Refractive Index Of Liquid Research Articles

Dual-core-enhanced surface plasmon resonance for sensing high refractive index liquid based on photonic crystal fiber

A dual-core photonic crystal fiber sensor based on surface plasmon resonance is theoretically proposed for the high-sensitive detection of high refractive index liquid analytes. Dual-core construction can effectively enhance the coupling effect between the fiber-core mode and the surface plasmon polariton modes, leading to sharp loss peaks at the resonance wavelengths. As the refractive index of the targeted analyte varies, the resonance condition will change as well and cause a certain shift of loss peak. Numeric results show that this dual-core fiber sensor exhibits an average linear sensitivity 9538 nm/RIU and a maximum sensitivity is 11400 nm/RIU with a resolution 8.77 × 10−6 RIU. The detected range is broad and covers the high refractive index range from 1.45 to 1.58 with an average figure of merit 284.5 RIU−1. The dependence of structure parameters and the thickness of coated-metal thin-film on sensing performance is performed systemically and suggests different responses. The proposed sensor is highly promising in detecting high refractive index liquid analytes in the fields of biological detection, environmental monitoring and chemical analysis.

Numerical Analysis of Solid-Core Photonic Crystal Fiber Based on Plasmonic Materials for Analyte Refractive Index Sensing

In this study, we presented a simple highly sensitive sensor based on commercially available solid-core photonic crystal fiber (PCF) and surface plasmon resonance (SPR) for measuring the refractive index (RI) of analytes. The numerical simulation based on the finite element method (FEM) has been examined to compute the optical properties such as confinement loss, power spectrum, and transmission intensity of the sensor. The most sensitive and inert plasmonic materials (gold and silver) have been assumed to be coated inside the fiber with the range of analyte RI from 1.32 to 1.40. The performance of the proposed sensor has been evaluated by tracing the several optical features like wavelength sensitivity, amplitude sensitivity, resolution of the sensor, and figure of merit. As a result, the comparative study between silver and gold elements has been carried out in which the maximum sensitivity received was 1.15 μm/RIU and 1.10 μm/RIU, respectively. Whereas, on the base of power spectrum, the obtained sensitivity was 513 μm/RIU for the gold layer. Moreover, the effect of other structural parameters (air holes and plasmonic layer thickness) on the sensing performance has been taken into an account. According to the simulation analysis and results, this sensor would have a great potential in various sensing applications of biomedical and liquid refractive index.

Spatially Modulated Fiber Speckle for High-Sensitivity Refractive Index Sensing.

A fiber speckle sensor (FSS) based on a tapered multimode fiber (TMMF) has been developed to measure liquid analyte refractive index (RI) in this work. By the lateral and axial offset of input light into TMMF, several high-order modes are excited in TMMF, and the speckle pattern is spatially modulated, which affects an asymmetrical speckle pattern with a random intensity distribution at the output of TMMF. When the TMMF is immersed in the liquid analyte with RI variation, it influences the guided modes, as well as the mode interference, in TMMF. A digital image correlations method with zero-mean normalized cross-correlation coefficient is explored to digitize the speckle image differences, analyzing the RI variation. It is found that the lateral- and axial-offsets-induced speckle sensor can enhance the RI sensitivity from 6.41 to 19.52 RIU-1 compared to the one without offset. The developed TMMF speckle sensor shows an RI resolution of 5.84 × 10-5 over a linear response range of 1.3164 to 1.3588 at 1550 nm. The experimental results indicate the FSS provides a simple, efficient, and economic approach to RI sensing, which exhibits an enormous potential in the image-based ocean-sensing application.

Non-Contact Real-Time Measurement of Refractive Index of Flowing Liquid Based on Optical Coherence Tomography

The refractive index (RI) is one of the liquid’s most important physical parameters of liquid. The change of RI usually indicates the change of liquid properties, and this relation leads to broad application. This paper proposes a method based on optical coherence tomography (OCT) to measure the RI of liquid in real time. A series of targeted image-processing techniques play a vital role in this method. Benefiting from the advantages of OCT, this method does not require the operators to come into direct contact with liquids. Moreover, the principles and techniques adopted in this method imply that the measuring range of RI of unknown liquids is unlimited. The effectiveness of this method is validated by the experiment measuring the RI of sucrose liquids with gradient concentration. Another experiment thoroughly verifies this method’s feasibility in predicting sucrose concentration based on real-time measured RI. This simple and easy proposed method indicates an immense potential application prospect in the industry and scientific research.

High-Sensitivity Carcinoembryonic Antigen Detection Using Open Cavity Fabry-Perot Immunosensor Based on Vernier Effect

A cost-efficient fiber immunosensor based on an open-cavity Fabry–Perot interferometer (FPI) with the Vernier effect for tumor biomarker named carcinoembryonic antigen (CEA) detection is proposed and experimentally shown. A short single-mode fiber (SMF) with the length of 206 μm is spliced between a lead-in SMF and a 217 μm SMF with a large lateral offset to generate a compact open-cavity FPI configuration where a tightly connected open cavity and the silica cavity with slightly various free spectrum ranges are used as the sensing element and the reference element, respectively, to generate the Vernier effect. The refractive index (RI) liquids or biological materials can directly and easily interact with optical signals because of the presence of the open-cavity. The upper envelope's experimental RI sensitivities and open-cavity are −8535 and 1174 nm/RIU, respectively, with linear correlation coefficients of 0.99 and 0.998, respectively, at an RI range of 1.335–1.3388, which perfectly matches with theoretical simulation findings (−8247 and 1171 nm/RIU, respectively). RI sensitivity is enhanced by a factor of 7 using the Vernier effect. Furthermore, the fabricated open-cavity FPI is functionalized with the 50 μg /mL anti-CEA antibody for different concentrations of CEA detection with a limit of detection (LoD) of 36.14 fg/mL. The biosensor's response time is less than 30 min. Additionally, the proposed Fabry–Perot biosensor has low LoD, excellent stability, reproducibility, specificity, and high sensitivity for CEA detection, which allows it to function as a platform for diseases/medical diagnostics. More crucially, the robust biosensor provides the possibility for in situ detection.

Design and research of a dual-parameter photonic crystal fiber sensor

We propose a dual-parameter photonic crystal fiber (PCF) sensor based on a surface plasmon resonance (SPR). It is used to detect a change in the refractive index (RI) and the temperature of the liquid. The contact area between the PCF and the liquid to be tested increases by polishing the PCF up and down. The large air holes that are on the upper and lower sides of the fiber core are plated with gold and silver film, respectively, to detect the RI of the external liquid. Moreover, polydimethylsiloxane (PDMS) is introduced into the large upper air hole to detect the temperature of the external liquid. Based on the finite element method, the diameter of the large air hole, the diameter of the ordinary air hole, the period, and the thickness of the metal layer are analyzed and discussed to find the most suitable parameter values to improve the sensor’s performance. The simulation results show that when the RI detection is in the range of 1.34–1.46, and the temperature detection is in the range of 20°C–30°C, the maximum RI sensitivity is 8400 nm/RIU and the maximum temperature sensitivity is 4.5 nm/°C. The proposed design is simple in structure and principle and solves the problem of multiparameter cross-sensitivity.

Refractive index measurement of uniform liquid using an improved laser speckle method

Based on the refraction characteristic of uniform and transparent liquid, the measurement error of the liquid refractive index using the internal standard method is analyzed, and an improved laser speckle method is proposed. This method designs a double-cell structure composed of two identical rectangular parallelepiped glass cells with one cell containing the liquid to be measured and the other one being empty. This double-cell structure is placed in the built optical system based on laser speckle, and then the refractive indices of sodium chloride solution and sucrose solution with various concentrations are measured by the improved method. Compared with the measurement values of the Abbe refractometer and the internal standard method, the results show that the improved method can significantly reduce the measurement error and improve the measurement accuracy.

Experimental Study of Dual-Parameter SPR Sensor With Integrated Sensing Channel

In order to meet the actual requirements for sensor miniaturization and integration, we propose a compact dual-parameter surface plasma resonance (SPR) fiber sensor, which can simultaneously measure the refractive index and temperature of liquid. The sensor is composed of input-output couplers and two sensing arms. The no-core fibers (NCFs) and microstructured optical fiber (MOF) with deposited films are used as input-output couplers and sensing arms, respectively. One sensing arm is the MOF with silver film for refractive index measurement, and another is that with silver film and PDMS for temperature measurement. Numerical simulation results show its cladding mode is more advantageous in stimulating the SPR effect. Experimental results demonstrate the maximum sensitivity of liquid refractive index is 4139 nm/RIU in the range of 1.333-1.365, and that of liquid temperature is 4.7 nm/°Cin the range of 20-70 °C. The compact structure makes the proposed sensor unique and has a promising application in refractive index and temperature monitoring.

Highly Efficient Refractive Index Sensor Based on a Dual-Side Polished SMS Fiber Enabled by Femtosecond Laser Writing.

Fiber-optic refractive index (RI) sensors based on wavelength-shift-based interrogation continue to present a challenge in achieving high sensitivity for a wide detection range. In this paper, we propose a sensor for determining the RI of liquids based on femtosecond laser (fs-laser) writing of a dual-side polished singlemode-multimode-singlemode (SMS) fiber. The proposed sensor can determine the RI value of a surrounding liquid by detecting the dip wavelength in the transmission spectrum of the light propagating through the sensing area. The high RI sensitivity is attributed to the increased interaction area established by the fs-laser, which creates hydrophilic surfaces and maintains the wide detection range of the SMS structure. The results of the wavelength-shift-based interrogation reveal that the fabricated device exhibited a high sensitivity of 161.40 nm per refractive index unit (RIU) over a wide RI detection range of 0.062 RIU. The proposed device has high processing accuracy and a simple manufacturing process. Hence, it has the potential to be used as a lab-on-fiber sensing platform in chemical and biotechnological applications.

Sự ảnh hưởng của nhiệt độ lên chiết suất cacbon disunphua

In this paper, the effect of temperature on the refractive index of Carbon disulfide liquid based on the influence of temperature on the Sellmeier coefficient has been presented. The effect of temperature on the liquid refractive index of Carbon disulfide in the visible and infrared regions according to the expression of M. Chemnitz was also investigated. From the survey results, it is concluded that as the wavelength increases, the refractive index of Carbon disulfide decreases, but when the temperature is increased then the refractive index of Carbon disulfide decreases faster.

Two Kinds of Liquid Crystal Filled PCFs Temperature and RI Sensors Based on SPR

We propose two novel kinds of liquid crystal (LC) filled D-shape photonic crystal fibers (PCFs) to realize the simultaneous measurement of refractive index (RI) and temperature. The gold film is selected as the plasmonic metal and coated on the D-shaped air hole of the PCF to excite the surface plasmon resonance (SPR). According to the position where the RI liquid is filled in the air hole, the PCFs are named type-1 and type-2. Simulation results show that the proposed sensors have good temperature and RI sensing performance in the detection ranges of 15 °C–50 °C and 1.47–1.55, respectively. For the type-1 sensor, the temperature and RI sensitivities of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${y}$ </tex-math></inline-formula> -polarized core mode are 2.7 nm/°C and 2200 nm/RIU, respectively, and the corresponding linear fitting degrees are 0.95756 and 0.98771. The temperature and RI sensitivities of type-2 are 3.2 nm/°C and 2567 nm/RIU, respectively, and the corresponding linear fits are 0.93135 and 0.98771. The designed dual detection sensors have a great potential and are expected to be applied in environmental, biological, and biochemical sensing.

Nanobubble size distribution measurement by interactive force apparatus under an electric field

Nanobubbles have been applied in many fields, such as environmental cleaning, material production, agriculture, and medicine. However, the measured nanobubble sizes differed among the measurement methods, such as dynamic light scattering, particle trajectory, and resonance mass methods. Additionally, the measurement methods were limited with respect to the bubble concentration, refractive index of liquid, and liquid color. Here, a novel interactive force measurement method for bulk nanobubble size measurement was developed by measuring the force between two electrodes filled with bulk nanobubble-containing liquid under an electric field when the electrode distance was changed in the nm scale with piezoelectric equipment. The nanobubble size was measured with a bubble gas diameter and also an effective water thin film layer covered with a gas bubble that was estimated to be approximately 10 nm based on the difference between the median diameter of the particle trajectory method and this method. This method could also be applied to the solid particle size distribution measurement in a solution.

New oil derivative refractive index sensor using ribbon of multi-walled carbon nanotubes

In this work, we propose a new liquid refractive index (RI) sensor based on one-dimensional (1D) regular array of multi-walled carbon nanotubes (MWCNTs) for sensing oil derivatives (ODs), for the first time. The proposed sensor is a ribbon consisting of 10 MWCNTs grown inside an AAO (Al2O3) template as the host material, which can sense the change of host material RI with high precision up to △n = 0.0015 corresponding to the sensitivity S = 930 nm/RIU. Replacing the host material with ODs changes the reflection in the range of visible wavelengths. The reflection spectrum of sensor is calculated for the RI range of 1.3888–1.5306 belonging to various ODs. The RI difference △n = 0.1418 between Butanol (C4H10O) and Nitrobenzene (C6H5NO2) host materials results in 130 nm wavelength shift. By removing one or two cylinders of MWCNTs and creating a point defect within the sensor structure, whereas ODs are injected into the defect area, we achieved a sensitivity up to 430 nm/RIU. The proposed sensor with un-reactive nature of MWCNTs can be used in environments with high temperature and pressure such as oil refinery industry.

Portable Multihole Plastic Optical Fiber Sensor for Liquid-Level and Refractive Index Monitoring

In this article, we report a low-cost method to fabricate plastic optical fiber (POF) liquid-level and refractive index (RI) sensors integrated with smartphones by molds and drilling microholes in side-growing POFs (SGPOFs) with high-temperature metal wire. These sensors can be used for real-time liquid-level and RI monitoring, especially under situations requiring portability and illumination. When the liquid level changes, the change of the RI around the microholes leads to a change in the light intensity transmitted in the fiber, enabling us to measure the liquid level and RI. Utilizing one sensor with six holes (0.45 mm radius and 15 mm spacing) in 2.0-mm SGPOF, the results of level and RI measuring are in good agreement with the theory. The liquid-level measurement of the sensor is carried out for water with an RI of 1.333, the level sensitivity is 0.29%/cm ± 0.02%/cm. In the RI measurement, the RI sensitivity of the sensor is −22.8%/RIU ± 0.6%/RIU in the measurement range from 1.333 to 1.475.

Compact and Highly Sensitive Refractive Index Sensor Based on Embedded Double-Ring Resonator Using Vernier Effect

A compact and highly sensitive liquid refractive index (RI) sensor using Vernier effect achieved with embedded double-ring resonator is proposed and demonstrated. Unlike these conventional sensors using cascaded double-ring resonators to achieve Vernier effect, in our proposed embedded double-ring sensor (EDRS) the sensing ring is embedded on the reference ring, which makes the sensor more compact while achieving high sensitivity. Our typical fabricated EDRS with polymer material, which has a footprint of 1500 μm × 850 μm, achieves the RI sensitivity as high as 7390 nm/RIU in aqueous medium, which is in excellent agreement with the theoretical one.

Measurements of liquid surface tension and refractive index using a tapered microfiber

In this letter, a tapered microfiber (TMF) liquid surface tension (LST) sensor is proposed and demonstrated. Due to the strong evanescent field and weak stiffness of the TMF, the LST can be measured. The processse of the TMF immersion into liquid and leaching from the liquid are divided into multiple stages, and the dip wavelength shifts at different stages of the immersion process are attributed to refractive index (RI) and bending changes, but those of the process of leaching only are attributed to bending change. By both theory and experiment, it is found that the sensitivity has a obvious response to the waist diameter of the TMF. In addition, the RI of solutions can be measured by monitoring the variation of the wavelength difference of the TMF in liquid and in air. Experimental results show that the RI and LST sensitivity are 14.56 pm/(N/m) and 211.51 nm/RIU, respectively. By using the known RI and LST of the liquid as reference, the RI of the unknown solutions can be obtained and the LST of them can be qualitatively estimated by measurement of wavelength shifts.

Simultaneous Measurement of Dual Parameters Based on Periodically Embedding MMF-Induced Ultralong-Period Fiber Grating

In this article, an ultralong period fiber grating (ULPFG) based on periodically embedding multimode fiber into single mode fiber (PEM-ULPFG) is proposed to simultaneously measure the liquid refractive index (RI) and temperature with high sensitivity. Five resonant dips belong to different cladding modes, and diffraction mode orders appear in the transmission spectrum. The responses of the dips to RI and temperature are different. Therefore, high sensitivity and dual-parameter measurement are realized. Numerical simulation based on the beam propagation method (BPM) is also carried out to design and optimize the parameters of the device. Experimental results show that the maximum RI sensitivity of −1230 nm/RIU in the range of 1.4021–1.4383 RIU is achieved by tracing the target dip (dip 4). The temperature response of dip 4 is also characterized to be as low as 52.6 pm/°C. Another dip (dip 5) is used for measuring temperature with the temperature sensitivity of 92.3 pm/°C. Different responses to the external changes of the dips obtained by the PEM-ULPFG make the proposed sensor competitive in the field of high sensitivity and dual-parameter sensing.

Real-time measuring system for liquid refractive index based on Fourier transform spectrum analysis

Real-time measuring system for liquid refractive index based on Fourier transform spectrum analysis

Measurement of liquid refractive index by quantitative phase reconstruction of single frame dual-wavelength digital hologram

A measurement method of liquid’s refractive index by means of single-shot dual-wavelength off-axis digital holographic microscopy system and a microfluidic chip is presented. The refractive index of liquid filled in the microchannel of a microfluidic chip can be calculated directly with the unwrapped phase map obtained at the synthetized wavelength, without requirement of knowing another liquid’s refractive index as a measurement reference. Moreover, it also avoids the influence of the accuracy of the known refractive index on the refractive index to be measured. The refractive indices of salt solutions and sucrose solutions in the several concentrations are achieved in the experiments, which verifies that the measurement of liquid’s refractive index is accurate and reliable. With the merit of accurate measurement of liquid’s refractive index based on the one-frame dual-wavelength hologram, it is expected that this approach will be employed to detect in real-time the fluid’s parameters related to its refractive index.

A liquid level optical fiber sensor with refractive index compensation through cascading double multi-mode interferences

A liquid level (Li-Le) optical fiber sensor with refractive index (RI) compensation through cascading double multi-mode interferences (MMIs) sensors was experimentally investigated. Previous researches showed that the sensitivities of Li-Le sensor were interfered by the variation in liquid RIs significantly, which illustrated the necessity of RI compensation in Li-Le sensors. In this work, we designed a Li-Le sensor by cascading a Li-Le sensor and a RI sensor, where the RI sensor was used for the RI compensation in Li-Le detection. The sensitivity of Li-Le sensor varied with the increase of liquid RI. The RI sensor could achieve the RI compensation in the RI range of 1.333–1.370. A contour map was plotted to effectively determine the Li-Le from the disturbing of liquid RI. The maximum sensitivity of Li-Le was 875 pm/mm when the liquid RI was 1.4164, which was higher than most of the previous works. This designed RI compensation Li-Le sensor could become a competitive candidate in the field of accurate detection of Li-Le for the advantages of high sensitivity, simple structure, and RI compensation.