Optical Disk Research Articles

Fundus Imaging-Based Healthcare: Present and Future

A fundus image is a two-dimensional pictorial representation of the membrane at the rear of the eye that consists of blood vessels, the optical disc, optical cup, macula, and fovea. Ophthalmologists use it during eye examinations to screen, diagnose, and monitor the progress of retinal diseases or conditions such as diabetes, age-marked degeneration (AMD), glaucoma, retinopathy of prematurity (ROP), and many more ocular ailments. Developments in ocular optical systems, image acquisition, processing, and management techniques over the past few years have contributed to the use of fundus images to monitor eye conditions and other related health complications. This review summarizes the various state-of-the-art technologies related to the fundus imaging device, analysis techniques, and their potential applications for ocular diseases such as diabetic retinopathy, glaucoma, AMD, cataracts, and ROP. We also present potential opportunities for fundus imaging–based affordable, noninvasive devices for scanning, monitoring, and predicting ocular health conditions and providing other physiological information, for example, heart rate (HR), blood components, pulse rate, heart rate variability (HRV), retinal blood perfusion, and more. In addition, we present different types of technological, economical, and sociological factors that impact the growth of the fundus imaging–based technologies for health monitoring.

Deep Learning-assisted Retinopathy of Prematurity (ROP) Screening

Retinopathy of prematurity (ROP) is a leading cause of blindness in premature infants worldwide, particularly in developing countries. In this research, we propose a Deep Convolutional Neural Network (DCNN) and image processing-based approach for the automatic detection of retinal features, including the optical disc (OD) and retinal blood vessels (BV), as well as disease classification using a rule-based method for ROP patients. Our DCNN model uses YOLO-v5 for OD detection and either Pix2Pix or a U-Net for BV segmentation. We trained our DCNN models on publicly available fundus image datasets of size 1,117 and 288 for OD detection and BV segmentation, respectively. We evaluated our approach on a dataset of 439 preterm neonatal retinal images, testing for ROP Zone and 6 BV masks. Our proposed system achieved excellent results, with the OD detection module achieving an overall accuracy of 98.94% (when IoU 0.5) and the BV segmentation module achieving an accuracy of 96.69% and a Dice coefficient between 0.60 and 0.64. Moreover, our system accurately diagnosed ROP in Zone-1 with 88.23% accuracy. Our approach offers a promising solution for accurate ROP screening and diagnosis, particularly in low-resource settings, where it has the potential to improve healthcare outcomes.

Quantum vortices of strongly interacting photons

Vortices are topologically nontrivial defects that generally originate from nonlinear field dynamics. All-optical generation of photonic vortices—phase singularities of the electromagnetic field—requires sufficiently strong nonlinearity that is typically achieved in the classical optics regime. We report on the realization of quantum vortices of photons that result from a strong photon-photon interaction in a quantum nonlinear optical medium. The interaction causes faster phase accumulation for copropagating photons, producing a quantum vortex-antivortex pair within the two-photon wave function. For three photons, the formation of vortex lines and a central vortex ring confirms the existence of a genuine three-photon interaction. The wave function topology, governed by two- and three-photon bound states, imposes a conditional phase shift of π per photon, a potential resource for deterministic quantum logic operations.

Spin Hall effects in the sky

In many areas of physics, the propagation of wave packets carrying intrinsic angular momentum is generally influenced by spin–orbit interactions. This is the main mechanism behind spin Hall effects, which result in wave packets following spin-dependent trajectories. Spin Hall effects have been observed in several experiments for electrons in condensed matter systems and for light propagating in inhomogeneous optical media. Similar effects have also been predicted for wave packets propagating in inhomogeneous gravitational fields. We give a brief introduction to gravitational spin Hall effects, emphasizing the analogies with the spin Hall effect of light in optics. Furthermore, we review the most promising astrophysical avenues that could lead to experimental observations of the gravitational spin Hall effect.

Transparent hexagonal Yb: S-FAP ceramics: Investigation of HP sintering kinetics on densification process and microstructural evolution

Given the downsizing and high integration of laser diodes in recent decades, Yb: Sr5(PO4)3F (S-FAP) crystal materials are predicted to be employed as an all-solid laser medium to produce more energy for inertial nuclear fusion. The effects of various sintering conditions on the microstructure evolution and properties of 2 at. % Yb: S-FAP transparent ceramics by hot pressing sintering were systematically investigated in this work, which including sintering temperature, sintering pressure, heating rate, and holding time. When other sintering variables are held constant, the results reveal that a sintering temperature of up to 1050 °C results in visible grain development, substantial optical scattering, and even a significant carburizing impact at 1100 °C. Excessive sintering dwell time will result in grain development, and a high sintering holding time will result in the emergence of intergranular pores, lowering the optical quality of ceramics. The optimal heating rate range for as-synthesized ceramic is found to be 5–15 °C/min. Moreover, the grain development process of Yb: S-FAP transparent ceramics is determined to be grain boundary diffusion, with an activation energy of 239.4 kJ/mol during hot pressing sintering. Meanwhile, the as-prepared sample has excellent mechanical properties such as Vickers hardness of 7.47 ± 0.045 GPa, which are highly competitive when compared to other Yb-doped optical ceramic media such as Y2O3, YAG, Lu2O3, and so on. Finally, the transmittance was interpreted based on the microstructures of the as-synthesized ceramic samples and the Rayleigh-Gans-Debye scattering theory.

Spectroscopic properties of Er3+-doped barium phosphate glasses for optical gain media

Barium metaphosphate glasses (PBaLa) doped with erbium (Er3+) ions have been prepared by melt quenching method and studied their optical, structural characteristics by using FT-IR, absorption, radiative de-excitation spectra, decay curves and up-conversion measurements. Judd-Ofelt (Ωλ, λ = 2,4 and 6) parameters have been determined using the absorption transitions of the Er3+(1.0 mol %)-doped glasses which are in turn taken to predict the radiative characteristics that include branching ratio (βR), radiative emission probability (AR) and lifetime (τR) of some important fluorescent levels of Er3+:glasses. Visible emission spectra measured under 378 nm excitation reveals three emission transitions at 663 (4F9/2 → 4I15/2), 547 (4S3/2→ 4I15/2) and 524 nm (2H11/2 → 4I15/2) corresponding to Er3+ ions. Among these, the green emission at 547 nm is relatively intense. Near-Infrared emissions were measured by exciting at 980 nm which exhibits broad emission at 4I13/2→ 4I15/2 (1.53 µm). The stimulated emission cross-section (σemi), FWHM and gain bandwidth (σemi× FWHM) were predicted to be 13.58 × 10-21 cm−2, 59 nm and 801.2 cm3, respectively, for PBaLaEr1.0 glass. The lifetime of 4I13/2 level has been shortened from 2.53 to 0.8 ms with an increase in Er3+ ions concentration from 0.1 to 2 mol %. NIR to visible up-conversion has also been measured for various concentrations of Er3+-doped PBaLaEr glasses with 980 nm excitation. These findings indicate that the Er3+-doped PBaLaEr glasses can be considered for waveguide laser and optical amplifier applications at 1.53 µm.

An effective semilocal model for wave turbulence in two-dimensional nonlinear optics

The statistical evolution of ensembles of random, weakly interacting waves is governed by wave kinetic equations (WKEs). To simplify the analysis, one frequently works with reduced differential models of the wave kinetics. However, the conditions for deriving such reduced models are seldom justified self-consistently. Here, we derive a reduced model for the wave kinetics of the Schrödinger–Helmholtz equations in two spatial dimensions, which constitute a model for the dynamics of light in a spatially nonlocal, nonlinear optical medium. This model has the property of sharply localizing the frequencies of the interacting waves into two pairs, allowing for a rigorous and self-consistent derivation of what we term the semilocal approximation model (SLAM) of the WKE. Using the SLAM, we study the stationary spectra of Schrödinger–Helmholtz wave turbulence, and characterize the spectra that carry energy downscale, and waveaction upscale, in a forced-dissipated setup. The latter involves a nonlocal transfer of waveaction, in which waves at the forcing scale mediate the interactions of waves at every larger scale. This is in contrast to the energy cascade, which involves local scale-by-scale interactions, familiar from other wave turbulent systems and from classical hydrodynamical turbulence.

New mathematical formulas for more accurate physical descriptions of the optical and optoelectric conductivities of an optical medium

New mathematical formulas for more accurate physical descriptions of the optical and optoelectric conductivities of an optical medium

Kinematic analysis of the super-extended H I disk of the nearby spiral galaxy M 83

We present new H I observations of the nearby massive spiral galaxy M 83 taken with the JVLA at 21″ angular resolution (≈500 pc) of an extended (∼1.5 deg2) ten-point mosaic combined with GBT single-dish data. We study the super-extended H I disk of M 83 (∼50 kpc in radius), in particular disk kinematics, rotation, and the turbulent nature of the atomic interstellar medium. We define distinct regions in the outer disk (rgal> central optical disk), including a ring, a southern area, a southern arm and a northern arm. We examine H I gas surface density, velocity dispersion, and noncircular motions in the outskirts, which we compare to the inner optical disk. We find an increase of velocity dispersion (σv) toward the pronounced H I ring, indicative of more turbulent H I gas. Additionally, we report over a large galactocentric radius range (until rgal ∼ 50 kpc) where σv is slightly larger than thermal component (i.e., > 8 km s−1). We find that a higher star-formation rate (as traced by far UV emission) is not necessarily always associated with a higher H I velocity dispersion, suggesting that radial transport could be a dominant driver for the enhanced velocity dispersion. Furthermore, we find a possible branch that connects the extended H I disk to the dwarf irregular galaxy UGCA 365 and that deviates from the general direction of the northern arm. Lastly, we compare mass flow rate profiles (based on 2D and 3D tilted ring models) and find evidence for outflowing gas at rgal ∼ 2 kpc, inflowing gas at rgal ∼ 5.5 kpc, and outflowing gas at rgal ∼ 14 kpc. We caution that mass flow rates are highly sensitive to the assumed kinematic disk parameters, in particular to inclination.

Tuning of the Brillouin scattering properties in microstructured optical fibers by liquid infiltration

We demonstrate the possibility to modify the Brillouin scattering properties of a microstructured pure-silica core optical fiber, by infiltrating a liquid inside its holes. In particular, we show that the dependence of the Brillouin frequency shift (BFS) on the temperature can be reduced by infiltration, owing to the large negative thermo-optic coefficient of the liquid. Infiltrating a chloroform-acetonitrile mixture with a refractive index of 1.365 inside the holes of a suspended-core fiber with a core diameter of 3 µm, the BFS temperature sensing coefficient is reduced by ≈ 21%, while the strain sensitivity remains almost unaltered. Besides tuning the temperature sensing coefficient, the proposed platform could find other applications in Brillouin sensing, such as distributed electrical and magnetic measurements, or enhanced Brillouin gain in fibers infiltrated with high nonlinear optical media.

Pure quartic wave modulation in optical fiber with the presence of self-steepening and intrapulse Raman scattering response

Modulational instability (MI) is addressed in an optical fiber under competing effects between pure-quartic dispersion (PQD), self-steepening, and intrapulse Raman response. The self-steepening parameter reduces the maximum MI gain and the frequency bandwidth. Under the combined effects of the self-steepening and intrapulse Raman scattering, more spectral windows appear in the gain spectrum, induced by the increasing Raman effect. Numerical results fully concur with the theoretical predictions. The MI is manifested by the emergence of ultrashort pulses trains and rogue wave breathing trains. Under increasing self-steepening effect, asymmetric sidebands, reversible via the Raman scattering effect, appear in the spectral and temporal evolution of the pulse trains, which probes the tunability of energy transfer between the mode during signal propagation. Our results open up further perspectives for exploring mechanisms to generate ultrashort pulses in PQD optical media under higher-order nonlinearities, with applications to silicon photonic crystal waveguides and silica photonic crystal fibers.

Architecture of Hardware and Software for Unidirectional Data Transmission in Computer Networks

The results of a study of the architecture of hardware and software for unidirectional data transmission in computer networks are presented. The architecture is presented in the form of optical galvanic isolation, media converters and proxy servers, excluding bidirectional data transmission at the hardware level. Work on unidirectional data transmission is carried out on the basis of the UDP transport protocol, which provides operation without establishing bidirectional interaction. Unidirectional data transfer is carried out by a proxy server running a special sender’s software that performs unidirectional data file transfer. This software converts the source data file into a unidirectional stream of UDP datagrams. To receive a unidirectional stream of UDP datagrams, a proxy server is used, on which the recipient’s special software is running. The receiving proxy server receives, processes and generates the source data file. The reliability of the unidirectional transmission of data files is ensured by redundancy (multiple transmission) and checksum verification.

Optical solitons in curved spacetime

Light propagation in curved spacetime is at the basis of some of the most stringent tests of Einstein’s general relativity. At the same time, light propagation in media is at the basis of several communication systems. Given the ubiquity of the gravitational field, and the exquisite level of sensitivity of optical measurements, the time is ripe for investigations combining these two aspects and studying light propagation in media located in curved spacetime. In this work, we focus on the effect of a weak gravitational field on the propagation of optical solitons in non-linear optical media. We derive a non-linear Schrödinger equation describing the propagation of an optical pulse in an effective, gradient-index medium in flat spacetime, encoding both the material properties and curved spacetime effects. In analyzing the special case of propagation in a 1D optical fiber, we also include the effect of mechanical deformations and show it to be the dominant effect for a fiber oriented in the radial direction in Schwarzschild spacetime.

Random lasing in composites of CdSe/CdZnS colloidal quantum wells and silica nanoparticles

Colloidal quantum wells (CQWs) are a new type of atomic flat semiconductor nanocrystals, which present excellent opportunities as optical gain materials owing to their ultranarrow emission linewidth, tunable emission wavelength, suppressed Auger effect, and large gain cross-section. Here we synthesized monodispersed silica nanospheres and CdSe(4ML)/CdZnS core/shell CQWs. We observed random lasing by optically pumping the composites of CdSe(4ML)/CdZnS core/shell CQWs and silica nanoparticle scattering layer. The random lasing ranges from 615 nm to 625 nm with a threshold of 0.55 mJ cm−2. Fourier analysis reveals that sufficient Rayleigh scattering is the primary reason for the low threshold in the spatial frequency spectrum of the random laser. Our findings suggest that CQWs can serve as an efficient optical gain medium for random lasing, enabling various applications such as speckle-free laser imaging, random number generation for secure communication, chemical and biological sensing, high brightness and energy-efficient lighting, and label-free bioimaging.

Reflection of stepwise twisted stratified anisotropic optical media

Stratified optical films have fascinating optical properties and many important applications. Here we report a theoretical study of stepwise twisted stratified anisotropic optical media. We used Fourier transform to analyze the helical component of the dielectric tensor of the media. We then used the Berreman 4 × 4 method to calculate the reflection spectrum of the media. We discovered that right-handed and left-handed helices could coexist in stepwise twisted layers, which producing a simultaneous reflection of right-handed and left-handed circularly polarized light. This feature can be used to produce films with superior reflection properties, such as high reflectance, broad bandwidth reflection and short wavelength reflection.

Chirped periodic and localized waves of the (1+2)-dimensional chiral nonlinear Schrödinger equation

We study the existence and stability of nonlinearly chirped periodic waves and soliton structures in an optical medium wherein the pulse propagation is governed by the (1+2)-dimensional chiral nonlinear Schrödinger equation. An exact periodic wave solution is presented for the model equation in the presence of all physical processes by using the complex envelope traveling-wave ansatz. A class of optical gray-type solitons is obtained in the special long wave limit. The properties of these structures such as the velocity and wave number are determined by the system parameters. It is found that the frequency chirp accompanying these optical waves is inversely proportional to the intensity of the wave and its amplitude can be controlled by choosing the dispersion parameter appropriately. In addition, the stability of these waveforms is discussed numerically under some initial perturbations. The results show that those nonlinear waves can propagate in a stable fashion in the nonlinear medium under finite initial perturbations, such as amplitude and white noise.

Segmentation of optic disc in retinal images for glaucoma diagnosis by saliency level set with enhanced active contour model

<p>Glaucoma is an ophthalmic disease which is among the chief causes of visual impairment across the globe. The clarity of the optic disc (OD) is crucial for recognizing glaucoma. Since existing methods are unable to successfully integrate multi-view information derived from shape and appearance to precisely explain OD for segmentation, this paper proposes a saliency-based level set with an enhanced active contour method (SL-EACM), a modified locally statistical active contour model, and entropy-based optical disc localization. The significant contributions are that i) the SL-EACM is introduced to address the often noticed problem of intensity inhomogeneity brought on by defects in imaging equipment or fluctuations in lighting; ii) to prevent the integrity of the OD structures from being compromised by pathological alterations and artery blockage, local image probability data is included from a multi-dimensional feature space around the region of interest in the model; and iii) the model incorporates prior shape information into the technique, for enhancing the accuracy in identifying the OD structures from surrounding regions. Public databases such as CHASE_DB, DRIONS-DB, and Drishti-GS are used to evaluate the proposed model. The findings from numerous trials demonstrate that the proposed model outperforms state-of-the-art approaches in terms of qualitative and quantitative outcomes.</p>

A Numerical Mode Matching (NMM) Method for Optical Fibers With Kerr Nonlinearity

Recently, the reshaping of the transverse light field profile in nonlinear multimode fibers (MMFs) has attracted great attentions. However, the electromagnetic (EM) fields in such nonlinear media cannot be easily and accurately calculated by using the traditional computational electromagnetics methods due to the nonlinearity of Kerr optical materials in graded-index (GRIN) MMFs. The iterative division method based on the 2.5-D spectral element numerical mode matching (SNMM) method is developed to address this problem. The SNMM method is a semi-analytical method, which can effectively reduce the computational costs to obtain highly accurate solutions. Starting from the numerical results of SNMM, the iterative division method solves electromagnetic fields of the linear-to-nonlinear transition process together iteratively. In this work, several improvements are proposed to extend the SNMM for Kerr optical nonlinear MMFs. The governing equations with anisotropic permittivity with Kerr optical nonlinear media are established in the cylindrical coordinate system. The absorbing boundary condition (ABC) is introduced to replace the perfectly matched layer (PML) so that the eigenmodes of a waveguide can be obtained accurately. Numerical results show the validity, accuracy and advantages of the proposed method in simulated MMFs.

Infrared fiber bundle image super-resolved based on computational imaging

As the representative of flexibility in optical imaging media, in recent years, fiber bundles have emerged as a promising architecture in the development of compact visual systems. Dedicated to tackling the problems of universal honeycomb artifacts and low signal-to-noise ratio (SNR) imaging in fiber bundles, the iterative super-resolution reconstruction network based on a physical model is proposed. Under the constraint of solving the two subproblems of data fidelity and prior regular term alternately, the network can efficiently “regenerate” the lost spatial resolution with deep learning. By building and calibrating a dual-path imaging system, the real-world dataset where paired low resolution (LR) - high resolution (HR) images on the same scene can be obtained simultaneously. Numerical results on both USAF target and complex target objects demonstrate that the algorithm can restore high contrast images without pixilated noise. On the basis of super-resolution reconstruction, compound eye image composition based on fiber bundle is also realized in this paper for the actual imaging requirements. The proposed work is the first to apply a physical model-based network structure to fiber bundle imaging in the long-wave infrared band, effectively promoting the engineering application of thermal radiation detection.

Spectacle, Surveillance, and the Ironies of Visual Politics in the Age of Autonomous Images

Considering formative twentieth-century theories in relation to contemporary technosocial developments, this article examines ideas of spectacle and surveillance as ways of approaching visual politics. I argue that the historically important relationship between the visual and political fields is now intensifying and mutating. First discussing Guy Debord’s The Society of the Spectacle, I show how his influential approach proves inadequate to the politics of image-saturated societies. I next show how critics of imperial and racial spectacles, from Michael Rogin to Claudia Rankine and Tina Campt, provide better ways of engaging power and political contestation in the visual field. Third, I examine how Michel Foucault deployed notions of spectacle in his own work but argued for leaving the term behind, presenting surveillance as not just a different modality of power but also spectacle’s temporal successor. This account remains essential for both historical understanding and reckoning with contemporary surveillance. Fourth, however, as Simone Browne argues, Foucault’s separation between spectacle and surveillance is too stark, his history too prone to occlude race. Furthermore, recent surveillance technologies and practices have changed in ways that confound his terms, while extending and also altering the racial dynamics explored earlier in the essay. Today, even surveillance based on optical media contributes to a “postvisual” image world in which algorithmic, machine-machine communication abets forms of power neither tied to human perception nor graspable as subject formation. With surprising assistance from Debord, I end by discussing the significant theoretical and political challenges posed by the ironies of postvisual visuality.