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In this paper, an all-fiber Lyot-like filter with tunable free spectral range (FSR) and selectable sensitivity is proposed and experimentally demonstrated for simultaneous sensing of axial strain and temperature. Compared to the traditional fiber-based Lyot filter, the Lyot-like filter has an additional single-mode fiber (SMF) based polarization controller (PC), which is placed between two sections of polarization-maintaining fiber (PMF). In our experiment, the tunable FSR is achieved by adjusting the PC at a special angle, and a small FSR value of 6.58 nm and a large FSR value of 18.49 nm are obtained, respectively. Moreover, the experimental results show that the small FSR has low axial strain and temperature sensitivity, while that of the large FSR is high. By detecting the wavelength shifts of the filter spectra dip points, the simultaneous sensing of axial strain and temperature can be realized easily using a dual-parameter matrix. The proposed Lyot-like filter has the advantages of tunable FSR, selectable sensitivity, and simultaneous measurement of temperature and axial strain, which shows potential sensing applications in aerospace, chemical production, and bridge condition monitoring. [ABSTRACT FROM AUTHOR]

Multiparameter sensors that can individually monitor mechanical and thermal signals from multiple stimuli have attracted immense attention. Due to interferences caused by signal crosstalk, it is a challenge for multiparameter sensors to simultaneously differentiate mechanic and thermal stimuli within a broad working range. Herein, a liquid‐metal‐based stretchable dual‐parameter sensor that can simultaneously detect deformation (0–4.5 mm) and temperature (0–60 °C) is fabricated. The sensor adopts a multilayer structure in which a capacitive deformation‐sensing unit is stacked on top of a resistive temperature‐sensing unit. The deformation unit possesses excellent linear responses (R2 = 0.999) and ultralow detection limit (0.04 mm, ≈0.02%). Attributed to these merits, the deformation unit can be used to monitor physiological actions (e.g., finger bending, swallowing, and speaking). The temperature unit exhibits strong stability under multiple stimuli. With the cooperation of the two units, the dual‐parameter sensor can accurately differentiate deformation and temperature stimuli with an average error of 0.04 mm and 0.82 °C. Because of these remarkable performances, the sensor can achieve real‐time acquisition of the deformation and temperature change during finger movements. The dual‐parameter sensing abilities of the sensor indicate its promising potential in human motion monitoring and wearable devices. [ABSTRACT FROM AUTHOR]

An optical fiber sensor is proposed and experimentally demonstrated for simultaneous measurement of high temperature and transverse load. The sensor is designed by splicing a silica capillary tube (SCT) to a single-mode fiber (SMF) and then heating the SCT to form an air bubble. SCT simultaneously functions as a Fabry Perot (F-P) microcavity and an anti-resonant reflection waveguide. These sensing mechanisms lead to high contrast sensitivity values of temperature and transverse load (1.89pm/°C,190.48pm/N and 24.93pm/°C, 16.68pm/N). Remarkably, the temperature sensitivity of this sensor is eleven times higher than that of the current fiber-tip micro-cavity (2.1 pm/°C). The sensor is also more advantageous in quantitative production and practical application due to its low cost, ease of fabrication, good mechanical strength, and convenient reflection probe.

• An optical fiber MZI is designed and demonstrated for the simultaneous measurement of strain and temperature. • The MZI sensor is fabricated simply by on-line fiber cutting-welding method. The maximum strain sensitivity is -16.3 pm/μɛ. The temperature sensitivity of 10.45 nm/℃ is the highest to our best knowledge. An optical fiber Mach-Zehnder interferometer (MZI) is designed and demonstrated for the simultaneous measurement of strain and temperature. One microcavity fabricated by no-core-fiber (NCF) offset splicing is used to generate two different light paths for MZI, then sealed with polydimethylsiloxane (PDMS) to enhance the strain and temperature sensing ability. The strain and temperature sensing characteristics were simulated theoretically and investigated experimentally. The maximum strain sensitivity of −16.3 pm/μɛ was obtained in the range of 0–500 μɛ, and the ultrahigh temperature sensitivity of 10.45 nm/℃ was obtained in the range of 20–40 °C. The influence of microcavity length was analyzed in detail and the dual-parameter demodulation was demonstrated by solving a two-dimensional sensing matrix. The designed sensor with the merits of simple structure, easy fabrication and highly sensitive to weak strain and temperature, make it of great potential for the structural safety monitoring or wearable strain and temperature detections. [ABSTRACT FROM AUTHOR]

We proposed a simple and compact Fabry-Perot (FP) sensor for simultaneous measurement of water pressure and temperature, composed of a standard fiber ferrule connector/flat contact (FC/FC) connector and aluminum foil attached to a thin metal plate. Two dips in the interference spectrum are selected to illustrate the response of the FP sensor to the water pressure and temperature, we can obtain the simultaneous measurement via a method of sensitivity coefficient matrix. Experimental results show the maximum sensitivity of −2.948 nm/kPa for water pressure sensing in 0~9 kPa and 1.119nm/°C for temperature sensing in 33~45 °C. In addition, the dual-parameter sensor has the advantages of compactness, stability, simple production, small size, and high sensitivity, making it suitable for a wide range of practical applications. [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]

• Magnetic field and temperature sensing are realized with no core fiber coated with magnetic fluid and polydimethylsiloxane. • High sensitivity is obtained with the gold-clad no core fiber probe. • Reflection-like probe is convenient for magnetic field and temperature detection in narrow space. A kind of reflection-type magnetic field and temperature dual-parameter sensor based on surface plasmon resonance (SPR) effect was proposed and investigated. The sensing probe was fabricated with a section of no-core fiber, which was evenly divided into two parts. One part was immersed in magnetic fluid (MF) for magnetic field sensing (Channel 1, referred as CH1). The other part was coated with polydimethylsiloxane (PDMS) for temperature sensing (Channel 2, referred as CH2). The issue of magnetic field and temperature cross-sensitivity was resolved ingeniously. In the magnetic field intensity range of 0–55.1 mT, the maximum magnetic field sensitivity of 122.67 pm/mT was obtained. In the temperature range of 30–70 ℃, the maximum temperature sensitivity was 1662.64 pm/◦C. The sensor has the advantages of simple structure, small size, and potentials for applications in narrow space. [ABSTRACT FROM AUTHOR]

We proposed and demonstrated a compact inline optical fiber sensor for curvature and temperature measurement with low cross sensitivity. The device consists of a 5 mm long hollow-core fiber (HCF) spliced between two single-mode fibers. Two up-tapers were fabricated at each splicing joint forming a Mach-Zehnder Interferometer (MZI). The HCF acted as the anti-resonant reflecting optical waveguide (ARROW), giving periodic dips at resonant wavelengths in the optical transmission spectrum. The cross sensitivity of curvature and temperature problem is solved by demodulating the wavelength shift of the MZI for temperature sensing and intensity variation of ARROW dips for curvature sensing. The curvature and temperature sensitivities are experimentally measured to be -4.28 dB/m-1 and 25.76 pm/°C, respectively. The cross sensitivities for ARROW is measured to be 0.0056 m-1/°C. The structure of the sensor is simple and compact, which can be used for structural health monitoring in a complex environment.

We proposed and demonstrated a compact inline optical fiber sensor for curvature and temperature measurement with low cross sensitivity. The device consists of a 5 mm long hollow-core fiber (HCF) spliced between two single-mode fibers. Two up-tapers were fabricated at each splicing joint forming a Mach-Zehnder Interferometer (MZI). The HCF acted as the anti-resonant reflecting optical waveguide (ARROW), giving periodic dips at resonant wavelengths in the optical transmission spectrum. The cross sensitivity of curvature and temperature problem is solved by demodulating the wavelength shift of the MZI for temperature sensing and intensity variation of ARROW dips for curvature sensing. The curvature and temperature sensitivities are experimentally measured to be −4.28 dB/m−1 and 25.76 pm/°C, respectively. The cross sensitivities for ARROW is measured to be 0.0056 m−1/°C. The structure of the sensor is simple and compact, which can be used for structural health monitoring in a complex environment. [ABSTRACT FROM AUTHOR]

• A dual-parameter sensor based on four-core fiber (FCF) with a hybrid sensing mechanism is proposed. • The surface of FCF is covered with gold film to excite the SPR and MZI for measuring refractive index (RI) and temperature. • The proposed sensor exhibits a high RI sensitivity of 2091 nm/RIU and a temperature sensitivity of 0.0398 nm/°C. A dual-parameter sensor based on a hybrid sensing mechanism of surface plasmon resonance (SPR) and Mach–Zehnder interference (MZI) using a four-core fiber (FCF), is proposed and implemented. The designed sensor is fabricated by cascading a sandwich structure of the FCF, multimode fiber and lead-in/out single-mode fiber. The gold-coated FCF as the critical component, enabling the excitation of the SPR and MZI for measuring refractive index (RI) and temperature. The proposed sensor exhibits a high RI sensitivity of 2091 nm/RIU and a temperature sensitivity of 0.0398 nm/°C. The proposed dual-parameter sensor based on FCF provides a new insight for the design of fiber SPR sensor, which can be used to measure multiple physical parameters in various fields such as biochemistry, gene diagnosis, environmental monitoring, and so on. [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]

A dual-parameter sensor for strain and temperature measurement featuring cascaded long period fiber grating and Fabry-Perot (LPFG-FP) structure has been proposed and realized both theoretically and experimentally. The sensor structure is theoretically proved to be efficient, where the LPFG serves as a passive filter. The direct point-by-point method of CO 2 laser system is used for LPFG fabrication. The FP structure is fabricated by splicing the chemically etched SMF and the end of LPFG. The total sensor length is 3.6 cm, and three dips at 1544.18 nm, 1556.27 nm, and 1566.92 nm are chosen for following analysis. The strain experimental results show that in the range of 0–450με, the strain sensitivities are 1.7 pm/με, −8.2 pm/με, and 1.5 pm/με of three dips, respectively. The temperature experimental results show that in the range of 40–70℃, the temperature sensitivities are 6.8 pm/℃, 21.0 pm/℃, and 7.1 pm/℃ of three dips, respectively. By analyzing wavelength shifts and parameter response characterization of the resonant wavelengths, the sensitivity matrix can be determined. The experimental results demonstrated the satisfactory performance of strain and temperature measurement. [ABSTRACT FROM AUTHOR]

• A simple fiber sensor that measures micro-displacement and temperature simultaneously is proposed. • The proposed sensor is highly sensitive to micro-displacement and temperature. • The proposed fiber sensing system has the advantages of low manufacturing cost, easy manufacture, and no need of other complex processing technology. A dual-parameter sensor based on balloon-like single-mode fiber (SMF) cascaded with Sagnac interferometer (SI) to measure displacement and temperature simultaneously is proposed, and the experimentally proved. The balloon-like structure made by bending SMF is sensitive to micro-displacement and temperature. The SI is inserted into a polarization maintaining fiber (PMF). The SI can be utilized not only for temperature measurement but also as temperature compensation for micro-displacement measurement by balloon-like SMF. By optimizing the length of the PMF, the resonant dips of the two structures are independent of each other. Experimental results indicate that the displacement and temperature sensitivities of the composite sensor reach to –326 pm/um and –1.317 nm/℃, respectively. Additionally, this fiber sensor has the advantages of simple structure, high sensitivity, and good stability, which exhibits applications in fields that require precise temperature control. [ABSTRACT FROM AUTHOR]

A dual-parameter sensor based on a liquid-infiltrated microstructured optical fiber (MOF) is constructed by selective liquid infiltration of one particular cladding air hole in the MOF. The fundamental core mode could be simultaneously coupled to several higher order modes of the adjacent liquid rod waveguide when the phase-matching condition is satisfied, resulting in the emergence of multiple resonance peaks with different sensing characteristics. Our proposed liquid-infiltrated MOF sensor has several advantages, such as high sensitivity and a large measurement range. Moreover, it is able to resolve the temperature-force cross-sensitivity issue that is commonly encountered in most practically deployed sensing components.

• 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 multi-components interferometer based on partially filled dual-core photonic crystal fiber (D-C PCF) was fabricated for measuring temperature and strain. The partially filled D-C PCF was prepared by manual gluing method, and the cladding air holes surrounding one core were selectively filled with refractive index liquid while remaining other air holes unfilled. A multi-components interference with a large spectrum envelope and fine interference fringes was observed in the transmission spectrum. Theoretical and experimental investigations revealed that the large spectrum envelope was originated from the interference between the fundamental modes of two cores of the PCF, while the fine interference fringes were generated by the interference between the fundamental mode and higher order modes in one core that surrounded by unfilled air holes. The proposed device can be used to monitor temperature and strain simultaneously through matrix demodulation, with a high temperature sensitivity of 5.43 nm/°C. [ABSTRACT FROM PUBLISHER]

The influence of dual-parameter sensor resolution on the demodulation results is usually ignored. We present a cascaded photonic crystal nanobeam cavities sensor (CPCNCS) on the silicon-on-insulator (SOI) platform that can effectively suppress demodulation deviations. The sensor consists of a slotted photonic crystal (PhC) nanobeam cavity (c a v 1) and an unslotted PhC nanobeam cavity (c a v 2). To describe the ability for suppressing demodulation deviations, we propose the concept of demodulation stability factor and perform a quantitative analysis. The vectorization analysis method provides a clear design idea for dual-parameter sensors with high demodulation stability factor. The demodulation stability factor of the proposed CPCNCS is as high as 2497 nm RIU−1 K−1, indicating that the proposed sensor has a superior performance in demodulating refractive index and temperature. • The ingenious combination of two nanobeam cavities is very beneficial to reduce the demodulation deviations. • The concept of demodulation stability factor (Ds) is proposed. • The Ds is analyzed by the vectorization method combined with the Taylor series and arithmetic–geometric average inequality. • The calculation method of Ds is given. [ABSTRACT FROM AUTHOR]

A hybrid fiber interferometer sensor is proposed and demonstrated for simultaneous measurement of strain and temperature with insensitivity to external refractive index. This sensor consists of a 5 cm few-mode fiber (FMF) cascaded with a 37 μ m hollow-core fiber (HCF). The other end of the FMF is offset spliced to the lead-out single-mode fiber (SMF) to excite high-order modes inside the core. A Fabry–Perot interferometer (FPI) micro-cavity is formed by the HCF and two splicing interfaces, the interference pattern of which can be observed in the reflection spectrum. The FMF-based core-mismatched structure forms a Mach–Zehnder interferometer (MZI) and the interference pattern can be collected in the transmission spectrum. The simulation result shows that the interference in MZI is mainly generated from the LP 11 and LP 21 mode in the FMF. A cross coefficient matrix for dual-parameter sensing can be achieved by the different responses of FPI and MZI to strain and temperature. Experimental results show that proposed sensor has the maximum strain sensitivity of 5.89 pm/ μ ε and the maximum temperature sensitivity of -38.8 pm/°C. We also tested the refractive index characteristics of this sensor and results show that it is insensitive to the variation of external refractive index. In addition, the cross coefficient matrix of this scheme has a good condition number of 6.72. • A hybrid fiber interferometer sensor for simultaneous measurement of strain and temperature is proposed and experimentally demonstrated. • The proposed dual-parameter sensor is insensitive to external refractive index. • The proposed dual-parameter sensor has a good condition number of 6.72. • The maximum strain sensitivity and temperature sensitivity are 5.89 pm/ μ ε and -38.8 pm/°C respectively. [ABSTRACT FROM AUTHOR]

• Each single TFBG sensor can detect simultaneously temperature and strain variations. • Any two resonance peaks in the spectrum can be used by the demodulation technique. • Steady-state analysis of composite + optical fibre FEMs matches TFBG measurements. • The accuracy of the TFBG can be increased by improving its thermal resolution. • The thermomechanical state of a composite can be monitored by embedding a TFBG. A simultaneous two-parameter single sensor based on weakly tilted Fibre Bragg Grating (TFBG), embedded in a 1 mm glass fibre/epoxy composite plate, is demonstrated to measure independently the temperature and strain variations induced in the material by the exposure to heating lamps. The spectrum of weakly TFBGs is composed of several peaks that can be used for different sensing purposes. Here, the shifting of the Bragg and the Ghost peaks are considered to calculate the strain and temperature variations through thermomechanical sensitivity coefficients of the selected peaks. To prove the reliability of the TFBG measurements, the resulting strain values were compared with the strain measurements obtained from the TFBG when compensated by a K-thermocouple embedded close to the optical fibre sensor. Furthermore, the numerical simulation of the full Finite Element Model (FEM) (composite + TFBG) and partial FEM (composite only) models were carried out by assuming a 3-D Gaussian temperature profile. This allowed the TFBG experimental measurements to be compared with the simulated results. A study focused on the strain deviation showed a good match between the full FEM and the TFBG measurements with an average error of ~5% in the case of the dual-parameter sensor and ~2% for the compensated TFBG. [ABSTRACT FROM AUTHOR]

Multiparameter integrated sensors are required for the next generation of flexible wearable electronics. However, mutual interference between detected signals is a technical bottleneck for a flexible tactile sensor to realize pressure-strain monitoring simultaneously and sensitively. Herein, a flexible dual-parameter pressure-strain sensor based on the three-dimensional (3D) tubular graphene sponge (TGS) and spider web-like stretchable electrodes is designed and fabricated. As the pressure-sensitive module, the unique 3D-TGS with an uninterrupted network of tubular graphene and high graphitic degree demonstrates great robust compressibility, supporting compression to ∼20% without shape collapse. The spider web-like stretchable electrodes as the strain-sensitive module are fabricated by a spray-embedded process based on the hierarchical multiscale hybrid nanocomposite of Ag nanowires (NWs) and carbon nanotubes (CNTs) with an optimal mass ratio. By comparing the output signals of spider web-like flexible electrodes, the magnitude and direction of the applied force can be effectively monitored simultaneously. Moreover, the potential applications of the flexible dual-parameter pressure-strain device in human-machine interaction are also explored, showing great promise in artificial intelligence and wearable systems.