Fiber-based Surface Plasmon Resonance Sensor Research Articles

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.

Silver-TiO2 coated D-shaped photonic crystal fiber based SPR sensor for ultrasensitive refractive index detection: design and FEM analysis

Photonic crystal fiber (PCF) based surface plasmon resonance (SPR) sensors are emerging as a promising technology for ultrasensitive detection of various biological and chemical analytes. This paper presents a novel D-shaped PCF based SPR sensor, which has shown great potential for highly sensitive detection of refractive index (RI) changes. The D-shaped configuration is achieved through the polishing of the upper side of the PCF fiber. To enhance sensitivity, a 0.1 μm silver layer is strategically placed between the fiber and analyte, intensifying light–matter interactions. Additionally, a 0.05 μm titanium dioxide (TiO2) layer is employed not only to further boost sensitivity but also to shield the metal from oxidation, ensuring the longevity and stability of the sensor. The finite element method (FEM) is employed to optimize the structural parameters of the sensor design. The findings demonstrate that the proposed SPR sensor is sensitive to RI changes in the 1.31–1.35 range, achieving a peak wavelength sensitivity of 30000 nm RIU−1 and an amplitude sensitivity of −185.33 RIU−1. The sensor holds promise for diverse applications, including chemical and biological sensing, making it a versatile tool with promising implications for advancing sensing technologies in various domains.

A comparative analysis of fiber-based surface plasmonic resonance sensors utilizing various fluoride glass cores and the influence of different oxide layers on the sensor performance in near-infrared

In a fiber-based surface plasmon resonance (SPR) sensor, with multiple layers, including fluoride glass core, cladding, metal (Ag), graphene and alcohols as the analyte, we focused on comparing the effects of 12 different types of fluoride glass cores from three main groups of fluorozirconate (ZrF4-based), fluoroaluminate (AlF3-based) and fluoroindate (InF3-based). The comparison was conducted to evaluate the sensor’s sensitivity and figure of merit (FOM) at specific near infrared (NIR) wavelengths (785 nm, 852 nm, 895 nm and 980 nm) while keeping other parameters constant. The highest FOM was consistently observed at the wavelength of 980 nm for all three categories of fluoride glass cores. Among them, the fluoride glass core IZBSC (40 InF3-20 ZnF2-15 BaF2-20 SrF2-5 CaF2) from InF3-based group presented the largest FOM = 1459.15 RIU−1. Furthermore, we observed that the FOM of the fiber types belonging to the ZrF4-based and InF3-based categories increased with the wavelength. However, the fluoroaluminate fibers showed different trend and they also exhibited the smallest FOM values at 852 nm, 895 nm and 980 nm wavelengths. To enhance the sensor’s performance, we explored the incorporation of an oxide layer into the to the SPR sensor with a ZBLAN (55.8 ZrF4-14.4 BaF2-5.8 LaF3-3.8 AlF3-20.2 NaF) core. We analyzed the effects of various oxide coatings (Sc2O3, Lu2O3, Al2O3, GeO2, TeO2, Ta2O5, MgO, TiO2, and ZnO) on the Ag layer, which has not previously studied, to the best of our knowledge. Among the different oxide coatings, the Ta2O5 layer, with optimized thickness, exhibited a significant enhancement, achieving FOM of 1631.43 RIU−1.

Air-silica core microstructured optical fiber-based SPR sensor for temperature and refractive index measurement

We propose an air-silica core microstructured optical fiber-based surface plasmon resonance (SPR) sensor to simultaneously measure temperature and refractive index (RI). The sensing channel is formed by coating the outside of the fiber with a gold film and a polydimethylsiloxane (PDMS) layer as a temperature sensing medium, and then being immersed into the liquid analyte. The plasmon mode can penetrate through the PDMS layer and then into the analyte, therefore both the temperature and the analyte RI changings can lead to the variations of SPR spectra that will be measured. Our numerical results demonstrate that the proposed sensor can support two resonance peaks in the x-polarized core mode and one resonance peak in the y-polarized core mode, therefore providing two detection approaches, peak-based and polarization-based approaches. By measuring the two peaks in the x-polarized core mode, for the peak-based approach, the temperature coefficients are −2.077 nm/°C and −2.723 nm/°C, and the RI coefficients are 1252 nm/RIU and 1931 nm/RIU, respectively. While by measuring the second peak in x-polarized core mode and the peak in y-polarized core mode, for the polarization-based approach, the temperature coefficients are −2.723 nm/°C and −3.401 nm/°C, and the RI coefficients are 1931 nm/RIU and 2973 nm/RIU, respectively.

Performance comparison and analysis of D-type single and dual-core PCF-SPR sensors

Surface plasmon resonance sensors, based on photonic crystal fibers, have demonstrated immense potential in various application fields, owing to their structural design flexibility, operability, and superior sensing capabilities. Despite the potential, the design of photonic crystal fibers with various structures has been a challenging task, due to manufacturing constraints. Thus, this paper aims to explore the design rules of photonic crystal fibers based on surface plasmon resonance, by proposing and designing four photonic crystal fiber sensors with distinct structures. The study investigates the influence of single-core, double-core, and large and small air holes on the sensor’s performance, through theoretical analysis, numerical simulation, data acquisition, and analysis. Through our research, we have discovered that by altering the size of pores surrounding the fiber core, as well as the fiber core’s single-mode and dual-mode configurations, we were able to increase the sensitivity of the sensor from its lowest value of 266 nm RIU−1 to as high as 2066 nm RIU−1, an improvement of nearly eightfold. The findings suggest that the sensor with double-core air hole structure exhibits relatively better performance. This analysis is expected to aid in the design of high-performance photonic crystal fiber-based surface plasmon resonance sensors.

Machine learning methods for estimating bent photonic crystal fiber based SPR sensor properties

In the recent years, the use of machine learning approaches in optical devices and fibers is increasing. However, most methods concentrate on the use of Artificial Neural Network (ANN) methods due to the ability of automatically fitting to the problem. In this work, a classical non-linear regression method, namely k-Nearest Neighbor Regression (KNNR) is proposed for determining the loss characteristics of a photonic crystal fiber (PCF) based surface plasmon resonance (SPR) sensor in the presence of a bend in either x or y direction. Although KNNR is a simple method, it is very well known that in certain systems it can out-perform ANN. It is believed that PCF based structures can be a good candidate for this comparison. In order to judge the performance of different regression techniques, we have built a database that contains 1180 samples. The dataset contains PCF structure data for non-bent(straight fiber), bent in x and y-directions. Experiments show that KNNR outperforms both ANN and Linear Least Square Regression methods even when a feature space expansion method is employed. In addition, KNNR does not require any lengthy training process, allowing it to be used instantly once the training data is available. This can be exploited to complement existing simulation techniques.

High-sensitivity biconical optical fiber SPR salinity sensor with a compact size by fiber grinding technique

For seawater salinity measurement, a high-sensitivity, ultra-compact, and corrosion-resistant biconical optical fiber surface plasmon resonance (SPR) sensor deposited with a 40 nm thick gold film based on fiber grinding technique was fabricated and demonstrated in this article. The ultra-compact biconical sensing structure with different grinding angles were fabricated by applying the optical fiber grinding machine, and the length of the sensing region was only hundreds of microns. The experimental results indicated that when the grinding angle was 14°, the sensor showed the highest sensitivity: a high refractive index sensitivity of 3965 nm/RIU and a high salinity sensitivity of 0.6898 nm/‰. Meanwhile, this biconical sensor had acceptable repeatability and stability. Therefore, this article demonstrated the feasibility of the biconical structure to improve the sensitivity of fiber-based SPR sensors, and provided a novel and practical solution for seawater salinity measurement.

Photonic crystal fiber-based SPR sensor for broad range of refractive index sensing applications

Until now, the use of photonic crystal fiber (PCF) based sensors has been limited. Environmental monitoring, the chemical industry, the food industry, and biomedicine are merely some of the fields. In this work, a surface plasmon resonance (SPR) sensor based on PCF is designed and simulated for a wide range of refractive index (RI) sensing applications with high sensitivity. The outer surface of PCF is coated with gold (Au), and a thin coating of titanium dioxide serves as an adhesive between the Au and silica. Using the SPR interaction between the core mode and Surface Plasmon Polariton mode of the proposed sensor, the RI of the analyte is detected. The simulated sensor has shown wavelength sensitivity of 10000 nm/RIU, sensor resolution of 2 × 10−5 RIU and amplitude sensitivity of 1115 RIU−1. Its operating wavelength ranges from 0.5 µm to 1.35 µm and it can detect the RI ranges from 1.35 to 1.40. The proposed sensor is exceptional for biochemical sensing, medical testing, and environmental monitoring due to its extensive range of RI detection and sensing.

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.

Mechanically hot-pressed flattened plastic optical fiber-based SPR sensor and its RI sensing

This paper presents a surface plasmon resonance (SPR) sensor based on a flattened plastic optical fiber (POF) for refractive index (RI) sensing. The flattened POF is fabricated by mechanical hot pressing. Afterwards, a thin film of Ag and Au is first deposited on one side of the flat surface to excite the SPR effect. The results show that the flattened POF-based SPR probe coated with the Au film has a sharper SPR peak and a narrower peak width than the probe coated with Ag film. To improve the SPR effect, two flat surfaces of the flattened POF are coated with metal film (Ag and Au). It was found that the sensor showed better RI sensing performance compared to the sensor with only one flat surface coated with metal film. For the flattened POF with two flat surfaces coated with Ag film, achieving the highest RI sensitivity of 2507 nm/RIU in the RI range of 1.33–1.39. The proposed sensor is a low-cost solution for RI measurement with potential applications in the medical and biochemical fields.

Plastic Optical Fiber Based SPR Sensor for Simultaneous Measurement of Refractive Index and Liquid Level

In this work, a 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 sensor probe is fabricated by polishing the POF and drilling several micro-holes with equal pitch along the fiber axial, after depositing a layer of gold film on the polished region, the SPR probe is obtained. The effects of the micro-hole on the sensing performance are investigated and the structural parameters of the micro hole are optimized. Experimental results show that the changes of the liquid RI can be detected by monitoring the wavelength position of the SPR peak, and the liquid level can be measured by monitoring the deepness of the SPR peak. An RI sensitivity of 2024.41 nm/RIU was obtained in the RI range of 1.335-1.40, and a resolution of 5 mm and measurement range of 25 mm for liquid level measurement were achieved for the probe. The proposed sensor is compact in size and has a very small cross sensitivity for the RI and liquid level measurement, which is useful in the biomedical and industrial sensing fields.

An Optical Fiber-Based Surface Plasmon Resonance Sensor for Simultaneous Measurement of Temperature and Magnetic Field Intensity

In this article, a surface plasmon resonance (SPR) sensor was designed based on the no-core optical fiber (NCF) for the simultaneous measurement of magnetic field intensity and ambient temperature. The sensor structure was mainly comprised of two NCF segments spliced between two multimode optical fibers, and different metal films were deposited on the NCF surface to generate the SPR effect: the NCF coated by silver and wrapped by MF was used for magnetic field sensing and the NCF coated by gold and wrapped by PDMS was used for temperature sensing. The proposed sensor successfully avoided the influence of temperature on magnetic field sensing, and vice verse. Detailed experimental investigation showed that in the magnetic field intensity range of 0–248 Gs, a maximum sensitivity of 132 pm/Gs was obtained with good linearity (coefficient of determination 0.991), and in the temperature range of 20 °C–60 °C, the corresponding sensitivity was −1.960 nm/°C with a linearity higher than 0.997. The proposed sensor can perform an accurate sensing even in weak magnetic field environment and simultaneously provide information about temperature variation. Being simple in structure, easy to manufacture and stable in performance, this sensor provides a feasible solution for the integration and miniaturization of multi-parameter measurement.

Surface Plasmon Plastic Optical Fiber Resonance with Multi-Layer as Chemical Sensor

A chemical optical fiber sensor based on surface plasmon resonance (SPR) was developed and implemented using multimode plastic optical fiber. The sensor is used to detect and measure the refractive index and concentration of various chemical materials (Urea, Ammonia, Formaldehyde and Sulfuric acid) as well as to evaluate the performance parameters such as sensitivity, signal to noise ratio, resolution and figure of merit. It was noticed that the value of the sensitivity of the optical fiber-based SPR sensor, with 60nm and 10 mm long, Aluminum(Al) and Gold (Au) metals film exposed sensing region, was 4.4 μm, while the SNR was 0.20, figure of merit was 20 and resolution 0.00045. In this work a multimode plastic optical fiber with a core diameter of 980 μm, fluorinated polymer cladding of 20 μm and a numerical aperture of 0.51 was used.

High-performance surface plasmon resonance refractometer based on a no-core fiber coated with a silver film

Owing to their high sensitivity, surface plasmon resonance (SPR)-based sensors depict broad application prospects in biochemical detection, environmental monitoring, and food safety. In this paper, an optical fiber-based SPR sensor is proposed and demonstrated for the refractive index (RI) detection of liquid samples. This sensor is composed of a multimode fiber (MMF), a no-core fiber (NCF), and another MMF that is connected in sequence. The length of the NCF is 2 cm. A thin silver film is deposited on the NCF surface to stimulate the SPR effect. Experimental results indicated that the shift amount of resonance dip wavelength is as high as 303.6 nm as RI increases from 1.333 to 1.4107. A sensitivity of 2507.58 nm/RIU with a fitting linearity R 2 of 0.9931 is obtained in the lower RI region of 1.333–1.3723, while the sensitivity and R 2 reaches 5228.21 nm/RIU and 0.97395, respectively, in the higher RI region of 1.3723–1.4107. Compared with previously reported RI sensors, the proposed fiber optic SPR sensor exhibits the advantages of simple structure, small volume, low cost, high sensitivity, and wide detection range.

An Enhanced Plastic Optical Fiber-Based Surface Plasmon Resonance Sensor with a Double-Sided Polished Structure.

An enhanced plastic optical fiber (POF)-based surface plasmon resonance (SPR) sensor is proposed by employing a double-sided polished structure. The sensor is fabricated by polishing two sides of the POF symmetrically along with the fiber axis, and a layer of Au film is deposited on each side of the polished region. The SPR can be excited on both polished surfaces with Au film coating, and the number of light reflections will be increased by using this structure. The simulation and experimental results show that the proposed sensor has an enhanced SPR effect. The visibility and full width at half maximum (FWHM) of spectrum can be improved for the high measured refractive index (RI). A sensitivity of 4284.8 nm/RIU is obtained for the double-sided POF-based SPR sensor when the measured liquid RI is 1.42. The proposed SPR sensor is easy fabrication and low cost, which can provide a larger measurement range and action area to the measured samples, and it has potential application prospects in the oil industry and biochemical sensing fields.

Parallel Polished Plastic Optical Fiber-Based SPR Sensor for Simultaneous Measurement of RI and Temperature

In this work, a parallel polished 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 is fabricated by double polishing the POF symmetrically and depositing a layer of gold film on both sides of the polished regions. By coating the polydimethylsiloxane (PDMS) layer on one of the polished sides, another resonance peak for the temperature sensing can be observed in the transmission spectrum. When the RI and temperature vary, the two resonance peaks will change, and the RI and temperature could be measured simultaneously by monitoring the wavelength shifts of the two peaks. Experimental results show that the sensor has an RI sensitivity of 1174 nm/RIU in the RI range of 1.335–1.37 and a temperature sensitivity of −0.7 nm/°C in the temperature range of 30 °C–80 °C. In addition, the results show that the crosstalk between the two sensing channels of the proposed sensor is negligible. The parallel polished structure is helpful to develop the multiparameter measurement sensors, which has potential application prospects in the biochemical sensing fields.

Titanium dioxide (TiO2) coated optical fiber-based SPR sensor in near-infrared region with bimetallic structure for enhanced sensitivity

A multimode optical fiber-based surface plasmon resonance (SPR) sensor is proposed and theoretically analyzed by using the finite element method (FEM) and transfer matrix method (TMM) based numerical simulations. A bimetallic structure of silver (Ag) and gold (Au) is used as SPR active material, followed by titanium dioxide (TiO2) layer. The TiO2 material is used as a dielectric to enhance the proposed sensor's performance with optimized thickness. The results show that the properties of the proposed sensor are highly dependent on the width of the metal and dielectric coatings, which allows the resonance wavelength tuning. For an aqueous solution of the analyte with a refractive index of 1.37 RIU, the maximum sensitivity of the optimized structure was found to be 14,340 nm/RIU, with a figure of merit (FOM) of 35.7 RIU−1 theoretically. The sensitivity of the sensor and FOM is improved on state of the art, ultimately opening new windows of study in the areas of chemical sensing.

Multianalyte sensing analysis with multilayer photonic crystal fiber-based surface plasmon resonance sensor

In this work, we proposed multianalyte multichannel Photonic Crystal Fiber (PCF)-based Surface Plasmon Resonance sensor with gold- and silver-doped plasmonic layers. The Full Vectorial Finite Element Method (FV-FEM) with perfectly matched layers (PML) are employed for numerical analysis of the proposed sensor. The key propagation features, such as confinement loss, resonance condition, resolution, and sensitivity of the proposed sensor, have been reported for all possible refractive index variations. According to the spectral sensitivity analyses, the average sensitivities for fixed RI values are obtained as 4100 nm/RIU and 3820 nm/RIU for Ch1 and Ch2, respectively. On the other hand, results for varying RI values are obtained as 3600 nm/RIU and 3700 nm/RIU for Ch1 and Ch2, respectively. Moreover, the maximum average sensitivity of proposed sensor reaches to 4250 nm/RIU for varying RI at Ch2 and 4200 nm/RIU for varying RI at Ch1.

Air-hole attributed performance of photonic crystal fiber-based SPR sensors

Photonic crystal fiber (PCF) based surface plasmon resonance (SPR) sensors show great promise in different fields due to their flexibility, remote accessibility, and remarkable sensing capability. To improve the performance (e.g. sensitivity) of PCF-based SPR sensors, two strategies are generally employed: (i) use of new plasmonic materials, and (ii) engineering the air-hole geometry. In particular, air-holes geometry plays a crucial role in maintaining both core and surface plasmon polariton (SPP) modes in SPR sensors. This work aims at investigating the effect of air-holes geometry on the performance of PCF-based SPR sensors. Here, three PCF models namely A, B, and C have been built with different air-hole geometries, and their effect on refractive index (RI) sensitivity is explored systematically through design, numerical simulation, data acquisition, and interpretation. Performance parameters such as confinement loss (CL), sensitivity, and sensing range of analytes (i.e. RI) have also been evaluated. Model A and B exhibit same maximum wavelength sensitivity and resolution of 5000 nm/RIU and 2 × 10−5 RIU−1 respectively, where model B's air holes are rotated 90° compared to model A. Otherwise, model C introduces a small air hole at the middle of PCF, where the maximum wavelength sensitivity and resolution are found to be 8000 nm/RIU and 1.25 × 10−5 RIU−1, respectively. Moreover, model C exhibits CL much higher than model A and B. In addition, model C shows larger detection ranges of analyte's RI. This analysis would be helpful in designing highly sensitive PCF-based SPR sensors for detecting a wide range of analyte's RI.

Highly sensitive fiber optic surface plasmon resonance sensor employing 2D nanomaterials

Optical fiber-based surface plasmon resonance sensors using, silver layer (Ag), platinum (Pt), and indium tin oxide in addition to 2D nanomaterials such as graphene are presented in this research. In terms of sensitivity (S) and figure of merit (FoM), the performance analysis of the proposed and configured sensor has been demonstrated. The proposed sensors are based on the scheme of Kretschmann for obtaining the transmitted power using the transfer matrix method and the equations of Fresnel. With theoretical and numerical studies, the reported sensor exhibits a good wavelength sensitivity which is improved to the maximum value of 4150 nm/RIU. Full width half maximum values are minimized to be 59 nm and the FoM is optimized to be 70 RIU−1 which gives better sensing properties in comparison with other published articles.