Simultaneous Measurement Of Refractive Index Research Articles

Simultaneous measurement of refractive index and temperature using a balloon-type optical fiber sensor

In the food industry, acetic acid is a compound often used as a preservative or additive, but it is also produced during the fermentation of various food products and constitutes a key marker of food safety and quality. Although accurate, sensitive, and selective, the traditional methods for determining acetic acid are also expensive and time-consuming. In this regard, optical fiber sensors have emerged as a possible alternative for the real-time monitoring of small molecules. In this work, we propose an optical fiber sensor for the simultaneous measurement of refractive index (RI) and temperature using a balloon-shaped structure with a single sensing element. The sensor, based on cladding modal interference, was characterized by its response to RI in the range from 1.320 to 1.352 RIU, using acetic acid solutions with concentrations between 0% and 50%(v/v), and by its response to temperature between 23 and 43 °C. A maximum sensitivity of 170.66 nm/RIU was obtained for RI, equivalent to 110.7 pm/%(v/v) in terms of concentration, and a maximum sensitivity of −119.2 pm/°C was obtained for temperature.

Ultrasensitive RI and temperature sensor based on cascaded microfiber MZIs with Vernier effect

A sensitivity amplified optical fiber sensor based on Vernier effect by cascaded microfiber Mach-Zehnder interferometers (MZIs) is proposed and demonstrated for the simultaneous measurement of refractive index (RI) and temperature. The traditional single mode fiber is tapered into micrometer near the dispersion turning point to constitute MZI, and then cascaded to generate Vernier effect for the sensitivity enhancement. A novel phenomenon that the envelope of Vernier effect shifted in opposite directions decided by the free spectral ranges of the sensing and reference arms is clarified and demonstrated for the first time. Experimental results show that the RI sensitivity can be improved from 944 nm/RIU of single MZI to 18504 nm/RIU of Vernier effect, while the temperature sensitivity can be improved from −0.53 nm/℃ of single MZI to 9.49 nm/℃ of Vernier effect. Moreover, the proposed sensor with the merits of low hysteresis effect, good repeatability, high stability and good reliability, making it of great potential for biochemical trace detections without temperature-induced cross-sensitivity.

Dual D-shaped plastic optical fiber for simultaneous measurement of refractive index and temperature based on specklegram

The refractive index (RI) measurment of the liquid often changes with the sensor's temperature. Accurate RI measurements require simultaneous measurements of the liquid temperature to calibrate the RI measurement. This study proposed what we believe to be a novel dual D-shaped plastic optical fiber sensor capable of simultaneously measuring both RI and temperature. A fluorescent material made of rhodamine B (RhB) is embedded in one of the D-shaped structures of the dual D-shaped fiber, which can be excited by a green laser to produce orange fluorescence. The fluorescence and the input laser of the fiber are superimposed at the output end of the fiber to form a specklegram containing information of two wavelengths. It was found through experiments that the effects of temperature and RI change on the red and green channels of the specklegrams are different, and the neural network can learn this feature to complete the measurement of both RI and temperature parameters. For RI sensing, the maximum error between the average predicted value and the true value of the test set is 0.0005. For temperature sensing, the maximum error between the average predicted value and the true value of the test set is 0.26°C. In addition, because the intensity change of the fluorescence varies linearly with RI and temperature, the sensor also has good stability.

Cascaded dual-channel broadband SPR fiber optic sensor based on Ag and Ag/ZnO/PDMS film structure.

In order to broaden the sensing bandwidth of surface plasmon resonance (SPR) sensors, we propose and demonstrate a dual-channel SPR fiber optic sensor with wide bandwidth. The sensor is fabricated using no-core fiber (NCF), in which the film consists of a silver film and a ZnO film. The sensing characteristics are investigated by simulation and experiment. The resonance wavelength range of the SPR sensor can be significantly tuned by varying the thickness of the ZnO film. In the experiments, a dual-channel SPR sensor that can be used for simultaneous detection of temperature and refractive index was realized by cascading ZnO/Ag film with Ag film. The experimental results show that the two sensing channels are independent without crosstalk. The sensitivity of this sensor is 3512 nm/RIU in the range of 1.333 ∼ 1.385 and 4.6 nm/°C in the range of 0 ∼ 60 °C, which is better than most of the current dual-channel SPR sensors. In addition, the experimental results show that this sensor has good stability in use. The sensor proposed in this work has the advantages of a wide operating wavelength range, simple and compact structure, and high sensitivity. It has a broad application prospect in the simultaneous measurement of refractive index and temperature of liquids.

Cascaded plastic optical fiber based SPR sensor for simultaneous measurement of refractive index and temperature.

A cascaded side-polish plastic optical fiber (POF) and FONTEX optical fiber based surface plasmon resonance (SPR) sensor is proposed for simultaneous measurement of refractive index (RI) and temperature. The side-polish POF and FONTEX optical fiber are connected by using the UV glue in a Teflon plastic tube. The SPR phenomenon can be excited at both of the side-polish region and the FONTEX fiber cladding. The polydimethylsiloxane (PDMS) is coated on the side-polish POF to get a temperature sensing channel. Due to the low RI sensitivity of the FONTEX optical fiber, the cascaded fiber sensor can obtain a broader RI measurement range with a low crosstalk. An RI sensitivity of 700 nm/RIU in the RI measurement range of 1.335-1.39 and a temperature sensitivity of -1.02 nm/°C measured in deionized water with a range of 20-60 °C are obtained. In addition, the cascaded POF based SPR sensor has potential application prospects in the field of biochemical sensing.

All-fiber sensor for simultaneous measurement of refractive index and temperature based on hole-assisted three-core fiber.

A hole-assisted three-core fiber (HATCF) has been proposed as a sensor for simultaneous measurement of refractive index (RI) and temperature. An 8 mm long HATCF is fused between two single mode fibers (SMFs). One air hole of the HATCF is opened by femtosecond laser ablation technique to expose a suspended core to the external environment. Due to the same diameters of the two suspended cores, the resonance couplings between the center core and the two suspended cores occur at the same wavelength, which leads to a strong resonance dip. When the solution is filled into the open air hole, the resonance dip is split in two dips because the phase matching wavelength between center core and the suspended core in the open air hole is changed. Simultaneous measurement of RI and temperature can be achieved by monitoring the wavelengths of the two dips. The measured RI and temperature sensitivities are 1369 nm/RIU in the range of 1.333-1.388 and 83.48 pm/°C in the range of 25-70 °C. The proposed sensor has outstanding advantages such as simple structure, high integration and dual parameter measurement, making it a potential application in the field of biological detection.

Simultaneous measurement of refractive index and dispersion using optical coherence tomography for restoration of transparent works of art

We describe a novel in situ non-invasive and non-contact technique for simultaneous measurement of refractive index and dispersion of transparent solid materials using optical coherence tomography (OCT). The technique requires multi-angle OCT imaging. It gives typical precision of 0.02 for the refractive index and 0.03 mum^{-1} for dispersion. The method can be applied to the restoration of modern sculptures made from plastics where it is important to have precise measurement of the refractive index of an object using a non-contact method, so that a resin-based adhesive with a matching refractive index could be found to restore a scratched or broken transparent works of art.

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.

Application of a Multiple Regression Model for the Simultaneous Measurement of Refractive Index and Temperature Based on an Interferometric Optical System

Interferometric optical systems have been proposed for implementing dual-parameter optical sensors. For this type of sensors, the sensitivity matrix equation is generally used to determine the parameters to be measured based on the sensitivity of each parameter to one particular feature of the output reflective spectrum of the interferometric system. One of the disadvantages of this method is that the measurement ranges will be very short if the sensitivities are not linear or if these present cross-sensitivity. In this work, a multiple regression model for the simultaneous detection of refractive index and temperature based on an interferometric optical sensor is proposed. Here, the mathematical model is a weighted sum of features used to estimate the values of two response variables. These features are functions of an initial set of 27 explanatory variables whose values were extracted of the output reflective spectrum of the interferometric system. Besides, in order to sustenance the model application, the sensor was modeled and experimentally carried out. Three cases were studied: the estimation of temperature at different refractive indices, the estimation of temperature when refractive index is equal to one, and the estimation of refractive index at different temperatures. For each one of these cases, an optimal basis of functions was founded with the algorithm proposed and used to estimate the values of the response variables. Besides, a technique to reduce the initial set of variables was implemented. Finally, for the experimental data, For each one of these cases, an optimal basis of functions was founded with the algorithm 1 proposed and used to estimate the values of the response variables.

Simultaneous measurement of refractive index and temperature based on a side-polish and V-groove plastic optical fiber SPR sensor.

A simple plastic optical fiber (POF) based surface plasmon resonance (SPR) sensor is proposed and demonstrated for simultaneous measurement of refractive index (RI) and temperature. The sensor consists of a series of V-grooves along the POF and a side-polish structure at the other side of the fiber. The V-groove structure can alter the SPR excitation angle and act as a mode filter, effectively enhancing the SPR effect and narrowing the SPR wavelength width. After coating a layer of thermosensitive material-polydimethylsiloxane (PDMS) film on half part of the fiber probe, a dual-parameter sensor probe is obtained for RI and temperature measurement. Experimental results show the RI sensitivity of the prepared probe can reach 1546 nm/RIU in the RI range of 1.335-1.37 RIU and the temperature sensitivity is -0.83 nm/°C in the temperature range of 20-80°C. The sensor is simple in structure and low cost, and has potential applications in the biochemical sensing fields.

Design and manufacturing of a surface plasmon resonance sensor based on inkjet 3D printing for simultaneous measurements of refractive index and temperature

Design and manufacturing of a surface plasmon resonance sensor based on inkjet 3D printing for simultaneous measurements of refractive index and temperature

Side-Opening Grapefruit Fiber-Based SPR Sensor for Simultaneous Measurement of Refractive Index and Temperature

A novel side-opening grapefruit fiber-based SPR sensor is designed to realize simultaneous measurement of refractive index (RI) and temperature. The open section of the grapefruit fiber is coated with a gold layer, which can support two main resonance peaks. The variations of RI and temperature can influence the coupling efficiency between core-guided mode and plasmon mode, thus lead to the two peaks shifts that can be used to determine the variations of RI and temperature. Simulation results demonstrate that the RI coefficients of Peak I and Peak II are 1400 nm/RIU and 226 nm/RIU, respectively. The temperature coefficients of Peak I and Peak II are 34 pm/°C and 527.2 pm/°C, respectively.

Simultaneous Measurement of Refractive Index and Temperature Based on SMF-HCF-FCF-HCF-SMF Fiber Structure.

In this research, we proposed and experimentally verified a compact all-fiber sensor that can measure refractive index (RI) and temperature simultaneously. Two segments of hollow-core fiber (HCF) are connected to the two ends of the four-core fiber (FCF) as a beam splitter and a coupler, and then spliced with two sections of single-mode fibers (lead-in and lead-out SMF), respectively. The two hollow-core fibers can excite the higher-order modes of the four-core fiber and recouple the core modes and higher-order modes into the outgoing single-mode fiber, thereby forming inter-mode interference. The different response sensitivities of two interference dips to RI and temperature manifest that the proposed structure can achieve simultaneous measurement. From the experimental results, it can be seen that the maximum sensitivity of the sensor to RI and temperature is 275.30 nm/RIU and 94.4 pm/°C, respectively. When the wavelength resolution is 0.02 nm, the RI and temperature resolutions of the sensor are 7.74 × 10-5 RIU and 0.335 °C. The proposed dual-parameter optical sensor has the advantages of high sensitivities, good repeatability, simple fabrication, and structure. In addition, it has potential application value in multi-parameter simultaneous measurement.

Rainbow refractometry using partial rainbow signals

Rainbow refractometry can offer simultaneous measurement of refractive index and size of droplets and has recently undergone interesting developments in spray measurement applications. Nevertheless, recording of incomplete rainbow signals from droplets with varying refractive index or at long working distances is often encountered, and these incomplete signals are usually considered invalid and are rejected. This study develops rainbow measurement using incomplete signals by systematically investigating the feasibility and accuracy. The partial degree of the rainbow signal was quantified by the newly defined dimensionless signal partial ratio (SPR). Simulations and inversions of typical incomplete standard rainbow and global rainbow patterns of droplets with three size distributions (normal, log-normal and bimodal normal) at various SPR were conducted. The retrieved refractive indices, size or size distributions and fitted signals were analyzed. SPR = 1 is the threshold for the deterioration of inversion quality. Inversion using signal fitting is far superior to the approaches using only specific characteristic points in terms of accuracy and precision. The above conclusions were also verified in laboratory experiments. For SPR≤ 1, rainbow refractometry can achieve absolute and relative errors of refractive index and size within 6×10−4, 3% for monodisperse droplet and 2×10−4, 8% for spray droplets.

Multiparameter Sensor Based on DCF Composite Tapered Structure Cascaded LPFGs for the Simultaneous Measurement of Refractive Index, Temperature, and Axial Strain

In this article, a fiber optic sensor based on double-cladding fiber (DCF) composite tapered structure cascaded long-period fiber gratings (LPFGs) for measuring refractive index (RI), temperature, and axial strain is designed. The two ends of a Section of DCF are, respectively, fused with single-mode fiber (SMF) and LPFG1 to form two up-tapers, and then the DCF is formed into a down-taper. Another end of LPFG1 is cascaded with LPFG2, and the center wavelengths of the two LPFGs are different. LPFG1, LPFG2, and tapered DCF generate three resonance peaks, namely, dip1, dip2, and dip3, respectively, whose sensitivity in response to different parameters is different. When external parameters change, the dips will have spectral shifts. The experimental results indicate that, when the RI is changed within 1.3355–1.3715, the sensitivity of dip1, dip2, and dip3 is –52.12, – 132.58, and 37.61 nm/RIU, respectively. When the temperature varies from 30 °C to 80 °C, the sensitivity of dip1, dip2, and dip3 is 74.05, 98.02, and 26.33 pm/°C in turn, respectively. When the axial sensitivity of dip1, dip2, and dip3 is – 1.95, – 2.58, and –3.24 pm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> , respectively. The resolutions for RI, temperature, and axial strain are 0.0005 RIU, 1.3375 °C, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$14.0886 \mu \varepsilon $ </tex-math></inline-formula> , respectively. The three parameters can be monitored simultaneously using the coefficient sensitivity matrix. The designed sensor has high repeatability and good linearity, and it is practical in the field of multiparameter detection.

Simultaneous measurement of refractive index and temperature based on tapered no-core fiber cascaded with a fiber Bragg grating

A Mach-Zehnder interference fiber-optic sensor for simultaneous measurement of temperature and refractive index (RI) is proposed and fabricated. In the sensing structure, no-core fiber (NCF) is cascaded with fiber Bragg grating (FBG), two enlarged tapers between NCF and the single-mode fiber serve as the light coupler, and the shrinked taper between two NCFs is used to enhance the interference effect. The different diameter influence of the shrinked taper on the sensing performance of RI and temperature has been evaluated, and the optimum diameter has been obtained. By monitoring the wavelength shift of FBG and the interference dip in the transmission spectra, the simultaneous measurement of temperature and RI is achieved. The maximum sensitivities of the attenuation peak to RI and temperature are 201.7157 nm/RIU and 87.4 pm/°C, respectively. The sensitivities of FBG to RI and temperature are 80.6 pm/RIU and 13.5 pm/°C, respectively. The transformation matrix has also been given. Own to the simple fabrication and high sensitivity, the sensor has the potential application in simultaneous measurement of multiple parameters.

Design of a Mach-Zehnder Interferometric Fiber Sensing System Based on PCA-Assisted OAM Interrogation for Simultaneous Measurement of Refractive Index and Temperature

We propose and numerically design a Mach-Zehnder interferometric sensing system using principal-component-analysis-based orbital angular momentum (OAM) interrogation for simultaneous measurement of refractive index (RI) and temperature. A capillary-assisted Mach-Zehnder interferometer (CAMZI) encapsulated into a microfluidic channel serves as the sensor probe, which is introduced in the Gaussian interference arm of the sensing system. Temperature-sensitive liquid and RI sample are respectively loaded inside and outside the silica capillary to discriminate the cross sensitivity between refractive and temperature. As the output light of the CAMZI carrying intensity and phase information in response to the variations in RI and temperature interferes with the OAM beam, the intensity and rotation angle of the spiral interferogram would change accordingly. And by performing principal component analysis (PCA) on these interference patterns, RI and temperature variations could be retrieved. The proposed sensing system based on PCA-assisted OAM interrogation is anticipated to resolve cross-sensitivity for dual-parameter sensing, and moreover it paves new way toward developing OAM-related photonic devices.

Simultaneous measurements of refractive index and temperature based on a no-core fiber coated with Ag and PDMS films

A compact surface plasmon resonance (SPR) fiber optic sensor, being utilized to simultaneously measure refractive index (RI) and temperature, is proposed and experimentally demonstrated in this paper. One part of a no-core fiber (NCF) was coated with a silver (Ag) film, and the other part was coated with a silver/polydimethylsiloxane (Ag/PDMS) composite film to stimulate the SPR effect. Due to the two heterogeneous films, two dips appeared in the transmission spectrum and were used to achieve the dual-parameter measurements. The experimental results showed that the RI sensitivity reached 2121.43 nm/RIU and 0 nm/RIU, while the temperature sensitivity reached –0.32 nm/°C and –2.21 nm/°C for the two dips, respectively. Based on the obtained transfer matrix, the measurements of RI and temperature could be demodulated. This designed sensor showed the merits of simple structure, easy to implement, and high sensitivity, demonstrating application prospects in dual-parameter monitoring.

A gold film coated dual-core photonic crystal fiber for refractive index and temperature sensing with high isolation

• When measuring RI of an analyte, the measurement is often affected by temperature. the simultaneous measurement of RI and temperature has important significance. • In this paper, a gold film coated dual-core photonic crystal fiber (DC-PCF) was proposed and numerically investigated for both RI and temperature sensing. • The maximum sensitivity of the RI reached 8100 nm/RIU, while the maximum sensitivity of temperature reached 1.3 nm/°C. • The design of dual independent cores in DC-PCF not only avoids the problem of cross-sensitivity; but also improves the isolation of the sensor. When measuring the refractive index (RI) of an analyte, the measurement is often affected by temperature. Therefore, the simultaneous measurement of RI and temperature has important research significance. In this paper, a gold film coated dual-core photonic crystal fiber (DC-PCF) was proposed and numerically investigated for both RI and temperature sensing. In order to stimulate the surface plasmon resonance (SPR) with high sensitivity to the surrounding, two gold films were coated on the polished surface and inner wall of a cladding air hole in the DC-PCF, respectively. Numerical results showed that the measurement sensitivities of RI and temperature reached 8100 nm/RIU based on Core I and 1.3 nm/°C based on Core II, respectively. It should also be noted that the designed sensor showed a high isolation. This designed sensor can be used where the RI of analyte should be detected at a high temperature accuracy.

Side-Polish Plastic Optical Fiber Based SPR Sensor for Refractive Index and Liquid-Level Sensing.

In this work, a simple side-polish plastic optical fiber (POF)-based surface plasmon resonance (SPR) sensor is proposed and demonstrated for simultaneous measurement of refractive index (RI) and liquid level. The effects of side-polish depths on the sensing performance were studied. The experimental results show that the SPR peak wavelength will be changed as the RI changes, and the SPR peak intensity will be changed with the liquid level variation. By monitoring the changes in peak wavelength and intensity, the RI and liquid level can be detected simultaneously. Experimental results show that an RI sensitivity of 2008.58 nm/RIU can be reached at an RI of 1.39. This sensor has the advantages of simple structure and low cost, which has a good prospect in the field of biochemical sensing.