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A new dielectric constant estimation approach for the lunar surface using Mini-RF synthetic aperture radar (SAR) data and Chandrayaan-2 SAR data is presented in this work. Both the SAR systems are based on a hybrid-polarimetry (hybrid-pol) configuration that transmits a circularly polarized wave and coherently measures the backscattered wave by dual orthogonal linearly polarized channels. From the three-component hybrid-pol SAR decomposition technique, the ratio of the Fresnel reflection coefficients for horizontal and vertical polarization transmission can be estimated. This ratio, which is referred to as the co-polarization ratio, is used by the proposed methodology to find the real value of the dielectric constant. For performance validation, the proposed method is implemented on the Mini-RF hybrid-pol SAR data acquired over Apollo 17 landing sites. The values of the real part of dielectric constant are estimated for six different regions covering the collection sites of six Apollo 17 samples: 72,441, 73,241, 74,241, 75,081, 76,001, and 79,135. The results obtained using the proposed method are found to be in good agreement with the laboratory-measured results of the corresponding samples. Furthermore, the proposed methodology is also implemented on the Chandrayaan-2 hybrid-pol SAR data acquired over the Biot crater region. Various small areas possessing different possible surface characteristics, situated inside and outside the Biot crater, are being analyzed for validation.

This paper proposes a fiber length matching method that reduces the influence of Fresnel reflection in a hybrid fiber resonator for the resonant fiber optic gyroscope (RFOG). A transfer model of the fused points inside and outside the fiber resonator is first built. Using the transfer model, we find that when the optical path ratio of the photonic bandgap fiber (PBF) is half of the entire fiber ring, the secondary resonant frequency points caused by Fresnel reflection coincide with the main resonant frequency points of the resonator, and the resonant depth becomes equal. The simulation result of the resonance curve demonstrates this theory. To validate our deduction, two hybrid resonators are obtained with PBF and polarization-maintaining fiber (PMF). The optical path ratio of one resonator is 0.5, and the other is approximately 0.2. The results show that after the fiber length matching, the resonance depth difference of the resonator is less than 1.8%, which is the best reported index of a fused PBF fiber resonator to our knowledge and 24.9% less than that of the other resonator. The experimental result also shows that the total loss of the two PBF-PMF fused points is less than 1.3 dB. Our scheme effectively reduces the effect of the Fresnel reflection at the fusing point in the PBF-PMF resonator, which is expected to achieve accurate resonance frequency detection of the RFOG.

The diffraction of light by reflective holographic gratings in a layer placed between the coating and the substrate having refractive indices different from the average refractive index of the inserted layer is investigated. Significant differences between the reflection and transmission coefficients of the light diffracted on such a holographic grating with a change in the modulation amplitude of the refractive index of the layer, and the reflection and transmission coefficients of reflection gratings in matched structures are established. It is shown that at a large width of the layer in which the reflective holographic grating is located, there is a significant rotation of the plane of polarization of reflected and transmitted diffracted waves with a change in the modulation amplitude of the layer, caused by Fresnel reflection of light at the layer boundaries.

We demonstrate co-doped phosphor-in-glass (PiG) for high performance white light-emitting diodes (WLEDs) employing reduction of red/green phosphors interaction and antireflection coating (ARC). In this study, the novelties are a suitable selection of the 650-nm red and 540-nm green phosphor materials to reduce the mutual interaction between the emission of green phosphor and the absorption of red phosphor, evidenced by photoluminescence spectroscopy, and then an ARC on both sides of the PiG to reduce Fresnel reflection loss. Therefore, the PiG with high luminous efficiency of 63 lm/W, high color rendering index (CRI) of 96, and less amount of phosphor material are obtained. The overall luminous efficiency of the PiG-based WLED is improved by about 15% and the total amount of phosphors is reduced by about 58%. This proposed of co-doped PiG with excellent performance and less amount of phosphor material usage is essential to meet the economic requirement for high-quality WLEDs indoor lighting applications.

In this paper, a new optical fiber corrosion sensor based on metallic bilayers is described. The detection region is located at a fiber end facet and we present simulations as well as experimental results in controlled lab conditions for Ti(10 nm)/Al(10 nm) and Ni(5 nm)/Al(5 nm) bilayers. We perform the characterization of the device by numerical simulations using the COMSOL Multiphysics software, and with an analytical model, which makes use of the Fresnel equations. According to the simulations, the change in the reflected optical signal over time is related to variations in the thickness of the metallic films by the corrosive process and, consequently, the corrosion rate in each metal of the bilayer can be obtained. Upon the simulation results, sensor devices were fabricated by depositing thin metallic films on the cleaved facet of the optical fiber using the sputtering method. We show that the use of a metallic bilayer as a transducer, instead of a monolayer, improves the sensor measuring interval (20 ± 1 nm) and provides information about the corrosion rate along the corrosion process.

In this paper, a new robust computational method that applies the geometrical theory of diffraction (GTD) in conjunction with the ray tracing (RT) technique is developed to evaluate the electromagnetic scattering pattern due to a plane wave represented as beam of parallel rays incident on a rough surface of quite arbitrary statistical parameters. The development of the proposed technique is explained in detail taking into consideration the generation of the geometrical model of the rough surface. The Fresnel reflection model is applied under the assumption of arbitrary electrical and optical properties of the rough surface material. Also the polarization of the plane wave primarily incident on the rough surface is taken into consideration. The algorithm developed in the present work accounts for multiple bounces of an incident ray and, hence, it can be considered arbitrary higher-order GTD-RT technique. The accuracy of the obtained results is verified through the comparison with the experimental measurements of the scattering pattern of a light beam incident on rough sheets with specific statistical properties. The numerical results of the present work are concerned with investigating the dependence of the scattering pattern on the surface roughness, refractive index, angle of incidence, and the resolution of the geometric model of the rough surface. Also, it is shown that, for limited resolution of the rough surface model, the accuracy of the calculated scattered field depends on the angle of incidence of the primary beam and the surface roughness.

Terahertz (THz) spectroscopy is a powerful tool for unambiguously extracting complex-valued material properties (e.g., refractive index, conductivity, etc.) from a wide range of samples, with applications ranging from materials science to biology. However, extracting complex refractive indices from THz time-domain spectroscopy data can prove challenging, especially for multilayer samples. These challenges arise from the large number of transmission-reflection paths the THz pulse can take through the sample layers, leading to unwieldy strings of Fresnel coefficients. This issue has often been addressed using various approximations. However, these approximations are only applicable to specific classes of samples and can give erroneous results when misapplied. An alternative to this approach is to programmatically model all possible paths through the sample. The many paths through the sample layers can be modeled as a tree that branches at every point where the paths diverge, i.e., whenever the pulse can either be transmitted or reflected. This tree can then be used to generate expressions relating the unknown refractive index to the observed time domain data. Here, we provide a freely available open-source package implementing this method as both a MATLAB library and a corresponding graphical user interface, which can also be run without a MATLAB license (https://github.com/YaleTHz/nelly). We have tested this method for a range of samples and compared the results to commonly used approximations to demonstrate its accuracy and wide applicability. Our method consistently gives better agreement than common approximations.

This letter proposes a low-cost non-line-of-sight (NLOS) identification and mitigation technique for ultra-wideband (UWB) ranging in both static and dynamic environments. Unlike conventional ranging that employs one mobile tag and a single fixed anchor at a known location, this technique utilizes two anchors and one tag. By utilizing Fresnel zones, this approach is effective in variable environments without requiring large quantities of prior knowledge. The proposed method was evaluated using simulations and experiments, achieving an identification accuracy of 96.41%. After error mitigation, ranging errors were reduced by 88.80%, 69.91%, and 96.12% in line-of-sight (LOS), NLOS, and dynamic NLOS environments, respectively.

İki boyutlu (2B) malzemeler, bu malzemelerin ürettiği cihazların yüksek performans göstermesi nedeniyle birçok araştırmacının ilgisini çekmiştir. 2B malzeme elde etmek için solüsyon tabanlı kimyasal sentez, kimyasal buhar biriktirme (KBB), moleküler ışın epitaksisi, atomik katman biriktirme, darbeli lazer biriktirme (DLB) gibi işlemler sırasında saatler gerektiren farklı üretim yöntemleri bulunmaktadır. 2B yapılar elde edildikten sonra, kusurları da dahil olmak üzere özellikleri farklı karakterizasyon araçları ile ortaya çıkarılmalıdır. Karakterizasyon süreci de üretim süreci gibi zaman ve uzmanlık gerektirir. Bu açıdan, üretilen örneklerin pratik ve hızlı sınıflandırılması için Evrişimli Sinir Ağları (ESA) gibi derin öğrenme yöntemleri bir çözüm olabilir. Ancak, yukarıda bahsedilen uzun deneysel süreçler nedeniyle araştırma laboratuvarlarının çoğunda yeterli sayıda örnek bulunmamaktadır. Bu çalışmada, farklı elektronik uygulamalarda yüksek potansiyele sahip, yaygın olarak çalışılan bir 2B yarı iletken olan MoS2'nin yapay olarak oluşturulmuş görüntülerini kullanan bir CNN algoritmasının performansı sunulmaktadır. Normal ve kusurlu MoS2 pullarını içeren sentetik optik mikroskobik görüntüler, Fresnel Denklemleri kullanılarak farklı malzemeler üzerine gelen ışığın yoğunlukları ile oluşturulur. Normal ve kusurlu örnekleri tespit etmek için derin bir CNN algoritması oluşturulmuştur. Doğruluk ölçümlerinin sonuçları, CNN'nin gelecekte yeterli sayıda gerçek görüntü ile iki boyutlu malzemelerin karakterizasyonu için kullanılabileceğini göstermiştir.

Based on previous reports on the optical microscopy contrast of mechanically exfoliated few layer CrCl 3 transferred on 285 nm and 270 nm SiO 2 on Si(100), we focus on the experimental determination of an effective mean complex refractive index via a fitting analysis based on the Fresnel equations formalism. Accordingly, the layer and wavelength-dependent absorbance and reflectance are calculated. Layer and wavelength-dependent optical contrast curves are then evaluated demonstrating that the contrast is significantly high only around well-defined wavelength bands. This is validated a posteriori, by experimental UV-Vis absorbance data. The present study aims to show the way towards the most reliable determination of thickness of the 2D material flakes during exfoliation.

We report a theoretical framework to explain the characteristics of Fabry-Pérot (FP) resonances excited in a thin film-based grating consisting of a thin gold layer and a rectangular dielectric grating in the sub-wavelength and near-wavelength grating regimes. The zeroth-order diffraction inside the grating layer forms an FP resonant cavity with effective refractive index arising from an averaging effect between the refractive indices of the grating material and the filling material between the grating grooves. A simplified model based on Fresnel equations and phase matching condition is proposed to predict the FP resonant mode for the grating structure, this is compared with rigorous coupled-wave analysis to determine its range of validity. We also compare the performance of the proposed structure with other thin film-based interferometers for refractive index sensing applications, in terms of, sensitivity, full width at half maximum, figure of merit and dynamic range. The proposed structure has a full width at half maximum around 10 times to 60 times narrower than conventional surface plasmon resonance and conventional FP resonators. Thus, the figure of merit is higher than Kretschmann based surface plasmon resonance and FP structures by a factor of 20 and 2 respectively with a wider dynamic range. The total energy stored in the grating resonant cavity is 5 and 20-fold greater than the surface plasmon resonance configuration and the conventional FP structures. Since the resonator discussed here is an open structure, it is far better suited for liquid sensing compared to a closed FP structure.

In this work, we propose a signal processing algorithm to enlarge the refractive index dynamic range (RIDR) of the Fresnel reflection-based fiber Fabry–Perot (FR-FFP) sensors. In this approach, the reflected spectrum of the FR-FFP interferometer is modulated by an impulse function. The processed optical spectrum includes the superposition of the original wavelength-modulated interference pattern and an ultra-narrow peak, produced by the impulse function. The wavelength of that peak coincides with a maximum of the interference fringe. In Fourier domain, the spectrum exhibits the characteristic interference peaks superimposed to a broad step. In Fourier domain the amplitude of one of the interference peaks is modulated by refractive index (RI) of the external medium, but the amplitude of the step is not affected. It was possible to stablish a simple correspondence between the amplitude of the interference peak and the RI of the external medium in a wide dynamic range [1.000, 2.000]. The inclusion of the impulse function, which produces the step in the Fourier domain, eliminates the RI ambiguity of the FR-FFP allowing the enlargement of the RIDR.

This article investigates wireless power transfer in the Fresnel zone using cylindrical vector beams. First, a generalized coupling coefficient between two circular apertures in the Fresnel zone is derived. From the generalized coupling coefficient, explicit coupling coefficients between two circular (focused or unfocused) apertures supporting Gaussian, Bessel–Gaussian, and Laguerre–Gaussian beams are found in closed form. The analytically derived coupling coefficients and corresponding efficiencies are compared with those obtained through numerical integration of the reaction integral, as well as the results of a commercial electromagnetic solver. Then, it is demonstrated that a finite aperture, which supports a cylindrically apodized Bessel beam, is close to the optimal illumination. Also, it is shown that Bessel beams have a higher coupling coefficient than conventional Gaussian beams. Finally, the optimal aperture illumination is found numerically by constructing an aperture field from a summation of Bessel beams with different axicon angles. That is, the complex amplitude of each Bessel beam is found that maximizes coupling between the two apertures. The optimal illumination radiates a magnetic field equal to the complex conjugate of the receiver aperture’s electric field. This observation agrees with those for optimal illumination in the context of a confocal optical resonator.

Introduction. Landing is the most challenging and dangerous part of the helicopter flight. The development of systems facilitating safe landing is a priority task for both Russian and foreign engineering companies. Landing on unprepared sites covered with snow and ice may be determined by the need to deliver cargo and ammunition in combat conditions, during search and rescue operations, evacuations of victims, etc.Aim. Development of a method for remote assessment of the snow and ice cover based on the results of oblique sensing of the underlying surface with a radio signal with vertical polarization.Materials and methods. In the MatLab environment, the authors conducted numerical simulations of Fresnel reflection coefficients of echo signals with vertical polarization in the 40–90 degree sensing range in the operating frequency range when solving the direct and inverse problem of reconstruction of the parameters of snow and ice layers.Results. Intervals of the Brewster angle values were obtained at which the value of the Fresnel reflection coefficient from the boundaries of the snow and ice cover takes minimal. Thus, was found to be – 47...55°, – 55...58° and – 58...61° for dry snow, dry firn and dry ice, respectively. The depth resolution when using an ultra-wideband LFM signal with a frequency from 2 to 8 GHz is about 4 cm. The methodological error in determining the dielectric permittivity of layers by the Brewster angle comprises not more than 3 %.Conclusion. The error in determining the relative permittivity and the depth of k layers under an increase in the RMS values of the noise level from 3.8 to 4.8 with a step of 0.1 for 100 implementations of each with a probability of 0.95 does not exceed 10 %, which confirms the validity of this method. The implementation of which allows you to automate the process of evaluating the possibility of a safe landing, thereby reducing the decision-making time and increasing the level of safety.

Device-free localization (DFL) is becoming one of the attractive techniques in wireless sensing field, due to its advantage that the target does not need to be attached to any electronic device. However, most of the existed approaches for DFL can only obtain satisfactory localization performance in specific small area, they cannot function well when implemented to complex and large area. In order to tackle this issue, in this article, a hierarchical framework is developed for large-scale DFL based on data and knowledge twin driven integration, which consists of two phases, including the offline training phase and the online localization phase. In the offline training phase, the complex and large monitoring area is first divided into some subdomains by the K-means clustering algorithm, and then training corresponding number of broad learning (BL)-based DFL models for each subdomain using the Fresnel phase difference as the fingerprints. Meanwhile, a class-specific cost regulation extreme learning machine (CCR-ELM) classifier is also trained for determining the attribution of the reference points, which can alleviate the impacts of imbalanced data distribution on classification results. In the online localization phase, the attributions of the testing points are first judged through the trained CCR-ELM classifier, after that, estimating the target’s location in the corresponding subdomains using BL-based DFL models. The validity of the proposed hierarchical framework is evaluated both in small and larger areas, respectively.

According to Faraday rotation effect and Fresnel reflection theory, a novel magnetic field intensity sensor is theoretically proposed and experimentally demonstrated by introducing a 6.4-cm-long tellurite (76.5TeO2-6BiO3-11.5Li2O-6ZnO) no core fiber (TBLZ NCF) into the loop of Sagnac interferometer. The large Verdet constant of TBLZ NCF will bring about an apparent Faraday rotation angle in magnetic field sensing, and the large refractive index difference between TBLZ and silica fibers makes the Fresnel reflection more obvious. The designed sensor demonstrates a sensitivity of 13.51 pm/Gs with an accuracy of 1.47 Gs in the measuring range of 0–380 Gs. It has satisfactory linearity, repeatability, and stability, and does not require additional utilization of expensive magnetic field sensitive materials, exhibiting great application potential.

We propose an experimental setup to measure the refractive index (RI) of two independent liquid samples by analyzing a single optical signal. We spliced a section of a seven-core fiber (SCF) into each arm of a 1 × 2 fiber coupler and spliced additional single mode fiber (SMF) to use as fiber probe tips. As the spatial frequency of the characteristic sinusoidal response of an SCF is a function of the fiber length, we used two different lengths (3 and 10 cm) in our realization. A superluminescent diode (SLD) is used as the light source, and the reflected light by both fiber tips is acquired through an optical circulator. An optical spectrum analyzer (OSA) is used to analyze the spectral response of the combined signals from both fiber tips. We characterized this sensing system by immersing the fiber tips in liquid samples with a RI between 1.3175 and 1.4040. We show that the two independent RI measurements can be retrieved by performing a Fourier transform on the recorded optical spectrum. In particular, we demonstrate that with adequate calibration, the Fresnel coefficients can be calculated independently. The presented approach represents a straightforward and cost-effective fiber implementation for multipoint sensing.

International audience; A new approach based on the change detection technique is proposed for the estimation of surface soil moisture (SSM) from a time series of radar measurements. A new index of reflectivity (IR) is defined that uses radar signals and Fresnel coefficients. This index is equal to 0 in the case of the smallest value of the Fresnel coefficient, corresponding to the driest conditions and the weakest radar signal, and is equal to 1 for the highest value of the Fresnel coefficient, corresponding to the wettest soil conditions and the strongest radar signal. The Integrated Equation Model (IEM) is used to simulate the behavior of radar signals as a function of soil moisture and roughness. This approach validates the greater usefulness of the IR compared with that of the commonly used index of SSM (ISSM), which assumes that the SSM varies linearly as a function of radar signal strength. The IR-based approach was tested using Sentinel-1 radar data recorded over three regions: Banizombou (Niger), Merguellil (Tunisia), and Occitania (France). The IR approach was found to perform better for the estimation of SSM than the ISSM approach based on comparisons with ground measurements over bare soils.

10.1119/10.0001882.1A rather delightful optical phenomenon, related to sun glints observed by the seashore, is illustrated: tiny spots of lights can be seen to move randomly in front of an observer wearing sunglasses with polarized lenses. On the seabed beneath the shallow waters, luminous wriggles can also be detected with or without sunglasses. By means of Fresnel equations, a plausible explanation of these two optical phenomena is given.

A simple water level measurement method based on wavelength division multiplexing (WDM) is proposed and demonstrated. The measurement principle is based on the change of Fresnel reflection occurring at the end facet of the optical fiber tip (OFT). To increase the spatial resolution of water level sensing, a broadband light source (BLS) and an arrayed waveguide grating (AWG) are employed. The OFTs are multiplexed with the dedicated wavelength channels of AWG. By measuring all of the reflection powers reflected at the OFTs with a proposed on-site reflectometer, the water level can be monitored continuously for a fast emergency response. Moreover, it can be implemented easily with the commercially available optical components and devices with the simple configuration.

Relevance and materials . The soil humidity being a major factor of its fertility can meaningfully change at the earth surface. R esults of researches of dependence of soil reflectance spectrum from soil type and its wetness parameters are described proanalytic conditions achievements high values of the signal reflected from wet soil are analyzed in relation to a series of measurements on multiple fields with different values of the Fresnel reflection. Results . It is shown that taking into account the possible change in the mutual dynamics of changes in f w and d from in phase to ant phase, the averaged reflected signal reaches a minimum when the specified parameters are in-phase mutually changed. On the basis of the discovered fact, a heuristic recommendation was given to use that area of the volumetric water content in the soil, where the ant phase change of the indicated indicators is provided.

Introduction. Currently, the development of safe helicopter landing systems as the most complex and dangerous stage of a flight is one of the priority tasks. A significant number of companies in Russia and abroad are engaged in its solution. Landing on unprepared (unequipped) sites with snow-ice cover may be caused by the need to deliver units, cargo and ammunition in combat conditions, search and rescue operations, evacuations of victims, etc. A key factor for a landing decision is information about the height of snow and about the depth of ice cover. In the paper remote identification of the state of snow-ice cover, excluding the need to present any person (crew member or rescue worker) on a landing site is proposed.Aim. To develop a method for the remote identification of the state of snow-ice cover used to determine the possibility of a helicopter - type aircraft safe landing on a reservoir with snow-ice cover.Materials and methods. Numerical simulation of echo signals Fresnel reflection coefficients polarization ratio was realized in MatLab. Vertical and horizontal polarizations in the range from 25 to 45 degrees were simulated.Results. Intervals of polarization relations correspond to the interval density of snow-ice layers for fixed angles. For example, when θ = 34 for dry snow ρds = 100…500 kg/m3 (ε'ds = 1.162…1.984) – Prm = 5.6915...3.3266, dry firn ρdf = 500…700 kg/m3 (ε'df = 1.984…2.51) – Prm = 3.3266...2.8311, dry ice ρdi = 700…913 kg/m3 (ε'di = 2.51…3.179) – Prm = 2.8311...2.4753. A layer reconstruction inverse problem was solved by indirect determining of complex relative permittivity of each successive underlying layer with 10-2 real part resolution. The identity of the obtained characteristics of snow-ice layers with calculated (standard) values was established.Conclusion. Remote identification of components of a snow-ice cover structure allows one to automate the process of evaluating of landing possibility. Thereby it reduces a decision-making time and increases a level of safety. In contrast to the known methods of identification of the surface layer the identification of multilayer medium layers was carried out.

Device-free localization (DFL) is a hot topic in passive sensing such as intrusion detection, pose estimation, and contact-tracing. To improve the performance, we propose a novel fine-grained DFL method using the phase response shift (PRS) to localize targets, which can mitigate the effect of multipath, and noise without phase ambiguity. The phases of received multi-frequency signals are linearly fitted as the phase response (PR). The shift of target-induced PR with respect to non-target PR is considered as the PRS. The PRSs at every location of the monitored area are observed with different length communication links, and are summarized as a PRS weight model. The PRS-based radio tomography imaging (PRSRTI) localization model is derived, and utilizes the PRS, and the weight model to localize targets. Experimental results validate that its performance is obviously higher than the received signal strength based radio tomography imaging (RTI).

The relationship between the dielectric and radio brightness characteristics of aqueous solutions of (NH4)2[PdCl4] at low concentrations at 298.15 K were considered. The dielectric relaxation parameters representing the disturbance of the H-bond network in the transition from water to solution were calculated from experimental data on the complex permittivity near the maximum of dispersion of water and solutions. These data and the Fresnel equations were used to find the quasi-optical coefficients and radio brightness characteristics of aqueous solutions in the centimeter and millimeter bands. The radio brightness characteristics of model solutions were determined with a high-sensitivity radiometer at a frequency of 61.2 GHz. The radio brightness temperature in the model solutions decreases in the transition from water to solution according to both experimental and calculated data. It was shown that the intrinsic radiation of the solution reflects the contributions of both dipole and ionic losses, which still remain significant in the millimeter band. They may even determine the difference in the signs of the changes in the radio brightness. Basics of a new approach to studying solutions containing complex ions based on their intrinsic radiation in the millimeter band were developed.

The series of three diamond-like carbon films was fabricated using Plasma – Enhanced Chemical Vapor Deposition setup designed for deposition of amorphous silicon films. The deposited films were analyzed by Spectroscopic ellipsometer Semilab SE-2000 in terms of optical properties. All the measurements were analyzed and modeled by the Fresnel equations. Three parameters were identified: refractive index, extinction index, and thickness. The range of these values indicates that the films can be used as antireflection coatings. The obtained values for n, k, and d are located in ranges: for n - 1.484 and 1621, for k - 0.345 and 0.062, and for d- 136.20 and 74.66. Плівки аморфного гідрогенізованого вуглецю а-С:Н завдяки таким властивостям, як хімічна інертність, інфрачервнева прозорість, твердість, зносостійкість, низький коефіцієнт тертя та біосумісність знаходять застосування в оптиці і електроніці, машинобудуванні та медицині. В представленій роботі плівки аморфного вуглецю досліджуються з метою подальшого їх застосування в якості антивідбиваючого покриття на інфрачервневих вікнах з германію, а також для орієнтування рідких кристалічних шарів в рідкокристалічних модуляторах світла. В роботі наведено технологічні чинники плазмохімічного осадження плівок з газової фази як одного з найпоширеніших та результативних технологічних методів. Серія з трьох алмазоподібних вуглецевих плівок була виготовлена за допомогою плазмохімічної установки для осадження a-C:H плівок. Осаджені плівки аналізували спектроскопічним еліпсометром Semilab SE-2000, що являє собою унікальну модульну оптичну платформу, що включає спектроскопічний еліпсометр з обертовим компенсатором. Спектральний еліпсометр дозволяє проводити безконтактний, неруйнівний оптичний аналіз одно- і багатошарових структур на кремнії, склі, плівковому носії, а також визначати товщину тонкоплівкових зразків і їх оптичні властивості такі як: коефіцієнт заломлення, показник поглинання, оптична ширина забороненої зони. В роботі наведено залежності отриманих еліпсометричних коефіцієнтів. На основі отриманих залежностей було виконано розрахунки з використанням матриць та рівнянь Френеля. На основі вимірювань залежності коефіцієнта відбиття від кута падіння монохроматичного випромінювання реалізовані можливості багатопараметричного, локального, експрес-неруйнівного визначення товщини, показників заломлення та поглинання шарів від кількох нанометрів до десятих мікрометра. Отримані значення для n, k і d знаходяться в діапазонах: для n - 1,448 - 1,621, для k - 0,345 - 0,062, а для d від 136,20 нм до 74,66 нм. Для використання вуглецевих плівок в якості антивідбивних покриттів необхідно, щоб його показник заломлення мав значення близько 2,0. Отримані значення показника заломлення є меншими, що не відповідає вимогам для антивідбивних покриттів. Але значення n - 1,448 - 1,621 задовольняє вимогам використання плівок для формування однорідної орієнтації рідких кристалів в пристроях на їх основі.

The aim is to investigate how the sensing features of a surface plasmon resonance sensor based on the Kretschmann configuration are affected when the optical substrate is an anisotropic medium. The investigation considers the use of two different uniaxial anisotropic crystals, one made of barium titanate and another made of lithium niobate, as the optical substrate. It also considered that the sensor operates in the angular interrogation mode at the gold–water interface. The Fresnel equations and the finite element method were employed to determine the sensing features. The present study revealed that both formulations provide almost identical results for the resonance angle (difference less than 1%). On the other hand, the two formulations provide results with significant differences for additional features like the sensitivity and the full width at half maximum.

Fiber-optic magnetic field sensors are attracting interest for applications in navigation, magnetic resonance, geophysics, space systems, power transformers, and generators, especially for harsh environments, at long distances, and for multiple monitoring points. This article presents a computational modeling for optical fiber-based magnetic field sensors using the magnetooptical Faraday and Kerr effects on the polar configuration. We propose two sensor profiles: one using a thin film of Fe and the other using a Ce:YIG layer. A simplified analytical model based on Fresnel equations is used to guide the numerical modeling built on COMSOL Multiphysics. The sensors’ design methodology is also presented, which optimizes the sensor operating range and sensitivity. The proposed sensor sensitivity, resolution, and operating range are presented and compared to others found in the literature. The results indicate the possibility of building high-resolution sensors for a restricted range of magnetic field intensities or a wide-operating range sensor.

In this letter, we propose a signal processing method for improving the resolution of a multi-point fiber refractometer from 10 -4 to 10 -6 . The fiber refractometer uses the Fresnel reflection at the fiber tip to measure the refractive index (RI), based on the coherent optical frequency domain reflectometry (C-OFDR) technique; using a standard four-pin coaxial pigtailed DFB diode laser as the optical source. The proposed method is divided into two steps; first the raw signal is processed to reduce the nonlinearity generated by the optical frequency sweeping laser, and then a pattern that repeats itself in the sensing signal is identified, extracted and replicated several times to improve the sensing signal used to calculate the RI. In the experimental results, using 30 ms of effective acquisition time, and the proposed method, an improvement of two orders of magnitude in the resolution of the system was obtained.

Fresnel reflection at the air–substrate interface of a solar cell inevitably occurs causing an important optical loss in photovoltaic conversion efficiency. Transparent materials with a low reflect...

A light intensity-modulated optical fiber sensor for continuous level measurement is proposed and demonstrated. The sensor is constructed by vertically arranging groups of fibers on the oblique surface which reflects all the incident light when the fibers are in the air but a small proportion of light when the fibers are immersed in the liquid. In order to implement easy modulation and detection, the angle of oblique surface is specially designed to get the maximum intensity modulation according to Fresnel reflection. The fiber groups consist of emitting and receiving fibers, which are tightly fixed to make it easy to detect reflected light based on side coupling effect. The calculation model of the oblique structure and the light path simulation by finite element analysis are used to optimize the oblique angle and prove the feasibility of the sensor. Gradient level experiments and stability tests in the laboratory indicate that the sensor has high sensitivity of 0.21mW/cm, superior resolution and good stability. © 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.

Transversely isotropic (TI) formation is the most popular anisotropic electrical model for computing the electromagnetic (EM) field in multilayered media. However, the TI formation considers only electric parameters such as resistivity along the horizontal and vertical directions, which are not always available in real-life situations. The realistic electric parameter distribution mainly depends on the sedimentary formation environment and could be in arbitrary directions. This article developed a fast-forward algorithm used to calculate the EM field in multilayered media with arbitrary uniaxially electrical anisotropy. Formation resistivity, anisotropic dip, and anisotropic azimuth are adopted to characterize the arbitrary uniaxial anisotropic resistivity media. Half-space Fresnel coefficients are defined and used to analyze the EM reflection and transmission characteristics between different anisotropic media. Generalized reflection and transmission matrices are derived to express the EM field in arbitrary layers. To validate the proposed algorithm, we modeled the traditional logging while drilling (LWD) and triaxial induction tool responses under different conditions. The numerical results agree with the finite element results, demonstrating the feasibility, robustness, and stability of the algorithm.