We propose a dual-channel sensor based on surface plasmon resonance capable of simultaneously detecting seawater salinity and temperature. The sensor's primary structure consists of a cascade of optical fibers coated with composite films (Ag and Ag/ZnO/PDMS), enabling wide-range, high-sensitivity detection. The salinity detection range is 5‰–215‰ with a maximum sensitivity of 0.3769 nm/‰, while the temperature detection range is -10°C–100°C with a maximum sensitivity of 5 nm/°C. Additionally, this sensor demonstrates excellent performance in terms of cross-sensitivity and stability for practical measurement applications. A data-driven matrix is provided for demodulating cross-sensitivity. Based on this, multiple calibration experiments and stability tests were conducted, demonstrating that the sensor's error range is controllable and exhibits strong stability.

Existing devices often suffer from cross-sensitivity, complex structures, or low sensitivity when monitoring temperature and relative humidity (RH) simultaneously. To address these critical challenges, we proposed a dual-side polished photonic crystal fiber (PCF) sensor with polyvinyl alcohol (PVA) and polydimethylsiloxane (PDMS) as selective sensitive materials. Silver films deposited on the two polished surfaces of the PCF efficiently excite surface plasmon resonance (SPR), while a TiO2 modulation layer was introduced to shift the SPR peak of the temperature-sensing channel to the near-infrared region-enabling complete spectral separation of the two sensing channels. The Ag/PVA composite film on one side realizes RH detection, and the Ag/TiO2/PDMS stack on the other side achieves temperature measurement. The sensor reliably detects temperature (10-50 degrees C) and RH (60%-100% RH) within the wavelength range of 500-1350 nm, with average sensitivities of -7.875 nm degrees C-1 and -7.475 nm/%RH, respectively. By monitoring shifts in resonance wavelengths and core mode loss spectra, the sensor achieves interference-free simultaneous measurement of temperature and RH, offering a solution for environmental monitoring in vegetable greenhouses. This work provides a novel design paradigm for high-performance dual-parameter optical fiber sensors, advancing their practical application potential.

In this paper, an experimental study using NCF and MOF-based sensors was conducted for simultaneous measurement of refractive index (RI) and temperature (T) detection. The magnetron sputtering machine was used for metal coatings where thickness was controlled by sputtering time. The RI sensing section uses only Ag film for both NCF and MOF-based sensors. For temperature sensing, NCF was coated with a composite of Ag and PDMS, and MOF uses copper (Cu), Ag and PDMS in sensing probes. Upon testing for the final sensor fabrication, an optimum length of 2.0 cm was used as sensing probes for both sensors. An NCF-based sensor demonstrated a wide detection range for simultaneous RI and T measurements of 1.333-1.381 RI and 0-70 degrees C, with RI and temperature sensitivities of 4000 nm/RIU and 3.5 nm/degrees C, respectively. The MOF-based sensor has further enhanced detection ranges to 1.333-1.399 RI and 0-100 degrees C, with maximum RI and temperature sensitivities of 5333.3 nm/RIU and 6.5 nm/degrees C, respectively in simultaneous RI and T measurements. At last, a dual-parameter stability test was conducted and it was found that both sensors faced negligible error variation upon repeated experiments. Featuring good stability, high sensitivity, and easy fabrication, our proposed sensors are expected to have a wide range of applications in biochemical sensing.

This article proposes a surface plasmon resonance (SPR) sensor that can achieve ultra-high sensitivity detection in the near-infrared (NIR) region. Molybdenum disulfide (MoS2) in transition metal disulfide compound materials is used as a composite film material to modulate the spectral detection range of the sensor. The sensor probe also uses a photonic crystal fiber (PCF) with a large cladding area as a substrate. From a theoretical perspective, the modulation of the MoS2 film thickness was investigated to shift the resonance valley moving from the visible light band to the NIR band, effectively improving the detection sensitivity. The feasibility and effectiveness of the designed sensor in the NIR band sensing test were verified by simulation. The experimental test results show that the maximum refractive index (RI) sensitivity of the NIR sensor is as high as 25800 nm/RIU when the RI is between 1.415 and 1.420. To further investigate the temperature sensing performance of the NIR band sensor, a layer of PDMS thin film was deposited on the MoS2 film surface of the sensor for temperature testing. Its temperature test range is from 0 degrees C to 100 degrees C, with a maximum temperature sensitivity of 9.81 nm/degrees C. This NIR sensor is not only easy to prepare but also has ultra-high sensitivity in parameter detection, which provides a new direction for the development of SPR sensing technology in the NIR field.

Methane gas, due to its high flammability, is convenient for people’s daily lives, but its flammability poses safety hazards. Methane tends to explode when mixed with air. Therefore, it is particularly important to be able to effectively detect methane gas concentrations. A new methane gas sensor is presented in this paper. It is extremely sensitive to the reaction of methane gas. It consists of two fiber Sagnac interferometer (SI) loops, which utilize the vernier effect. The two fiber SI loops remain parallel. The optical fiber structure of the effective sensing in the sensing SI loop and the effective sensing in the reference SI loop are the same. Both of them adopt the polarization-maintaining photonic crystal fiber (PM-PCF) designed in this paper. However, the sensing SI loop uses a two-step filling technique to block small air holes and an immersion technique to deposit methane gas sensitive film on large air holes in PM-PCF. The sensing capability of the methane gas sensor was evaluated utilizing the finite element method (FEM). The numerical simulation results show that under the condition of the concentration of methane gas in the environment is 0-3.5%, the average sensitivity of two parallel Sagnac loops is 260.86 nm/%. Compared with other fiber optic methane gas sensors, the sensitivity of the sensor designed by this scheme is significantly improved, which provides a valuable reference and direction for the development of new methods and the design of ultra-sensitive methane gas sensors.

Sensing bandwidth is a key factor limiting multi-channel surface plasmon resonance (SPR) sensor detection performance. To further improve the detection performance of the SPR sensor, a cascaded dual-channel fiber sensor has been used for simultaneous detecting RI and temperature in this paper, in which a section of PCF coated with Ag/WO3 film as a refractive index (RI) sensing channel, and a section of PCF coated with Ag/MoS2/ PDMS film as a temperature sensing channel. As a representative of metal oxide materials, the excellent effective refractive index of WO3 can achieve an optimal modulation effect in the visible light band. In contrast, as a representative of disulfide materials, MoS2 can induce the SPR valley to shift toward the near-infrared (NIR) band. PDMS can be used as a thermosensitive material to achieve high sensitivity to temperature detection. We have designed a dual-channel SPR sensor that can simultaneously measure the liquid refractive index and temperature. The experimental results show that the maximum sensitivity of 20095 nm/RIU can be achieved within the detection range of the ocean spectrometer from RI 1.333 to 1.420, and the maximum sensitivity achieved within the spectral range of the Yokogawa spectrometer is 11.15 nm/degrees C for detecting temperatures between 0 degrees C and 100 degrees C. This dual-channel fiber sensor combines the advantages of high sensitivity and a wide detection range, and this method will promote the development of fiber SPR sensing technology in the future.

Due to the need for multi-parameter sensors to have multiple resonance valleys within the spectral range for parameter detection. Therefore, it is necessary to achieve high sensitivity and precision detection within a limited spectral range. In this article, we explore the use of cascaded no-core fiber (NCF) and photonic crystal fiber (PCF) to achieve higher accuracy detection. A surface plasmon resonance (SPR) dual-parameter sensor with cascaded Ag and Ag/WO3 thin-film structures was designed. The NCF sputtered Ag film region is used for refractive index (RI) sensing, while the PCF deposited Ag/WO3/PDMS region is used for temperature sensing and can simultaneously detect both liquid RI and external temperature parameters. The feasibility of using NCF and PCF for sensing has been verified by software simulation. The experimental results indicate that silver-based PCF has higher detection accuracy compared to silver-based NCF. The maximum sensitivity of the sensor's external RI in the range of 1.333-1.395 is as high as 5255.2 nm/RIU; when the external temperature is in the range of 20 degrees C-90 degrees C, the maximum temperature sensitivity can reach 4.5 nm/degrees C. The sensor developed in this study exhibits the advantages of broad detection range, compact structural configuration, high measurement accuracy, and enhanced sensitivity, offering a novel approach for achieving high-precision multi-parameter sensing in the near-infrared (NIR) spectral region.

A dual-core photonic crystal fiber (PCF) based surface plasmon resonance (SPR) sensor for measuring refractive index (RI) and temperature sensing and polarization filtering performance, is presented in this paper. The proposed sensor's cladding upper polished surface was coated with a gold film for refractive index sensing (RI) while lower polished surface with a composite film of silver and polydimethylsiloxane (PDMS) for temperature sensing. Proposed sensor was designed and simulated using finite element method (FEM) through commercially available Comsol Multiphysics software. Wavelength sensitivity of 18400 nm/RIU along with resolution of 5.43 x 10(-6) RIU and amplitude sensitivity of 150.74 RIU-1 were obtained for core 1 as RI sensing, while wavelength sensitivity of 12.0 nm degrees C-1 along with resolution of 8.33 x 10(-3) degrees C for core 2 as temperature sensing. It has a maximum loss of 30822 dB m(-1) towards Y-polarization which makes it ideal for polarization filtering, as Y has a higher loss than X-polarization. An extinction ratio (ER) of -92.31 dB at a transferring length of 3 mm was obtained showing its polarization filtering capabilities. Overall results indicate that our sensor is highly sensitive for both RI and temperature sensing and expected to perform better in polarization filtering performances. Its wide detection range in RI combined with temperature sensing increases its potential applications in the medical, chemical, environmental, and biosensor detection industry.

We propose a highly sensitive torsion and curvature sensor based on Mach-Zehnder interference using a helical elliptical-core polarization maintaining (HEPM) fiber embedded in a multimode fiber, and the sensitive region of the sensor is the HEPM fiber. The sensor can recognize the direction of torsion and maintain excellent stability under different torsions. Experimental results show that the free spectral range (FSR) of interference spectrum gradually increases as the length of the HEPM fiber is shortened, and the sensitivity of the torsion sensor increases accordingly. The maximum torsion sensitivity of 426.09 pm/(rad/m) was achieved in the torsion range from -90 degrees to 150 degrees when the length of the HEPM fiber was 0.7 cm, and the length of the multimode fiber was 1.0 cm. Similarly, as the length of the HEPM fiber decreases, the curvature sensing sensitivity is improved. The maximum curvature sensitivity of 2.33381 nm/m(-1) was achieved when the length of HEPM fiber was 0.7 cm, and the length of multimode fiber was 1.0 cm in the curvature range from 0 to 18 m(-1). We also experimentally tested the temperature stability of the sensor by setting up a sensing matrix that can simultaneously measure torsion and temperature, eliminating the temperature-influenced error. The proposed sensor can measure torsion and curvature changes with good linear response. The sensor can not only recognize the direction of torsion in torsion sensing, but also has a wide measurement range in curvature sensing. Moreover, the sensor has simple linear structure, so it has great potential in practical applications.

With the widespread application of fiber surface plasmon resonance (SPR) sensors in the field of biochemical sensing, especially in the detection of large molecules such as proteins, the sensitivity of traditional fiber SPR sensors has made it difficult to meet the requirements of detection accuracy in practical applications. This article proposes and proves an effective method for selecting the optimal metal oxide material to improve the sensing performance of SPR sensors. Metal oxides (TiO2 and ZnO) can improve the sensitivity by enhancing the evanescent field of fiber SPR phenomenon. Through simulation, it was found that when the metal oxide film of the composite film sensor maintains the same thickness, the metal oxide with a high effective refractive index (RI) has a better improvement effect on the sensitivity of the SPR sensor. Experimental results show that the maximum RI sensitivity of TiO2 composite film sensors and ZnO composite film sensors in the RI range of 1.333-1.420 is 15,200 nm/RIU and 13,600 nm/RIU, respectively. Compared to silver-based sensors, RI sensi-tivity has increased by 16.92 % and 4.62 %, respectively. To further verify the enhancement effect of different metal oxides on fiber sensors, another layer of PDMS film is deposited on TiO2 and ZnO films. Within the temperature sensing range, the maximum temperature sensitivity of these two composite film temperature sensors is 4.9 nm/degrees C and 4.3 nm/degrees C, respectively. Overall, metal oxides with high RI can improve the sensing performance of fiber optic sensors.

Twist detection is of great significance in industrial production, aerospace, biomedicine and other fields. Aiming at the problem of the low sensitivity of the twisted sensor, this paper proposed and prepared a kind of fiber twist sensor with high sensitivity based on Sagnac interference. The sensitive area of the sensor is a helical elliptical-core polarization maintaining (HEPM) fiber, the optical fiber with an elliptical core has linear birefringence property, and when the fiber is rotated, it has circular birefringence property. The HEPM fiber is plugged into the light loop to form Sagnac interference. Since circular birefringence is proportional to the degree of fiber distortion, the interference spectral trough will respond to different angles of fiber torsion. In addition, the sensor can not only identify the twist direction but also maintain good stability in different twist directions. The experimental results show that the free spectral range (FSR) of the interference spectrum increases and the sensitivity of twist sensing increases as the length of the used HEPM fiber decreases. The maximum twist sensitivity that can be achieved is 8740.64 pm/(rad/m) when the length of HEPM fiber is 15 cm in the twist range of plus or negative 120°, which is higher than the sensitivity of existing studies. The proposed sensor can be used for high-sensitivity distortion sensing. The temperature stability of the sensor is studied experimentally, and a sensing matrix is established that can simultaneously measure the torsion and temperature to eliminate the error caused by temperature. In summary, the proposed sensor not only has high sensitivity but also has an excellent linear response and can identify the twist direction, which has great potential in practical distortion detection.

Sensitivity is an important index parameter for evaluating the performance of a sensor. To improve the sensitivity of the sensor, we propose and demonstrate a surface plasmon resonance (SPR) fiber sensor based on Ti 3 C 2 T x -Mxene/silver film. A V-shaped photonic crystal fiber (V-PCF) is used as the sensing probe, and a silver film is deposited on its surface by magnetron sputtering to excite the SPR effect. Multimode fibers are used to transmit signals at both ends of the sensor probe. Simulation results show that light can be stably transmitted in the cladding of the V-PCF. Experimental results show that the refractive index (RI) measurement range of the sensor is between 1.333 and 1.420, and the maximum RI sensitivity is 20188 nm/RIU; In order to extend the detection function of the sensor, we coated PDMS film on the Ti 3 C 2 T x -MXene/silver film. When the sensor is used to measure temperature, the maximum temperature sensitivity is 9.33 nm/℃ in the range of 0 ℃-100 ℃. Therefore, the proposed composite film structure sensor in this paper has the advantages of ultra-high detection sensitivity and oxidation resistance, which can have a great competitive advantage in the sensing field.

We have experimentally demonstrated an ultra-high sensitivity gold-based fiber refractive index (RI) sensor whose main structure is composed of multimode fiber (MMF) and photonic crystal fiber (PCF). The gold film is deposited on V-shaped PCF by magnetron sputtering, and sensing experiments are performed based on the principle of surface plasmon resonance (SPR). Numerical simulation results indicate that the cladding mode of the V-shaped PCF is more capable of stimulating the SPR effect than the core mode. The experimental results show that the RI measurement range of the sensor is 1.333~1.421, with a maximum sensitivity of 10015nm/RIU. In addition to RI sensing, sensing probes can be coated with polydimethylsiloxane (PDMS) on a gold film for temperature sensing. For temperature detection, the range is from 10 to 100 °C and the maximum sensitivity is 3.5nm/℃. Besides high sensitivity in RI measurement, the proposed sensor also has good sensing performance in temperature sensing. With the advantages of high sensitivity, good stability, and easy preparation, this sensor has become an important reference in the field of high-performance sensing.

Wide sensing bandwidth is a prerequisite for dual-channel sensors to have a wide detection range and high sensitivity. To obtain a dual-channel optical fiber sensor with wide sensing bandwidth, a Na-based photonic crystal fiber sensor based on the surface plasmon resonance effect is proposed. The proposed sensor structure is numerically analyzed by finite element method. The sensor builds the fiber core in the center of the fiber, chooses alkali metal Na as the plasma material to stimulate the SPR effect, and polymethyl methacrylate and polydimethylsiloxane (PDMS) will be coated on the Na film as the protective layer. As a temperature-sensitive material, PDMS also takes into account the role of constructing temperature-sensing channels. The sensor bandwidth covers 600-1700 nm. The results show that when the RI range of the measured object is 1.33-1.42, the maximum sensitivity of the refractive index sensor is 11100 nm/RIU, and when the temperature range of the measured object is -40-20 degrees C, the maximum sensitivity of the temperature sensor is 6.4 nm/degrees C. Meanwhile, the loss peak of the sensor has a lower half-height width and greater detection accuracy. It has a good application prospect in the fields of biosensing and environmental monitoring.

In chemical and biological analysis, different substances have different requirements for RI detection. In this article, we propose and experimentally validate a molybdenum disulfide (MoS2)-modulated surface plasmon resonance (SPR) sensor. Due to the high effective refractive index (RI) of MoS2, the detection accuracy of the sensor after MoS2 modulation is good. The numerical simulation results verify that the MoS(2 )film has a good improvement effect on the performance of fiber sensing. The sensor is fabricated by coating a silver film and a MoS2 film on a photonic crystal fiber (PCF) using a magnetron sputtering method. First, the optimal sensing length and sputtering time of the silver film are determined experimentally, and the MoS2 film is coated on the optimal silver-based sensor. Experimental results show that the maximum sensitivity of the MoS2-modulated sensor in the detection range of RI from 1.415 to 1.420 is 16000 nm/RIU. The RI sensitivity of the MoS2-modulated sensor is increased by 167.35% compared with that of silver-based sensors, which means that the sensor is suitable for high-sensitivity detection applications of specific substances.

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.

In order to cope with the crosstalk between temperature and refractive index (RI) caused by high-temperature environments, this study proposes to modify the surface plasmon resonance (SPR) fiber optic sensors with molybdenum disulfide (MoS 2 ). MoS 2 efficiently modulates the resonance wavelength, enabling the sensor to operate in high-temperature environments. The effect of MoS 2 film thickness on the resonance wavelength was investigated by depositing MoS 2 film on the surface of no-core fiber (NCF) using the magnetron sputtering method. The analysis shows that MoS 2 can induce a significant redshift of the resonance dip, and the degree of redshift is related to the film thickness. In addition, a dual-parameter SPR sensor capable of detecting RI at high temperatures was prepared in this work by selecting the optimal Ag film thickness and MoS 2 film thickness. The sensor was obtained by cascading an Ag-based NCF with an Ag/MoS 2 -based NCF, which was simulated and tested experimentally. The results show that the maximum temperature sensitivity is 4.3 nm/°C over the 50-90 °C temperature range. The maximum RI sensitivity is 5243.4 nm/RIU over the RI range of 1.333-1.395. The test results also show that the two channels of the sensor are independent of each other and have good stability. Therefore, Ag/MoS 2 -based SPR sensors have the advantages of adjustable bandwidth, dual-parameter independent detection, and high sensitivity. These are essential in the future fields of multiparameter sensing, compensated detection, and real-time biomonitoring.

Facing the diversity and complexity of the types of parameters to be measured, multi-channel surface plasmon resonance (SPR) fiber sensors provide an excellent solution. However, the sensing bandwidth is a key factor affecting the sensor performance. In this paper, we explore a method to modulate the sensing bandwidth using the TiO2 film. A dual-channel SPR sensor with a wide sensing bandwidth is proposed. In this sensor, no-core fiber (NCF) is used as the sensing probe, and multimode fibers are used for the transmission of optical signals. The sensor has a cascaded composite film structure, the region coated with Ag film as the refractive index sensing region and the region coated with Ag/TiO2/PDMS as the temperature sensing region. The experimental results show that the sensing bandwidth of the sensor varies for different TiO2 coating times. It indicates that the TiO2 film can regulate the sensing bandwidth flexibly. Therefore, to achieve the optimal sensing effect, the TiO2 coating time can be flexibly adjusted according to the RI characteristics of the environment. The maximum sensitivity of this dual-channel sensor is 4.5 nm/degrees C and 3151 nm/RU when the temperature range is between 10 and 80 degrees C and the RI range is between 1.333 and 1.385, respectively. In addition, we discuss the repeatability and stability of this dual-channel sensor.

Multi-parameter surface plasmon resonance (SPR) sensors generally have low detection sensitivity due to detection wavelength limitations. We developed a two-parameter SPR sensor for refractive index (RI) and temperature detection by cascading Ag/WO3 film photonic crystal fiber (PCF) and Ag/MoS2 film PCF together. By using WO3 film with a low effective refractive index to prevent oxidation of silver-based PCF and maintain a wider RI sensing channel detection band; at the same time, MoS2 film with a high effective refractive index is used to modulate the detection range of temperature sensing channel. The detection performance and stability of the two-parameter SPR sensor were verified by software simulation and experiments. The data results indicate that the sensor can perform stable and independent tests during RI and temperature detection. The maximum sensitivity of the sensor within the RI detection range of 1.333 to 1.395 is as high as 6443 nm/RIU; the maximum temperature sensitivity within the temperature detection range of 40 °C∼90 °C is 8.72 nm/°C. This sensor can achieve high-sensitivity RI measurement in a high-temperature environment. This will have broad application prospects in the field of biochemistry.

This article proposes a curling pot shaped photonic crystal fiber (PCF) sensor based on surface plasmon resonance (SPR), which utilizes two parallel polished surfaces in the cladding to achieve dual parameter measurements of liquid refractive index (RI) and temperature. The mode characteristics and sensing performance of the designed PCF sensor are studied using the finite element method, and the effects of changes in structural parameters such as pore radius, spacing, and gold film thickness on the resonance spectrum are analyzed. The sensing accuracy of the sensor is insensitive to the change of structural parameters, and it has the characteristics of a wide detection range, high sensitivity, and easy manufacture. When the measured RI is in the range of 1.33 similar to 1.42, the maximum RI sensitivity is 20400 nm RIU-1, and the maximum FOM is 483.3 RIU-1. When the temperature ranges from -10 degrees C to 100 degrees C, the maximum sensitivity is 15.4 nm degrees C-1, and the maximum FOM is 0.43 RIU-1. The tight structure design of the sensor core close to the polishing surface and the anti-spill light design with a uniform arrangement of air holes enhance the SPR effect, which is the essential reason for achieving a wide detection range and high sensitivity.