Wide Range Of Refractive Indices Research Articles

Comprehensive Analysis of Optical Resonances and Sensing Performance in Metasurfaces of Silicon Nanogap Unit

Metasurfaces composed of silicon nanogap units have a variety of optical resonances, including bound states in the continuum (BIC). We show comprehensive numerical results on metasurfaces of Si-nanogap units, analyze the optical resonances, and clarify optically prominent resonances as well as symmetry-forbidding resonances that are the BIC, based on the numerical analyses of optical spectra and resonant electromagnetic field distributions. Introducing asymmetry in the unit cell, the BIC become optically allowed, being identified as magnetic dipole, electric quadrupole, and magnetic quadrupole resonances. Moreover, the optical resonances are examined in terms of refractive index sensing performance. A pair of the resonances associated with electric field localization at the nanogap was found to be sensitive to the refractive index in contact with the metasurfaces. Consequently, the gap mode resonances are shown to be suitable for a wide range of refractive index sensing over 1.0–2.0.

Mathematical model for highly sensitive photonic crystal fiber sensor based on hyperbolic black holes

In this paper, the photonic crystal fiber sensor based on the geometry of hyperbolic black holes is proposed. As the hyperbolic black hole concentrates the electromagnetic radiation in its powerful gravitational field, the designed sensor has resulted in the concentration of the most electromagnetic field in the core of fiber. The extraordinary sensitivity of the sensor is due to the topology and exact geometry, which originates from the idea of the black hole. All the parameters related to the geometry of the structure are optimized by the Nelder-Mead algorithm, also, a unique three variable equation for the behavior of the structure is provided, which allows obtaining the possible errors due to the construction based on the geometry of the structure. In addition, the calculated equation leads to saving the simulation time. The proposed sensor has an amplitude sensitivity of 4650 (RIU-1) and wavelength sensitivity of 7000 (nm/RIU) and covers a wide range of refractive indices (1.31–1.42) in the bio and chemical range. Because of the amazing options that represent the functionality of the sensor, its construction is highly recommended.

Predicting refractive index of inorganic compounds using machine learning

Refractive index (RI) is one of the most important optical properties of materials. Due to the high importance of this physical parameter, there has always been a demand to find a method that provides the most optimal estimation. In this research, we utilize experimentally measured RI values of 272 inorganic compounds to build a machine learning model capable of predicting the RI of materials with low computational cost. Considering the significant relationship between the band gap and RI, we select this parameter as a predictor. In addition to the band gap, the atomic properties related to the building elements of the compounds form our data set in this work. To find the most optimal model and set of suitable predictors, we examine our data in four categories with 1, 5, 10, and 21 features. In addition, we compare the predicted RIs of 6 different independent regression methods, namely, ordinary least squares (OLSR), Gaussian process (GPR), support vector (SVR), random forest (RFR), gradient boosted trees (GBTR), and extremely randomized trees regression(ERTR). We notice that ERTR predicts RI with the highest accuracy compared to other regression methods. The prediction strength of our model excels in empirical relations and provides accurate results for a wide range of RIs. Thus, we demonstrate the high potential of machine learning methods for evaluating the RI, especially when it comes to providing an estimation of a desired physical quantity.

High-sensitivity and wide-range refractive index sensing based on the envelope spectrum of the subwavelength grating waveguide racetrack microring resonator.

Integrated microring resonators (MRRs) on silicon on insulator (SOI) are attractive candidates for excellent performance sensing systems. In this work, a novel, to the best of our knowledge, subwavelength grating waveguide racetrack microring resonator (SWGW-RMRR) on SOI with high-sensitivity and wide-range refractive index (RI) sensing is proposed and demonstrated experimentally. Owing to the exceptional evanescence field of the Bloch mode for the SWGW, the SWGW-RMRR provides highly sensitive RI sensing. Meanwhile, the SWGW-RMRR makes the free of free spectral range (FSR) limitation on the detection range (DR) by monitoring the envelope spectrum. By combining the advantages of the evanescent field and envelope spectrum, a SWGW-RMRR sensor has been demonstrated with a RI sensitivity of 860.8 nm/RIU, a limit of the detection value of 1.9 × 10-5 RIU, and a wide range of detection range. The measured Q-factor of the SWGW-RMRRs with an 88.8 µm total cavity length is 6200. This work can successfully realize high-sensitivity and wide-range RI sensing, showing the promising applications of silicon photonics sensors on chips.

Multi-Frequency Asymmetric Absorption-Transmission Metastructures-Photonic Crystals and Their Application as a Refractive Index Sensor.

In this paper, a kind of metastructure-photonic crystal (MPC) with multi-frequency asymmetric absorption-transmission properties is proposed. It is composed of various dielectric layers arranged in a periodically tilting pattern. When electromagnetic waves (EMWs) enter from the opposite direction, MPC shows an obvious asymmetry. EMWs are absorbed at 13.71 GHz, 14.37 GHz, and 17.10 GHz in forward incidence, with maximum absorptions of 0.919, 0.917, and 0.956, respectively. In the case of backward incidence, transmission above 0.877 is achieved. Additionally, the MPC is utilized for refractive index (RI) sensing, allowing for wide RI range detection. The refractive index unit is denoted as RIU. The RI detection range is 1.4~3.0, with the corresponding absorption peak variation range being 17.054~17.194 GHz, and a sensitivity of 86 MHz/RIU. By adjusting the number of MPC cycles and tilt angle, the sensing performance and operating frequency band can be tailored to meet various operational requirements. This MPC-based RI sensor is simple to fabricate and has the potential to be used in the development of high-performance and compact sensing devices.

Plasmonic sensor using generative adversarial networks integration

Machine learning (ML) has emerged as a pivotal force in enhancing the capabilities of sensing technologies across a broad spectrum of applications, from environmental monitoring and biosensing to agriculture, industrial automation, and so on. This study explores integrating ML techniques with photonic crystal fiber (PCF)-based plasmonic sensing techniques to elevate sensor performance. The PCF has two open channels to augment mode coupling, effectively reducing the gap between the analyte channel and core. Moreover, a thin layer of gold within the open channels of the PCF initiates efficient plasmon generation. The results demonstrate a maximum wavelength sensitivity of 9000 nm/refractive index unit (RIU), which can detect a wide range of analyte refractive index (RI) values from 1.33 to 1.40. The sensor exhibits the maximum amplitude sensitivity of 490.41 RIU−1. It also boasts a resolution of 1.11 × 10−5 RIU and the maximum figure-of-merit (FOM) achieved is 138.04 RIU−1 at an analyte RI of 1.39. Furthermore, this research introduces a method utilizing generative adversarial networks (GAN) to expand training data for an artificial neural network (ANN) model. This approach substantially improves the prediction of confinement loss across various analytes and wavelengths in a unique geometric configuration. The sensor’s versatility makes it ideal for various applications, including chemical sensing and medical diagnostics.

Optical steelyard: high-resolution and wide-range refractive index sensing by synergizing Fabry–Perot interferometer with metafibers

Refractive index (RI) sensors play an important role in various applications including biomedical analysis and food processing industries. However, developing RI sensors with both high resolution and wide linear range remains a great challenge due to the tradeoff between quality (Q) factor and free spectral range (FSR) of resonance mode. Herein, the optical steelyard principle is presented to address this challenge by synergizing resonances from the Fabry–Perot (FP) cavity and metasurface, integrated in a hybrid configuration form on the end facet of optical fibers. Specifically, the FP resonance acting like the scale beam, offers high resolution while the plasmonic resonance acting like the weight, provides a wide linear range. Featuring asymmetric Fano spectrum due to modal coupling between these two resonances, a high Q value (~ 3829 in liquid) and a sensing resolution (figure of merit) of 2664 RIU−1 are experimentally demonstrated. Meanwhile, a wide RI sensing range (1.330–1.430 in the simulation and 1.3403–1.3757 in the experiment) is realized, corresponding to a spectral shift across several FSRs (four and two FSRs in the simulation and experiment, respectively). The proposed steelyard RI sensing strategy is promising in versatile monitoring applications, e.g., water salinity/turbidity and biomedical reaction process, and could be extended to other types of sensors calling for both high resolution and wide linear range.

Refractive index in the JUNO liquid scintillator

In the field of rare event physics, it is common to have huge masses of organic liquid scintillator as detection medium. In particular, they are widely used to study neutrino properties or astrophysical neutrinos. Thanks to its safety properties (such as low toxicity and high flash point) and easy scalability, linear alkyl benzene is the most common solvent used to produce liquid scintillators for large mass experiments. The knowledge of the refractive index is a pivotal point to understand the detector response, as this quantity (and its wavelength dependence) affects the Cherenkov radiation and photon propagation in the medium. In this paper, we report the measurement of the refractive index of the JUNO liquid scintillator between 260–1064 nm performed with two different methods to cover wide range of refractive index (an ellipsometer and a refractometer), with a sub percent level precision. In addition, we used an interferometer to measure the group velocity in the JUNO liquid scintillator and verify the expected value derived from the refractive index measurements.

Multi-modal flexible and inexpensive plasmonic metasurface for wide range of refractive index sensing

Abstract A plasmonic metasurface containing nanobumps of sub-wavelength feature size arranged in a hexagonal pattern on a flexible substrate and covered with a thin film of gold is investigated as a refractive index sensor. The chosen polymer patterns coated with gold aid in activating the surface plasmon polariton modes. Using numerical calculations, it is shown that this surface can exhibit plasmonic effect with an extremely shallow pattern height of 92.5 nm and minimal thickness of 25 nm of gold over it. The excitation of the plasmonic modes is confirmed using electric field profiles calculated at the relevant wavelengths. As the surface is highly sensitive to changes in the cladding index, and the chosen design aids in exciting three plasmon modes that are suitably well-separated in wavelength, this surface can be used for an extremely wide range of refractive index sensing because each mode contributes uniquely to a different range of refractive index. The results establish that the metasurface is suitable for a variety of applications, including gas detection with a sensitivity of 633 nm/RIU using mode-1, identifying SARS-CoV-2 viral molecules with a sensitivity of 428 nm/RIU using mode-2 and 238 nm/RIU using mode-3, and discriminating between normal and diseased brain tissues in the cerebrospinal fluid in the high-index range using mode-3. The prototype metasurface is made using a cost-effective soft lithography technique using an economical master mould. The inexpensive technique of fabrication, use of very thin metal film, and wavelength of detection lying within the visible to near infrared range imply a low-cost sensor. The structural and optical characterization of the prototype validates the numerical study of the sample.

Nanosensors Based on Bimetallic Plasmonic Layer and Black Phosphorus: Application to Urine Glucose Detection.

This paper presents a new biosensor design based on the Kretschmann configuration, for the detection of analytes at different refractive indices. Our studied design consists of a TiO2/SiO2 bi-layer sandwiched between a BK7 prism and a bimetallic layer of Ag/Au plasmonic materials, covered by a layer of black phosphorus placed below the analyte-containing detection medium. The different layers of our structure and analyte detection were optimized using the angular interrogation method. High performance was achieved, with a sensitivity of 240 deg/RIU and a quality factor of 34.7 RIU-1. This biosensor can detect analytes with a wide refractive index range between 1.330 and 1.347, such as glucose detection in urine samples using a refractive index variation of 10-3. This capability offers a wide range of applications for biomedical and biochemical detection and selectivity.

Envelope Spectrum of the Subwavelength Grating Slot Waveguide Microring Resonator for High-Sensitivity and Wide-Range Refractive Index Sensing Applications

Envelope Spectrum of the Subwavelength Grating Slot Waveguide Microring Resonator for High-Sensitivity and Wide-Range Refractive Index Sensing Applications

Numerical analysis of a single channel exposed core elliptical shaped PCF based highly sensitive SPR sensor for wide RI sensing.

This study presents a numerical study of a highly sensitive photonic crystal fiber (PCF) surface plasmon resonance (SPR) sensor capable of detecting five types of cancer and bacterial contamination in water. By precisely arranging only two air holes in a single channel of an elliptical-shaped PCF, the sensor maximizes interaction between core-guided modes and surface plasmon polaritons (SPP) along the fiber. Evaluation using COMSOL Multiphysics simulation software, based on finite element method (FEM), demonstrates outstanding sensor performance across a wide refractive index (RI) range (1.33 to 1.43). With a maximum wavelength sensitivity (WS) of 188,000 nm/RIU and amplitude sensitivity (AS) of -22,377.99 RIU-1, the sensor achieveStructural Design and Methodologys a sensor resolution (SR) of 5.3191 × 10-7 RIU and figure of merit (FOM) of 854.55 RIU-1. Notably, it exhibits AS and WS values tailored for specific cancer cell types and water contamination. These results endorse the sensor's potential in diverse biological and molecular analyte RI detection applications within the visible to near-infrared (VNIR) range (0.55 to 4 µm), offering high sensitivity, affordability, wide sensing range, good linearity, low propagation loss, and simplicity in construction.

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

A photonic crystal fiber (PCF) sensor based on surface plasmon resonance (SPR) with a graphene coating on the cladding is designed for refractive index (RI) detection in the range of 0.3–0.5 THz, especially for liquid bioanalytical sensing. The adjustability of the graphene chemical potential (E f ) enables dynamic tuning of the loss spectra over a wide frequency range with a tuning sensitivity of 570 GHz/eV at the SPR frequency. According to the analysis by the finite element method (FEM), the highest wavelength sensitivity and maximum amplitude sensitivity of 4254.11 µm/RIU and 25.62RIU−1 (n a =1.34) are achieved in the RI range of 1.15–1.35, respectively, together with a resolution of 5.93×10−5RIU. The graphene PCF-SPR sensor boasting high-sensitivity detection in a wide RI range has broad application prospects in multiple fields.

Silicon‐Rich Nitride Refractive Index as a Degree of Freedom to Maximize Nonlinear Wave Mixing in Nanowaveguides

Silicon nitride is widely used in integrated photonics for optical nonlinear wave mixing due to its low optical losses combined with relatively high nonlinear optical properties and a wide‐range transparency window. It is known that a higher concentration of Si in silicon‐rich nitride (SRN) magnifies both the nonlinear response and optical losses, including nonlinear losses. To address the trade‐off, four‐wave mixing (FWM) is implemented in over a hundred SRN waveguides prepared by plasma‐enhanced chemical vapor deposition in a wide range of SRN refractive indices varying between 2.5 and 3.2 (measured in the C‐band). It is determined that SRN with a refractive index of about 3 maximizes the FWM efficiency for continuous‐wave operation, indicating that the refractive index of SRN is indeed a crucial optimization parameter for nonlinear optics applications. The FWM efficiency is limited by large nonlinear optical losses observed in SRN waveguides with indices larger than 2.7, which are not related to two‐photon absorption. Finally, the third‐order susceptibility and the nonlinear refractive index are estimated for multiple SRN refractive indices, and, specifically, the nonlinearities as large as and are estimated in a waveguide with an SRN refractive index of 3.2.

Terahertz metasurfaces to demonstrate an extremely wide range of refractive indices in the 0.3-THz band

Terahertz metasurfaces to demonstrate an extremely wide range of refractive indices in the 0.3-THz band

A sensitivity study on radiative effects due to the parameterization of dust optical properties in models

Abstract. Most of the dust models underestimate the load of the large dust particles, consider spherical shapes instead of irregular ones, and have to deal with a wide range of the dust refractive index (RI) to be used. This leads to an incomplete assessment of the dust radiative effects and dust-related impacts on climate and weather. The current work aims to provide an assessment, through a sensitivity study, of the limitations of models to calculate the dust direct radiative effect (DRE) due to the underrepresentation of its size, RI, and shape. We show that the main limitations stem from the size and RI, while using a more realistic shape plays only a minor role, with our results agreeing with recent findings in the literature. At the top of the atmosphere (TOA) close to dust sources, the underestimation of size issues an underestimation of the direct warming effect of dust of ∼ 18–25 W m−2, for DOD = 1 (dust optical depth) at 0.5 µm, depending on the solar zenith angle (SZA) and RI. The underestimation of the dust size in models is less above the ocean than above dust sources, resulting in an underestimation of the direct cooling effect of dust above the ocean by up to 3 W m−2, for aerosol optical depth (AOD) of 1 at 0.5 µm. We also show that the RI of dust may change its DRE by 80 W m−2 above the dust sources and by 50 W m−2 at downwind oceanic areas for DOD = 1 at 0.5 µm at TOA. These results indicate the necessity of including more realistic sizes and RIs for dust particles in dust models, in order to derive better estimations of the dust DRE, especially near the dust sources and mostly for studies dealing with local radiation effects of dust aerosols.

PCF Based Four-Channel SPR Biosensor With Wide Sensing Range.

In this article, we have demonstrated a highly sensitive four-channel photonic crystal fiber (PCF) based surface plasmon resonance (SPR) biosensor which can detect four different analytes simultaneously. To ease practical implementation, four analyte sensing layers and plasmonic materials such as gold (Au) and gold (Au) with Tantalum Pentoxide (Ta2O5) are placed on the exterior of the four arms of the square shaped structure. The sensor's structure consists of only nine circular air holes, making it simple and easy to fabricate using currently available technologies. Finite element method (FEM) based numerical analysis is used to evaluate the sensing performance of the proposed sensor. With optimum structure parameters, the sensor achieves maximum wavelength sensitivity of 11000, 25000, 11000 and 25000 nm/RIU for Channel-1, Channel-2, Channel-3, and Channel-4 respectively. It shows maximum amplitude sensitivity of 803.732, 709.171, 803.827, 709.146 RIU -1 for Channel 1, 2, 3, and 4 respectively. It also shows maximum FOM of 232.55, 352.36, 231.57, 352.36 RIU -1 in Ch-1, Ch-2, Ch-3 and Ch-4 respectively. Moreover, the proposed sensor shows a wide range of refractive index sensing capability from 1.30 to 1.41. Due to multi-analyte detection capability, large sensing range, and excellent sensitivity the proposed sensor unfolds unrivalled capacity of detecting chemicals, carcinogenic agents, biomolecules, and other analytes.

Highly sensitive Borophene-metal-Si based multilayered Terahertz frequency spectrum based refractive index sensor

We presented the numerical investigation of a multilayered borophne-metal-Si-based refractive index sensor for the wide range of the THz frequency. The proposed structure is worked for the frequency range of 1 to 15 THz. The structure is formed to identify reflectance variation, resonating frequency and other physical parameters over the broad frequency spectrum. The overall structure is simulated using FEM (Finite element method) computational techniques with a periodic boundary condition-based two-port model. The resonance effect of the structure is also investigated for the different shapes of the top metal resonator structure, which significantly influences the overall frequency shift. The proposed structure is investigated for the X and Y polarized input incident condition for the entire frequency band where the oblique angle incident stability is observed up to 80°. The proposed structure offers the maximum variation in sensitivity up to 3.5 THz/RIU (∼ 11600 nm/RIU) for X-polarized and 5.5 THz/RIU (∼10600 nm/RIU) for Y-polarized incident wave conditions. We have applied the artificial neural network algorithm (ANN) to predict the overall behaviour of the structure from the data points generated in the simulated results. We used the Relu optimizer to train the model, generating promising results for our collected data. The machine learning model gives RMSE = 0.049422, MAE = 0.018531, MSE = 0.00328 and R2 = 0.93768 for the testing data set. Similarly, the model generated the minimum RMSE values = 0.045955, MAE = 0.017392, MSE = 0.00295, and R2 = 0.97673 for the training data set for 2500 epochs. The proposed results in the manuscript give the future scope to design borophene a wide range of refractive index (RI) sensor designs used in biosensors, gas sensors and other environment sensors where the refractive index range is between 1 and 2.4.

Refractive index sensor based on fano-magnetic toroidal quadrupole resonance enabled by bound state in the continuum in all-dielectric metasurface.

For the first time, an all-dielectric metasurface ultra-sensitive refractive index (RI) sensor with very high quality factor (QF) and figure of merit (FOM), with Fano-magnetic toroidal quadrupole (MTQ) resonance enabled by bound state in continuum (BIC) in terahertz (THz) region was designed. Furthermore, the MTQ resonance in the THz due to a distortion of symmetry-protected bound states in the continuum in the designed structure was investigated. Also, to achieve the dark mode, a combination of three methods including (i) breaking the symmetry, (ii) design of complex structures, and (iii) changing the incident angle was utilized. The broken symmetry in the structure caused a new mode to be excited, which is suitable for sensing applications. The designed metasurface was able to sense a wide range of RI in MTQ resonance, where its properties were improved for the value of sensitivity (S) from 217 GHz/RIU to 625 GHz/RIU, for FOM from 197 RIU-1 to 2.21 × 106 RIU-1 and for QF from 872 to 5.7 × 106.

Design and analysis of arc-shaped single core photonic crystal fiber sensor based on surface plasmon resonance

The selection of a suitable plasmonic material is crucial for achieving high-performance photonic crystal fiber-based surface plasmon resonance (PCF-SPR) sensors. However, most numerical investigations have been limited to PCF-SPR sensors with conventional circularly coated plasmonic metals due to their availability and rigid properties. In this work, a single-core arc-shaped PCF is designed and studied with sensing ingredients coated outside the fiber. The simulation and numerical analyses are performed using the full-vector finite element method to examine the effects of using gold as an active metal and also the deposition of Ta2O5 on gold. The results show that the arc-shaped sensor with gold film can obtain the maximum wavelength interrogation sensitivity (WIS) of 9500 nm/RIU within the refractive index (RI) range of 1.25–1.39 while the maximum amplitude interrogation sensitivity (AIS) reaches 579.26 RIU−1 at 1.39 and resolution is 1.05 × 10−5. However, depositing Ta2O5 on the gold gives an improved maximum WIS and AIS of 22,000 nm/RIU and 1209.21 RIU−1, respectively. With the coating of Ta2O5, the resolution improves to 4.55 × 10−6, making the proposed sensor design undoubtedly effective in detecting food chemicals such as butyl acetate and hydrocarbons along with different bio-analyte samples with a wide range of RI.