Refractive Index Unit Research Articles

Highly sensitive photonic spin Hall effect sensor with graphene-coated surface exciton polariton structure

The photonic spin Hall effect (PSHE) in a graphene-coated surface exciton polariton (SEP) structure is investigated in this work. The transverse shift of 32.95λ0 (17.53 μm) is achieved with the optimum graphene-coated SEP structure in the gaseous environment under λ0 = 532 nm illumination, which provides a 2.46-fold improvement compared to the optimum conventional SEP structure. The transverse shift is further improved to 76.39λ0 (i.e., 40.64 μm) with the graphene-coated long-range SEP (LRSEP) in the aqueous environment. Refractive index sensors based on the enhanced PSHE are proposed for sensing applications in the gaseous and aqueous environment, respectively, which possess the bulk refractive index sensitivities of 24424.4λ0 (12993.78 µm) 1/RIU (RIU: refractive index unit) and 57336.6λ0 (30503.1 µm) 1/RIU. The combination of SEP (LRSEP) and graphene layers provides a promising approach for enhancing the transverse shift of PSHE, and may find potential applications in gas sensing, chemical sensing, and biosensing base on the enhanced PSHE.

Physical, optical properties and antibacterial activity of silver nanoparticles: Nanoclusters to nanoparticles formation on glass substrate by in-situ annealing

Silver nanoparticles (AgNPs) formed on in-situ annealed microscopic glass substrates from silver nanoclusters (AgNCs) generated by DC magnetron sputtering with inert gas condensation (IGC) technique. The substrate’s annealing temperature was below and above the glass transition temperature of 500 ºC and 600 ºC. The influence of annealing temperature on the surface morphology was studied using atomic force microscopy (AFM). X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) were employed to investigate the surface composition, chemical states, and electronic states of the AgNPs on the glass substrates. On the in-situ annealed glass substrate at 500 ºC, the produced AgNPs revealed accumulation and aggregation. For in-situ annealed at 600 ºC, a homogeneous distribution of AgNPs on the glass substrate was witnessed. The refractive index test revealed that AgNPs deposition at 600 ºC achieved higher sensitivity with 27nm/RIU (Refractive index unit). The antibacterial activity of AgNPs was also investigated using Escherichia coli and Bacillus cereus. In contrast, better antibacterial activity was obtained with in-situ annealing at 500 ºC, where 4-fold reductions compared with the control sample. Pre-determined properties can be precisely executed to achieve the desired performance as the so-called application-oriented engineered surface in the UHV system is established. This research highlighted the differences between two different annealing temperatures' effect on the base substrate material, which subsequently impacts the structure of AgNPs and their applications. Furthermore, the outcome of this work could contribute to the multifunctional surface for detecting heavy metals, various organic pollutants, and disinfection of water and food-borne pathogenic diseases.

Enhanced Sensing of Diseased Blood Samples through One-Dimensional MgO-SiO2 Photonic Crystal Sensor

In this investigation, we present a tailored one-dimensional photonic crystal sensor (1D PCS), magnesium oxide (MgO) and silicon dioxide (SiO2) layers designed for the specific detection of diseased blood samples components, including plasma, platelets, red blood cells, and uric acid concentrations. The sensor structure is architecturally optimized for 6, 8,10,12,14, and 20 periods, encapsulating a central defect cavity that facilitates the interaction with the blood samples. Upon introducing the blood samples into this cavity, the transmittance spectrum is meticulously analyzed using the transfer matrix method to observe the variations in the defect mode’s wavelength. The study is conducted over a range of incident waves from wavelength 450 to 750 μm, enhancing the understanding of the sensor’s effect on the detection mechanism. In this context, our sensor demonstrates a remarkable sensitivity of approximately 815 nm per refractive index unit (RIU-1). It achieves a detection limit of 10–5, showcasing an exceptional ability to detect low concentrations of the infected blood components.Moreover, Q Factor of 3795 and FOM of 3369.18 indicate the sensor’s high precision in differentiating between healthy and infected blood samples.These findings underscore the potential of the proposed MgO-SiO2-based 1D PhC sensor in serving as a high-fidelity tool for biosensing application.

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.

A simulation-based analysis of optical read-out for electrochemical reactions using composite vortex beams.

We propose an optical read-out method for extracting faradaic current in electrochemical (EC) reactions and analyze its performance using opto-EC simulations. Our approach utilizes structured electrodes to generate composite optical vortex (COV) beams upon optical illumination. Through opto-EC simulations, we demonstrate that the EC reaction of 10 mM potassium ferricyanide induces a refractive index (RI) change, RI, of approximately RI units, leading to the rotation of the COV beam's intensity profile with a peak rotation of . This rotation's magnitude is proportional to RI, while the rate correlates with the faradaic current ( ) density responsible for RI. As the opto-EC information is from bulk RI, it remains unaffected by interfering non-faradaic components at the interface and is advantageous for studying intermediate species and bulk homogeneous reactions. Furthermore, as rotation depends on density rather than itself, this method proves beneficial in low scenarios, such as when employing micro-electrodes to decrease solution resistance or obtain localized EC data. Even in low density scenarios, like monitoring slow EC reactions, our method enables signal amplification by accumulating rotation over time. This interdisciplinary approach holds promise for advancing EC research and addressing critical challenges across various fields, including energy storage, corrosion protection, environmental remediation, and biomedical sciences.

[formula omitted] modified U-shaped fiber surface plasmon resonance sensor with high sensitivity

Design of optical fiber structure and sensitive material coating are two effective performance improvement approaches for fiber optic surface plasmon resonance (SPR) sensors. Here, a tungsten diselenide (WSe2) modified U-shaped fiber optic SPR sensor is proposed. It is found that the sensing performances of the proposed U-shaped probe can be controlled with the thickness of gold film, WSe2 layers, and bending radius of the U-shaped fiber. A sensitivity of 27520 nm/RIU (RIU: refractive index unit) is obtained with the optimized U-shaped probe, which is about 11.56-fold and 12.29-fold improvements over the traditional in-line transmission fiber optic SPR sensors without WSe2 coating and with monolayer WSe2, respectively. These results demonstrate a promising approach for sensitivity improvement of fiber optic SPR sensors, and the proposed WSe2 modified U-shaped fiber optic SPR sensor may have prospective potential applications in biological sensing, chemical sensing, and environmental monitoring.

High-Sensitivity Janus Sensor Enabled by Multilayered Metastructure Based on the Photonic Spin Hall Effect and Its Potential Applications in Bio-Sensing.

The refractive index (RI) of biological tissues is a fundamental material parameter that characterizes how light interacts with tissues, making accurate measurement of RI crucial for biomedical diagnostics and environmental monitoring. A Janus sensor (JBS) is designed in this paper, and the photonic spin Hall effect (PSHE) is used to detect subtle changes in RI in biological tissues. The asymmetric arrangement of the dielectric layers breaks spatial parity symmetry, resulting in significantly different PSHE displacements during the forward and backward propagation of electromagnetic waves, thereby realizing the Janus effect. The designed JBS can detect the RI range of 1.3~1.55 RIU when electromagnetic waves are incident along the +z-axis, with a sensitivity of 96.29°/refractive index unit (RIU). In the reverse direction, blood glucose concentrations are identified by the JBS, achieving a sensitivity of 18.30°/RIU. Detecting different RI range from forward and backward scales not only overcomes the limitation that single-scale sensors can only detect a single RI range, but also provides new insights and applications for optical biological detection through high-sensitivity, label-free and non-contact detection.

Metal-insulator-metal plasmonic sensor utilizing grating-defect waveguide and cavities for temperature sensing and biological applications

This paper proposes a novel plasmonic temperature and refractive index (RI) sensor that utilizes a Metal-Insulator-Metal (MIM) waveguide with two neighboring hexagonal cavities working based on Surface Plasmon Resonance (SPR). The study demonstrates that the structural parameters, including coupling distance and the number of gratings, have a substantial influence on both Full Width at Half Maximum (FWHM) and the transmission spectrum. The findings of this study demonstrated a maximum temperature sensitivity of 0.91 nm.°C−1 for carbon disulfide and a corresponding maximum temperature figure of Merit (FoM) of 0.0180 °C−1 for chloroform. The RI-sensitivity (RIS) of this sensor is found to be 1147.22 nm per RI unit (RIU) as well as its FoM is 37.1 RIU−1. Furthermore, the sensor exhibits the ability to quantify blood glucose concentration with a maximum sensitivity of 0.136 nm.g−1.L and measure blood plasma concentration with a maximum sensitivity of 0.211 nm.g−1.L. This sensor differentiates the RI between healthy and cancer cells and can be utilized to identify both healthy red blood cells and those infected with malaria. Adding gratings to the waveguide and within the hexagonal cavities has a significant impact on the transmission intensity. The proposed plasmonic sensor can be used in optoelectronics, cancer cell sensors and photonic circuits.

Versatile tunable metastructure based on liquid crystal-VO2 for polarization conversion and refractive index sensing

This paper presents a metastructure device (MSD) modulated by liquid crystal (LC) and vanadium dioxide (VO2), suitable for circular-to-linear polarization conversion and refractive index (RI) sensing. The MSD employs a 2 × 2 array as a unit cell, forming a circular-to-linear polarization conversion. Filling the MSD with analytes of different RIs can cause changes in the electromagnetic properties of the MSD, thus realizing the sensing function. Furthermore, the detection range of the sensing can be modified by changing the long-axis pointing of the LC molecules under an applied voltage, resulting in multi-range detection. The RI unit is denoted as RIU. Without an applied voltage, the RI detection range is 1.949–2.607, with a sensitivity of 199 GHz/RIU; under full-bias conditions, the detection range is 2.828–3.391, with a sensitivity of 143 GHz/RIU. In the initial state of LCs, this paper also explores the use of the phase transition of VO2 to adjust the conductivity of VO2 to achieve changes in the detection range. In the insulating state, the detection range is 2.12–2.607, with a sensitivity of 225 GHz/RIU, while in the metallic state, the detection range is 1–2, with a sensitivity of 183 GHz/RIU. Furthermore, altering the thickness of the analyte also affects the electromagnetic properties of the device, causing a shift in the peak axial ratio frequency, making the MSD suitable for analyte thickness detection. The MSD has a wide detection range, high sensitivity, and adaptability, making it suitable for identifying cancer cells and giving a new method of monitoring human health.

Label-Free Biosensor Based on Particle Plasmon Resonance Coupled with Diffraction Grating Waveguide.

Particle plasmon resonance (PPR), or localized surface plasmon resonance (LSPR), utilizes intrinsic resonance in metal nanoparticles for sensor fabrication. While diffraction grating waveguides monitor bioaffinity adsorption with out-of-plane illumination, integrating them with PPR for biomolecular detection schemes remains underexplored. This study introduces a label-free biosensing platform integrating PPR with a diffraction grating waveguide. Gold nanoparticles are immobilized on a glass slide in contact with a sample, while a UV-assisted embossed diffraction grating is positioned opposite. The setup utilizes diffraction in reflection to detect changes in the environment's refractive index, indicating biomolecular binding at the gold nanoparticle surface. The positional shift of the diffracted beam, measured with varying refractive indices of sucrose solutions, shows a sensitivity of 0.97 mm/RIU at 8 cm from a position-sensitive detector, highlighting enhanced sensitivity due to PPR-diffraction coupling near the gold nanoparticle surface. Furthermore, the sensor achieved a resolution of 3.1 × 10-4 refractive index unit and a detection limit of 4.4 pM for detection of anti-DNP. The sensitivity of the diffracted spot was confirmed using finite element method (FEM) simulations in COMSOL Multiphysics. This study presents a significant advancement in biosensing technology, offering practical solutions for sensitive, rapid, and label-free biomolecule detection.

Machine learning approach in multi-channel fiber-optic SPR sensors

Fiber-optic surface plasmon resonance (SPR) sensors have been increasingly used due to their advantages such as compact size, stable physical and chemical properties, high sensitivity, and resistant to electromagnetic interference. In this paper, a dual-channel side-polished fiber-optic SPR sensor system is established to detect the refractive index of liquids and the liquid temperature. High sensitivity of ∼2000 nm/RIU (refractive index unit) and linear sensitivity of ∼−2.0 nm/°C is achieved for two-channel SPR sensors, which are integrated for simultaneously RI temperature sensing and easily scaled to multi-channel SPR sensor array. The resonant wavelengths of the two sensors are located in the range of 600–700 nm and 700–800 nm respectively, which could avoid overlapping the resonance dips. Then, we propose an approach using five machine learning algorithms to predict the resonant wavelength of the second channel of SPR temperature sensor using the normalized transmission spectrum data with a wavelength range of 760–889 nm. After error analysis, it is found that the Categorical Boosting (CatBoost) is the best among five algorithms in terms of accuracy and resolution. The results provide clear evidence that accurate SPR resonant wavelength can be obtained with machine learning approach using a more compact spectrometer.

Optical Detection of Underwater Propeller Wake Based on a Position-Sensitive Detector

The study of underwater vehicle wake detection is of significant importance within the field of target detection, localisation, and tracking of underwater vehicles. Given that propellers are the propellers of modern ships and underwater vehicles, the propeller wake field represents the principal target source for wake detection in underwater vehicles. The objective of this paper is to propose a method for measuring the wake of an underwater propeller based on a position-sensitive detector. A theoretical model of the relationship between the laser spot displacement and the change in the refractive index of the wake field is established on the basis of the principle of laser beam deflection. A prototype experimental setup for underwater propeller wake measurement was constructed based on the aforementioned optical measurement method. Furthermore, the simulation of the propeller wake flow field with strong density stratification and linear density stratification was conducted based on the experimental setup. Furthermore, experiments were conducted to detect the flow field of a propeller wake. The experimental results indicate that the wake dissipation times of the propeller in a strong density-stratified water environment are approximately 800 s and 750 s. Following the stabilisation of the wake field density, the laser spot position is observed to be stable at 0.341 mm and 0.441 mm, respectively, with a corresponding refractive index change of 2.99 × 10−6 RIU (refractive index unit) and 3.87 × 10−6 RIU, respectively. These experimental results are found to be in general agreement with the simulation results of the propeller wake field. A comparison of the experimental wake measurements based on the device with the wake measurements based on a CTD (conductivity–temperature–depth) device reveals a consistent trend. The realisation of this detection technique is of great significance for the advancement of research in the field of optical detection of underwater vehicle wake streams.

Graphene-based metamaterial: Achieving perfect absorption across multiple spectral bands with high sensitivity

In this paper, propose a highly sensitive absorber that utilizes graphene-based patterns to achieve perfect absorption on three different spectral bands. This absorber is designed as a traditional metamaterial structure, optimized to achieve perfect absorption. With the participation of surface plasmon resonance, the absorber achieved absorption rates of 99.14 %, 98.21 %, and 99.32 % at resonance wavelengths of 2933.53 nm, 2956.05 nm, and 3360.45 nm, respectively. Considering factors such as impedance matching and electric field, provide a comprehensive physical explanation for the generation of these absorption peaks. In addition, demonstrated how can modify the wavelength of the absorption peak by adjusting the Fermi energy, and fine tune the absorption rate of a fixed wavelength by manipulating the relaxation time, thereby demonstrating the versatility of our design. In addition, this research explored the complex relationship between the Fermi level and the resonant wavelength and studied the influence of the refractive index of the dielectric layer on the resonant wavelength. It is worth noting that this relationship can be expressed as a strict linear function. As the external refractive index changes, calculated the sensitivity of the absorber, with a peak sensitivity of 768.75 nm/RIU (refractive index unit). This high sensitivity corresponds to a quality factor of 93.31 for the absorption peak. At the same time, our absorber also has good insensitivity to incident angles. In summary, due to its outstanding performance characteristics, this research proposed absorber has broad application prospects in fields such as optoelectronic detection and high sensitivity sensors.

Broadband Enhancement of Magneto-Optical Effects in Hybrid Waveguide-Plasmonic Surfaces for Sensing.

Conventional magnetophotonic nanostructures typically function within narrow wavelength and incident angle ranges, where resonance is observed and magneto-optical (MO) effects are amplified. Expanding these operational ranges may allow for improved applications, including in (bio)sensing devices. In this study, we describe a hybrid magnetoplasmonic waveguide grating (HMPWG) in which the coupling of plasmonic resonances and waveguide modes leads to enhanced MO effects and sensitivity, according to full-wave electromagnetic simulations. High transverse magneto-optical Kerr effect (TMOKE) signals were observed for the full range of wavelengths and angles investigated, i.e., for θinc ≥ 1° and 500 nm ≤ λ ≤ 850 nm. As a proof-of-concept we verified that using the HMPWG nanostructure with an aqueous solution as superstrate one may obtain a sensitivity in variation of the refractive index unit (RIU) of S = 166°/RIU and S = 230 nm/RIU in angle and wavelength interrogation modes, respectively. Upon comparing with conventional magnetoplasmonic gratings, which only enable excitation of plasmonic resonances, we demonstrate that HMPWG nanostructures can be further optimized to reach not only high sensitivity but also high resolution in sensing and biosensing.

Highly sensitive near-field leakage-enhanced optical fiber SPR sensor based on gold nanoarrays modulation

A novel near-field leakage-enhanced optical fiber surface plasmon resonance (NLF-SPR) sensor based on the synergistic sensitization of cuboid gold nanoarrays and WSe2 film is proposed for the first time to our knowledge. The sensor is composed of a side-polished multimode fiber, a continuous gold film, a continuous tungsten selenide (WSe2) film, and well-arranged cuboid gold nanoarrays. The sensor leverages the high carrier mobility characteristic of the WSe2 film, the near-field leakage enhancement arising from the nanoarrays structure, and the localized electric field enhancement property introduced by nanotips to enhance the refractive index sensitivity. In order to optimize the spectral characteristic, the modulation of electric field distribution and spectral characteristic by the structural parameters of gold nanoarrays is investigated through three-dimensional (3D) finite element simulation. Results show that in the refractive index range of 1.3332–1.3432 refractive index unit (RIU), the average sensitivity of the NLF-SPR sensor can reach up to 10108 nm/RIU, and the highest sensitivity can reach up to 14692.46 nm/RIU. The average sensitivity and the highest sensitivity are 1.87 times and 2.56 times higher, respectively, than those of the side-polished fiber SPR sensor with a monolayer gold film. Furthermore, the experimental results demonstrate that the near-field leakage enhancement introduced by gold nanoarrays improves the performance of the fiber SPR sensor, resulting in a 49.3 % increment in sensitivity. The experimental results are in agreement with the trend of the simulation results. Even better performance improvements have been achieved compared to existing methods and a more flexible approach to performance tuning is provided. With the maturity and development of various nanoarray processing techniques such as focused ion beam, electron beam lithography, and nanoimprint lithography, the proposed NLF-SPR sensor has the potential to be fabricated on a large scale and is expected to be widely employed in biomedical, clinical applications, and other fields.

Mid-Infrared Dispersion Spectroscopy as a Tool for Monitoring Time-Resolved Chemical Reactions on the Examples of Enzyme Kinetics and Mutarotation of Sugars.

Ongoing technological advancements in the field of mid-infrared (MIR) spectroscopy continuously yield novel sensing modalities, offering capabilities beyond traditional techniques like Fourier transform infrared spectroscopy (FT-IR). One such advancement is MIR dispersion spectroscopy, utilizing a tunable quantum cascade laser and Mach-Zehnder interferometer for liquid-phase analysis. Our study assesses the performance of a custom MIR dispersion spectrometer at its current development stage, benchmarks its performance against FT-IR, and validates its potential for time-resolved chemical reaction monitoring. Unlike conventional methods of IR spectroscopy measuring molecular absorptions using intensity attenuation, our method detects refractive index changes (phase shifts) down to a level of 6.1 × 10-7 refractive index units (RIU). This results in 1.5 times better sensitivity with a sevenfold increase in analytical path length, yielding heightened robustness for the analysis of liquids compared to FT-IR. As a case study, we monitor the catalytic activity of invertase with sucrose, observing the formation of resultant monosaccharides and their progression toward thermodynamic equilibrium. Anomalous refractive index spectra of reaction mixtures, with substrate concentrations ranging from 2.5 to 25 g/L, are recorded, and analyzed at various temperatures, yielding Michaelis-Menten kinetics findings comparable to the literature. Additionally, the first-time application of two-dimensional correlation spectroscopy on the recorded dynamic dispersion spectra correctly identifies the mutarotation of reaction products (glucose and fructose). The results demonstrate high precision and sensitivity in investigating complex time-dependent chemical reactions via broadband refractive index changes.

State primary special standard of complex refractive index and length in the field of measuring the thickness of optical coatings GET 203-2024

In many areas of science and technology, there is a task to measure the optical and geometric characteristics of thin fi lms. The need to ensure the uniformity of measurements in this area led to the creation of the State primary standard of complex refractive index units GET 203-2012. In it, the complex refractive index was measured using spectral ellipsometry by measuring ellipsometric angles. However, this standard did not provide metrological support for coating thickness measurements when measuring their complex refractive index. In the period 2020–2023, VNIIOFI GET 203-2012 improved and expanded its functionality in terms of reproducing the unit of length in the fi eld of thickness measurements of optical coatings. The improved standard has been approved as the State primary special standard for units of complex refractive index and units of length in the fi eld of thickness measurements of optical coatings GET 203-2024. GET 203-2024 ensures the unity of measurements of complex refractive index and units of length in the fi eld of optical thickness measurements in the range from 1 nm to 50 μm. The range expansion was achieved by introducing an ellipsometer with an infrared range wavelength range equipped with an FTIR Fourier spectrometer. This range expansion is important for such industries as optics, microelectronics, optoelectronics, integrated optics and other areas of science and technology. This article presents the composition, operating principle and main metrological characteristics of GET 203-2024.

Exciting Surface Plasmon Resonances on Gold Thin Film‐Coated Optical Fibers Through Nanoparticle Light Scattering

AbstractSurface plasmon resonance (SPR) conventionally occurs at the interface of a thin metallic film and an external dielectric medium in fiber optics through core‐guided light. However, this work introduces theoretical and experimental evidence suggesting that the SPR in optical fibers can also be induced through light scattering from Au nanoparticles (NPs) on the thin metallic film, defined as nanoparticle‐induced SPR (NPI‐SPR). This method adheres to phase‐matching conditions between SPR dispersion curves and the wave vectors of scattered light from Au NPs. Experimentally, these conditions are met on an etched optical fiber, enabling direct interaction between light and immobilized Au NPs. Compared to SPR, NPI‐SPR exhibits stronger field intensity in the external region and wavelength tuning capabilities (750 to 1250 nm) by varying Au NP diameters (20 to 90 nm). NPI‐SPR demonstrates refractive index sensitivities of 4000 to 4416 nm per refractive index unit, nearly double those of typical SPR using the same optical fiber configuration sans Au NPs. Additionally, NPI‐SPR fiber configuration has demonstrated its applicability for developing biosensors, achieving a remarkable limit of detection of 0.004 nm for thrombin protein evaluation, a twenty‐fold enhancement compared to typical SPR. These findings underscore the intrinsic advantages of NPI‐SPR for sensing.

Double tunable Fano resonance based on a metal–insulator–metal waveguide with double coupled cavities and its application

A metal–insulator–metal (MIM) waveguide with a ring cavity (RC) and a half ring cavity (HRC) is proposed to realize the detection of two mediums simultaneously based on independently tunable double Fano resonances. Utilizing numerical simulation of the finite element method, the transmission characteristics and magnetic field distribution are investigated. The simulation findings indicate that the structure is capable of generating double Fano resonances, and the two Fano resonances are tuning independently. The maximum sensitivity and figure of merit (FOM) are 2385 nm/RIU (refractive index unit) and 31886RIU−1, respectively, and these values are achieved by changing the structural parameters and the refractive index of the insulator. Moreover, the sugar content in flavor and the concentration of ethanol solution can be detected at the same time, which indicates the high efficiency of the sensor. Therefore, these performances demonstrate that the tunable double Fano resonance based on a MIM waveguide is a hopeful method for chemical detection.

Responsive refractive index sensor based on actively tuning liquid crystal topological edge states

In this paper, using the electric field regulation and low loss properties of liquid crystal materials, a tunable polarization-separated liquid crystal (LC) topological edge state is proposed, whose potential in responsive sensors (RSs) is explored. Adjustment of the measuring range and sensitivity of the RS can be realized by controlling the orientation angle of LC and the analyte proportion. In the case of a low ratio of analytes, as the LC orientation angle changes from 18° to 0°, the measurement range will also vary from 1–1.8 RIU (refractive index unit) to 1.8–2.3 RIU. When adding the proportion of analytes and the number of periods, the normalized sensitivity will be increased from 0.0759 c/d/RIU (c is the propagation speed of light in vacuum, and d is the normalized thickness) to 0.299 c/d/RIU, leading to a reduction in the detection limit from 2.75 × 10−4 to 5 × 10−6 RIU, so biological indicators such as bacteria Leptospira in rodent urine can be detected.