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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 10015 nm/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 3.5 nm/℃. 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. • This work proposes a refractive index sensor with ultra-high sensitivity, with a maximum sensitivity of 10015 nm/RIU. • The sensor uses PCF with a large cladding area as the substrate and is easy to prepare. • The sensor selects a stable gold film, which is not easily oxidized, as the plasma material. • The maximum sensitivity of this sensor used in the field of temperature sensing is 3.5 nm/°C. [ABSTRACT FROM AUTHOR]

• Metal oxides with high RI will improve the sensing performance of fiber sensors. • Compared to silver-based sensors, the maximum sensitivity of TiO 2 composite film sensors has increased by 16.92 %. • Compared to silver-based sensors, the maximum sensitivity of ZnO composite film sensors has increased by 4.62 %. • The maximum temperature sensitivity of the two composite membrane sensors is 4.9 nm/℃ and 4.3 nm/℃, respectively. 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 (TiO 2 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 TiO 2 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 sensitivity 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 TiO 2 and ZnO films. Within the temperature sensing range, the maximum temperature sensitivity of these two composite film temperature sensors is 4.9 nm/°C and 4.3 nm/°C, respectively. Overall, metal oxides with high RI can improve the sensing performance of fiber optic sensors. [ABSTRACT FROM AUTHOR]

• A broadband dual-parameter sensor is proposed and demonstrated. • The sensor cascaded gold film and silver film, which made the range of parameters to be measured larger. • The two detection channels are independent of each other and do not affect each other. • The sensor is simple in structure and easy to prepare. Dual-parameter sensor has relatively small detection range because of restriction on resonance wavelength range. To overcome this problem, we propose a cascaded gold and silver SPR dual-parameter sensor. As the resonance wavelength ranges of gold and silver are different, cascading the two metals to make one sensor broadens the resonance wavelength range, thus increasing the sensor's detection range. The sensor uses no-core fiber as the probe and multimode fiber (MMF) as the input (output) coupler, which constitutes an MMF-NCF-MMF sensing structure. By using Magnetron sputtering, gold and silver are deposited on the outer surface of NCF. The effects of coating time and NCF length on the sensing performance were experimentally investigated to determine the optimal coating time and NCF length. The experimental results shows that the two channels of the sensor are independent of each other without crosstalk and have an extensive range of parameters to be measured. The maximum sensitivity is 3231 nm/RIU in the RI range of 1.333–1.385. It has a maximum temperature sensitivity of 6.68 nm/°C from 0 to 80 °C. In addition, the sensor has good stability and repeatability. The proposed sensor has a simple and integrated structure and is suitable for applications requiring large detection range sensing. [ABSTRACT FROM AUTHOR]

• A compact dual-channel sensor is proposed and demonstrated. • The sensor can detect temperature and refractive index simultaneously. • The two detection channels are independent and do not interfere with each other. • The sensor structure is simple and easy to prepare. To improve the integration of sensors and meet the trend of miniaturization of devices, we propose and demonstrate a compact dual-channel surface plasmon resonance (SPR) fiber sensor for detecting refractive index (RI) and temperature. In this sensor, we chose the simplest structure of optical fiber: no-core fiber (NCF), as the sensing probe. Then the silver film was deposited on the NCF surface using magnetron sputtering to excite the SPR effect. Two sensing channels were constructed on the NCF, one channel deposited with silver film for RI detection, and another channel deposited with PDMS and silver film for temperature detection. Such a construction makes the sensor compact and small. The performance of the proposed sensor is studied theoretically and experimentally. The experiment shows that the maximum sensitivity of the sensor is 3039 nm/RIU and 3.53 nm/°C when the RI ranges from 1.333 to 1.375 and the temperature ranges from 0 °C to 70 °C, respectively. The significant advantage of our proposed sensor is its simple, compact, and easy-to-prepare structure, which opens up a new direction for device miniaturization. [ABSTRACT FROM AUTHOR]

• The deposition of sodium and silver on PCF broadens the sensing bandwidth, thus enlarging the measurement range of the two parameters. • The two parameters to be measured can be represented in the same spectrum without secondary measurement; the number of light sources and spectrometers can be reduced. • The two channels for measuring RI and temperature have no mutual interference. • The sensor has a simple structure and high tolerance. When temperature and refractive index are measured in same spectrum, the measurement range of parameters is generally narrow due to bandwidth limitation. We proposed a sensor for simultaneous measurement of them in a wide wavelength range for this problem. The proposed sensor is a dual-channel structure based on the photonic crystal fiber (PCF) with three air holes and a polished plane. The silver film deposited on the polished plane is responsible for refractive index measurement, and the sodium film and polydimethylsiloxane (PDMS) filled in an air hole for temperature measurement. According to research findings, the two kinds of metal films work in different wavebands, which increases the sensing bandwidth and the measurement range of the parameters to be measured. Numerical results show that when the refractive index of analyte is 1.35 ∼ 1.41 and the temperature is 10 ∼ 60℃, the maximum spectral sensitivity of the sensor is 8400 nm/RIU and 10.2 nm/℃, respectively. The results show that the performance of the sensor is not sensitive to structural parameters. It makes the sensor easy to manufacture. The excellent performances and wide detection range make the proposed sensor have a good application prospect in biochemical detection, environmental monitoring, medical sensing, and other fields. [ABSTRACT FROM AUTHOR]

• This work explains that TiO 2 and ZnO can significantly modulate the resonance wavelength range of SPR sensors. • It is experimentally demonstrated that the two oxide films have the effect of enhancing the sensitivity of the SPR sensor. • The dual-channel sensor prepared using the cascade method of two oxide films has a wide sensing bandwidth. • The performance of the proposed dual-channel sensor is highly stable and not easily oxidized. In order to broaden the bandwidth of SPR dual-channel sensors, this work proposes to tune the resonance wavelength range of the sensors using a cascade of ZnO and TiO 2 films. The two oxides are transversely deposited on Ag-based no-core fiber to form a dual-channel sensor that can be used for refractive index (RI) and temperature measurements. Among them, Ag/ZnO is used for RI sensing and Ag/TiO 2 /PDMS is used for temperature sensing. The simulation and experimental results show that ZnO and TiO 2 have the effect of broadening the resonance wavelength range by 44 nm and 72 nm, respectively. In addition, when the two oxides are added to the Ag-based sensor, the SPR valley is red-shifted, and the sensitivity is enhanced. The experimental results also show that the two oxides make the silver film less susceptible to oxidation and enhance the stability of the sensor. Numerical results show that the maximum RI sensitivity of the sensor is 4630 nm/RIU, and the temperature sensitivity is 5.8 nm/°C. The range of the object to be measured is 1.333–1.385, 0–50 °C. This ability to broaden the sensor bandwidth provides a new direction for designing and applying high-performance multi-channel SPR sensors. [ABSTRACT FROM AUTHOR]

• This work utilizes TiO 2 film to tune the sensing bandwidth and the resonance wavelength range to the near-infrared band. • A dual-channel sensor with wide bandwidth is proposed. • The experimental results show that the RI range of the sensor is 1.333–1.385, and the temperature range is 10–80 ℃. • The sensor has simple structure and good repeatability. 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 TiO 2 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/TiO 2 /PDMS as the temperature sensing region. The experimental results show that the sensing bandwidth of the sensor varies for different TiO 2 coating times. It indicates that the TiO 2 film can regulate the sensing bandwidth flexibly. Therefore, to achieve the optimal sensing effect, the TiO 2 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/°C and 3151 nm/RU when the temperature range is between 10 and 80 °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. [ABSTRACT FROM AUTHOR]