Light Dispersion Research Articles

DUICM Deep Underwater Image Classification Mobdel using Convolutional Neural Networks

Classification of underwater images is a challenging task due to wavelength-dependent light propagation, absorption, and dispersion distort the visibility of images, which produces low contrast and degraded images in difficult operating environments. Deep learning algorithms are suitable to classify the turbid images, for that softmax activation function used for classification and minimize cross-entropy loss. The proposed deep underwater image classification model (DUICM) uses a convolutional neural network (CNN), a machine learning algorithm, for automatic underwater image classification. It helps to train the image and apply the classification techniques to categorise the turbid images for the selected features from the Benchmark Turbid Image Dataset. The proposed system was trained with several underwater images based on CNN models, which are independent to each sort of underwater image formation. Experimental results show that DUICM provides better classification accuracy against turbid underwater images. The proposed neural network model is validated using turbid images with different characteristics to prove the generalization capabilities.

Influence of fourth-order dispersion on the Anderson localization

Anderson localization, which consists in the absence of wave dispersion due to disorder, brought to the field of optics and matter waves has greatly improved our understanding of fundamental processes, such as transport and multiple dispersion of light. In this paper, we investigate the existence of Anderson localization in the interplay of a standard group velocity dispersion and a fourth-order dispersion term in the nonlinear Schrodinger (NLS) equation in the presence of a quasiperiodic linear coefficient. We employ a variational approach with a Gaussian ansatz to describe the center of the localized state, while the tails are studied by direct numerical simulations of the NLS equation. These two approaches are important to distinguish the region of the solution presenting exponential decay, which is the main signature of the Anderson localization. The existence of Anderson localization has been confirmed by numerical simulations even when the system presents a small defocusing nonlinearity. In this sense, we reported how the fourth-order dispersion effect changes the existence region of the localized state by changing the critical values for the transition between the localized and delocalized states.

Dispersive effects in imaging polarimetry based on a wire-grid polarizer

We explore effects of light dispersion by a wire-grid polarizer (WGP) in imaging polarimetry. The dispersive characteristics of a WGP, combined with off-axis scene incidence, cause significant non-uniformity. The normalized performance measure of contrast due to dispersion of WGP exceeded 0.84 for transmittance and 0.90 for extinction ratio (maximum non-uniformity at 1 and 0 for uniform performance). Dispersion also produces a lateral spread in the imaging plane, which may induce spectral image misregistration. Without higher-order excitation, the misregistration can be at the least a few pixels long in the detector. In the presence of higher-order modes, the dispersive misregistration can be severe and critical for polarized scene extraction. The results emphasize the need for an imaging polarimeter to be designed to manage the dispersive effects.

Oscillation spectrum of ferroelectric inclusions in the ferroelectric-dielectric nanocomposite

The spectrum of oscillation of ferroelectric nanoparticles of different shapes was analyzed by the method of finding eigenvalues and eigenfunctions. The oscillation spectrum for elliptical particles obtained by an exact solution using numerical methods. The spectrum of eigenvalues of a particle of elliptic shape better coincides with the spectrum of a particle in the form of a parallelepiped of similar size. The obtained results provide a fundamental opportunity to construct the Green’s function and to evaluate the contribution of the ferroelectric component to the thermodynamic properties of the sample, to the dispersion of light and X-ray waves, etc.

Polariton MultiMode Interferometer Controlled by Optical Stark Shift in WS2 Microcavity

Applications based on the formation of exciton polariton in microcavities provide new avenues for the realization of low-energy consumption and ultrafast devices in areas of photo-electronic and quantum information. Here, we propose a way to design polaritonic multi-mode interferometers in a WS2 microcavity by an all optical control method. The interference phenomenon of polariton is controlled by the well-known optical Stark effect. The optical Stark light changes dispersion (e.g., effective refractive index) of the illuminated region, and generates a waveguide region therein, thus supporting different guided modes of polariton. Multi-mode interference of polariton is then guided by changing the beam pattern or intensity of the Stark light. This proposed method is then theoretically analyzed and proved via effective refractive index calculation and eigenmode analysis of plane waveguide.

Dispersion of Light in the 1D Photonic Crystal

We propose a novel, Kurosawa-like model to evaluate the 1D (Bragg stack-like) mesoporous aluminium oxide photonic crystal. To do this, we analyze the internal potential of the photonic crystal superlattice and get it describing the set of the medium’s polar oscillators. Unlike the atomic oscillators for a common crystal, these ones are the abstract ones. This way, the real photonic crystal can be dealt as an abstract oscillators’ ensemble. The result is fully agreed with the thermodynamics, and makes the theory very powerful. To obtain the oscillators parameters, we compare the theory with the secondary emission spectrum of the crystal, and get the natural frequency and the force for each oscillator. This phenomenological approach allow us to calculate photonic crystal’s optical characteristics, such as the dispersion law for the light in the nanostructure, the secondary emission spectrum of the composite, the speed of light in the crystal and the effective mass of the speed quanta. We establish the room-temperature Bose-Einstein condensation of polaritons in crystal at the photonic bandgap edge. The results are important to the solid-state detection of paraphotons.

(Invited) Electroluminescent Hyperbolic Cooling of Graphene Field Effect Transistors

Heat management is critical for the performance of most modern electronic devices. It was recently proposed that radiative heat transfer - which is usually negligible in the solid state - could be increased in hyperbolic metamaterials, i.e., materials having a hyperbolic electromagnetic dispersion relation. [1] However, artificial metamaterials can be difficult to fabricate and integrate.Fortunately, most of Van der Waals materials are natural hyperbolic metamaterials. Indeed, due to their anisotropic layered structure, the in-plane and out-of-plane optical phonon energy splitting results in a hyperbolic dispersion of light in the Resstrahlen bands. As a consequence, in these materials, the strong light-matter coupling can give rise to a 102-105 increase in the e.m. local density of states, resulting in a dramatic enhancement of the radiative heat transfer. Moreover, the radiative character of heat exchange results in a propagative heat transport via hyperbolic phonon-polariton (HPhP) modes on micrometric scales.We have studied heat transfer in graphene on hexagonal boron nitride: a natural 2D hyperbolic material. In our devices, graphene is used as a versatile heat source in the near field of a hyperbolic material, and as a sensitive noise thermometer. [2] Using mono-, bi- and trilayer graphene, we demonstrate a strong increase of the electron gas cooling resulting in a large temperature drop when the emission of HPhP sets in. This process shares many analogies with electroluminescence, except that it involves near-field modes. We experimentally evidence that the case of graphene is unique, with cooling powers reaching few milliwatts per micron square [3], i.e., nine orders of magnitude larger than previously reported in the literature. Bibliography [1] S. Biehs, et al "Hyperbolic metamaterials as an analog of a blackbody in the near field." Phys. Rev. Lett. 109, 104301 (2012)[2] W. Yang, et al "A Graphene Zener–Klein Transistor Cooled by a Hyperbolic Substrate." Nat. Nanotech. 13, 47 (2018)[3] E. Baudin, et al "Hyperbolic Phonon Polariton Electroluminescence as an Electronic Cooling Pathway", Adv. Funct. Mat.1904783 (2019) Figure 1

Optical Dispersion Characteristics of Polyvinyl Alcohol Reinforced with a Nanoceramic Filler

Polymer films with high refractive index are suitable for a wide range of applications, such as optical fibers, lens and other components for optoelectronic devices. In this work, polyvinyl alcohol films were prepared from aqueous solutions, which were homogenized by ultrasonication. In order to increase the refractive index, the polymer was reinforced with barium titanate nanoparticles, which are previously ultrasonicated for an adequate dispersion inside the host polymer. The dispersion of the refractive index in visible domain was analyzed as a function of filler percent introduced in polymer, showing that an increase in sample s polarizability determined an increase in the refractive index values. The reinforcement caused a decrease of Abbe number indicating a higher light dispersion in the samples. Optical dispersion parameters were extracted from dispersion curves, revealing a reduction of band gap from 3.448 eV for pure polymer to 2.605 eV for the sample containing 2% barium titanate. Doping with the ceramic nanofiller determined a increase in optical conductivity and real part of dielectric constant as a result of appearance of new level states in the band gap. The increase of third order nonlinear optical susceptibility and nonlinear refractive index indicates the suitability of the analyzed nanocomposites for nonlinear optics applications.

An edge detection mechanism using L*A*B color-based contrast enhancement for underwater images

In Ocean investigations, particularly those deployed by the Autonomous Underwater Vehicles, underwater object detection and recognition is an essential task. Edge detection places a key role and considered one of the pre-processing techniques for several deep learning applications. In an underwater environment, the illumination of light, turbulence in the water, suspended particles present in the seafloor are challenging issues to acquire the quality image. The two major problems in underwater imaging are light scattering and color change. In the former case, the vision sensors connected to the underwater vehicles or dive lights used by the divers themselves cause light dispersion and shadows in the seafloor. In the latter case, the occurrence of color distortion is mainly due to the attenuation of the light, hence the images are having dominant colors in the latter case. The conventional techniques are failed to detect the quality edges in the case of underwater images. Our mechanism focused, instead of applying the edge detection algorithm on the input image directly, it is better to apply edge detection algorithm after color correction and contrast enhancement using L*A*B model. Qualitative and quantitative test results demonstrate that the proposed mechanism is giving better results compared with state-of-the-art methods.

Influence of modified light dispersion theory on fermion tunneling radiation in the Einstein–Maxwell–dilaton–axion black hole**This work was supported by the National Natural Science Foundation of China (grant 11273020), the Sichuan Science and Technology Program (grant 2018JY0502) and the Natural Science Foundation of Shandong Province (grant ZR2019MA059).

Based on a light dispersion relationship derived from string theory and quantum gravitational theory, we make an accurate modification to the quantum tunneling radiation rate and black hole temperature at an event horizon in a stationary axial-symmetric Einstein–Maxwell–dilaton–axion black hole. We also analyze our new results and carry out some significant discussions. This work enriches the research content and methods of the frontiers of black hole physics.

Influence of Lorentz Invariation Violation on Arbitrary Spin Fermion Tunneling Radiation in the Vaidya-Bonner Space-Time

In the space-time of the nonstationary spherical symmetry Vaidya-Bonner black hole, an accurate modification of Hawking tunneling radiation for fermions with arbitrary spin is researched. Considering a light dispersion relationship derived from string theory, quantum gravitational theory, and the Rarita-Schwinger equation in the nonstationary spherical symmetry space-time, we derive an accurately modified dynamic equation for fermions with arbitrary spin. By solving the equation, the modified tunneling rate of fermions with arbitrary spin, Hawking temperature, and entropy at the event horizon of the Vaidya-Bonner black hole are presented. We find that the Hawking temperature will increase, but the entropy will decrease compared with the case without the Lorentz Invariation Violation modification.

Remote actuation of light activated shape memory polymers via D-shaped optical fibres

Shape memory polymers (SMPs) and their composites (SMPCs) can hold a programmed temporary shape and recover to their original shape once exposed to a particular external stimulus. The stimulus light has the advantage of being both an excitation energy source and a control signal carrier for remote actuation of SMP materials. Here we present the capability of D-shaped optical fibres to send near infrared (NIR) light into a light activated shape memory polymer composite (LASMPC) which generates the adequate photothermal effect necessary for the shape recovery process of relatively large samples. A D-shaped optical fibre enables dispersion of light through the polished area around the fibre than the dispersion of light through the tip of the fibre. Embedment of a D-shaped optical fibre in a LASMPC creates a single unit smart actuator, which can be remotely activated by light. Remotely controllable smart actuators can be located at any difficult to reach positions and controlled safely with light energy. It would be a breakthrough technology for biomedical, aerospace and many other engineering applications.

Application of Cellulose Nanofibrils Isolated from an Agroindustrial Residue of Peach Palm in Cassava Starch Films

Cellulose nanofibrils (CNF) isolated from the external sheaths of palm peach (Bactris gasipaes) were evaluated as improvers of several characteristics of cassava starch films. The cellulosic material of 10 to 30 nm diameter was produced by mechanic defibrillation. All films were characterized by scanning electron microscopy, thermal analysis, water vapor permeability (WVP), Fourier transform infrared spectroscopy, physical characterizations (solubility, humidity, water activity, thickness, tensile strength and elongation) and optical analysis. The incorporation of CNF as reinforcement caused changes in all properties analyzed, thus differing from the control film (without cellulosic reinforcement). Physical reinforcement was the main effect observed in films containing CNF, according to the mechanical resistance and permeability analyses. Furthermore, such analyses confirmed the increase in tensile strength in 306% and reduction in 26% of WVP for films containing 5.37% nanofibrils, when compared to the control. Higher opacity was verified as more CNF was added to the filmogenic matrix, as a result of the dispersion of light by nano-sized fibrils. No variations in the thermal profiles occurred in films containing CNF or not. Spectroscopic data revealed a possible crosslinking formation between starch and CNF, which can influence positively the tensile strength of such films.

Preparation and mechanical properties of acryl/glass cloth composite materials with low light dispersion

The aim of this study was to prepare transparent acryl/glass cloth composite materials with low light dispersion and high mechanical properties (modulus and strength) by using E-glass cloth and photo-curable acrylate monomers. The influences of the refractive index of the matrix, and the addition of comonomers and silica nanoparticles treated with silane coupling agent on the transparency, wavelength dependence of transmittance, and tensile properties of the composite materials were investigated. The acryl/glass cloth composite material prepared with E-glass cloth and 2,2-bis[4-(acryloxy diethoxy) phenyl] propane (ABPE4) indicated high transmittance at 600 nm, while the transmittance at 400 nm was reduced due to the scattering at the interface of the matrix and the glass fibers because the refractive index difference was large at shorter wavelengths. The usage of a comonomer with a lower refractive index than ABPE4 was an effective way to decrease the refractive index mismatch between the matrix and the glass fibers, and the transparency of the resulting composite material was improved. Moreover, the mechanical performance of the acryl/glass cloth composite material was increased by adding comonomer with a high affinity for glass cloth to matrix. The addition of silica nano particles treated with a silane coupling agent to the matrix was also a useful method for not only improving the transparency, but also improving the mechanical performance, because the nano particles on the fiber surface reduced the refractive index difference and increased the surface area and bonding strength at the interface of the matrix and the fibers.

Underwater Image Enhancement based on Histogram Manipulation and Multiscale Fusion

Abstract The underwater images are a good source of information which explores idea about sea creatures, to study about seafloor hydrother-mal vents. Low contrast, color distortion and poor visual appearance are the major issues that an underwater image has to undergo. Such problems were caused by dispersion and refraction of light as they penetrate from rarer to denser media. The scattering of light reduces color contrast. The influence of water in underwater images is not only due to scattering but also due to the presence of underwater organisms. Here we introduce an improved method for underwater image enhancement based on the fusion method that is capable to restore accurately underwater images. The proposed work takes a single image as the input and a sequence of operations such as white balancing, gamma correction, sharpening, manipulating weight maps are performed on the input image. Finally multiscale image fusion of the inputs is done to obtain the resultant output. In the initial stage, color distorted input image is white balanced to remove the color casts maintaining a realistic subsea image. In the second stage, CLAHE is performed on the gamma corrected image. CLAHE plays a significant role in luminance enhancement of underwater images. At the same time, histogram equalization is performed on the sharpened image. The weight maps analyze image characteristics that properly specify the spatial pixel relationship. Finally in the last stage, multiscale pyramidal fusion of the inputs and weight maps are performed. The fusion performed here is the Pyramidal fusion. Result analysis depict the improvement of the underwater images using proposed method.

Designing refractive index fluids using the Kramers-Kronig relations.

For a number of optical applications, it is advantageous to precisely tune the refractive index of a liquid. Here, we harness a well-established concept in optics for this purpose. The Kramers-Kronig relation provides a physical connection between the spectral variation of the (real) refractive index and the absorption coefficient. In particular, a sharp spectral variation of the absorption coefficient gives rise to either an enhancement or reduction of the refractive index in the spectral vicinity of this variation. By using bright commodity dyes that fulfil this absorption requirement, we demonstrate the use of the Kramers-Kronig relation to predictively obtain refractive index values in water solutions that are otherwise only attained with toxic specialised liquids.

The endotoxin influence on the deformability of red blood cells. (in vitro)

Experiments with endotoxin is an interesting direction for medical applications. It is known that certain abnormalities in the microcirculation in endotoxin shock are related to a reduction of the surface electrical charge and the deformability of red blood cells. The intravascular coagulation of blood cells or “sludge phenomenon” has been observed in endotoxin and other types of shock. To gain a more comprehensive insight into the effect of endotoxin on erythrocyte membranes an assessment was made of the light dispersion in electric field by erythrocyte suspension. Its adoption enables to investigate better the dynamics of endotoxin interaction with erythrocyte membranes, changes in deformability and the like.

Dispersion Engineering With Photonic Inverse Design

Dispersion engineering, such as the design of slow light waveguide systems, is an effective tool for a wide range of photonic applications, but presents a difficult optical design challenge. Most applications require a slow light waveguide design that mitigates group velocity dispersion, and efficient coupling solutions over the slow light operating bandwidth. In this work, we optimize the slow light dispersion relation of a photonic crystal waveguide with three dimensional (3D) inverse design methods. In addition, we design mode couplers for the photonic crystal waveguide. The optimized waveguide supports a slow light mode with a group index of n <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> = 25 and a normalized bandwidth group index product of of 0.38. A compact mode coupler to a strip waveguide is designed with an average efficiency of 92.7% within the slow light operating bandwidth. Lastly, we design a fully etched grating which couples directly to the slow light mode with a 32.5% average efficiency.

Achromatic refractive–diffractive double-relief microprisms

The Fresnel-prism technique has become an important medical option for the diagnostics and treatment of strabismus in children. However, the application of prisms in ophthalmology generally involves chromaticity problems: the formed optical images are distorted due to the dispersion of white light at the microrelief and the applied microprisms reduce the contrast of the images of the test charts, and in turn, the accuracy of eye diagnostics drops. In this study, a novel method was developed for the total chromatism compensation using a special microprismatic refractive–diffractive structure with double microrelief: the first refractive microrelief was used for light beam deflection, whereas the second diffractive one was used for compensating the chromatism of the first microprism. The dispersion chromatism of the first refractive prism and the diffraction chromatism of the second microprism grating are oppositely directed. Thereby, dispersion chromatism can be completely compensated by diffraction grating. The optimal characteristics of these achromatic refractive–diffractive structures were calculated, and the necessary angles and optimal relief pitches of the ophthalmic microprisms were obtained. Achromatic structures were manufactured according to the calculated parameters, and their optical characteristics were experimentally investigated. The main advantage of such optical devices is that they are flat and very thin. The findings indicate the possibility of designing effective achromatic microprisms.

Commercially Available Phototherapy Devices for Treatment of Depression: Physical Characteristics of Emitted Light.

Objective:The purpose of this study was to evaluate key physical properties of commercially available light devices for the treatment of seasonal or nonseasonal depression and to determine whether the devices met clinical criteria, derived from evidence‐based clinical guidelines, for generating adequate light at a reasonable distance, over a reasonable field of illumination, and with an adequate degree of user acceptability.Methods:Twelve manufacturers loaned or donated 24 light therapy devices: 16 light boxes, one light column, four light‐emitting diode beam devices, and three light visors. Each device was evaluated for spectral power distribution, light dispersion, subjective discomfort from glare, adequacy of diffusion, photopic illuminance (in lumens per square meter [lux]), melanopic illuminance relative to photopic illuminance (efficacy ratio), and blue light hazard relative to melanopic illuminance (protection ratio).Results:Physical properties of emitted light varied widely among devices. Only seven larger light boxes satisfied the three clinical criteria. Some devices advertised as “10,000‐lux” devices produced this intensity only at unreasonably close distances, over a restricted field, or with unacceptable glare or unevenness of illumination. Five other devices emitted light with physical properties whose efficacy is less supported by research, although these devices may be useful for some patients.Conclusions:These results should help clinicians identify appropriate devices for patients seeking light therapy for seasonal or nonseasonal depression. Device selection is key to ensuring that patients receive evidence‐supported doses of light.