Variation Of Refractive Index Research Articles

Trans-reflective tunable color filter using electro-optic material

This research presents designing a tunable trans-reflective color filter utilizing Barium Titanate (BTO) and optimizing its performance by applying an artificial intelligence (AI) based inverse design model. The AI-based color filter design process is efficient and minimizes design challenges. The AI model comprising two sub-blocks is trained using a dataset that correlates geometrical parameters, refractive index, and input voltage variations with desired color outputs to precisely control the color filter's performance. The first is the parametric optimization block (POB), which employs two deep neural networks (DNNs) in the forward and inverse directions to achieve the optimized geometry of the proposed meta-atoms. Once the optimal parameters are completed, the next block, i.e., voltage tuning block (VTB), is employed to map specific colors onto the refractive index and the applied voltage of the BTO layer. In this way, by changing the voltage of the BTO layer, we can leverage BTO's tunable optical properties, which allow for a broad range of vibrant and customizable colors. The optimized color filter demonstrates enhanced tunability and efficiency, opening up new possibilities for applications in displays and imaging devices.

Evolution of Airy Beams in Turbulence Plasma Sheath

In order to study the transmission characteristics of Airy beams in the plasma sheath, the flow field around a hypersonic vehicle was numerically simulated and analyzed based on the Navier–Stokes (N-S) equation and a turbulence model. Then, according to the characteristics of the thickness of the plasma flow field around the supersonic vehicle at the centimeter level, the double fast Fourier transform (D-FFT) algorithm and multi-random phase screens theory were used to predict the propagation characteristics of the Airy beams in the turbulent plasma sheath. The results show that the lower the height and the higher the speed, the smaller the thickness of the plasma sheath shock layer. The refractive index variation in the sheath shock layer has a significant influence on Airy beam transmission. At the same time, the transmission distance and the attenuation factor of the Airy beams also change the transmission quality of the Airy beams. The larger the attenuation factor, the smaller the drift, and the standard deviation decreases with an increase in the refractive index. Airy beams have smaller drifts compared to Gaussian beams and have advantages in suppressing turbulence.

Impacts of variations in aerosol refractive index on the retrieving of the light-absorption and hygroscopicity of ambient black carbon-containing aerosols using SP2

Black carbon (BC) aerosols directly influence the earth's climate system by absorbing the light intensity and indirectly by interacting with clouds. The microphysical properties of BC-containing aerosols were determined by their core diameter and shell thickness, which can be derived from the measurement of a single-particle soot photometer (SP2). Traditionally, a constant real part of the shell's refractive index (RRI) was employed to retrieve the shell thickness of BC-containing aerosols using the measured scattering signals from SP2. Recent field measurements in East China show that ambient aerosol RRI varies over a wide range between 1.36 and 1.56. The influences of aerosol RRI variation on the retrieving of BC-containing aerosol shell thickness from the measurements of SP2 are investigated with simulation studies. Results show that the variation in ambient aerosol RRI can lead to a variation in the coating thickness of BC-containing aerosols by 9.4%. The corresponding uncertainties in the light absorption enhancement reach up to 29% due to the influence of aerosol RRI. The critical mean supersaturation (SS) of the BC-containing aerosol varies significantly between 0.044% and 0.055% due to the uncertainties in the derived shell thickness using a constant RRI. This study highlights the demand for the real-time measurement of ambient aerosol RRI when deriving the microphysical properties of ambient BC-containing aerosols from the SP2 measurement.

Spectral Engineering of Optical Microresonators in Anisotropic Lithium Niobate Crystal.

On-chip optical microresonators are essential building blocks in integrated optics. The ability to arbitrarily engineer their resonant frequencies is crucial for exploring novel physics in synthetic frequency dimensions and practical applications like nonlinear optical parametric processes and dispersion-engineered frequency comb generation. Photonic crystal ring (PhCR) resonators are a versatile tool for such arbitrary frequency engineering, by controllably creating mode splitting at selected resonances. To date, these PhCRs have mostly been demonstrated in isotropic photonic materials, while such engineering can be significantly more complicated in anisotropic platforms that often offer more fruitful optical properties. Here, the spectral engineering of chip-scale optical microresonators is realized in the anisotropic lithium niobate (LN) crystal by a gradient design that precisely compensates for variations in both refractive index and perturbation strength. Controllable frequency splitting is experimentally demonstrated at single and multiple selected resonances in LN PhCR resonators with different sizes, while maintaining high quality-factors up to 1 × 106. Moreover, a sharp boundary is experimentally constructed in the synthetic frequency dimension based on an actively modulated x-cut LN gradient-PhCR, opening up new paths toward the arbitrary control of electro-optic comb spectral shapes and exploration of novel physics in the frequency degree of freedom.

Quantification and characterization of an ultrasound-induced polarization wavefront aberration in the phase space.

Light propagation wavefront and photon composition variations occur when the beam encounters acoustic waves, bringing mechanical and chemical inhomogeneity-induced light-intensity modulation, while phase variations, which carry more information about the acoustic-optical coupling in the medium, are often overlooked. This paper investigates the coupling of the light beam with the propagating ultrasound and the polarization aberration of the optical wave induced by the ultrasound. A model was developed to express the variation of the ultrasound-induced polarization aberration (UIPA). The ultrasound-induced refractive index variation of the sample was observed in both the simulation and experiments. The phase differences in various ultrasound states (valley dominant state, peak dominant state) are characterized in detail. The UIPA expressed in the phase space provides a way to quantify multidimensional polarization information of the ultrasound-tagged optical waves and allows refraction-sensitive polarization parametric imaging, which may be exploited for directional high-contrast photoacoustic imaging with ultrasound tagging.

Micro-patterned glass for energy-efficient windows

Development of novel energy-efficient components is a topic of prime importance in building design. In this contribution, we propose a micro-patterned glass window which can be designed to efficiently reduce the energy demands of buildings located within an area of hot and cold seasons. The proposed patterned structure can be applied to any panes of glass in single or multi-pane windows. We first define the total positive power as a characteristic parameter for evaluating the effectiveness of using the designed window in reducing the average thermal power demands of a given building. Then, a full-wave numerical method is employed to analyze the performance of the proposed structure with respect to the defined characteristics. Our model accurately accounts for sunlight incident angle variations corresponding to different times of the days in every season. In addition, the variations of glass refractive index throughout the solar spectrum, non-polarized nature of the sun light, and typical dimension scales used in building windows are taken into account. Our numerical results show more than 80 W and 160 W total positive power for an optimized single-pane micro-patterned window with unit area and a double-pane one, respectively. We also present the design procedure of the proposed structure for a given geographical location of the building.

MIM plasmonic sensors based on single-side ring cavity with one stub and their applications

A plasmonic sensor is proposed, comprising a metal–insulator–metal (MIM) straight waveguide and a ring cavity with one stub (RCS). Using the finite element method, its transport properties are simulated and systematically analyzed. By optimizing the structure parameters, the sensor obtains the maximum sensitivity (S) of 2010 nm/RIU and the maximum figure of merit (FOM) of 49219.04 RIU−1. It demonstrates a sensing resolution (SR) of 4.98 × 10−7 RIU in the detection of refractive index variation. Based on the optimized parameters, temperature sensing is investigated utilizing Polydimethylsiloxane (PDMS) as the temperature-sensitive medium, and the temperature sensitivity is found to be −0.90 nm/°C. In addition, multiple independently tunable resonances are achieved by adding a ring cavity (RC) above the straight waveguide. This derived structure enables the simultaneous detection of electrolyte samples (Na+ and K+) in blood with bio-sensing sensitivities reaching 0.1833 nm·dL/mg and 0.2 nm·dL/mg. These results have directive significance for the development of multifunctional and ultra-compact plasmonic sensor.

Multi-wavelength interference phase imaging for automatic breast cancer detection and delineation using diffuse reflection imaging

Millions of women globally are impacted by the major health problem of breast cancer (BC). Early detection of BC is critical for successful treatment and improved survival rates. In this study, we provide a progressive approach for BC detection using multi-wavelength interference (MWI) phase imaging based on diffuse reflection hyperspectral (HS) imaging. The proposed findings are based on the measurement of the interference pattern between the blue (446.6 nm) and red (632 nm) wavelengths. We consider implementing a comprehensive image processing and categorization method based on the use of Fast Fourier (FF) transform analysis pertaining to a change in the refractive index between tumor and normal tissue. We observed that cancer growth affects tissue organization dramatically, as seen by persistently increased refractive index variance in tumors compared normal areas. Both malignant and normal tissue had different depth data collected from it that was analyzed. To enhance the categorization of ex-vivo BC tissue, we developed and validated a training classifier algorithm specifically designed for categorizing HS cube data. Following the application of signal normalization with the FF transform algorithm, our methodology achieved a high level of performance with a specificity (Spec) of 94% and a sensitivity (Sen) of 90.9% for the 632 nm acquired image categorization, based on preliminary findings from breast specimens under investigation. Notably, we successfully leveraged unstained tissue samples to create 3D phase-resolved images that effectively highlight the distinctions in diffuse reflectance features between cancerous and healthy tissue. Preliminary data revealed that our imaging method might be able to assist specialists in safely excising malignant areas and assessing the tumor bed following resection automatically at different depths. This preliminary investigation might result in an effective "in-vivo" disease description utilizing optical technology using a typical RGB camera with wavelength-specific operation with our quantitative phase MWI imaging methodology.

Excitation of optical tamm state for photonic spin hall enhancement

This work presents a dielectric material-based optical Tamm state (OTS) excitation technique with modified dispersion characteristics for photonic spin hall effect (PSHE) enhancement. The dispersion analysis of the structure is carried out to validate OTS’s localization and corresponding PSHE generation for a given polarization at 632.8 nm incident wavelength. The exceptional points are optimized by considering thickness-dependent angular dispersion analysis. PSHE-based transverse displacement (PSHE-TD) is dependent on the defect layer thickness. The optimized structure provides 10.73 times lambda (or 6.78 upmum) PSHE-TD at an incidence angle of 41.86{}^{circ }. The PSHE-TD of the optimized structure is sufficiently high due to the much narrower resonance than the plasmonic-based structures. Further, the structure’s potential to function as a PSHE-TD-based optical sensor is assessed. The optimized structure shows an analytical average sensitivity of about 43,789 upmum/RIU showing its capability to detect the analytes with refractive index variations in the 10^{-4} range. The structure demonstrates a three-time sensitivity improvement compared to similar resonance designs. Considering only dielectric materials in the proposed structure and considerably enhanced PSHE-TD, the development of highly efficient PSHE-TD-assisted commercial structures is anticipated.

Field theory description of the non-perturbative optical nonlinearity of epsilon-near-zero media

In this paper, we introduce a fully non-perturbative approach for the description of the optical nonlinearity of epsilon-near-zero (ENZ) media. In particular, based on the rigorous Feynman path integral method, we develop a dressed Lagrangian field theory for light–matter interactions and discuss its application to dispersive Kerr-like media with order-of-unity light-induced refractive index variations. Specifically, considering the relevant case of Indium Tin Oxide (ITO) nonlinearities, we address the novel regime of non-perturbative refractive index variations in ENZ media and establish that it follows naturally from a scalar field theory with a Born–Infeld Lagrangian. Moreover, we developed a predictive model that includes the intrinsic saturation effects originating from the light-induced modification of the Drude terms in the linear dispersion of ITO materials. Our results extend the Huttner–Barnett–Bechler electrodynamics model to the case of non-perturbative optical Kerr-like media providing an intrinsically nonlinear, field-theoretic framework for understanding the exceptional nonlinearity of ITO materials beyond traditional perturbation theory.

Dual-polarization photonic integrated biosensor in a Mach-Zehnder interferometer with coherent phase readout

Photonic integrated biosensors have garnered considerable attention due to their promising applications in various fields such as healthcare. Differentiating specific targets from interfering background effects is a challenging task. In this work, a dual-polarization Mach-Zehnder interferometer (MZI) with coherent phase readout is proposed to identify refractive index changes from different layers above the waveguide surface, thus improving sensor specificity. All the system building blocks have been designed for a 300 nm-thick silicon nitride platform, fabricated and characterized. The first experimental results show a bulk waveguide sensitivity of 0.17 RIU/RIU for TE polarization and 0.25 RIU/RIU for TM, confirming the correct functioning of the sensors when operating for each polarization separately. Future work will focus on simultaneous sensing with both polarizations and experiments with layered variation of refractive indices.

Refractometric sensing with plasmon resonances in dimer, trimer and quadrumer ensembles of gold nanoparticles

We studied by FDTD computer simulations the dependence of the surface plasmon resonances in linearly arranged gold nanospheres on incident light polarization, spheres number and diameter, and interparticle gap. The observed scattering spectra of large particles show a particularly interesting behaviour, with coupled plasmon resonances that can be either red or blue shifting with the modification of the interparticle gap. The sensitivity of the various observed coupled plasmon modes to refractive index variations is then evaluated.

Fully Connected Feedforward Neural Network for the Prediction of Amorphous Silicon Grating Couplers Efficiency

Photonic circuits are an enabling technology for the development of novel solutions in different fields such as healthcare, quantum computing, neural networks, communications, and manufacturing. Interconnections between devices and systems require low-loss light coupling strategies. Grating couplers are a promising solution to couple light between photonic circuits and optical fibres due to their off-plane coupling capabilities. Hydrogenated amorphous silicon (a-Si:H), which can be deposited by PECVD over a substrate of silica or glass, is a suitable low-cost solution for the production of such light coupling devices. In this work we developed, trained and tested a fully connected feedforward neural network for coupling efficiency prediction in a-Si:H grating couplers. The light coupling gratings were simulated by twodimensional finite-difference time-domain (FDTD) analysis and field distributions were analysed with the Finite Element Method (FEM). Simulated gratings include non-apodized, linear and quadratic refractive index variation designs featuring full or partial etching, operating at 1550 nm. Not featuring any type of bottom reflector, the couplers exhibit coupling efficiencies up to about 40 % (~ -4 dB). The neural network multiclass grating coupler efficiency classifier was trained with over 3000 simulation results, reaching an accuracy over 85%, for coupling efficiencies between 0 and 30%+.

Advancing Sensitivity in Guided-Wave Surface Plasmon Resonance Sensor through Integration of 2D BlueP/MoS2 Hybrid Layers.

The surface plasmon resonance (SPR) signal, generated from the Kretschmann configuration, has been developed as an effective detection technology in chemical and biological sensors. The sensitivity of SPR signals to changes in the surrounding media makes it a valuable tool, as even a slight variation in refractive index can cause a significant change in SPR signals, such as phase, intensity, and resonance angle. However, the detection of ultralow changes in refractive index, which occur in chemical reactions or biological actions, remains a challenge for conventional SPR sensors due to their limited sensitivity. To overcome this limitation, we theoretically propose a novel guided-wave SPR (GWSPR) configuration coated with a few-layer blue phosphorene (blueP)/MoS2 hybrid structure. This configuration aims to enhance the electric field and subsequently achieve a significant improvement in sensitivity. The results of our study demonstrate that the proposed blueP/MoS2-based GWSPR sensor exhibits a high sensitivity of 290°/RIU, which represents an impressive enhancement of approximately 82.4% compared to the conventional Au-based SPR sensor. This advancement addresses the challenge of detecting ultralow changes in refractive index and offers significant potential for enhancing the performance of chemical and biological sensors.

Advanced Integration of Glutathione-Functionalized Optical Fiber SPR Sensor for Ultra-Sensitive Detection of Lead Ions.

It is crucial to detect Pb2+ accurately and rapidly. This work proposes an ultra-sensitive optical fiber surface plasmon resonance (SPR) sensor functionalized with glutathione (GSH) for label-free detection of the ultra-low Pb2+ concentration, in which the refractive index (RI) sensitivity of the multimode-singlemode-multimode (MSM) hetero-core fiber is largely enhanced by the gold nanoparticles (AuNPs)/Au film coupling SPR effect. The GSH is modified on the fiber as the sensing probe to capture and identify Pb2+ specifically. Its working principle is that the Pb2+ chemically reacts with deprotonated carboxyl groups in GSH through ligand bonding, resulting in the formation of stable and specific chelates, inducing the variation of the local RI on the sensor surface, which in turn leads to the SPR wavelength shift in the transmission spectrum. Attributing to the AuNPs, both the Au substrates can be fully functionalized with the GSH molecules as the probes, which largely increases the number of active sites for Pb2+ trapping. Combined with the SPR effect, the sensor achieves a sensitivity of 2.32 × 1011 nm/M and a limit of detection (LOD) of 0.43 pM. It also demonstrates exceptional specificity, stability, and reproducibility, making it suitable for various applications in water pollution, biomedicine, and food safety.

An all-fiber system biosensor for trace β-lactam antibiotics detection enhanced by functionalized microfiber and fiber bragg grating

An all-fiber-optic system for rapid detection of antibiotic concentration, based on an optical enzyme biosensor with microfiber interferometer (MFI) and fiber gratings (FBGs) power variation, is proposed and experimentally validated. During the experiment, β-lactamase(β-LS) is fixed on the polyaniline (PANI)-coated optical fiber by cross-linking through glutaraldehyde (GA) covalent bonding. β-LS can hydrolyze β-lactam antibiotics to generate acidic by-products that transform polyaniline from the form of the emerald base to emerald salt, which results in the surface refractive index (RI) variation of MFI, to convert MFI wavelength and FBGs power macroscopic change for feedbackingly detecting the concentration of β-lactam antibiotics. The detection of amoxicillin (AMX) in deionized water at concentrations in the range of 0.01–100 nM resulted in a wavelength change sensitivity of 0.6 nm/nM, and FBGs power difference change sensitivity of 1.3 dB/nM, with a detection limit LOD = 0.04 nM in real food and urine samples. The sensing system by the same calibration technique can detect antibiotic concentrations in different substances (tap water, milk and artificial urine). This developed all-fiber-optic system can be used as a rapid solution for the measurement of β-lactam antibiotic residues in food and the environment.

Refractivity of P2O5-Al2O3-SiO2 Glass in Optical Fibers

A significant change in the refractive index profiles for the large mode area phosphoroaluminosilicate (PAS) core optical fibers was observed in comparison to that in preforms. This study shows that the refractive index of the PAS core can vary from negative (in preform) to positive (in fiber), and the difference in the refractive index between the core and preform can exceed a few thousand. By measuring a large set of fibers with different concentrations of P2O5 and Al2O3, we define the refractivity of each dopant (P2O5, Al2O3 and AlPO4 joint) after drawing fiber from the preform and discuss the possible origin of the observed refractive index variation.

A controllable humidity sensitivity measurement solution based on a pure FPI fiber tip and the harmonic Vernier effect

Hygroscopic films used to enhance the humidity sensitivity of fiber-optic sensors often experience material aging and nonlinear response issues. To address this issue, this study proposes a controllable humidity sensitivity measurement solution that offers a simple and cost-effective fabrication process without requiring humidity-sensitive material sensitization. The solution is based on a Fabry-Perot interferometer (FPI) fiber tip and the harmonic Vernier effect. By employing a cascade structure of single-mode fiber (SMF)-hollow core fiber (HCF)-no core fiber (NCF) with fiber grinding techniques, the FPI-based fiber sensing probe constructed a resonance cavity to detect small variations in air refractive index (RI) induced by humidity. A reference spectrum, which can flexibly control parameters, such as free spectral range (FSR), contrast, phase, and intensity, is superimposed onto the sensing spectrum acquired by the FPI fiber sensing tip. By extracting features from the internal envelope generated by the harmonic Vernier effect, the mapping relationship between the center wavelength of the inner envelope and the humidity is determined. The harmonic Vernier effect amplifies the humidity sensitivity of the fiber-optic FPI sensing tip, with the magnification factor determined by the optical path length (OPL) detuning of the created reference and sensing spectra. For the harmonic order j = 4, a humidity sensitivity of approximately 76.01 pm/% RH@ 24 ℃ was achieved without using hygroscopic material sensitization. The proposed solution offers numerous advantages and enables high-precision and high environmental reliability humidity monitoring.

Solubilities of Components in the Сa(ClO3)2∙NH4Сl–H2O System

The Сa(ClO3)2∙NH4Сl–H2O system has been studied in its constituent binary systems and seven inner sections, and its polythermal solubility diagram has been plotted in the range of temperatures from–42.5 to 87.5°С. The solubility diagram features the crystallization fields of ice; calcium chlorate hexahydrate, tetrahydrate, and dihydrate; and ammonium chloride. Three ternary points exist in the system. The system belongs to the complex eutonic type; its components retain their individuality and show good solubility in water. In the [40% Сa(ClO3)2 + 60% H2O]–[NH4Сl] section of the studied system, variations in crystallization temperature, viscosity, density, pH, and refractive indices of the solution have been determined. The thus-obtained results have been used to plot the composition–property diagram of the [40% Сa(ClO3)2 + 60% H2O]–[NH4Сl] section of the Сa(ClO3)2∙NH4Сl–H2O system.

Variation of refractive index of a hydrogenic impurity in a parabolic quantum well

Variation of refractive index of a hydrogenic impurity in a parabolic quantum well