Wide Range Of Refractive Indices Research Articles

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.

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

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.

Flow Characterisation Using Fibre Bragg Gratings and Their Potential Use in Nuclear Thermal Hydraulics Experiments

With the ever-increasing role that nuclear power is playing to meet the aim of net zero carbon emissions, there is an intensified demand for understanding the thermal hydraulic phenomena at the heart of current and future reactor concepts. In response to this demand, the development of high-resolution flow analysis instrumentation is of increased importance. One such under-utilised and under-researched instrumentation technology, in the context of fluid flow analysis, is fibre Bragg grating (FBG)-based sensors. This technology allows for the construction of simple, minimally invasive instruments that are resistant to high temperatures, high pressures and corrosion, while being adaptable to measure a wide range of fluid properties, including temperature, pressure, refractive index, chemical concentration, flow rate and void fraction—even in opaque media. Furthermore, concertinaing FBG arrays have been developed capable of reconstructing 3D images of large phase structures, such as bubbles in slug flow, that interact with the array. Currently a significantly under-explored application, FBG-based instrumentation thus shows great potential for utilisation in experimental thermal hydraulics; expanding the available flow characterisation and imaging technologies. Therefore, this paper will present an overview of current FBG-based flow characterisation technologies, alongside a systematic review of how these techniques have been utilised in nuclear thermal hydraulics experiments. Finally, a discussion will be presented regarding how these techniques can be further developed and used in nuclear research.

Highly sensitive dual core photonic crystal fiber-based LSPR sensor with simultaneous multi-analyte detection of a wide refractive index range

This manuscript introduces an anisotropic highly sensitive dual core photonic crystal fiber sensor based on localized surface plasmon resonance, possessing the ability to detect multiple analytes simultaneously. Liquid analytes having a refractive index (RI) within the range of 1.25 to 1.5 RIU have been investigated using the proposed sensor. The numerical analysis of the sensing parameters for the proposed sensor shows a maximum wavelength sensitivity of 47,500 nm/RIU for x-polarization (Channel 1) and 18,050 nm/RIU for y-polarization (Channel 2), respectively using the wavelength interrogation technique. Maximum amplitude sensitivity of 625 RIU−1 and 437 RIU−1 is obtained for x−pol. and y−pol., respectively using the amplitude interrogation technique. Maximum sensor resolution of 2.11 × 10−6 RIU and 5.01 × 10−6 RIU is obtained for x−pol. and y−pol., respectively. The linear relationship of the resonant wavelength with the RI produces R2 = 0.9976 and R2 = 0.9979, corresponding to a degree (3) for x−pol. and y−pol., respectively. The figure of merit for x−pol. and y−pol. are 84 RIU−1 and 123 RIU−1.

Femtosecond laser direct writing of long period fiber grating sensor with high refractive index sensitivity

Long-period fiber grating sensors with high refractive index sensitivity were designed and validated using femtosecond laser direct writing. The device consists of a single-mode fiber and a 2 cm long thin-core fiber fused. The refractive index is changed periodically by direct writing of a femtosecond laser pulse at the core of the thin-core fiber. Fiber gratings with periods of 80 μm, 150 μm, and 300 μm were selected for the study and showed maximum refractive indices of 1.4054, 1.4215, and 1.4326, respectively. With an 80 μm period, the maximum refractive index sensitivity increases significantly with wavelength and reaches 1430 nm/RIU. The temperature sensitivity is 7.6 pm/°C between 30 °C–430 °C and 14.4 pm/°C between 430 °C–630 °C. The sensor is high-temperature resistant, robust, simple to fabricate, and has a wide range of measurable refractive indices. This thin-core long-period fiber grating can better reduce crosstalk due to temperature effects in refractive index testing.

SPR Sensor Based on a Concave Photonic Crystal Fiber Structure with MoS2/Au Layers.

We propose a surface plasmon resonance (SPR) sensor based on the concave photonic crystal fiber (PCF) coated with molybdenum disulfide (MoS2) and Au layers, which can detect the refractive index (RI) of the analyte. The finite element method (FEM) was used to verify our design, and the loss spectra of the fundamental mode are calculated. Compared with the SPR sensor with only a Au layer, the wavelength sensitivity can be improved by from 3700 to 4400 nm/RIU. Our proposed sensor works in near-infrared band and has a wide RI range from 1.19 to 1.40. The influences of the geometrical parameters of PCF and the thicknesses of Au and MoS2 layers on the loss spectra are discussed in detail, and the maximum wavelength sensitivity of 5100 nm/RIU can be achieved. Meanwhile, a high resolution of 1.96 × 10-5 RIU and the largest FOM of 29.143 can be obtained. It is believed that our findings show the sensor's excellent potential in medical testing, unknown biological detection, environmental monitoring and organic chemical detection.

Theoretical study of perovskite nano material based surface plasmon resonance biosensor for cancers cell detection

The present study reports screening of cancer cells at the earliest stages using prism coupling-based surface plasmon resonance biosensors in a theoretical manner. The SPR sensors designed on Kretschmann configuration consisting of several layers like silver (Ag) metal, beryllium oxide (BeO) and hetero-structure BlueP/WSe2 layer deposited over BK7 glass prism. For maximum light absorption, a perovskite nano material, barium titanate (BaTiO3) layer is placed between BeO and hetero-structure BlueP/WSe2 to enhance the angular sensitivity. The light of 633 nm wavelength has been used for excitation of surface plasmon at metal dielectric interface. The refractive index of cancer cells lies between 1.360 and 1. 400. The optimized angular sensitivity of 216°/RIU and 360°/RIU for PCI-2 (normal, adrenal gland cancer), 248°/RIU and 254°/RIU for MDA-MB-231(normal, breast cancer cell) as well as 248°/RIU and 254°/RIU for MCF-7 (normal, breast cancer cell) respectively has been obtained. The maximum optimized angular sensitivity for adrenal gland cancer is 360°/RIU on employing perovskite layer. The sensor offers excellent performance parameters and covers wide range of refractive index sensing.

Designing multifunctional silica coatings for enhanced broadband antireflection and microfiber contamination sensing

Multifunctional silica coatings find diverse applications in solar energy conversion and pollution monitoring sensors due to their suitability for mass manufacturing. However, the challenge lies in producing robust silica coatings on a large scale with tunable refractive index. This work presents a two-step acid/base catalyzed sol–gel process for synthesizing multifunctional silica coatings with adjustable refractive index. The coatings' porous microstructure allows them to be used as double-layer broadband antireflective coatings and enhances the sensitivity of contamination sensors. The optimized double-layer coatings, designed using computer-aided techniques, demonstrate excellent broadband antireflective performance in the visible regions and high environmental durability. They achieve a maximum transmittance of 99.87% at 591 nm, with an average transmittance of 99.40% in the visible region (400–800 nm) and 98.63% from 400 nm to 1100 nm. Additionally, the coatings exhibit robust abrasion resistance and enhanced surface hydrophobicity with a water contact angle increased from 30° to 126° through HMDS treatment. This work investigated the particle growth mechanism and the relationship between silica nanoparticle microstructure and antireflective coating properties. Furthermore, the coatings' presence of abundant micropores allows successful application onto microfiber contamination sensors, the additional loss increases from 26.40 dB to 37.69 dB over 140 min and decreases to 31.55 dB within one minute, demonstrating rapid adsorption and desorption rates. The work successfully achieves a wide range of adjustable refractive index while maintaining excellent mechanical and optical properties, addressing the traditional trade-off between high porosity and poor mechanical stability. These rationally designed multifunctional silica coatings hold great potential for high-quality broadband antireflection and high sensitivity in microfiber contamination sensing.

Metamaterial as perfect absorber for high sensitivity refractive index based biosensing applications at infrared frequencies

In this paper, we introduce a novel design of a metamaterial unit cell absorber, which is based on a metal/insulator/metal sandwich structure. The design is subjected to comprehensive finite element method computational analysis to ensure accurate and reliable results. The proposed metamaterial sandwich structure demonstrates exceptional absorption performance, achieving a nearly perfect absorption rate of 99.996% at the resonance infrared frequency of 39.8 THz. To provide a detailed theoretical explanation of nearly perfect absorption, we employ the effective medium theory, impedance matching, and field distribution analysis. Additionally, we have optimized the structural parameters of the sensor to maximize its absorption peak. This includes optimizing the thickness of the gold (Au) layer (from 0.03 to 0.28 μm), the distance between the L shape corners (from 0.60 to 0.90 μm), and the thickness of SiC dielectric spacer (from 0.20 to 0.45 μm). Furthermore, we showcase the remarkable sensitivity of the proposed metamaterial unit cell in detecting subtle changes in the refractive index through the implementation of a sensing medium setup in our model. Remarkably, we achieve a frequency shift sensitivity of 3.74 THz/RIU, along with a quality factor of 10.33, for a wide range of refractive indices (1.0–2.0). Moreover, for cancer detection, we attain a sensitivity of 3.5 THz/RIU. These findings highlight the exceptional performance of our approach in accurately detecting changes in refractive index, making it a promising candidate for various sensing applications. The novelty of our work lies in the design of a metamaterial unit cell structure. This configuration exhibits several noteworthy features, including wide incident angle () coverage up to 60°, polarization insensitivity, exceptional frequency shift sensitivity, high absorption peaks across a wide range of refractive indices, and the ability to distinguish cancer cells from healthy ones.

Dual core photonic crystal fiber based plasmonic refractive index sensor with ultra-wide detection range.

In this study, an ultra-wide range plasmonic refractive index sensor based on dual core photonic crystal fiber is suggested and analyzed numerically. The proposed design achieves fabrication feasibility by employing external sensing mechanism in which silver is deposited onto the flat outer surface of the fiber as plasmonic material. A thin layer of titanium oxide (TiO2) is considered on top of the silver layer for preventing its oxidation problem. The sensor attains identification of a vast array of analytes consisting a wide range of refractive indices of 1.10 - 1.45. It achieves a maximum spectral sensitivity of 24300 nm/RIU along with its corresponding resolution of 4.12 × 10-6 RIU. The maximum figure of merit of the sensor is 120 RIU-1. The sensor also supports amplitude interrogation approach and exhibits a maximum amplitude sensitivity of 172 RIU-1. The impact of the design parameters such as radius of air holes, polishing distance, thickness of silver and titanium oxide layers are investigated thoroughly. An ultra-wide detection range with high sensitivity, fabrication feasibility, and easy application make the sensor a potential candidate for detection of a wide array of bio-originated materials, chemicals, and other analytes.

High-accuracy wide-range refractive index demodulation based on under-sampled fiber F-P cavity length spectrum.

A scheme of fiber Fabry-Perot (F-P) cavity refractive index (RI) demodulation named under-sampled length spectrum retrieval (ULSR) is proposed. Unlike the wavelength spectrum method, ULSR can be used for physical quantity detection with just a monochromatic laser and photodetectors, avoiding the need for wideband lasers or expensive infrared spectrometers. Eight F-P cavities of different lengths were fabricated to sample the cavity length spectrum, and then the obtained under-sampled length spectrum was used to demodulate the RI of F-P cavity fillings. It was demonstrated that the ULSR system can achieve an index measurement accuracy of 1 × 10-4 in the glucose solution index range of 1.3294-1.3746 at wavelength λ = 1.55 µm. An index demodulation with higher accuracy and wider range is expected when more than 8 F-P cavities are used. The proposed scheme, with advantages of low system complexity, low cost, high reliability, high detecting accuracy, and wide detecting range, holds great promise for facilitating the wide application of F-P cavity sensors. Additionally, ULSR liberates wavelength freedom, making it a strong candidate for multiplexed sensing based on wavelength division multiplexing.

High Sensitivity and Wide Range Refractive Index Sensor Based on Surface Plasmon Resonance Photonic Crystal Fiber.

In order to detect the refractive index (RI) of high refractive index materials such as trichlorobenzene and aniline in the near-infrared and mid-infrared spectra and expand the detection range of the refractive index, a surface plasmon resonance (SPR) photonic crystal fiber (PCF) sensor based on an elliptical sensing channel is proposed for high refractive index detection. The fiber core and the analyte channel are surrounded by two types of air holes with different sizes. When the surface plasmon resonance effect appears at the interface between the fiber core and the elliptical sensing layer, obvious resonance peaks appear in the near-infrared and mid-infrared bands. The full vector finite element method (FEM) is used to study the sensing characteristics of the sensor and the influence of structural parameters on the resonance peak. The results demonstrate that the sensor achieves detection in the refractive index range of 1.41-1.58, in the wavelength range of 1600-3200 nm. The average wavelength sensitivity is 9217.22 nm/RIU, and the refractive index resolution is 10.85 × 10-6 RIU. The proposed sensor realizes high refractive index detection in the near-infrared and mid-infrared bands, and obtains an ultra-wide detection range and higher sensitivity. The sensor has broad application prospects in chemical detection, biomedical sensing and other fields, and provides a theoretical reference for the design of a photonic crystal fiber surface plasmon resonance sensor.

Mesoporous Metal Fluoride Nanocomposite Films with Tunable Optical Properties Derived from Precursor Instability.

The precisely tailored refractive index of optical materials is the key to utilizing and manipulating light during its propagation through the matrix, thereby improving their application performances. In this paper, mesoporous metal fluoride films with engineered composition (MgF2 :LaF3 ) are demonstrated to achieve finely tunable refractive indices. These films are prepared using a precursor-derived one-step assembly approach via the simple mixing of precursor solutions (Mg(CF3 OO)2 and La(CF3 OO)3 ); then pores are formed simultaneously during solidification owing to the inherent instability of La(CF3 OO)3 . The mesoporous structures are realized through Mg(CF3 OO)2 and La(CF3 OO)3 ions, which interacted with each other based on their electrostatic forces, providing a wide range of refractive indices (from 1.37 to 1.16 at 633 nm). Furthermore, it is systematically several MgF2(1-x) -LaF3(x) layers with different compositions (x=0.0, 0.3, and 0.5) to form the graded refractive index coating that is optically consecutive between the substrate and the air for broadband and omnidirectional antireflection. An average transmittance of ≈98.03% (400-1100nm) is achieved with a peak transmittance of ≈99.04% (at 571nm), and the average antireflectivity is maintained at ≈15.75% even at an incidence of light of 65° (400-850nm).

Ag/CdS surface plasmon simulation systems for gas sensor

In this work, the Surface Plasmon Resonance (SPR) sensor simulated for a wide range of wavelengths and refractive index. The Kretschmann configuration of the suggested sensor is Silver (Ag) with a thickness of 45 ​nm, and Cadmium Sulfide (CdS) dielectric with variable thickness (10 ​nm–80 nm) that deposited on FD60 Dense flint prism. The sensing medium is gas which includes air and different refractive indexes (Δn ​= ​0, 0.02, 0.05, and 0.1) to consider most gas cases. The wavelength light range studied from 100 nm to 1000 ​nm. The results show that SPR appeared strongly in the Infrared range between 900 ​nm and 1000 ​nm. It is weakly appeared in the visible range and cannot be noticed in the ultraviolet region. The sharpest and longest SPR dip occurred in the Infrared range. The smallest value of full-width half maxima (FWHM) was 0.4° at CdS thickness of 10 ​nm, and the longest SPR dip has 0.97° at CdS thickness of 60 ​nm. The smallest and longest value of FWHM dip occurred at wavelength 1000 ​nm and n ​= ​0.02. Hence, the better detection accuracy and sensitivity of the SPR sensor were in the infrared region at wavelength 1000 ​nm and n ​= ​0.02 for the suggested sample. So, the range of working wavelengths depending on the sample design.