent waves was associated with a corresponding surface plasmon polariton (SPP) mode of an insulator-metal-insulator-metal-insulator (IMIMI) structure. On the basis of such physical insight, evanescent waves of higher spatial frequency were effectively amplified via increasing propagation constants of symmetrically coupled short-range SPP (s-SRSPP) and antisymmetrically coupled short-range SPP (a-SRSPP), and evanescent waves of lower spatial frequency were appropriately diminished by approaching to cut off symmetrically coupled long-range SPP (s-LRSPP). A flat and broad optical transfer function of the imaging system was then achieved, and improved subwavelength imaging performance was validated by imaging an ideal thin object of two slits with a 20-nm width distanced by a 20-nm spacer, under 193-nm illumination. The resolution limit of the designed imaging system with double-layer superlens was further demonstrated to be at least ~λ/16 for an isolated two-slit object model. This work provided sound theoretical analysis and a systematic design approach of double-layer metal superlens for near-field subwavelength imaging, such as fluorescent micro/nanoscopy or plasmonic nanolithography. [ABSTRACT FROM AUTHOR]

In this study, we propose a method of evaluating the spectral resolution of crossed-asymmetric Czerny-Turner spectrometers by comparing the impact of different slit functions on the optical transfer function, and different slit widths, through simulation and experiments. The results show that, the Gaussian function is suitable for narrower slit widths, such as 25 μm, and the rectangle function or convolution of slit-scattering function with rectangle function is suitable for wider slit widths, such as 50 μm, 150 μm, and 200 μm. The proposed method can provide guidance in the evaluation of spectral resolution in the preliminary optical design process of spectrometers. [ABSTRACT FROM AUTHOR]

Fourier-based optical computing operations, such as spatial differentiation, have recently been realized in compact form factors using flat optics. Experimental demonstrations, however, have been limited to coherent light requiring laser illumination and leading to speckle noise and unwanted interference fringes. Here, the use of an optimized multilayer film, combined with dual color image subtraction, is demonstrated to realize differentiation with unpolarized incoherent light. Global optimization is achieved by employing neural networks combined with the reconciled level set method to optimize the optical transfer function of a multilayer film at wavelengths of 532 and 633 nm. Spatial differentiation is then achieved by subtracting the normalized incoherent images at these two wavelengths. The optimized multilayer film is experimentally demonstrated to achieve incoherent differentiation with a resolution of 6.2 𝛍m. The use of a multilayer film allows for scalable lithography-free fabrication and results in a system that could open the door to high-speed processing for a wide variety of incoherent, and coherent, imaging systems. [ABSTRACT FROM AUTHOR]

A three-criterion taxonomy of metrics to compute the spatial resolution of satellite imagers is presented and used to classify about thirty spatial resolution metrics found in the literature. A new metric, the “Spatial Resolution Function”, is proposed by applying the two-point source resolution criterion to sampled images. This new metric computes resolution distance as a function of the resolving contrast in the image plane, using the sensor’s Point Spread Function as input, and demanding that the output agrees with the Ground Sampling Distance metric for very low optical factors. Further, the application of the Rose criterion to the Spatial Resolution Function allows the dependence of resolution distance on signal to noise ratio to be considered. The procedure to compute the Spatial Resolution Function is applied to three quality types of generic satellite imaging scanners, computing their resolution distances in the along scan and across scan directions, for a wide range of optical factors encountered in Earth observation satellites. The Spatial Resolution Function is used to assess twelve commonly used spatial resolution metrics, the results indicate that all these metrics are biased, showing significant errors when used to compare different satellite imagers. The overall utility of spatial resolution metrics that use a property of the Point Spread Function to roughly estimate resolution distance is challenged, as by using this same function the Spatial Resolution Function allows its exact calculation.

The article discusses about an integrated photonics engine for correlation detection. Topics including effect of modern life and scientific tools on the amount of data generated exponentially, about computational memory engine and how it exploits the accumulative property of different cells, and experimental demonstration of identifying real-time correlations in data streams on different social media platform.

The underwater turbulence channel is modelled and a unified statistical distribution is applied for characterizing orbital angular momentum (OAM) propagation in underwater wireless optical communication (UWOC) systems. Based on Monte-Carlo simulations, the effects of turbulences are characterized by the multiple phase screens model considering both the coherence width and scintillation index. The phase screen samples are processed by the randomized spectral sampling discrete Fourier transform (DFT) technique. To validate the propagated field distribution, both the phase structure function and optical transfer function are derived and evaluated with the aid of ensemble-averaged results. The Generalized Gamma Distribution (GGD) enriched by an additional independent parameter is applied for modelling the probability density function (PDF) of both the reference-channels, fluctuating irradiance as well as the intermodal crosstalk irradiance between different OAM modes. Furthermore, based on the PDF, the performance metrics of both single input multiple output (SISO) and multiple input multiple output (MIMO) systems are analyzed, based on the average capacity, the bit-error rate and the outage probability. [ABSTRACT FROM AUTHOR]

Wave-based signal processing has witnessed a significant expansion of interest in a variety of science and engineering disciplines, as it provides new opportunities for achieving high-speed and low-power operations. Although flat optics desires integrable components to perform multiple missions, yet, the current wave-based computational metasurfaces can engineer only the spatial content of the input signal where the processed signal obeys the traditional version of Snell's law. In this paper, we propose a multi-functional metagrating to modulate both spatial and angular properties of the input signal whereby both symmetric and asymmetric optical transfer functions are realized using high-order space harmonics. The performance of the designed compound metallic grating is validated through several investigations where closed-form expressions are suggested to extract the phase and amplitude information of the diffractive modes. Several illustrative examples are demonstrated to show that the proposed metagrating allows for simultaneous parallel analog computing tasks such as first- and second-order spatial differentiation through a single multichannel structured surface. It is anticipated that the designed platform brings a new twist to the field of optical signal processing and opens up large perspectives for simple integrated image processing systems. [ABSTRACT FROM AUTHOR]

Subject of study. The authors propose an integrated approach to the problem of determining the aperture diameter of a probe laser that forms a laser reference star used in ground-based adaptive optoelectronic systems. The relevance of this study is due to the fact that modern large-aperture optical systems for tracking natural stars and artificial objects (spacecraft or fragments of space debris) widely implement the technology of forming laser stars and use them as reference sources for correcting phase distortions of a turbulent atmosphere. The choice of the energy and spatiotemporal characteristics of laser guide stars is related both to the parameters of the probe laser (radiation power and aperture diameter), which forms the guide star, and to the spatiotemporal characteristics of the atmosphere. Method. The diameter of the probe laser aperture (for the near and far radiation zones) is estimated taking into account the spatial coherence radius of the atmosphere r0, the radiation intensity and angular divergence of the laser beam, its random root-mean-square angular deviation (jitter) with respect to the calculated direction to the space objects. Main results. The estimation of the angular divergence of a laser beam is based on a comparative analysis and generalization of theoretical results obtained by calculating the optical resolution in systems for acquiring images of natural space objects. It is shown, in particular, that when determining the size of the aperture along with the value of the angular divergence of the probe beam, it is necessary to take into consideration the decrease in its radiation intensity with an increase in the diameter with respect to the radius of atmosphere coherence. The practical significance. The results are essential, firstly, for the development of ground-based adaptive optoelectronic systems for tracking artificial space objects, and secondly, for determining the geographic locations of the optoelectronic systems taking into account the astronomical climate.

Introduction: This study aims to compare preclinical visual-quality metrics and halo size of intraocular lenses (IOL) with enhanced intermediate vision to a standard monofocal lens. Methods: Three monofocal- IOL models with an extended-depth-of-focus (EDoF) intended for monocular implantation (Tecnis ICB00, AE2UV/ZOE, and IsoPure) and one for monovision (RayOne EMV) were compared against a standard monofocal lens (Tecnis ZCB00). An optical-metrology station was used in the assessment of IOLs' optical quality in polychromatic light. The imaging quality was compared with metrics derived from the optical transfer function. Halo size was estimated from the projection of the point spread function under scotopic pupil. Results: The monofocal IOL showed the highest image quality at the far focus. The ICB00's, the AE2UV/ZOE's, and the IsoPure's performance at − 1D was superior to that of the monofocal lens. The monocular defocus tolerance of the RayOne EMV was comparable with that of the ZCB00. The RayOne EMV's intermediate range was improved in a monovision configuration (− 1D offset). This approach, however, yielded the largest halo area, i.e., 53% of the ZCB00's halo, compared to 34% for the IsoPure, 14% for the AE2UV/ZOE, and 8% for the ICB00. Conclusion: The mono-EDoF models have a clear advantage over the standard monofocal lens by expanded imaging capability beyond − 0.5D. Although the RayOne EMV provided the largest (binocular) visual-range extension, it was at the expense of monocular vision and higher susceptibility to halo. The ICB00's and the AE2UV/ZOE's halo-profile was similar to that of the ZCB00, indicating their low potential to induce photic phenomena. [ABSTRACT FROM AUTHOR]

Analog computing has emerged as a promising candidate for real-time and parallel continuous data processing. This article presents a reciprocal way for realizing asymmetric optical transfer functions (OTFs) in the reflection side of the on-axis processing channels. It is rigorously demonstrated that the presence of cross-polarization exciting normal polarizabilities (CPENPs) of a reciprocal metasurface circumvents the famous challenge of Green’s function approach in implementation of on-axis reflective optical signal processing while providing dual computing channels under orthogonal polarizations. Following a comprehensive theoretical discussion and as a proof of concept, an all-dielectric optical metasurface is elaborately designed to exhibit the desired surface polarizabilities, thereby reflecting the first derivative and extracting the edges of images impinging from the normal direction. The proposed study offers a flexible design method for on-axis metasurface-based optical signal processing and also dramatically facilitates the experimental setup required for ultrafast analog computation and image processing. [ABSTRACT FROM AUTHOR]

Three‐dimensional (3D) transfer functions build the basis for a comprehensive characterization of optical imaging systems in the spatial frequency domain. Utilizing the projection‐slice theorem, the 2D modulation transfer function of an incoherent imaging system can be derived from a 3D transfer function by integration with respect to the axial spatial frequency. For a diffraction limited microscope with homogeneous incoherent pupil illumination, the modulation transfer function equals the 2D autocorrelation function of a circular disc. However, until now to the best of our knowledge no 3D transfer function has been published, which exactly leads to the 2D modulation transfer function of a diffraction limited microscope in reflection mode. In this article, we derive a formula, which after integration with respect to the axial spatial frequency coordinate perfectly fits to the diffraction limited 2D modulation transfer function. The inverse three‐dimensional Fourier transform of the 3D transfer function results in a complex‐valued 3D point spread function, from which the depth of field, the lateral resolution and, in addition, the corresponding 3D point spread function of both, a conventional and an interference microscope, can be obtained. [ABSTRACT FROM AUTHOR]

To achieve super-resolution imaging, the information in higher frequency of the observed sample is collected by illuminating with a structure beam for a limited optical transfer function. In this paper, tilt illumination mode is introduced to structured illumination microscopy (SIM) for enhancing lateral resolution. More sample spectrum more than traditional SIM, can be obtained by detector. Thus, SIM with tilt illumination can be improved at the aspect of lateral imaging resolution. [ABSTRACT FROM AUTHOR]

Integrated time delays are important for self-forced oscillation techniques in opto-electronic oscillators (OEO). Add-drop filters (ADFs) resonators using optical waveguide coupled to micro-ring resonators (MRR) are suitable for integrated optical time delays but suffer from a limited expected delay. 2-dimensional (2-D) photonic crystals (PhCs) with line defect are employed as confined optical waveguide to realize ADF resonators where longer optical delays than standard homogenous resonators are achieved by leveraging the slow-light effect. Moreover, achieving time delay up to microseconds (µs) is envisioned by cascading multiple identical ADFs based on dispersive 2-D PhC micro-resonators. The focus of this paper is to devise a hybrid modeling procedure for accurate calculations of achieved time delays in various complex structures, while a combined electromagnetic modeling and analytical calculation technique overcomes a substantial computational resources and long computation times for a brute forced full-wave design and modeling. This innovative hybrid modeling for time delay estimation of cascaded ADFs is proposed for the first time to optimize physical design within short time period. First, transfer function performance of a homogenous ADF resonator is simulated using finite-difference-timedomain (FDTD) for both the full structure and structures with bi-fold symmetry and compared against proven analytical solutions to demonstrate the accuracy of bi-fold symmetry while the computational resources are economized. The same modeling procedure is then extended to predicting performance of 2-D PhC based ADF resonator by quantifying key physical parameters of coupling factor, complex optical propagation constant, and optical transfer function for ADF resonator for the ring radius of curvature about 1.5 µm with various coupling gaps between feed waveguide and resonator guide. These parameters and the effective group index calculated by OptiFDTD software are applied to the analytical expressions to estimate single 2-D PhC ADF and attain a simulated time delay of 200 ps. The estimated time delay of 70 cascaded 2-D PhC based ADF resonators with R of 100 µm is estimated to be about 925 ns for the on-resonance frequency of 1534 nm. [ABSTRACT FROM AUTHOR]

A double-layer metal superlens was rigorously analyzed and systematically designed to improve subwavelength imaging ability. It was revealed that transmission properties of the imaging system could be accurately interpreted by the five-layer waveguide mode theory—each amplification peak among the spatial frequency range of evanescent waves was associated with a corresponding surface plasmon polariton (SPP) mode of an insulator-metal-insulator-metal-insulator (IMIMI) structure. On the basis of such physical insight, evanescent waves of higher spatial frequency were effectively amplified via increasing propagation constants of symmetrically coupled short-range SPP (s-SRSPP) and antisymmetrically coupled short-range SPP (a-SRSPP), and evanescent waves of lower spatial frequency were appropriately diminished by approaching to cut off symmetrically coupled long-range SPP (s-LRSPP). A flat and broad optical transfer function of the imaging system was then achieved, and improved subwavelength imaging performance was validated by imaging an ideal thin object of two slits with a 20-nm width distanced by a 20-nm spacer, under 193-nm illumination. The resolution limit of the designed imaging system with double-layer superlens was further demonstrated to be at least ~λ/16 for an isolated two-slit object model. This work provided sound theoretical analysis and a systematic design approach of double-layer metal superlens for near-field subwavelength imaging, such as fluorescent micro/nanoscopy or plasmonic nanolithography.

In this study, we propose a method of evaluating the spectral resolution of crossed-asymmetric Czerny-Turner spectrometers by comparing the impact of different slit functions on the optical transfer function, and different slit widths, through simulation and experiments. The results show that, the Gaussian function is suitable for narrower slit widths, such as 25 μm, and the rectangle function or convolution of slit-scattering function with rectangle function is suitable for wider slit widths, such as 50 μm, 150 μm, and 200 μm. The proposed method can provide guidance in the evaluation of spectral resolution in the preliminary optical design process of spectrometers.