Information structure of a polarization state: the concept of metaspin

Jose Gil, Andreas Norrman, Ari Tapio Friberg, and Tero Setälä

DOI: 10.1364/JOSAA.521863 Received 19 Feb 2024; Accepted 29 May 2024; Posted 29 May 2024  View: PDF

Abstract: A complete description of the polarization properties of a random, stationary, generally three-dimensional (3D) optical field in a point is provided by the 3×3 polarization matrix. We show that its nine degrees of freedom can be represented by nine independent and decoupled parameters with simple and significant physical meanings. These cover the three orientation angles determining the intrinsic reference frame with respect to an arbitrary one, the three principal intensities representing the strengths of the components of the electric field along the respective intrinsic reference axes, and a novel real-valued vector, which we term metaspin, whose three components are given by the intrinsic correlations of the field components. Consequently, any given polarization state has an associated intensity-isotropic state, called the metaspin state, whose spin vector is fully determined by the metaspin vector. We also show that the concept of metaspin provides an illustrative synthesis procedure for 3D polarization states. The results can straightforwardly be applied to any 3×3 density matrix.

Study of the lateral shift due to atmospheric refraction: alternative analytical methods, and new results

Luc Dettwiller

DOI: 10.1364/JOSAA.522962 Received 04 Mar 2024; Accepted 28 May 2024; Posted 29 May 2024  View: PDF

Abstract: Atmospheric refraction modifies the apparent position of objects in the sky, and also produces a progressive lateral shift of the light rays received from these objects; in the case of a spherically symmetric atmosphere, for the first time, this shift has been numerically studied in 2022, and different analytical estimators have been compared (by Labriji et al.) for the total shift. This topic is important for the reconstruction of meteor trajectories, for the analysis of wavefront sensing in adaptative optics, etc. Always in the case of a spherically symmetric atmosphere, we show two other analytical methods to study this lateral shift, and to be able to estimate it analytically in the difficult case when the celestial object is seen near the astronomical horizon. One of these methods allows us deducing an estimator, not only of the total shift, but also of the shift of any point of the ray. We compare properties of the total lateral shift and of the refraction angle, and also the chromatism of the total lateral shift to the chromatism of the air refractivity, for rays coming from an object seen either high enough above the astronomical horizon, or on it. In this latter case, our first method shows departures from proportionality between the chromatisms of the air refractivity, of the astronomical refraction angle, and, even more, of the total lateral shift.

Tested Mirror Precision Alignment System using in Pinhole Point Diffraction Interferometer based on Machine Vision

Jiasheng Lu, Bing Li, Zhuo zhao, and Leqi Geng

DOI: 10.1364/JOSAA.523113 Received 18 Mar 2024; Accepted 28 May 2024; Posted 29 May 2024  View: PDF

Abstract: In the Pinhole Point Diffraction Interferometer (PPDI), proper alignment between the reflection spot of the tested component and the pinhole is critical to obtain accurate interferograms. At present, adjusting for tilt error requires manual manipulation, and defocus error cannot be corrected. These limitations impede the instrumentation process of PPDI. To address this issue, the proposed tested mirror alignment system utilizes diffraction theory to analyze the mathematical error caused by the misalignment of the tested mirror reflected beam and pinhole. An alignment system based on machine vision was designed according to specific requirements. This system incorporates a CCD camera with a zoom lens, the classic PPDI with a pinhole substrate containing a lithography-made mark, and a 3-DOF stepper motor adjusting frame to mount the tested mirror. Additionally, image processing algorithms and step motor driving programs were applied to achieve precise alignment. The system implementation and experimental results indicated that the tilt errors are well-controlled, achieving the defocus error modifying, making the interferogram acquisition process more convenient. From the results, this system offers desirable precision and efficiency for PPDI’s tested mirror alignment.

Image authentication with exclusive-OR operated optical vortices

RAHUL KUMAR, Praveen Kumar, Naveen Nishchal, and Ayman Alfalou

DOI: 10.1364/JOSAA.527399 Received 15 Apr 2024; Accepted 26 May 2024; Posted 29 May 2024  View: PDF

Abstract: Optical vortices carrying orbital angular momentum have drawn much attentionbecause they provide high-dimensional encoding. Employing an array of optical vortices, wedemonstrate an authentication verification system. For security authentication, an exclusiveOR logic operation has been implemented employing a light beam consisting of an array ofvortices. A liquid crystal spatial light modulator has been used to generate orthogonal statesof optical vortices. The proposed technique can provide a secure way of authentication withstraightforward implementation. We have presented simulation and experimental results toverify the proposed scheme.

Geometric construction of relativistic and non-relativistic distortion

Gordon Wells, YiChen Wu, Maik Locher, and Johannes Courtial

DOI: 10.1364/JOSAA.524591 Received 26 Mar 2024; Accepted 23 May 2024; Posted 24 May 2024  View: PDF

Abstract: To an observer moving through a scene with a relativistic velocity, the scene appears distorted. Here we present a simple geometric interpretation of this relativistic distortion. This interpretation is exact for pinhole cameras whose shutter coincides with the pinhole, and it can easily be modified to take into account time-of-flight effects only that lead to a "non-relativistic distortion", allowing a separation of the relativistic distortion into time-of-flight effects and "truly relativistic" effects. We make use of our construction in Einstagram, a web app designed for running on mobile devices that displays the video streams from the device cameras, relativistically or non-relativistically distorted for an arbitrary, user-defined, observer velocity. Our work facilitates an intuitive understanding of relativistic distortion.

Photonic crystal fiber based on graphene surface plasmon resonance for high-sensitivity terahertz refractive index sensing

JIE HE, Jianxin Wang, Wei Liu, Xili Lu, Jingwei Lv, Lin Yang, Paul Chu, and Chao Liu

DOI: 10.1364/JOSAA.521774 Received 19 Feb 2024; Accepted 20 May 2024; Posted 20 May 2024  View: PDF

Abstract: A photonic crystal fiber (PCF) sensor based on surface plasmon resonance (SPR) with a graphene coating on the cladding is designed for refractive index (RI) detection in the range of 0.3-0.5 THz, especially for liquid bioanalytical sensing. The adjustability of the graphene chemical potential (Ef) enables dynamic tuning of the loss spectra over a wide frequency range with a tuning sensitivity of 570 GHz/eV at the SPR frequency. According to the analysis by the finite element method (FEM), the highest wavelength sensitivity and maximum amplitude sensitivity of 4254.11 μm/RIU and 25.62 RIU-1 (na = 1.34) are achieved in the RI range of 1.15-1.35, respectively, together with a resolution of 1.42 × 10-3 RIU-1. The graphene PCF-SPR sensor boasting high-sensitivity detection in a wide RI range has broad application prospects in multiple fields.

Analytical study on the upward laser beam propagation in the turbulent atmosphere

QIAN LI, ZHIXIANG ZHANG, YIXUAN LI, Xiaoling Ji, and XIAOQING Li

DOI: 10.1364/JOSAA.521344 Received 09 Feb 2024; Accepted 20 May 2024; Posted 21 May 2024  View: PDF

Abstract: The upward laser beam propagation in the turbulent atmosphere is studied analytically, where the nonlinear self-focusing, turbulence and extinction effects are all taken into account. The analytical propagation expression of intensity is derived. Because of effects of diffraction, self-focusing, turbulence and extinction, the focal shift takes place. The focal shift can be compensated by the initial beam defocusing method. The analytical expressions of the focal length considering the initial beam defocusing and the corresponding target intensity are derived. Moreover, the analytical expressions of optimal beam power and the corresponding target intensity are also derived, and the target intensity is independent of the atmospheric extinction. In particular, the criterion for optimizing the target beam quality is derived by the initial beam defocusing method or the optimal beam power method. The choice of the two method depends on the laser beam and turbulent atmosphere parameters.

Innovative Methodology for Non-Invasive Spatial Mapping of Gold Nanoparticle Distribution in Tissues: Potential Applications in Biomedical Imaging and Therapy

Ana Mendes, Adamo Monte, and Rolf Saager

DOI: 10.1364/JOSAA.523717 Received 13 Mar 2024; Accepted 20 May 2024; Posted 21 May 2024  View: PDF

Abstract: Gold nanoparticles (Au NPs) have emerged as versatile agents in biomedical applications, particularly for enhancing contrast in tagged biological tissues for tumor imaging and diagnostics due to their strong absorption cross-section. In this study, we present a novel methodology for quantifying the spatial distribution of Au NPs within superficial tissue volumes. Utilizing silicone tissue phantoms as a background medium and spatial frequency domain imaging (SFDI) to measure tissues' optical properties, we constructed a lookup-table (LUT) to infer the optical properties of embedded Au NPs with varying spatial concentrations and depths across multiple spatial frequencies. An analytical solution derived from the LUT facilitated the determination of embedded NP concentration in-depth as a function of measured spatial frequency-dependent optical absorption. Notably, SFDI enabled the spatial localization of NPs in three dimensions. These findings lay the foundation for future in vivo studies on mapping NPs and hold significant promise for advancing biomedical imaging techniques.

Photoemission properties of the variable component GaInAsSb heterojunction nanopillar array cathode

zhidong Wang, Lei Liu, zhihao Cao, Jian Tian, and Xingyue Zhangyang

DOI: 10.1364/JOSAA.506364 Received 21 Sep 2023; Accepted 15 May 2024; Posted 15 May 2024  View: PDF

Abstract: The GaxIn1-xAsySb1-y heterojunction NPAs exhibit different properties depending on thematerial composition. Changing the Ga composition significantly affects the quantum efficiencyand broadening of the heterojunction nanopillar array, while varying the As composition affectsthe peak position of its quantum efficiency. The quantum efficiency of the heterojunction isnotably influenced by changes in the height of the top layer of the heterojunction, and when thereis a difference in quantum efficiency between the two materials, the quantum efficiency of theheterojunction exhibits extremum values. Furthermore, external electric fields significantly affectthe quantum efficiency of nanopillar arrays, providing important references and theoreticalfoundations for designing and optimizing resonantly enhanced GaInAsSb nanopillar arrayphotonic cathodes.

Analysis of far-field radiation pattern by a current loop in hyperbolic material

Aamir Hayat, Hafiza Khalid, and Muzamil Shah

DOI: 10.1364/JOSAA.519811 Received 24 Jan 2024; Accepted 15 May 2024; Posted 15 May 2024  View: PDF

Abstract: In this article, we investigate the radiations from a current loop in the hyperbolicmaterials. To encounter the arbitrary orientation of the loop, the results are presented when theloop axis is aligned parallel and perpendicular to the optic axis. Closed-form expressions aswell as numerical results are presented for both ordinary and extraordinary waves. The resultsindicate a strong dependence on the size of the loop, in contrast to the case of uniaxial dielectricmaterials. When the loop axis is parallel to the optic axis the pattern is quite similar to that ofuniaxial dielectric materials, however, a significant change in the pattern is observed when theoptic axis turns perpendicular to the loop axis. The results show a significant role of the size ofthe loop in the hyperbolic material as compared to the uniaxial dielectric material.

Does the quasi-static polarizability have principal axes?

Vadim Markel

DOI: 10.1364/JOSAA.523449 Received 11 Mar 2024; Accepted 14 May 2024; Posted 14 May 2024  View: PDF

Abstract: Beyond strict statics, the dipole polarizability tensor is a complex symmetric matrix. Such matrices may not be diagonalizable by an orthogonal similarity transformation (a rigid rotation of the reference frame). In this paper, we provide examples of polarizability tensors, which have no real principal axes and discuss the conditions under which this counter-intuitive phenomenon can occur.

Statistical insights of polarization speckle via von Mises-Fisher distribution on the Poincaré sphere

SOURAV CHANDRA, Rajeev Singh, and Rakesh Singh

DOI: 10.1364/JOSAA.519685 Received 22 Jan 2024; Accepted 14 May 2024; Posted 14 May 2024  View: PDF

Abstract: Polarization speckle generated via random scattering of light, are ubiquitous in natural and engineered systems. They not only manifest intensity fluctuations but also reveal a spatially fluctuating, random polarization distribution. The precise morphology of the polarization speckle pattern serves as a deterministic signature of the light's state of polarization fluctuation within a scattering medium. Given the inherent randomness of polarization speckle patterns, a statistical approach emerges as the most pragmatic method for their analysis. Stokes parameters, implemented as temporal or spatial averages are utilized for this purpose. However, within a polarization speckle field featuring a specific spatial average of Stokes parameters, the polarization state exhibits spatial variations across the speckle pattern. These random polarization fluctuations can be effectively modeled using a particular probability density function (PDF), visually represented on the Poincaré sphere. In this work, we propose and experimentally demonstrate a statistical analysis of polarization speckles using von Mises-Fisher (vMF) distribution on the Poincaré sphere. A complete theoretical basis is developed to investigate the spatial fluctuation of the state of polarization in the polarization speckle using vMF distribution on the Poincaré sphere, including the spatial mean direction, and spatial concentration parameter. Behaviour of the marginal vMF distribution on the axes of the Poincaré sphere and its association with the probability density function of the normalized at-the-point Stokes parameters for three different polarization speckles are examined by experiment and simulation. The experimental results are in good agreement with simulation results and confirm the usefulness of the developed theoretical framework for the analysis of the polarization speckles. Characterization of spatial polarization fluctuation offers significant applications such as in polarimetric analysis, optical sensing, as well as same analogy can be used in quantum optics.

Deep SBP+ 2.0: Physics-driven generation capability enhanced framework to reconstruct space-bandwidth product-expanded image from two image shots

Chen Li, zhibo xiao, and Shouyu Wang

DOI: 10.1364/JOSAA.516572 Received 20 Dec 2023; Accepted 13 May 2024; Posted 14 May 2024  View: PDF

Abstract: The space-bandwidth product (SBP) limitation makes it difficult to obtain an image with both high spatial resolution and a large field of view (FoV) through commonly used optical imaging systems. Though FoV and spectrum stitch provide solutions for SBP expansion, they rely on spatial and spectral scanning, which lead to massive image captures and low processing speed. To solve the problem, we previously reported a physics-driven deep SBP-expanded framework (Deep SBP+) [JOSA A 40, 833-840 20 ]. Deep SBP+ can reconstruct the image with both high spatial resolution and a large FoV from a low-spatial-resolution image in a large FoV and several high-spatial-resolution images in sub-FoVs. In physics, Deep SBP+ reconstructs the convolution kernel between the low- and high-spatial-resolution images and improves the spatial resolution through deconvolution. But Deep SBP+ needs multiple high-spatial-resolution images in different sub-FoVs, inevitably complicating the operations. To further reduce the image captures, we report an updated version of Deep SBP+ 2.0, which can reconstruct an SBP expanded image from a low-spatial-resolution image in a large FoV and another high-spatial-resolution image in a sub-FoV. Different from Deep SBP+, the assumption that the convolution kernel is a Gaussian distribution is added to Deep SBP+ 2.0 to make the kernel calculation simple and in line with physics. Moreover, improved deep neural networks have been developed to enhance the generation capability. Proven by simulations and experiments, the receptive field is analyzed to prove that a high-spatial-resolution image in the sub-FoV can also guide the generation of the entire FoV. Furthermore, we also discuss the requirement of the sub-FoV image to obtain an SBP-expanded image of high quality. Considering its SBP expansion capability and convenient operation, the updated Deep SBP+ 2.0 can be a useful tool to pursue images with both high spatial resolution and large FoV.

Color-appearance-matched data in high-dynamic-range luminance conditions

Jisoo Hwang, YESEUL BAEK, Youngshin Kwak, and YEJIN HONG

DOI: 10.1364/JOSAA.515516 Received 20 Dec 2023; Accepted 10 May 2024; Posted 10 May 2024  View: PDF

Abstract: We report color-appearance-matched data under high-dynamic-range luminance conditions. Theexperimental method and apparatus proposed in a previous study (J. Hwang et al., J. Opt. Soc. Am. A, 36 1940 (2019))were used to measure perceptual color shifts in the R, G, B, Y, RB, BG, GY, and YR groups of 16 samples under fourdual-illumination conditions at luminance levels of (300 cd/m2 and 4,500 cd/m2), (20 cd/m2 and 300 cd/m2), (80 cd/m2and 4,500 cd/m2), and (20 cd/m2 and 4,500 cd/m2). We observed a decrease in lightness for all samples, and hue shiftstoward blue in R, red in reddish YR, and green in BG samples when the luminance changed from low to high.Correlated changes in lightness and chroma, that is, an increase in lightness change and a decrease in chroma changeunder the highest luminance contrast (20 cd/m2 and 4,500 cd/m2), were observed for the Y, GY, and YR samples.

Three-dimensional surface reconstruction from reflectance direction fields with orthogonal multicolor filters

Hiroshi Ohno

DOI: 10.1364/JOSAA.521452 Received 12 Feb 2024; Accepted 10 May 2024; Posted 13 May 2024  View: PDF

Abstract: A three-dimensional (3D) freeform surface reconstruction method is proposed,specifically designed to handle complex surfaces, even those with steep inclinations. Thismethod utilizes a one-shot color mapping imaging system to obtain reflectance direction fieldsusing a stripe multicolor filter positioned in two orthogonal orientations. This imaging systemcan capture reflectance directions that are identifiable by corresponding colors. The multicolorfilter consists of multiple stripe regions, each with a different transmission spectrum.Theoretically, an equation that describes the relationship between reflectance direction fieldsand the reflective 3D surface can be derived based on the geometrical optics. By solving thisequation using a deep neural network (DNN) as a gradient descent method without any trainingdata, the 3D surface can be accurately reconstructed, even for surfaces with steep inclinations.The effectiveness of this method is validated through numerical demonstrations on several 3Dsurfaces, including complex ones with concave and convex areas, as well as steep inclinations.

Twisted vortex Gaussian Schell-model beams, generalized ABCD systems, and multidimensional Hermite polynomials

Milo Hyde, Benjamin Wilson, and Santasri Bose-Pillai

DOI: 10.1364/JOSAA.525568 Received 03 Apr 2024; Accepted 08 May 2024; Posted 09 May 2024  View: PDF

Abstract: We derive the cross-spectral density (CSD) function for a twisted vortex partially coherent beam at the output of a general ABCD system in terms of multidimensional Hermite polynomials (MDHPs). MDHPs, which to our knowledge have not been applied in classical optics, offer notational and computational advantages over prior CSD function representations, which use common (one-dimensional) Hermite polynomials. We explain how to compute MDHPs using the recurrence relation given in the literature and include MATLAB code to generate MDHPs of any order. Lastly, we validate our work experimentally by comparing the measured spectral density of a twisted vortex beam at the output of an asymmetric optical system to predictions from our theoretical CSD function.

Universal Scale Laws for Colors and Patterns in Imagery

Rémi Michel and Mohamed Tamaazousti

DOI: 10.1364/JOSAA.516720 Received 27 Dec 2023; Accepted 22 Apr 2024; Posted 30 Apr 2024  View: PDF

Abstract: Distribution of colors and patterns in images is observed through cascades that adjustspatial resolution and dynamics. Cascades of colors reveal the emergent universal propertythat Fully Colored Images (FCIs) of natural scenes adhere to the debated continuous linearlog-scale law (slope −2.00 ± 0.01) (L1). Cascades of discrete 2 × 2 patterns are derived from pixel squares reductions onto the seven unlabeled rotation-free textures (0000, 0001, 0011, 0012,0101, 0102, 01 ). They exhibit an unparalleled universal entropy maximum of 1.74 ± 0.013 atsome dynamics regardless of spatial scale (L2). Patterns also adhere to the Integral FluctuationTheorem (1.00 ± 0.01) (L3), pivotal in studies of chaotic systems. Images with fewer colorsexhibit quadratic shift and bias from L1 and L3 but adhere to L2. Randomized Hilbert fractalsFCIs better match the laws than basic-to-AI-based simulations. Those results are of interest inNeural Networks, out of equilibrium physics and spectral imagery.