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A surface plasmon resonance (SPR) biosensor based on dual-side polished photonic crystal fiber (PCF) has been presented in this paper. An external gold (Au) coating was used as a plasmonic material to detect changes in an analyte refractive index (RI). Sensor's structural parameters were optimized for better performance. The proposed sensor's simulation was conducted using the finite element method (FEM). Analytes within the RI range of 1.30 to 1.40 were used to develop a sensor. The numerical results are expected to have a wavelength sensitivity (WS) of 9400 nm/RIU and amplitude sensitivity (AS) of 27.27 RIU−1, respectively, and a spectral wavelength resolution of 1.063 × 10−5. Furthermore, it is expected to obtain maximum loss of 161,270 dB/m for a Y-polarization (Y-P) odd mode with an analyte RI = 1.37. We obtained an extinction ratio of − 321.54 dB for the polarization filter effect, which is considered to be good. This structure has the advantages of being easy to fabricate, affordable, and expected to show better sensitivity than many other sensors. It assumes to detect a wide range of analytes, making it suitable for organic chemical sensing, pharmaceutical inspection, and biosensor applications. [ABSTRACT FROM AUTHOR]

In this paper, we design and demonstrate an all-fiber-sensitive refractive index (RI) sensor based on the Mach–Zehnder interferometer (MZI). It is constructed by splicing two no-core fibers (NCFs) and a photonic crystal fiber (PCF) between two single-mode fibers (SMFs) to obtain an SMF–NCF–PCF–NCF–SMF composite structure (SNPNS). A study of the effect of varying PCF lengths on the RI reveals that the shorter the length, the higher the sensitivity. The maximum RI sensitivity of 176.9 nm/RIU is attained within the RI range of 1.3365–1.3767 when the PCF length in the SNPNS structure is 3 cm. Meanwhile, the sensor exhibits a high stability in water, with an RSD of only 0.0019% for the interference trough over a duration of two hours. This proposed sensing structure offers the advantages of a large extinction ratio, small size, low temperature sensitivity, and simple fabrication, exhibiting a great potential in RI measurements. [ABSTRACT FROM AUTHOR]

This study presents the design and analysis of a novel surface plasmon resonance sensor based on D-type photonic crystal fiber. The analyte channel in the sensor comprises an open ring with a thin gold film deposited on the channel, inducing the surface plasmon resonance effect to enhance the resonance effect and improve the spectral sensitivity of the sensor. The proposed design eliminates the need to introduce liquid into the analyte channel. Upon inserting the sensor into the vessel, the analyte automatically flows into the liquid channel. Simulations illustrate the capability of the proposed sensor to detect low refractive indices spanning from 1. 1 5 to 1. 2 6 , exhibiting a remarkable spectral sensitivity of up to 9000 nm/RIU. The surface plasmon resonance sensor presented in this study emerges as a competitive candidate for applications requiring low refractive index detection. It is all because of its promising sensing results, wide refractive index sensing range, and simple, compact fiber design. [ABSTRACT FROM AUTHOR]

In this paper, a novel D-shaped photonic crystal fiber (PCF) refractive index (RI) sensor based on surface plasmon resonance (SPR) effect is proposed. By introducing a smiley-faced hole and Ag-TiO2 composite micro-grating, the high RI sensing performances can be realized. With finite element method, the propagation characteristics of the proposed D-shaped SPR-PCF RI sensor are numerically investigated. The simulation results show that the average wavelength sensitivity (WS) is 5400 nm/RIU, and the maximum WS can reach 15,500 nm/RIU in the RI range from 1.30 to 1.39. Besides, the proposed D-shaped SPR-PCF RI sensor can obtain the maximum resolution (R) of 4.95 × 10−5RIU and the maximum figure of merit (FOM) of 423.78 RIU−1, respectively. It is believed that the proposed SPR-PCF RI sensor has potential applications in the fields of environmental monitoring, biomedical analysis, and food safety management. [ABSTRACT FROM AUTHOR]

In this research, we proposed and numerically investigated a D-shaped dual-core photonic crystal fiber (PCF) refractive index (RI) sensor based on surface plasmon resonance (SPR), and a plasma material indium tin oxide (ITO) is deposited on the polished surface of a D-shaped PCF to produce the SPR effect. The proposed PCF sensor incorporates a dual-core structure and innovatively introduces an elliptical air hole, which increases the coupling of the SPR effect, resulting in a notable improvement in sensor performance. This enhancement enables the sensor to efficiently detect variations in the RI of the analyte. Utilizing the finite element method (FEM), we analyzed the influencing characteristics of sensor performance, meticulously investigating and optimizing various structural parameters. In the RI sensing range spanning from 1.18 to 1.33, the designed PCF sensor exhibits an outstanding maximum wavelength sensitivity of 29,300 nm/RIU, along with the highest achievable amplitude sensitivity of 261.01 RIU−1. Upon analyzing the light signal modulated by the sensor, the findings unequivocally demonstrate that the proposed sensor displays outstanding sensitivity to changes in the analyte's RI via the SPR effect. This responsiveness enables effective and precise real-time detection. The proposed sensor is characterized by exceptional sensing performance, strong economic feasibility, and low manufacturing intricacy. Consequently, the proposed sensor can be used to detect medical oxygen, anesthetics, methane gas, glucose, fluorine-containing organics, etc., and it holds a diverse array of promising applications spanning industrial detection, biochemical analysis, and medical diagnostics. [ABSTRACT FROM AUTHOR]

An ultrahigh sensitivity surface plasmon resonance sensor based on double-side polished photonic crystal fiber is designed, and the gold film with a zigzag cross section is used as the plasmonic material. We study the refractive index sensing characteristics of the proposed sensor by numerical simulation. The results show that compared with the flat gold film structure, the zigzag gold film structure effectively improves the sensing performance, and the sensitivity and resolution of the sensor are significantly enhanced. The maximum wavelength sensitivity and resolution of the proposed sensor can reach 20,000 nm/RIU and 5.00 × 10−6 RIU, respectively. The working wavelength range of the sensor is between 590 and 1200 nm, and the refractive index range that can be used for detection is 1.350 RIU-1.400 RIU. This can be applied to precise detection of extracellular vesicles, breast cancer cell, and red blood cells. The proposed sensor has significant advantages such as stable structure, ultrahigh sensitivity, fast response, small size, and saving noble metal. It has great application potential in biomedical testing and medical equipment. [ABSTRACT FROM AUTHOR]

In this paper, we design and demonstrate an all-fiber-sensitive refractive index (RI) sensor based on the Mach–Zehnder interferometer (MZI). It is constructed by splicing two no-core fibers (NCFs) and a photonic crystal fiber (PCF) between two single-mode fibers (SMFs) to obtain an SMF–NCF–PCF–NCF–SMF composite structure (SNPNS). A study of the effect of varying PCF lengths on the RI reveals that the shorter the length, the higher the sensitivity. The maximum RI sensitivity of 176.9 nm/RIU is attained within the RI range of 1.3365–1.3767 when the PCF length in the SNPNS structure is 3 cm. Meanwhile, the sensor exhibits a high stability in water, with an RSD of only 0.0019% for the interference trough over a duration of two hours. This proposed sensing structure offers the advantages of a large extinction ratio, small size, low temperature sensitivity, and simple fabrication, exhibiting a great potential in RI measurements.

This paper combines molybdenum dioxide (MoO2) instead of the gold film with photonic crystal fiber (PCF) for the first time. A novel C-type micro-opening surface plasmon resonance (SPR) optical fiber sensor coated with MoO2 nanofilm is proposed. The polarization and sensing characteristics of the sensor coated with plasma film on the outer surface of the polished optical fiber are numerically analyzed by the finite element method (FEM). The simulation results show that when the plasma material deposited by the optical fiber micro-opening is noble metal gold, the sensor can realize the sensing detection of the refractive index of the analyte from 1.33 to 1.39, and the average wavelength sensitivity in the x-polarization direction reaches 1107 nm/RIU. It is most noteworthy that when the plasma coating material of the optical fiber is replaced by metal oxide MoO2, the sensor can realize the sensing detection of the refractive index of the analyte from 1.31 to 1.37, and the average sensitivity of the x-polarization direction can reach 4821 nm/RIU. By comparison, we can know that the sensor coated with plasma material MoO2 has excellent sensing characteristics. This research is of great scientific significance for expanding the application range of MoO2 materials and promoting the development of photonic crystal fiber sensors coated with new materials. [ABSTRACT FROM AUTHOR]

In the correspondence, a novel polished-D-shape photonic crystal fiber sensor structure on the basis of surface plasmon resonance is proposed for measuring analyte refractive index. With the help of the finite element method, sensing performances of the structure have been analyzed through numerical simulations along with a step-by-step optimization. In this design, different capillaries are gathered and processed to form a D-shape silica structure and nano-scale gold material is coated on the flattened surface. With utilization of a thin gold film and solid silica background, the resonance effect is excited and the loss curve has red shift along with an increase in refractive index, which is applied for sensing. From the simulation and calculation results, the final sensor structure achieves the optimal performance where values of maximum and average sensitivity reach 32,000 and 12,167 nm/RIU along with a sensing coverage of refractive index from 1.26 to 1.32. Also, the proposed design obtains a range of resonant wavelength from 1810 to 2540 nm. We believe the proposed sensor can be a potential candidate for organic and biological detection and related applications. [ABSTRACT FROM AUTHOR]

In this paper, a surface plasmon resonance-based photonic crystal fiber refractive index sensor has been simulated. It has a hexagonal core surrounded by a rectangular cladding of different size air holes. To enhance the sensing performance of the proposed sensor, an adhesive layer of TiO2 has been deposited between the interface of the plasmonic metal layer of gold (Au) and dielectric material fused silica. With the most promising method to detect sensitivity which is the wavelength (λ) interrogation method with amplitude sensitivity method, we have found a wavelength sensitivity of 40,000 nm/RIU, an average wavelength of sensitivity of 14,285 nm/RIU, and an amplitude sensitivity of 328 RIU−1 for the range of refractive index 1.32–1.39. The resolution of our proposed sensor is 10−6 RIU. Fabrication of this sensor can easily be done with numerous available technologies such as the stack and draw method, sol–gel method, and others. This proposed external mechanism-based PCF sensor will lead us to a new era of future for sensing in the dairy industry field for detecting milk of animals, a biomedical field such as blood testing, cancer cell detection, the biochemical field such as detecting antigens, and antibodies, protein, enzymes, and alcohol sensing based on their refractive index RI. [ABSTRACT FROM AUTHOR]

In this correspondence, a new photonic crystal fiber biosensor structure on the basis of surface plasmon resonance is proposed for the measurement of the refractive index (RI) and TSM temperature simultaneously. In this design, the central and external surface of the biosensor structure are coated with thin gold film. A hole adjacent to the inner gold film is filled with temperature-sensitive material (TSM). With the implementation of internal and external gold coatings along with TSM, the biosensor achieves the measurement of the RI and temperature with two disjoint wavelength coverage. Numerical simulations and calculation results illustrate that the average wavelength sensitivity of the biosensor structure, respectively, achieves 7080 nm/RIU and 3.36 nm/°C with RI coverage from 1.36 to 1.41 and temperature coverage from 0 to 60 °C. Moreover, benefiting from realization of different wavelength regions in RI and temperature sensing, it is believed that the proposed biosensor structure for the measurement of the RI and temperature will have range applications in the fields of medical diagnostics and environmental assessments. [ABSTRACT FROM AUTHOR]

Two-dimensional polymer perovskite (CH3NH3PbI3) has very potential properties in sensing applications. Hence, for high sensitivity, a lossy mode resonance refractive index sensor based on perovskite coating is proposed. The sensor uses a photonic crystal fiber (PCF) with three air holes and a polished surface. Perovskite is deposited on the PCF plane to form the Kretschmann structure. We analyzed its sensing characteristics by using the finite element method. A significant advantage of the sensor is its strong tunability, allowing it to be used in various operating environments by controlling the thickness of the film. In addition, two sharp resonant peaks in the loss spectrum can realize double resonant peak sensing and increase measurement accuracy. Numerical results show that the maximum sensitivity of the two resonant peaks is 36400 nm/RIU and 15400 nm/RIU, respectively, and the corresponding refractive index range is 1.39–1.43. The results also show that small structural changes do not cause a change in performance, meaning that the sensor has a high fault tolerance rate. The high sensitivity response with adjustable detection range makes the proposed sensor distinct. It has a good application prospect in water quality monitoring and biomolecular detection.

A compact temperature-refractive index (RI) flat photonic crystal fiber (PCF) sensor based on surface plasmon resonance (SPR) is presented in this paper. Sensing of temperature and RI takes place in the x- and y- polarization, respectively, to avoid the sensing crossover, eliminating the need for matrix calculation. Simultaneous detection of dual parameters can be implemented by monitoring the loss spectrum of core modes in two polarizations. Compared with the reported multi-function sensors, the designed PCF sensor provides higher sensitivities for both RI and temperature detection. A maximum wavelength sensitivity of −5 nm/°C is achieved in the temperature range of −30–40 °C. An excellent optimal wavelength sensitivity of 17,000 nm/RIU is accomplished in the RI range of 1.32–1.41. The best amplitude sensitivity of RI is up to 354.39 RIU−1. The resolution of RI and temperature sensing is 5.88 × 10−6 RIU and 0.02 °C, respectively. The highest value of the figure of merit (FOM) is 216.74 RIU−1. In addition, the flat polishing area of the gold layer reduces the manufacturing difficulty. The proposed sensor has the characteristics of high sensitivity, simple structure, good fabrication repeatability, and flexible operation. It has potential in medical diagnosis, chemical inspection, and many other fields. [ABSTRACT FROM AUTHOR]

In the correspondence, a novel polished-D-shape photonic crystal fiber sensor structure on the basis of surface plasmon resonance is proposed for measuring analyte refractive index. With the help of the finite element method, sensing performances of the structure have been analyzed through numerical simulations along with a step-by-step optimization. In this design, different capillaries are gathered and processed to form a D-shape silica structure and nano-scale gold material is coated on the flattened surface. With utilization of a thin gold film and solid silica background, the resonance effect is excited and the loss curve has red shift along with an increase in refractive index, which is applied for sensing. From the simulation and calculation results, the final sensor structure achieves the optimal performance where values of maximum and average sensitivity reach 32,000 and 12,167 nm/RIU along with a sensing coverage of refractive index from 1.26 to 1.32. Also, the proposed design obtains a range of resonant wavelength from 1810 to 2540 nm. We believe the proposed sensor can be a potential candidate for organic and biological detection and related applications.

In this paper, a surface plasmon resonance (SPR)-based photonic crystal fiber (PCF) sensor is proposed for simultaneously measuring the refractive index (RI) and temperature. In the design, the central air hole and external surface of the proposed PCF are coated with gold films, and an air hole is filled with the temperature-sensitive material (TSM). By introducing the inner and outer gold films and TSM, the RI and temperature can be measured simultaneously at different wavelength regions. The simulation results show that the average wavelength sensitivities of the proposed SPR-based PCF sensor can reach 4520 nm/RIU and 4.83 nm/°C in the RI range of 1.35~1.40 and a temperature range of 20~60 °C, respectively. Moreover, because of using the different wavelength regions for sensing, the RI and temperature detections of the proposed SPR-based PCF sensor can be achieved independently. It is believed that the proposed SPR-based PCF RI and temperature sensor has important applications in biomedicine and in environmental science. [ABSTRACT FROM AUTHOR]

In this study, a D–type photonic crystal fiber (PCF) based surface plasmon resonance (SPR) sensor is proposed for measurement of both refractive index (RI) and temperature. The RI sensing part is constructed by deposition of a silver layer on the plane of the D–type structure, and the temperature sensing part is formed by filling the silver nanowire and the liquid analyte into an elliptical hole in the PCF. The proposed design then can be used for temperature and analyte RI sensing through the coupling between the core guided modes and the surface plasmon modes around the nano silver rod and layer. We study the coupling characteristic and sensing performance of the sensor. The numerical results show that the maximal sensitivity in terms of RI units (RIU) is 6.9 μm/RIU in the range of 1.33–1.38, and the maximal temperature sensitivity is 3 nm /°C in the range of 27–67 °C. [ABSTRACT FROM AUTHOR]

A high-sensitivity refractive index (RI) sensor is proposed and designed, which is an in-line Mach–Zehnder interferometer (IMZI) with a photonic crystal fiber (PCF) and multilevel micro spindle structures fabricated by the arc-discharging and tapering method. To improve the sensitivity, a tapered multimode fiber (MMF) is inserted into the PCF. The performance of RI and temperature detection has been analyzed and discussed. The maximum RI sensitivity of −2958.875 nm/RIU is achieved by detecting the NaCl solution. In addition, the maximum temperature sensitivity is 6.4 pm/ o C in the range of 25 o C –65 o C , and the maximum measurement error changes caused by temperature is −0.0170‰/ o C. It shows that the sensor is very sensitive to RI yet insensitive to temperature. • An in-line Mach-Zehnder interferometer is proposed. It uses multilevel micro spindle structures, photonic crystal fibers and tapered multimode fiber structure to improve sensitivity and extinction ratio. • The sensor's refractive index sensitivity reaches to −2958.875 nm/RIU in the range of 1.33–1.334. The extremely high sensitivity for refractive index is able to detect the subtle change of liquid's refractive index. • In the range of 25 °C–65 °C, the maximum temperature sensitivity is 6.4 pm/°C. It shows that the sensor is insensitive to temperature which can avoid the crosstalk between the detection of refractive index and temperature. [ABSTRACT FROM AUTHOR]

In this paper, a novel refractive index sensor based on photonic crystal fiber and Sagnac ring is studied. The sensor adopts Mach-Zehnder interference principle. The production and experimental steps are as follows: The first step is to fuse the single-mode fiber with the photonic crystal fiber to form a basic sensing unit. The second part uses the coupling birefringence effect of the tapered coupler to fold and fuse the single-mode fiber together to form the Sagnac interferometer. Through this structure, the sensor has the characteristics similar to the polished photonic crystal fiber sensor, while the fabrication complexity is greatly reduced. The refractive index sensing capability and temperature stability of the two structures are analyzed experimentally. Simulation results show that the structure has high birefringence effect. Experimental results show that the proposed photonic crystal fiber combined with Sagnac ring sensor has good sensing performance in the refractive index range of 1.3355–1.3560. Compared with the sensor structure without Sagnac ring, the performance is greatly improved, the maximum sensitivity is up to 234 nm/RIU, and it has good temperature stability. The sensor has the advantages of miniaturization, high integration and high sensitivity, and can be used in industry, chemical detection, agriculture and other fields.

In this correspondence, a new photonic crystal fiber biosensor structure on the basis of surface plasmon resonance is proposed for the measurement of the refractive index (RI) and TSM temperature simultaneously. In this design, the central and external surface of the biosensor structure are coated with thin gold film. A hole adjacent to the inner gold film is filled with temperature-sensitive material (TSM). With the implementation of internal and external gold coatings along with TSM, the biosensor achieves the measurement of the RI and temperature with two disjoint wavelength coverage. Numerical simulations and calculation results illustrate that the average wavelength sensitivity of the biosensor structure, respectively, achieves 7080 nm/RIU and 3.36 nm/°C with RI coverage from 1.36 to 1.41 and temperature coverage from 0 to 60 °C. Moreover, benefiting from realization of different wavelength regions in RI and temperature sensing, it is believed that the proposed biosensor structure for the measurement of the RI and temperature will have range applications in the fields of medical diagnostics and environmental assessments.

We propose a surface plasmon resonance (SPR) sensor based on the U-shaped photonic crystal fiber (PCF) coated with Au-TiO2 layers, which can detect the refractive index (RI) of the analyte. We introduce elliptical air holes near the fiber core, which can break the symmetry of PCF structural and lead to a strong birefringence for achieving dual-polarization sensors. Besides, the TiO2 layer not only enhances the adhesion of Au and quartz but also improves the SPR effect. By using finite element method (FEM) numerical analysis, geometrical parameters are optimized to enhance sensors’ performances, and dual polarization demonstrates superior performance in different detection ranges, expanding the range of analyte detection. Finally, simulation results show that the detection range under the Y-polarization (X-polarization) is 1.20–1.30 (1.36–1.43), with a maximum wavelength sensitivity of 10200 nm/RIU (5900 nm/RIU). This sensor offers broad RI detection range and high sensitivity, promising extensive applications in environmental and medical diagnostics. [ABSTRACT FROM AUTHOR]

A compact temperature-refractive index (RI) flat photonic crystal fiber (PCF) sensor based on surface plasmon resonance (SPR) is presented in this paper. Sensing of temperature and RI takes place in the x- and y- polarization, respectively, to avoid the sensing crossover, eliminating the need for matrix calculation. Simultaneous detection of dual parameters can be implemented by monitoring the loss spectrum of core modes in two polarizations. Compared with the reported multi-function sensors, the designed PCF sensor provides higher sensitivities for both RI and temperature detection. A maximum wavelength sensitivity of −5 nm/°C is achieved in the temperature range of −30–40 °C. An excellent optimal wavelength sensitivity of 17,000 nm/RIU is accomplished in the RI range of 1.32–1.41. The best amplitude sensitivity of RI is up to 354.39 RIU−1. The resolution of RI and temperature sensing is 5.88 × 10−6 RIU and 0.02 °C, respectively. The highest value of the figure of merit (FOM) is 216.74 RIU−1. In addition, the flat polishing area of the gold layer reduces the manufacturing difficulty. The proposed sensor has the characteristics of high sensitivity, simple structure, good fabrication repeatability, and flexible operation. It has potential in medical diagnosis, chemical inspection, and many other fields.

In this paper, we propose a photonic crystal fiber (PCF) refractive index (RI) sensor based on the surface plasmon resonance (SPR) effect. The coupling and sensing characteristics of the proposed PCF-SPR RI sensor are investigated by the finite element method. The proposed PCF-SPR RI sensor can achieve the dual-wavebands measurement. By controlling the analytes height and incident light wavelength, the PCF-SPR RI sensor shows different sensing performances. The maximum wavelength sensitivities of the proposed PCF-SPR RI sensors can be up to 2000 and 4000 nm/RIU in the wavelength ranges of 0.75 to 1.0 and 1.2 to 2 μm, respectively. [ABSTRACT FROM AUTHOR]

Abstract A high sensitive refractive index sensor based on the cladding etched photonic crystal fiber (PCF) Mach-Zehnder interferometer (MZI) is proposed, which is spliced a section of photonic crystal fiber between two single modes fibers (SMFs).The interference fringe of the MZI shifts with the variation of the ambient refractive index (RI). It is found that the RI sensitivity slightly decrease with an increase in the interference length. The sensitivities of MZI with 35 mm PCF, 40 mm PCF, and 45 mm PCF are 106.19 nm/RIU, 93.33 nm/RIU, and 73.64 nm/RIU, respectively, in the range of 1.333 to 1.381. After etched, the RI sensitivity of the MZI could be improved obviously. The RI sensitivities of the MZI with 35 mm PCF are up to 211.53 nm/RIU and 359.37 nm/RIU when the cladding diameter decreases to 112 μm and 91 μm, respectively. Moreover, the sensor is insensitive to temperature, and the measured sensitivity is only 9.21 pm/°C with the range from 20°C to 500°C. In addition, the sensor has advantage of simple fabrication, low cost, and high RI sensitivity.

A surface plasmon resonance (SPR) sensor based on dual-layered air hole shaped photonic crystal fiber (PCF) is proposed to realize the simultaneous measurement of refractive index (RI). The plasma materials silver (Ag) and titanium dioxide (TiO2) were sequentially coated on the outer surface of PCF to obtain enhanced sensing properties. By carefully adjusting the geometrical parameters, the simulation results show a maximum wavelength sensitivity of 72,000 nm/RIU for analyte refractive indices ranging from 1.26 to 1.365, which realizes the high-sensitivity sensing in the visible to near-infrared optical band. Moreover, the sensor attains a maximum figure of merit (FOM) of 229 and RI resolution of 1.29 × 10− 6. This work shows great potential for real-time, affordable, and accurate measurement in biomedical, biological and organic chemical domains. [ABSTRACT FROM AUTHOR]

Abstract A numerical analysis on dual core photonic crystal fiber (DC-PCF) based surface plasmon resonance (SPR) refractive index sensor is presented. The guiding parameters and required sensing performances are examined with finite element method (FEM) based software under MATLAB environment. According to simulation, it is warrant that the proposed refractive index sensor offers the maximum amplitude sensitivity of 554.9 refractive index unit (RIU−1) and 636.5 RIU−1 with the maximum wavelength sensitivity of 5800 nm/RIU and 11 500 nm/RIU, and the sensor resolution of 1.72 × 10−5 RIU and 8.7 × 10−6 RIU, at analyte refractive index (RI) of 1.40 for x- and y-polarized modes, respectively. As the sensing performance in different wavelength ranges is quite high, the proposed sensor can be used in simultaneous detection for different wavelength ranges. Therefore, the proposed device is of a suitable platform for detecting biological, chemical, biochemical, and organic chemical analytes.

In this article, a single solid core flat fiber (SSCFF) refractive index sensor based on surface plasmon resonance (SPR) is proposed and analyzed numerically using the finite element method (FEM). The proposed flat fiber consists of a single array of five circular holes. Among them the central hole is made of GeO2-doped silica which is forming the core. Other holes are filled with air and situated symmetrically on both sides of the central solid core. The upper flat surface of the fiber is coated with a thin plasmonic gold layer which is protected by an active titanium dioxide layers. Analyte is situated on top of these layers. The wavelength interrogation technique is applied to study the coupling characteristics between the core-guided mode and the surface plasmon mode as well as for the refractive index measurement. Numerical analysis results show that this sensor is able to detect high refractive index analytes from 1.49 to 1.54 with a good linear response. Additionally, the dependence of surface plasmonic resonance wavelength on analyte refractive index is studied. The maximum wavelength sensitivity of this sensor is found to be 4782 nm/RIU with a high resolution of 2.09 × 10−5 RIU. The effects of different structural parameters on loss spectrum are studied in detail to optimize this SSCFF structure. In comparison to traditional PCF, this SSCFF structure is fabrication complexity free as well as a suitable candidate for developing portable devices and high refractive index analyte sensors, particularly chemical and protein sensors. [ABSTRACT FROM AUTHOR]

The amount of salt dissolved in a body of water is an important factor in determining physical characteristics like the heat capacity of the water. Here, we report a theoretical and numerical investigation on a seawater salinity sensor using a miniaturized fiber-optic probe based on a dual-core photonic crystal fiber (PCF). The sensing mechanism is based on interplay between fiber fundamental mode in the central core and a secondary mode in the water-filled hole of the PCF. Using finite element method analysis with Comsol Multiphysics Software, we show that a spectral sensitivity larger than 5500 nm/RIU can be achieved while varying the salt concentration from 0% to 100%. Furthermore, we demonstrate that the sensitivity for highly saline water bodies can be further improved by applying the permanent twist on the cladding air holes of the fiber. We studied the role of the twist directions and twist rates on the performance of the sensor including sensitivity and the absolute loss value. While the twist does not have any major impact on sensitivity of the sensor for low salinities, our results indicate that twisted PCF has an average higher sensitivity for salt concentrations over 50% and a maximum sensitivity of nearly 7000 nm/RIU is reported around salt concentration of 80%. [ABSTRACT FROM AUTHOR]

A surface plasmon resonance (SPR) sensor composed of photonic crystal fibers (PCFs) is designed for refractive index (RI) sensing with a high figure of merit (FOM). The dual Au-MgF2 layer is covered on the double-side polished D-type PCF to stimulate SPR. Our numerical analysis reveals that the maximum wavelength sensitivity and amplitude sensitivity of the PCF-SPR sensor are 59,000 nm/RIU and 6076 RIU−1, respectively, in the RI range of 1.25 ~ 1.43. The maximum FOM is 2033 RIU−1 and the resolution is 1.69 × 10−6. The results provide guidance and insights into the design of PCF-SPR sensors with high FOM. [ABSTRACT FROM AUTHOR]

This paper proposes a highly sensitive surface plasmon resonance (SPR) refractive index sensor based on the photonic crystal fiber (PCF). The optical properties of the PCF are investigated by modulating the refractive index of a liquid analyte. The finite element method (FEM) is used to calculate and analyze the PCF structure. After optimization, the fiber can achieve high linearity of 0.9931 and an average refractive index sensitivity of up to 14,771.4 nm/RIU over a refractive index range from 1.47 to 1.52, with the maximum wavelength sensitivity of 18,000.5 nm/RIU. The proposed structure can be used in various sensing applications, including biological monitoring, environmental monitoring, and chemical production with the modification and analysis of the proposed structure.

• The proposed SPR sensor can simultaneously detect the refractive index and temperature. • It avoids the coating and filling of the fiber holes for refractive index sensing. • It avoids selective coating and filling for temperature sensing. We propose an all-solid D-type photonic crystal fiber (PCF) based surface plasmon resonance sensor for simultaneous measurement of refractive index (RI) and temperature. The RI sensing portion is formed by coating the silver film on the plane of the D-type structure, and the temperature sensing portion is constructed by filling the silver nanowire and the liquid mixture (sensing medium) into the only orthogonally arranged hole in the PCF. This design can support two independent peaks with orthogonal polarizations which can be used to distinguish the RI and temperature changes. We investigate the coupling characteristic and sensing performance of the sensor, as well as the influence of the position of the silver nanowire in the air hole. The numerical results indicate that the maximal sensitivity in terms of RI units (RIU) is 10300 nm/RIU in the range of 1.41–1.42, and the maximal temperature sensitivity is 4.22 nm/°C in the range of −3 °C–15 °C with the volume ratio 6:4 in chloroform and ethanol mixture. [ABSTRACT FROM AUTHOR]

A high sensitive refractive index sensor based on the cladding etched photonic crystal fiber (PCF) Mach-Zehnder interferometer (MZI) is proposed, which is spliced a section of photonic crystal fiber between two single modes fibers (SMFs).The interference fringe of the MZI shifts with the variation of the ambient refractive index (RI). It is found that the RI sensitivity slightly decrease with an increase in the interference length. The sensitivities of MZI with 35 mm PCF, 40 mm PCF, and 45 mm PCF are 106.19 nm/RIU, 93.33 nm/RIU, and 73.64 nm/RIU, respectively, in the range of 1.333 to 1.381. After etched, the RI sensitivity of the MZI could be improved obviously. The RI sensitivities of the MZI with 35 mm PCF are up to 211.53 nm/RIU and 359.37 nm/RIU when the cladding diameter decreases to 112 μm and 91 μm, respectively. Moreover, the sensor is insensitive to temperature, and the measured sensitivity is only 9.21 pm/°C with the range from 20°C to 500°C. In addition, the sensor has advantage of simple fabrication, low cost, and high RI sensitivity. [ABSTRACT FROM AUTHOR]

A numerical analysis on dual core photonic crystal fiber (DC-PCF) based surface plasmon resonance (SPR) refractive index sensor is presented. The guiding parameters and required sensing performances are examined with finite element method (FEM) based software under MATLAB environment. According to simulation, it is warrant that the proposed refractive index sensor offers the maximum amplitude sensitivity of 554.9 refractive index unit (RIU−1) and 636.5 RIU−1 with the maximum wavelength sensitivity of 5800 nm/RIU and 11 500 nm/RIU, and the sensor resolution of 1.72 × 10−5 RIU and 8.7 × 10−6 RIU, at analyte refractive index (RI) of 1.40 for x- and y-polarized modes, respectively. As the sensing performance in different wavelength ranges is quite high, the proposed sensor can be used in simultaneous detection for different wavelength ranges. Therefore, the proposed device is of a suitable platform for detecting biological, chemical, biochemical, and organic chemical analytes. [ABSTRACT FROM AUTHOR]

Highlight • A high-sensitivity PCF sensor was designed for analyte detection. • This optimized sensor had an excellent linearity and good sensitivity. • The sensitivity within the refractive index range of 1.425–1.45 is 60,611 nm/RIU. • The corresponding minimum detection limit is 1.58 × 10−6 RIU. • The sensitivity within the refractive index range of 1.45–1.46 is 28,000 nm/RIU. • The corresponding minimum detection limit is 2.86 × 10−6 RIU. Abstract A high-sensitivity photonic crystal fiber (PCF) refractive index sensor based on the resonant coupling of core mode and defect mode is studied by the finite element method. The large liquid-filled is placed near to the core for easy coupling with the core mode. The simulation results show that when the refractive index of the analyte is 1.425–1.45 and 1.45–1.46, the average sensitivity is 60,611 and 28,000 nm/RIU respectively, and the corresponding minimum detection limits are 1.58 × 10−6 and 2.86 × 10−6 RIU. [ABSTRACT FROM AUTHOR]

An H-shaped photonic crystal fiber (PCF)-based surface plasmon resonance (SPR) sensor is proposed for detecting large refractive index (RI) range which can either be higher or lower than the RI of the fiber material used. The grooves of the H-shaped PCF as the sensing channels are coated with gold film and then brought into direct contact with the analyte, which not only reduces the complexity of the fabrication but also provides reusable capacity compared with other designs. The sensing performance of the proposed sensor is investigated by using the finite element method. Numerical results show that the sensor can work normally in the large analyte RI (na) range from 1.33 to 1.49, and reach the maximum sensitivity of 25,900 nm/RIU (RI units) at the na range 1.47−1.48. Moreover, the sensor shows good stability in the tolerances of ±10% of the gold-film thickness.

Two kinds of novel plasmonic high sensitivity of refractive index (RI) sensors based on analyte-filled photonic crystal fiber (AF-PCF) are proposed in this paper. The metallic gold and silver is used as the surface plasmon resonance activity metal. A full-vector finite-element method is applied to analyze and investigate the sensing and coupling characteristics of this designed AF-PCF with the gold or silver layer. Phase matching between the second surface plasmon polariton and fundamental modes can be met at different wavelengths as the analyte of the RI is increased from 1.40 to 1.42. The phase-matching wavelength of the designed AF-PCF with the gold layer is shifted to the longer wavelength direction compared with that with the silver layer, and the resonance strength is much stronger. The average sensitivities of 7040 and 7017 nm/RIU in the sensing are arranged from 1.40 to 1.42 with high linearity are achieved for the designed sensors with the gold and silver layers, respectively, which are almost the same. However, the figure of merit with the silver layer is much better than that with the gold layer.

Highlights • The proposed PCF structure is a combination of circular layout and D-shaped. • The gold film is deposited on the polishing surface, the analyte is placed on the outer layer of the D-shaped PCF. • The proposed PCF sensor is feasible for the structural parameters with fabrication tolerance of ±1%. • The proposed sensor easy to fabricate and has high sensitivity. Abstract A high sensitivity D-shaped photonic crystal fiber sensor based on surface plasmon resonance is proposed for refractive index sensing. By using finite element method, the sensing properties of the proposed sensor are investigated. The numerical results show a very high average sensitivity of 14600 nm/RIU with the high resolution of 6.80 × 10−6 RIU for refractive index (RI) of analytes ranging from 1.420 to 1.435. The layout of the air holes is designed to be circular and only two layers in this D-shaped photonic crystal fiber. The metallic gold is used as the surface plasmon resonance activity material, which is deposited on the polishing surface. The analyte is placed on the outer layer of the D-shaped photonic crystal fiber. This D-shaped photonic crystal fiber solves the difficulty of gold-plated film and fill analyte in the holes. The proposed PCF structure is a combination of circular layout and D-shaped, which also leads to the proposed sensor easy to fabricate and has considerable sensitivity. [ABSTRACT FROM AUTHOR]

By using degenerate four wave mixing (DFWM) analysis, we proposed a refractive index (RI) sensor in photonic crystal fiber. This novel nonlinear fiber optics-based RI sensor works on the basis of Stokes and anti-Stokes photons shift, through DFWM technique under the influence of fourth-order dispersion. Here, the frequency shift of generated photons, as a response to change in the analyte RI, is analyzed using an appropriately modified nonlinear Schrödinger equation. Sensitivity of the proposed sensor is well optimized by tuning the pump wavelength and the pump power. Finally, we achieve a maximum sensitivity of −10 200 nm/RIU for anti-Stokes shift and 56 200 nm/RIU for Stokes shift, respectively, with lattice pitch of 2.94- and 1.205- $\mu \text{m}$ diameter of the airhole and 1.5-kW pump power at the pumping wavelength of 1064.7 nm, which proves it to be an advancement in the field of biomedical and chemical applications. [ABSTRACT FROM AUTHOR]

We propose a simple hollow-core circular lattice photonic crystal fiber (PCF) based surface plasmon resonance (SPR) refractive index sensor. The sensing performance is investigated by using the finite element method (FEM). Silver is used as the plasmonic material for this design, which is placed on the outer surface of the PCF to facilitate the fabrication. The proposed sensor shows a maximum wavelength sensitivity of 4200 nm/RIU with a sensor resolution of 2.38 × 10 −5 RIU. Besides, a maximum amplitude sensitivity of 300 RIU −1 and a resolution of 3.33 × 10 −5 RIU is reported for an analyte refractive index of 1.37. Moreover, the effect of varying structural parameters on the sensing performance such as pitch, air hole diameter and silver layer thickness are also discussed thoroughly. Sensitivity analysis of the proposed sensor is performed in order to investigate the impact on loss depth and amplitude sensitivity. Thanks to high sensitivity and linearity characteristics, the proposed sensor can be potentially employed in practical bio-sensing and chemical sensing applications. [ABSTRACT FROM AUTHOR]

• The sensor can realize double resonant peak sensing in the same spectrum, significantly improving detection accuracy. • By adjusting the thickness of the perovskite, it can be used in different working environments. • The fiber base of the sensor is a simple PCF, and it is insensitive to changes in structural parameters. • The maximum sensitivity of the sensor for RI measurement is 36400 nm/RIU, and the corresponding FOM is 1170.04 RIU−1. Two-dimensional polymer perovskite (CH 3 NH 3 PbI 3) has very potential properties in sensing applications. Hence, for high sensitivity, a lossy mode resonance refractive index sensor based on perovskite coating is proposed. The sensor uses a photonic crystal fiber (PCF) with three air holes and a polished surface. Perovskite is deposited on the PCF plane to form the Kretschmann structure. We analyzed its sensing characteristics by using the finite element method. A significant advantage of the sensor is its strong tunability, allowing it to be used in various operating environments by controlling the thickness of the film. In addition, two sharp resonant peaks in the loss spectrum can realize double resonant peak sensing and increase measurement accuracy. Numerical results show that the maximum sensitivity of the two resonant peaks is 36400 nm/RIU and 15400 nm/RIU, respectively, and the corresponding refractive index range is 1.39–1.43. The results also show that small structural changes do not cause a change in performance, meaning that the sensor has a high fault tolerance rate. The high sensitivity response with adjustable detection range makes the proposed sensor distinct. It has a good application prospect in water quality monitoring and biomolecular detection. [ABSTRACT FROM AUTHOR]

This article presents a review of the numerical techniques employed in simulating plasmonic optical sensors based on metal-dielectric nanostructures, including examples, ranging from conventional D-type fiber sensors, to those based on photonic crystal D-type fibers and incorporating metamaterials, nanowires, among other new materials and components, results and applications. We start from the fundamental physical processes, such as optical and plasmonic mode coupling, and discuss the implementation of the numerical model, optical response customization and their impact in sensor performance. Finally, we examine future perspectives.