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A highly sensitive mid-infrared evanescent wave sensor based on side-polished (SPF) chalcogenide fiber (ChG) was proposed in this work. The optimum optical fiber parameters were determined via numerical simulation by detecting the leakage intensity of evanescent waves from the optical fiber of different polish depths. The SPF remarkably enhanced the evanescent wave sensing while maintaining fiber loss and strength. Graphene oxide (GO) was coated on the fiber to enhance the sensitivity of SPF sensor for butane (C 4 H 10). GO has a great specific surface area and abundant oxygen-containing functional groups, which enlarges the contact area of GO with gas molecules and enables to adsorb gas. Results show that the GO-SPF sensor can be three and five times more sensitive than the original fiber optic sensor and SPF sensor for butane gas detection, and has a fast response time and good repeatability. [ABSTRACT FROM AUTHOR]

Fiber optic intrusion detection is recognized as one of the most effective perimeter defense strategies against intruders and terrorists. Most current infiltration detection systems gather information via optical cables and trace invasions using classification techniques. This research introduces two intrusion detection algorithms and a hybrid approach to address the challenges of unstable and hard-to-extract fiber optic infiltration features, especially during rainy weather. The first method, known as the phase parameter-matching algorithm, calculates the system's disturbance covariance at any position and uses the Frobenius norm to identify intrusions by measuring the difference between disturbance covariances at distinct sites. The second method, the cross-rebuilding algorithm, employs the Kalman filter to reconstruct the output of each point based on the non-infiltration state parameters, detecting intrusions through cross-reconstruction error. Experimental tests were conducted to evaluate both methods. The results indicate that both methods are viable, with the phase parameter-matching algorithm being more robust but slower, and the cross-rebuilding algorithm being faster but less reliable. The hybrid algorithm combines the strengths of both approaches, offering a balanced solution with moderate computation time and enhanced resistance to environmental interference, leading to improved overall detection accuracy and reduced false positive rates. [ABSTRACT FROM AUTHOR]

In this paper, a D-shaped photonic crystal fiber (PCF) sensor based on a Sagnac interferometer is proposed, and it can achieve ultrahigh refractive index (RI) and temperature sensitivity when operating around the turning point of group birefringence (B g). We undertake a theoretical analysis on B g and a simulation calculation to study the sensing characteristics and obtain the optimized structure parameters of the D-shaped PCF sensor. The simulation results show that the maximum average RI sensitivities can reach 3253.33 and 15500 nm/RIU in the RI range of 1.33 to 1.35 and 1.40 to 1.42, respectively. When the temperature changes from -50 to 0 °C and 0 to 50 °C, the maximum average temperature sensitivities are up to 10.11 and 10.67 nm/°C, respectively. The proposed D-shaped PCF sensor can achieve dual-parameter sensing and has great potential for practical applications in biochemical and environmental science. • A novel D-shaped photonic crystal fiber sensor based on a Sagnac interferometer is proposed. • The proposed sensor can achieve ultrahigh sensitivity when operating around the turning point of group birefringence. • The proposed sensor can achieve the dual-parameters sensing, and has great potential for practical applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • An optical fiber sensor for SARS-CoV-2 N gene detection coated with gold nanorods has been prepared. • The sandwich structure was designed and demonstrated to couple particles side-to-side. • The sensor shows a wide detection range of 0.01 to 100 nm, and the limit of detection is 1 pM. • The response time of optical fiber sensor is 10 min and it performs well. A novel SARS-CoV-2 N gene optical fiber biosensor based on ASO-coated gold nanorods is proposed in this work. A fiber probe prepared by AuNRs self-assembly was used to detect N gene by complementary base pairing method. The detected material was processed into AuNRs-ASO2-N gene coupler by cross-linking, and the pairing of N gene with ASO1 connected to AuNRs on the surface of the optical fiber formed the hydrogen bonding. The coupling of AuNRs resulted in a left shift of the peak position and a decrease in absorbance in the LSPR spectrum. In this manuscript, it is verified for the first time by simulation and experimental characterization that the coupling mode of AuNRs on the surface of the optical fiber is side by side, which leads to a left shift of the peak position of the LSPR absorption peak on the optical fiber. It is also proved that sandwich method is superior to the traditional method of changing the refractive index. The response time of the sensor is 10 min, and the detection limit is 1 pM, and the results show that the optical fiber sensor based on ASO-coated AuNRs has excellent RNA detection performance in artificial body fluids and is very suitable for RNA detection. [ABSTRACT FROM AUTHOR]

We propose a Sagnac interferometric sensor for simultaneous strain, temperature, and torsion measurement based on a polarization-maintaining fiber (PMF). The Sagnac sensor consists of a single-mode fiber (SMF), PMF and SMF spliced sequentially to form an SMF-PMF-SMF structure. The designed Sagnac interferometric sensor exhibits different wavelength shifts for strain, temperature and torsion measurements. Therefore, we observed three selected dips in the interferogram and measured strain, temperature and torsion simultaneously by their wavelength shifts. The maximum sensitivity of the sensor to strain, temperature, and torsion were experimentally measured to be 28.9 pm/µε. (10-12 m), −1.7504 nm/°C, and −1.0964 nm/(rad/m), and the measurement ranges were 0∼720 με, 25 °C–39 °C, and −7.679 rad/m∼4.887 rad/m (−110°–70°), respectively. In the subsequent experiments, we also verified the feasibility of the sensor for simultaneous measurements, and the errors of the results obtained were less than 10%. And we have successfully increased the temperature measurement range to 25°C∼85°C by cascading FBG in the original structure. The designed sensor has the advantages of easy fabrication, high sensitivity, and bi-directional torsional measurement, which have a wide range of applications in the fields of structural health detection, industrial control, and aircraft attitude recognition. • The sensor has a high torsional sensitivity and the ability to determine the direction of torsion. • In terms of strain, the sensor also has a large sensitivity and is able to provide some significances for investigation. • Simultaneous measurement of three parameters of strain, torsion and temperature can be achieved. • The sensor has the advantages of simple structure, easy to reproduce and high sensitivity. [ABSTRACT FROM AUTHOR]

• The holes enclosing core fiber can block the diffusion of dopants from the core to the cladding. • The thermal blocking effect of holes enclosing core fiber is analyzed in simulation and experiment. • Long-period fiber grating devices based on holes enclosing core fiber have a more powerful potential for application in high-temperature and high-pressure environments. We have developed a variety of optical fibers with holes enclosing the core to increase the service life of fiber optic devices under high-temperature and high-pressure environments by blocking the diffusion of dopants in the core with the help of air holes. Simulation results show that the fiber with uniformly distributed holes enclosing the core, the more the hole number, the smaller the core hole distance, and the larger the hole radius, the more significant the blocking effect on thermal diffusion. By comparing the refractive index distribution of three kinds of holes enclosing core fibers and single-mode fibers after prolonged high-temperature heating treatment, the thermal diffusion blocking effect of the holes enclosing core fiber is verified. Long-period fiber gratings fabricated by periodic refractive index modulation of holes enclosing core fibers can realize the measurement of various physical parameters. The thermal diffusion blocking effect of the holes enclosing core fiber enables the long-period fiber grating devices to work for a long time under high-temperature and high-pressure environments, showing the potential for practical applications in various industrial processes. [ABSTRACT FROM AUTHOR]

In this work, a simple design and cost-effective displacement-curvature sensor based on macro-bend single-mode fiber (SMF) is planned and demonstrated. The optical fiber sensor encompasses a bending configuration and the macro-bending losses were exploited as the sensing process for the capturing of angular displacement motion in an angle span between 0° and 90° (that corresponds to curvature displacement between 0 and 49.5 cm). A straight SMF shape and other four bent sensor structures (U-like, drop-like, Knot-like, and eight-like) have been fabricated from sections of 90 cm length SMF. These five sensor configurations will provide high maneuvering for versatile applications. In these adjustable sensing schemes, the fiber sensors were described by monitoring the power loss corresponding to the diverse angular displacement at various bending structures in terms of the shape of the bend, the bending diameter, and the number of wrapping turns. Then, these measurement schemes based on the macro-bending losses were employed to detect the human motion elbow joint, and a proper sensing scheme was adopted to examine the flexion/extension joint motion in detail. The proposed sensors showed enhanced sensitivity to flexion/extension joint motion range between −0.25 and −0.477 dB/° and good sensitivity to curvature ranging between −0.552 and −1.052 dB/cm. The demonstrated and planned sensing techniques are adjustable and accessible for different types of human and mechanical movements. [Display omitted] • Wearable Optical Fiber Sensor based macro-bending loss for Biomechanical Motion Evaluation. • A simple design and cost-effective displacement-curvature sensor based on macro-bend single-mode fiber (SMF) has been integrated into elbow joint phantoms and measuring its response to various elbow joint movements in the range of 0°-90°. • A straight SMF shape and other four bent sensor structures (U-like, drop-like, Knot-like, and eight-like) have been exploited as the sensing process for the capturing of angular displacement motion in a span between 0 and 49.5 cm. • Adjustable sensing measurement schemes based on the macro-bending losses have been employed to detect the human motion elbow joint, and a proper sensing scheme has been adopted to examine the flexion/extension joint motion in detail. [ABSTRACT FROM AUTHOR]

• PEDOT:PSS is a promising material for pH detection. • The incorporation of poly(vinyl alcohol) with PEDOT:PSS enhances the usability of device. • PEDOT:PSS/PVA is resistant to measurements in highly acidc conditions. • The sensor exhibits temporal stability. In this work, a pH sensitive transducer element attached to a multimode optical fiber section is proposed. The sensitive element is a PEDOT:PSS/PVA composite film that exhibited sensitivity at low pH values in the range of 1–7 pH. The addition of PVA was important for the adhesion process to the optical fiber surface. The morphology of the PEDOT:PSS polymers allowed characterization at pH stimuli that were based on the optical power transmission generated from the interaction of the light propagating in the optical fiber core and the optical fiber section coated with the sensitive film. A sensitivity of −0.05 dB/pH and a linear fit R2 of 0.93 was obtained, the response time was 3 s, while the sensor recovery time was 50 s maintaining stability higher than 10 min. [ABSTRACT FROM AUTHOR]

• A high sensitivity and low temperature cross-talk magnetic field sensor with small dimension is proposed and investigated. • It is easily fabricated by sandwiching a tiny ferrofluid-filled capillary tube between two SMFs via a short MMF at the capillary tube's both ends. • The magnetic field sensitivity achieves up to 8.966 nm/mT and 4.264 nm/mT for weak longitudinal and vertical magnetic field, respectively, as well as good stability and accuracy. • The temperature cross-talk is very low. A ferrofluid-filled in-fiber Mach-Zehnder interferometer (MZI) is presented and validated for magnetic field sensing. It is constructed by embedding a short capillary tube filled with ferrofluid which is sandwiched between two SMFs through a short MMF at its both ends, and the device is experimentally proved having extreme high refractive index (RI) sensitivity. When the sensor is placed in an external magnetic field, the RI of the ferrofluid changes, causing a shift in the transmission spectrum of the interferometer. Experimental results show that the proposed sensor exhibits a high sensitivity of 8.9657 nm/mT and 4.2642 nm/mT for longitudinal and vertical magnetic field within the range of 0–1.5 mT and 0.8–2.2 mT, respectively. Furthermore, the sensor exhibits excellent low temperature cross-talk in longitudinal and transverse magnetic fields as low as 0.014 mT/°C and 0.030 mT/°C, respectively. The sensor offers advantages such as stable operation, compact size, and robust mechanical structure. [ABSTRACT FROM AUTHOR]

• A concise all-fiber hydrostatic pressure sensor is proposed. • High hydrostatic pressure sensitivity of −0.2358 nm/MPa in the range of 0.1 MPa to 16.1 MPa is obtained. • Ultra-low temperature–pressure cross-sensitivity of 0.04368 MPa/℃ proves our sensor more competitive in harsh environment applications. With the rapid development of physical ocean observation, high-performance pressure sensor integrated with stable mechanical strength, sufficient pressure sensitivity as well as negligible temperature crosstalk is highly desirable but still lack of research. This paper proposes an all-fiber optical sensor based on a Mach-Zehnder interferometer (MZI) for hydrostatic pressure measurement, utilizing a multi-mode fiber (MMF)-single-hole-dual-core fiber (SHDCF)-MMF structure. The MMF sections act as a beam splitter and coupler to enhance the Mach-Zehnder interference. The SHDCF serves as the pressure-sensing section. Under the action of the enclosed air hole in SHDCF, hydraulic variations cause changes in the structural parameters of the fiber, especially the refractive index change caused by the elasto-optical effect, which leads to the shift of the interference dips. The experimental results prove that the SHDCF-based MZI sensor has a higher hydrostatic pressure sensitivity than other hole-less silica fiber-based sensors. The max pressure sensitivity is −0.2358 nm/MPa in the range of 0.1 MPa to 16.1 MPa with good linearity and reliability. Moreover, the low temperature–pressure cross-sensitivity of 0.04368 MPa/℃ also proves our sensor more competitive in harsh environment applications. [ABSTRACT FROM AUTHOR]

• The sensitivity of FLRDS is improved by adopting a bi-cavity differential technology. • A novel sensor based on the improved FLRDS is developed for robot fingers. • A robot-finger sensing network system with great performances is proposed. Contemporary intelligent robots typically necessitate the implementation of a distributed sensing network system within their digits to execute a range of intricate tasks collaboratively. In this investigation, we have introduced a novel fiber sensor founded on an enhanced fiber-loop ring-down spectral technology. This sensor employs double differential ring-down cavities to mitigate prevalent sources of interference, such as temperature and humidity. Consequently, it exhibits a robust linear response with remarkable sensitivity, quantified at 105.2 n s / N for force measurement and 53.2 n s / m m for displacement measurement, as validated by experimental outcomes. Furthermore, the sensor boasts a compact and diminutive sensing structure that can be effortlessly integrated into the robotic finger casing. Of utmost significance, it facilitates a cost-effective time-division multiplexing system for distributed measurements. Considering these distinctive advantages, this sensor lends itself to the establishment of a practical robot-finger distributed network system, characterized by superior performance attributes, encompassing high precision (up to 19 μ m for contact detection and 0.0095 N for grasping and other manipulations), relatively modest expenses, and versatile applicability across a broad spectrum of scenarios, in stark contrast to the presently prevalent systems. In light of these noteworthy merits, the developed sensor exhibits tremendous potential for integration into robotics applications. [ABSTRACT FROM AUTHOR]

• A novel fiber Bragg Grating (FBG) based extensometer working on the magnetostatic interaction. • Borehole extensometer for ground settlement monitoring. • Real-time monitoring and data collection. Monitoring for sub-surface settlement in deep excavation construction and tunneling works will provide an early indication of potential settlement or sinkhole formation at the ground surface. Currently, rod and magnetic extensometers may be used to monitor sub-surface settlement, with the latter most commonly used. In this paper, a novel Fiber Bragg Grating (FBG) based extensometer is proposed working on the magnetostatic interaction between a ring magnet and a disc magnet. The proposed FBG extensometer can be automated for continuous monitoring, as compared with the commonly used magnetic extensometer which monitors manually at prescribed intervals. Multiple units of FBG extensometer can be connected together and easily installed in a deep borehole. The number of FBG extensometer used is not limited by the borehole size, as compared with the rod extensometer where a maximum of 3 tips per borehole is typically specified. The proposed extensometer with current instrumentation gives a measurement range of 80 mm with a measurement resolution of 0.65 mm/με. [ABSTRACT FROM AUTHOR]

For middle infrared fiber-optic evanescent wave spectroscopy, the single-index Ge 20 Se 80 and Ge 26 As 17 Se 25 Te 32 glass fibers are fabricated by a crucible method. The background optical loss in the Ge 20 Se 80 fiber is 1.5 dB/m in the 5–7.8 μm spectral range (minimum is 0.9 dB/m at 7.1 μm), and that in the Ge 26 As 17 Se 25 Te 32 fiber is 1 dB/m in the range of 5.5–8.5 μm (minimum is 0.65 dB/m at 6.6 μm). On the basis of these chalcogenide glass fibers, the middle infrared sensors with the different geometry of sensitive zone (straight, U-shaped form, one loop, two loops) are manufactured. By the example of diesel fuel, it is shown that when passing from the straight section of the sensitive zone to the double loop, the integrated intensity of the absorption bands increases by an order of magnitude. The method of regression analysis was applied to plot a calibration dependence for the additive concentration in diesel fuel in the range of 0.1–1 vol% using a U-shaped fiber sensor. The possibility of using the luminescent Pr(3+)-doped chalcogenide fiber as the source of mid-IR radiation for recording the absorption spectra of substances absorbing in the spectral range 4–5 μm is demonstrated. [ABSTRACT FROM AUTHOR]

A sensitivity-improved ultrasonic fiber optic sensor is proposed and demonstrated for ultrasound wave (UW) imaging of mural models. The sensor contains a Fabry-Perot (F-P) cavity at one end of a single-mode fiber (SMF) and a gold-coated ceramic ferrule. Because the gold film is 120 nm thick, the sensor has extremely high ultrasonic sensitivity. Compared to similar sensors in the literature, by changing its package structure, removing the acoustic lens and using a thinner film in the interference cavity, the signal-to-noise ratio (SNR) of the proposed sensor can reach 68.18 dB. Using the sideband filtering method, the echo wave signal can be extracted, the cross sectional image of hollows in the mural model can be obtained by 1D scanning, and 3D images can be reconstructed by 2D scanning. We calculated the thicknesses of the three hollows in the ground layer to be 0.1986 cm, 0.6752 cm, and 0.3873 cm, and the thickest part of the efflorescence area to be 2.857 cm. The ultrasonic sensor helps archaeological conservators to detect information on size of defects in the mural ground layer. [ABSTRACT FROM AUTHOR]

A dual core photonic crystal fiber (DCPCF) consisting single analyte channel is proposed in this article for the detection of petrol adulteration. The sensing probe is numerically studied using finite element method. The adulterated petrol sample is infiltrated in circular analyte channel which is situated at the center of the fiber between two solid light guiding cores. The mode coupling between these two cores as well as sensitivity of the designed probe are investigated by varying adulteration level of petrol. Also the structure is optimized step by step. The numerical simulation result shows very high sensitivity of 20,161.2 nm/RIU for practically usable small probe. A portable adulteration detection sensor can be manufactured using this simple structured DCPCF probe which will be useful to study environmental pollution, maintaining long engine lifetime, save revenue. [ABSTRACT FROM AUTHOR]

Abstract A novel bending self-compensating long period grating (LPG) is proposed and experimentally demonstrated in a hole-assisted eccentric-core fiber (HAEF). Two pieces of HAEFs are aligned along the core and spliced together after the core of one HAEF is rotated 180°around its geometrical center with respect to that of the other HAEF. The proposed structure can compensate for structural asymmetry of the fiber and thus reduce the bending response. A LPG, centered at the fusion splicing point, is fabricated in the HAEF by using a high-frequency CO 2 laser. The bending and temperature characteristics of the LPG are investigated. The experimental results show that the proposed LPG is insensitive to the bending but sensitive to the temperature. [ABSTRACT FROM AUTHOR]

Highlights • To our knowledge, this is the first study that demonstrates pp B-L B-Level methane gas detection using MIR LED in place of QC laser. The LED emitting spectrum was ∼400 nm, and can cover a group of absorption lines. • This design was really useful and inexpensive, and this work may be attractive to the following experiments. So the detection system using LED can be insensitive to the applied current and temperature and operated in the harsh environment. • With the advent of hollow core fiber, the optical path can be extended to 1 m. The hollow core of HCF provided a good overlap of light and methane gas. So the 17-ppb detection limit was achieved. • This scheme provides an engineering perspective to realize a low-cost, hand-held methane detector for remote and harsh environments. Abstract We present here an optical scheme for a trace methane gas detection system using mid-infrared (MIR) light emitting diode (LED) (λ = 3.3 μm) in a hollow-core fiber (HCF). When light from the MIR LED was focused on the HCF, the latter confines the interaction of light and methane gas within a fiber core of 0.5 mm diameter. The 1-m-long HCF provided enhanced optical path, and optimum light-gas interaction. By employing direct absorption spectroscopy, the detection limit of methane gas concentration was extended to as low as 17 ppb, and the dynamic range was estimated as 42 dB. The 400-nm bandwidth of a MIR LED can cover all strong absorption lines in the vicinity of 3.3 μm. This scheme provides an engineering perspective to realize a low-cost, hand-held methane detector for remote and harsh environments. [ABSTRACT FROM AUTHOR]

Highlights • A cryogenic sensor based on fiber Bragg grating is developed. • The fiber with pre-tensile force is adhered onto temperature sensitive metal. • The experimental results reveal that the maximum operating error is less than 0.35 °C. • The availability of the designed FBG sensor for LNG monitoring is investigated experimentally. Abstract Condition monitoring is critical for the safe usage of Liquefied Natural Gas (LNG). Temperature distribution is an important index of LNG storage and it can reflect the tendency of heat leakage and the situation of evaporation. However, traditional electric sensor may cause explosion due to spark. In this paper, a cryogenic sensor based on fiber Bragg grating (FBG) is developed in which the fiber with pre-tensile force is adhered onto temperature-sensitive metal. The liquefied nitrogen (LN 2) is used to test the designed sensor instead of LNG for safety consideration. By setting every 10 K as a testing point from 83 K to 193 K, the experimental investigation reveals that there is a positive linear relation between the reflected wavelength and the testing temperature. By using multiple linear functions to fit experimental data, the maximum measuring error of FBG sensor is less than ±0.35 K, which indicates the usability of this sensor in LNG storage. Finally, an experiment of temperature stratification is performed to validate usability of FBG sensor for LNG monitoring. The results indicate that the designed FBG sensor has enough accuracy to reveal LNG rollover and it has similar dynamic performance with RTD sensor. [ABSTRACT FROM AUTHOR]

• Strain-insensitive Sagnac interferometer with tapered high birefringence fiber. • Merged Sagnac and modal interferences in Sagnac interferometer. • Discrimination of temperature and strain. • Taper waist diameter dependent temperature and strain sensitivities. The relation of the temperature and strain sensitivities to the waist diameter of the tapered high birefringence fiber (THBF) in Sagnac interferometer is theoretically analyzed and experimentally demonstrated. With a large waist diameter, the occurred Sagnac interference shows sensitive to both temperature and strain. The temperature and strain sensitivities decline as the waist diameter decreases. By contrast, when the waist diameter of the THBF is sufficiently small, both Sagnac and modal interferences are simultaneously generated. The former is only sensitive to temperature, whereas the latter is sensitive to both temperature and strain. As the waist diameter of the THBF decreases, the temperature sensitivities of both the Sagnac and modal interferences diminish, but the strain sensitivity of the modal interference improves. Therefore, the proposed THBF Sagnac interferometer enables simultaneous measurement of temperature and strain variations. Importantly, the strain-insensitive characteristic of Sagnac interference facilitates the discrimination between temperature and strain variations. [ABSTRACT FROM AUTHOR]

In the work, a cholesteric liquid crystal film coated side polished fiber (CLCFC-SPF) is demonstrated to sense the volatile organic compound (VOC) gas. In the CLCFC-SPF, the wavelength selectively coupling from the SPF to the cholesteric liquid crystal film (CLCF) results in the resonant dips in the transmitted spectrum. It is found that the pitch of the CLCF increases with VOC gas concentration, which reduces the refractive index (RI) of CLCF and results in a blue shift of the resonant dips. By tracing the blue shift of the resonant dips, the VOC gas sensing characteristic of the CLCFC-SPF were investigated experimentally. For tetrahydrofuran, acetone and methanol gas, the sensitivities of the CLCFC-SPF are respectively measured as 7.08 nm·L/mmol, 3.46 nm·L/mmol, 0.52 nm·L/mmol. Using the wavelength selectively coupling theory, gaseous-optic coefficient of the CLC can also be obtained and were measured in the experiment as 6.6 × 10 −4 RIU·L/mmol, 2.9 × 10 −4 RIU·L/mmol, 0.6 × 10 −4 RIU·L/mmol, respectively, for tetrahydrofuran, acetone, and methanol gas. Additionally, the experimental results also show that both the sensitivity of CLCFC-SPF and the gaseous-optic coefficient of the CLCF increase with the molar mass of the VOC gas. The work provides a way to incorporate the sensitive liquid crystal onto the fiber for implementation of liquid-crystal-based fiber sensors. [ABSTRACT FROM AUTHOR]

A special fiber Bragg grating (FBG) that is inscribed over the core and innermost depressed-index cladding of a short multi-clad fiber (MCLF) by femtosecond laser side-illumination technique is proposed and demonstrated for orientation-dependent measurement, experimentally. Splicing the MCLF with standard single-mode fiber (SMF) provides a cladding-mode generation mechanism via core mismatch, and then “cladding FBG” in MCLF can simultaneously generate two resonances in reflection. The cladding mode shows a significant response to fiber bending due to novel refractive-index profile of MCLF and coupling in the splicing junction. And the asymmetry “cladding FBG” configuration relatively to fiber core center enables it to perform strong orientation-dependent response to the fiber bending. These two properties are well applied to measure acceleration with high resolution of 0.02 m/s 2 and orientation-dependence. The cladding and core mode also present linear wavelength-shifting with temperature variation but no intensity fluctuations. Furthermore, the accidental power perturbation or cross-sensitivity can be calibrated out by monitoring the fundamental core mode resonance. [ABSTRACT FROM AUTHOR]

A miniature and highly sensitive optic fiber temperature sensor using a PDMS-filled air-microbubble Fabry-Perot (FP) interferometer (PAFPI) in a hollow-core fiber (HCF) is proposed. The sensor is fabricated by fusion splicing a single mode fiber (SMF) with a HCF, which is filled with polydimethylsiloxane (PDMS) by capillary effect, to form an air microbubble cavity. As far as we know, this is the first time that PDMS is applied to fill the hollow core fiber. There are three main reflected surfaces in the PAFPI sensor, and the superimposed interference spectrum of double FPI (a thin FPI and a thick FPI) is formed. Hence, the proposed sensor combines two advantages that are the large free spectral range (FSR) of the thin FPI and the high resolution of the thick FPI, which improve the resolution of spectral demodulation while ensuring a large dynamic range. Experimental results show that the sensor has the high temperature sensitivity of 2.7035 nm/℃ with a high linear response (R-square: 0.9962) in the range of 51.2–70.5 ℃, which is almost three orders larger than that of the conventional all-fiber air-cavity FP temperature sensors (about 10 pm/℃). The stability experiment is also carried out, and the maximal variations of the wavelength shift and the extinction ratio of the interference fringes are 20.3 pm and 0.1262 dB, respectively, for a long-term testing. Therefore, it may be applied to the surrounding temperature sensing. [ABSTRACT FROM AUTHOR]

A novel and in-line fiber low-frequency vibration sensor based on Butterfly-Shape Mach-Zehnder Interferometer (BSMZI) is proposed and demonstrated experimentally. The sensing element is a tapered hollow-core fiber (HCF) sandwiched between two single-mode fibers (SMFs). The frequency measured by the Butterfly-Shape vibration sensor can well match with the applied frequency, and the presence of the higher harmonics can verify that the sensor does not distort the measured vibration signal. The maximum relative error of vibration frequency is 0.27%. The intensity of vibration signal (of the fiber sensor) is linearly proportional to the driving power of vibration platform. The vibration measurement sensitivity is 13.575 dB/w in the range of 0.1 w to 0.5 w under a constant vibration frequency of 50 Hz, and the linear fitting coefficient is 0.9556. The proposed sensor has a negligible temperature sensitivity in the range of 30.3 °C–69.5 °C. Because of its compact structure, easy preparation, low production cost, high frequency measurement accuracy of low-frequency vibration, and good linearity of vibration sensing, the proposed BSMZI sensor has potential application prospect in low-frequency vibration sensing field. [ABSTRACT FROM AUTHOR]

An optical fiber interference sensor with a fiber end groove structure that was fabricated by a femtosecond laser is presented for temperature and refractive index measurement. In the designed fiber sensor, a groove that was 40 μm deep and 50 μm wide was etched on the fiber end along the core at the SMF-28 fiber. The microstructure was manufactured by the femtosecond laser through a line-by-line scanning method. In an experiment, the sensor head was inserted into NaCl solution. The interferometer wavelength interval was 46 nm, and the stripe contrast was 17 dB. Under different vertical refractive indexes (RIs), the corresponding comb spectrum was obtained. Results showed that the proposed fiber filter exhibited an RI sensitivity of 3282.176 nm per refractive index unit (RIU) and 1317.351 dB/RIU, respectively. In addition, the temperature characteristic was measured. The wavelength variation was not obvious and the power fluctuation curve was linear within 50 °C–100 °C. The sensor spectrum had good repetition at high and low temperatures. The results demonstrated the satisfactory performance of the refraction and temperature sensor. [ABSTRACT FROM AUTHOR]

A novel fiber-optics landslide monitoring system is proposed to achieve distributed,high-sensitivity and high-resolution strain measurement. The whole system adopts Rayleigh backscatter-based coherent optical time-domain reflectometry (COTDR) technique to realize long-distance, real-time monitoring with a resolution of 0.1 μ ε and a spatial resolution of one meter. [ABSTRACT FROM AUTHOR]

In this paper, a new optical fiber sensor for relative humidity measurements is presented and characterized. The sensor is based on a SnO 2 sputtering deposition on a microstructured optical fiber (MOF) low-finesse Fabry-Pérot (FP) sensing head. The feasibility of the device as a breathing sensor is also experimentally demonstrated. The interrogation of the sensing head is carried out by monitoring the Fast Fourier Transform phase variations of the FP interference frequency. This method substitutes the necessity of tracking the optical spectrum peaks or valleys, which can be a handicap when noise or multiple contributions are present: therefore, it is low-sensitive to noise and to artifacts signal amplitude. The sensor shows a linear behavior in a wide relative humidity range (20%–90% relative humidity) in which the sensitivity is 0.14 rad/%; the maximum observed instability is 0.007 rad, whereas the highest hysteresis is 5% RH. The cross correlation with temperature is also considered and a method to lower its influence is proposed. For human breathing measurement, the registered rising and recovery times are 370 ms and 380 ms respectively. [ABSTRACT FROM AUTHOR]

A novel fiber-optic sensing structure based on miniaturized modal interferometer (MMI) for simultaneous refractive index (RI), strain and temperature measurement is proposed. It is mainly based on Mach–Zehnder interferometer (MZI) and formed by introducing a down taper between two adjacent up tapers in one single mode fiber (SMF). Experimental results demonstrate a RI sensitivity of 131.93 nm/RIU, a strain sensitivity of 0.0007 nm/ μ ε and a temperature sensitivity of 0.0878 nm/°C respectively. The sensor is merely made of SMF which is cheap and available, and the whole fabrication process contains only cleaving and splicing and can be well controlled by a commercial fiber splicer. [ABSTRACT FROM AUTHOR]

In this paper, a modified construction for the traditional ϕ -OTDR fiber sensor sensitive for all of distance is presented, the related numerical simulation and experiment analysis results show that this construction can reduce the gain imbalance for all of the distance along the fiber caused by the Rayleigh scattering loss of the fiber and the gain imbalance of Raman fiber amplifier in this fiber sensor system. In order to improve further the vibration sensitivity of this system, the possible methods to restrain the influences of modulation instability effect, Stimulated Brillouin effect, reduce the amplified spontaneous emission (ASE) noises of Raman laser (RL) and Erbium 3+ -doped fiber amplifiers (EDFA), double Rayleigh backscattering noise in this system are discussed, which will offer a great reference value for the science research and engineering application in the field of fiber sensor as we believe. [ABSTRACT FROM AUTHOR]

We present a surface plasmon resonance sensor based on photonic crystal fiber filled with gold–silica–gold (GSG) multilayer nanoshells for measurement of the refractive index of liquid analyte. The GSG multilayer nanoshells, composed of a silica-coated gold nanosphere surrounded by a gold shell layer, are designed to be the functional material of the sensor because of their attractive optical properties. Two resonant peaks are obtained due to the hybridization of nanosphere plasmon modes and nanoshell plasmon modes. It is demonstrated that the resonant wavelength of the two peaks can be precisely tuned in 560–716 nm and 849–2485 nm, respectively, by varying the structural parameters of the GSG multilayer nanoshells in a compact, sub-200 nm size range. The excellent spectral tunability makes the sensor attractive in a wide range of applications, especially in biosensing in near-infrared region. Furthermore, the influences of the parameters on the performance of the sensor are systematically simulated and discussed. It is observed that the spectral sensitivities of 1894.3 nm/RIU and 3011.4 nm/RIU can be achieved respectively by the two resonant peaks in the sensing range of 1.33–1.38. The existence of two loss peaks also provides the possibility to realize self-reference in the sensing process. [ABSTRACT FROM AUTHOR]

Elastic conductive fiber, owing to its soft and stretchable capability, makes it an ideal material for a wearable strain sensor. However, the incompatibility between the ultra-stretchable polymer matrix and the rigid inorganic conductors results in poor stretchability, low conductivity stability, and complex operation process. To overcome these drawbacks, high-stretched carbon nanotubes/thermoplastic polyurethane (CNTs/TPU) composite fibers have been fabricated through wet spinning in a simple one-step approach. By introducing rotating aqueous dispersion of CNTs as coagulating bath, the squeezed out TPU spinning solution could sufficiently adhere surrounding CNTs during double diffusion process of solvent and non-solvent medium. It has been demonstrated that the strain performance, strain sensing performance, and stability could be promoted by optimizing the rotation speed of the solidification bath. After being drafted and solidified in the bath with a rotation speed of 800 r/min (S-8), the obtained fiber has exhibited an outstanding working strain range of 200%, short response time of ≈ 0.18 s, and cyclic strain sensing performance. Besides, the obtained fiber has also exhibited exceptional Joule heating performance. • A rapid prototyping manufacturing strategy of the elastic conductive fibers via wet spinning. • Rotating coagulating bath was essential for CNTs adhesion on surface of TPU fiber. • Outstanding working range of 200% are obtained. [ABSTRACT FROM AUTHOR]

A novel refractive index (RI) sensor based on an asymmetrical Mach–Zehnder interferometer (MZI) with two different step-like tapers is proposed. The step-like taper is fabricated by fusion splicing two half tapers with an appropriate offset. By further applying offset and discharging to the last fabricated step-like taper of MZI, influence of taper parameters on interference spectrum is investigated using only one device. This simple technique provides an on-line method to sweep parameters of step-like tapers and speeds up the optimization process of interference spectrum, meanwhile. In RI sensing experiment, the sensor has a high sensitivity of −185.79 nm/RIU (refractive index unit) in the RI range of 1.3333–1.3673. [ABSTRACT FROM AUTHOR]

We demonstrated the refractive index sensing characteristics of a miniature fiber sensor composited by silica-hollow-tube (SHT) and Au-micro-sphere (AmS). The high sensitivity is obtained due to the evanescent field effect existing in the SHT with the inner diameter of ∼2.3 μm and the surface plasmon resonance effect excited on the surface of AmS with the diameter of ∼2 μm. Experimental results indicate that this sensor can continuously measure the glucose concentration in range of 0–60% with a good linearity. The high detection sensitivity up to 8.33 μmol/L (47.33 mW/RIU) enables its ability in determining the glucose concentration in either blood or body fluids. Furthermore, the tiny structure is promise to be integrated into the microchip or other injectable structures, and monitor the glucose concentration in real-time. [ABSTRACT FROM AUTHOR]

We proposed a composite microfiber using silica capillary and Ag microparticles, and demonstrated its optical sensing characteristics by changing the refractive index of surrounding environment using different concentrations of NaCl solution. Either the diameter or doping density of Ag microparticles contributes to the sensitivity change. The experimental results reveal that the diameter uniformity and distribution of Ag microparticles exerted impact on the sensing performance. The highest sensitivity of −7246 dB/RIU has been experimentally demonstrated in this work. The selectivity of this composite microfiber sensor will be explored by decorating its surface with some enzyme or other sensitive materials. [ABSTRACT FROM AUTHOR]

In this letter, we propose to use discrete wavelength channels of a single chip MG-Y laser to interrogate an ultra-short fiber Bragg grating with a wide Gaussian spectrum. The broadband Gaussian spectrum of USFBG is sampled by the wavelength channels of MG-Y laser, through which the center of the spectrum. The measurement inherits the important features of a common tunable laser interrogation technique, namely its high flexibility, natural insensitivity to intensity variations relative to common intensity-based approaches. While for traditional tunable laser methods, it requires to sweep the whole spectrum to obtain the center wavelength of the spectrum, for the proposed scheme, just a few discrete wavelength channels of laser are needed to be acquired, which leads to significant improvements of the efficiency and measurement speed. This reliable and low cost concept could offer the good foundation for USFBGs future applications in large scale distributed measurements, especially in time domain multiplexing scheme. [ABSTRACT FROM AUTHOR]

An extrinsic fiber Fabry-Perot interferometric acoustic sensor based on a large-area silver diaphragm is proposed. The thickness and diameter of the silver diaphragm are 160 nm and 2.4 mm, respectively. The flatness of the diaphragm is < 14 μm. Experimental results showed that the sensor has the acoustic sensitivity of − 124.8 dB re 1 V/μPa with a high linear pressure response in the range of 2.5–268 mPa. The mechanical sensitivity of the diaphragm is 28.57 nm/Pa. The sensor exhibits a flat frequency response in the range of 0.2–2.8 kHz. The noise equivalent acoustic signal level is 83 μPa/Hz 1/2 at 1 kHz. The sensor is expected to be used for weak acoustic sensing. [ABSTRACT FROM AUTHOR]

Based on the self-focusing characteristics of graded index multimode fiber, a fiber SPR micro displacement sensor can be constructed, which has two bottleneck problems of difficult to fabricate and the small displacement detection range. In this paper, we proposed and constructed a new heterocore structure of graded multimode fiber-single-mode fiber-graded multimode fiber to realize the micro displacement sensing, which has stable performance and simple fabrication. By increasing the core diameter of modulation graded multimode fiber and displacement fiber, the displacement detection range of probe was increased. The simulating and testing results indicate that the SPR micro displacement sensor based on the graded multimode heterogeneous core structure can well realize the two-parameter sensing of micro displacement, and its average wavelength and light intensity sensitivity can reach 1.23 nm/ μ m, and 0.00576 a.u./ μ m respectively, the measurement resolution is 0. 813 μ m. When using step multimode fiber with core diameter of 40 μ m in place of single-mode fiber as the displacement fiber, the displacement detection range reaches 50 μ m which is double that of the reported fiber SPR micro displacement sensor. The proposed fiber SPR micro displacement sensor well solved the two bottleneck problems above, which can be used in the field of micro displacement measurement of structural health monitoring. • In order to solve the problems of difficult fabrication and small detection range of fiber SPR micro displacement sensor, a new scheme of SPR micro displacement sensor based on graded index multimode fiber heterocore structure is proposed in this paper. • The maximum detection range of the sensor is 10-60 μ m, the maximum average sensitivity is 1.23 nm/ μ m, and the resolution 0.813 μ m. • Moreover, the probe has stable performance and simple fabrication. • And by increasing the fiber diameter in the modulation region and the core diameter of displacement, the displacement detection range reaches 50 μ m, which is double the reported detection range. [ABSTRACT FROM AUTHOR]

• The Vernier effect sensor could measure temperature and strain simultaneously. • MZI and FPI of the Vernier effect sensor have different responses to temperature and strain. • The MZI and FPI are highly symmetrical in structure, which are easy to fabricate and low in cost. A fiber sensor based on Vernier effect for simultaneous temperature and strain measurement is proposed and demonstrated, which consists of a Mach-Zehnder interferometer and a Fabry-Perot interferometer. The two fiber interferometers are highly symmetrical in structure, both contain a hollow core fiber. The interferometer with a hollow core fiber of larger air hole diameter serves as the Fabry-Perot interferometer, and the other one with a hollow core fiber of smaller air hole diameter functions as the Mach-Zehnder interferometer. The Mach-Zehnder interferometer was found to be sensitive to temperature as well as strain, whereas the Fabry-Perot interferometer was only sensitive to strain variation. Due to the different response of two interferometers, the sensor achieved simultaneous measurement of temperature and strain. Leveraging on the Vernier effect and with MZI served as the sensing unit, the sensor provided a temperature sensitivity of − 279.99 pm / ℃ and a strain sensitivity of − 5.95 pm/με, respectively. While using Fabry-Perot interferometer as the sensing unit, the sensor showed an enhanced strain sensitivity of 19.17 pm/με. [ABSTRACT FROM AUTHOR]

• A fast query system of FBG based on swept laser is proposed. • A fast and efficient neighborhood averaging algorithm is proposed. • Experimental results show that the proposed algorithm has strong stability and excellent demodulation accuracy and speed. A fast interrogation scheme for dynamic fiber Bragg grating (FBG) based on a swept laser is presented. A neighborhood average algorithm, meanwhile, is used to real-time and fast demodulate the Bragg wavelength. In this paper, the resolution of the system using neighborhood average algorithm is tested, and the dynamic interrogation of the system is verified using vibration signals. The proposed algorithm achieves a Bragg wavelength resolution of 0.11 pm when the laser scanning frequency is 40 kHz. The stability of the algorithm is compared with Buneman wavelength estimation algorithm. Compared with other commonly used FBG peak search algorithms, the new algorithm has the characteristics of low computational cost, high sensitivity and stability. [ABSTRACT FROM AUTHOR]

A McKibben artificial muscle consisting of a rubber tube and a mesh sleeve made from fibers is a promising actuator as an artificial muscle because of its high power, low weight, and flexibility. However, an external pressure sensor or an expensive electro/pneumatic regulator is generally required to control the pneumatic pressure to drive the actuator. A novel smart McKibben-type artificial muscle with a pressure-sensing function has been proposed and developed in this study. One fiber on the sleeve of the actuator is converted from a normal to a conductive material. The applied pressure is estimated by observing the electrical resistance of the conductive fiber. Therefore, the fiber works as both a sensor and an actuator element. The fabrication process of the smart artificial muscle is established in this report, and the basic characteristics are clarified. Moreover, a compact driving control system of the smart artificial muscle, which uses a small rotary pump without external sensors, electro/pneumatic regulator, or valves, is proposed. [ABSTRACT FROM AUTHOR]

We report a novel digital iteration algorithm for fluorescence lifetime (FL) measurement, which is proved suitable for the fluorescence lifetime-based multi-probe fiber thermometer application. The algorithm utilizes only one set of fluorescence decay sampling data to decide the FL by using the basic addition and subtraction computation. Iteration number of about 10–12 times is sufficient to reach the final stable value. As a result, the algorithm features robust, high efficiency, strong anti-noise and immune to background level. The algorithm has been successfully used in a sapphire fiber-based multi-probe thermometer covering the temperature range from room temperature to 1000 °C and confirmed suitable for practical application. [ABSTRACT FROM AUTHOR]

We demonstrate a fiber-optic dual parameter sensor based on a water filled Mach–Zehnder interferometer. Such a sensor is fabricated by asymmetrically infiltrating a twin core photonic crystal fiber with water, and splicing it between single mode fibers. Two sets of interference fringes which result from multi-mode interference are obtained by such a structure. By measuring the wavelength shift of the small fringe and the big envelop of the spectrum, strain and temperature can be determined simultaneously. [ABSTRACT FROM AUTHOR]

In this work, the fabrication and experimental investigation of multimode optical fiber with a cladding material replacement is presented. A short piece of fiber’s cladding is etched away and substituted by a polydimethylsiloxane (PDMS) material. This elastomer is characterized by a unique feature of refractive index changes with the increasing particle density. The device principle is based on total internal reflection. If the PDMS is pressed, there is a change of elastomer refractive index and modes confined within the fiber core are partially or totally irradiated. This demonstration paves the way for further development of fiber optic sensors, particularly attractive for weight, load, extension, and pressure parameters monitoring applications. [ABSTRACT FROM AUTHOR]

A fiber optic sensor for simultaneous measurement of multi-parameter is proposed. The fiber sensor is realized by a fiber loop mirror based on a piece of homemade side-leakage photonic crystal fiber. Affected by the group birefringence of the side-leakage photonic crystal fiber, which induced by the elliptical germanium-doped core and the linear side-leakage defect, the fiber loop mirror has different wavelength responses to torsion, strain and temperature at different interference fringe valleys. By monitoring the wavelength shifts of three selected valleys in the transmission spectrum, simultaneous measurement of torsion, strain and temperature is achieved. The maximal sensitivities to torsion, strain and temperature are 151.14 pm/°, 1 pm/με and 71 pm/°C, respectively. [ABSTRACT FROM AUTHOR]

An in-line fiber sensor for simultaneous measurement of refractive index (RI) and temperature is proposed and demonstrated. The sensor head is composed of an asymmetric Mach–Zehnder interferometer (MZI), which is combining the single mode-multimode-single mode (SMS) fiber structure and a peanut-shape structure. The transmission dips of the sensor will shift as the ambient RI or temperature variation due to the phase changing. The different wavelength transmission dips formed by the cladding modes interfering with the core mode have different sensitivity responses, so the simultaneous measurement of the RI and temperature can be achieved by monitoring the wavelength shifts of the two transmission dips. The experimental results show that the sensing sensitivities of RI and temperature are −86.7434 nm/RIU and 0.0590 nm/°C in the RI range from 1.3105 to 1.3517 and temperature range from 25 °C to 85 °C, respectively. The novel sensor processes easy fabrication, low cost, and high sensitivity, making it offers high potential applications in physical, biological and chemical sensing. [ABSTRACT FROM AUTHOR]

A novel dual-parameter optical fiber sensor based on a single-mode fiber (SMF) down-taper and multimode fiber (MMF) is proposed and demonstrated. The sensor structure is formed by cascading a down-taper and MMF through a segment of SMF. The transmission spectrum exhibits response of the interference between core and different cladding modes. Two interference dips can be observed within a certain range of detection. Due to the different wavelength shifts of the selected two dips, simultaneous measurement of temperature and liquid level can be achieved. Experiment results indicate a good linear relation between the wavelength shift and external parameters (temperature and liquid level). The measured temperature sensitivities are 0.02 nm/°C and 0.031 nm/°C, and liquid level sensitivities are 0.022 nm/mm and 0.07 nm/mm, respectively. In addition, the fiber sensor has the advantages of compact size, simple fabrication and cost-effective. [ABSTRACT FROM AUTHOR]

We propose a novel fiber micro-displacement sensor based on an embedded fiber dual cladding modes interferometer. This type of interferometer has a very high extinction ratio (ER) of 27.7 dB, with only one very deep resonance dip within C and L bands, enabling it to be used as an intensity-modulated sensor. With it embedded in a cured carbon fiber composites based beam, it shows a high sensitivity response to micro-displacement in ER variation. Experimental results show that there is a quasi-linear relationship between the micro-displacement and its ER variation, with the measurement resolution of 4.67 μm, and the dynamic measurement range of 0∼200 Hz. [ABSTRACT FROM AUTHOR]

In this paper, a copper (Cu) based fiber surface plasmon resonance (SPR) sensor using two-dimensional (2D) transition metal dichalcogenides (TMDs) is studied theoretically. As the number of layers of TMDs increases, the sensitivity first increases and then decreases, exhibiting a maximum value for each TMDs based fiber SPR sensor. The maximum sensitivities of the fiber SPR sensors with WS 2 , MoS 2 , WSe 2 and MoSe 2 are up to 47.664 µm/RIU, 44.164 µm/RIU, 46.704 µm/RIU and 48.816 µm/RIU, while their resonance wavelengths are 3481.1 nm, 3592.2 nm, 3500.8 nm and 3435.1 nm. In addition, the growth rate of sensitivity in the mid-infrared regime is obviously higher than that in the visible or near-infrared regime. The proposed Cu based fiber SPR sensor with 2D TMDs exhibits ultra-high sensitivity in the mid-infrared regime, and can be used for highly sensitive bio-sensing. • A copper based fiber SPR sensor with 2D TMDs is proposed. • There is an optimal sensitivity by optimizing TMDs layer. • Rapid improvement of sensitivity is exhibited in mid-infrared regime. • Highest sensitivity is 48.816 µm/RIU realized by 151 layers of MoSe 2. • Sensitivity increases with refractive index of sensing medium. [ABSTRACT FROM AUTHOR]

In this paper, a novel dual-core hollow optical fiber (DHOF) based Mach-Zehnder interferometer (MZI) is proposed for hydrostatic pressure sensing. For the proposed fiber, two cores of the dual-core fiber are separated by a large air hole, and a D -type platform is fabricated adjacent one core. The existence of the central large air hole enhances the pressure-induced refractive index change of the dual-core fiber and ensures the independent transmission of the guiding light in the two fiber cores. Meanwhile, the D -type platform ensures that the dual-core fiber is subjected to asymmetric hydrostatic pressure, which results in the pressure-induced guiding mode phase change. For the dual-core hollow optical fiber, Mach-Zehnder interferometer (MZI) can be integrated in the fiber. One core is to measure the external environment as a sensing arm, and the other core is used as a reference arm. Furthermore, a dual-platform dual-core hollow optical fiber (DDHOF) is proposed, which further improves the asymmetry of the hydrostatic pressure on the dual-core fiber to continuously increase the sensing sensitivity. The mode field distribution and light guiding properties of DHOF and DDHOF under different hydrostatic pressures are analyzed by the finite element method and beam propagation method. The results show that the DHOF has a sensitivity of 2.4125 nm/MPa for the measurement range from 0 MPa to 100 MPa and the temperature cross-sensitivity is − 0.0886 nm/ ℃, the DDHOF has a sensitivity of 9.23 nm/MPa for the measurement range from 5 MPa to 10 MPa. The proposed DHOF and DDHOF can achieve different ranges of hydrostatic pressure sensing and possess extremely low temperature cross-sensitivity, which is suitable for the field of deep-sea exploration. Furthermore, the sensors possess a flexible structure, low temperature cross-sensitivity, can be integrated in the fiber, is easy to manufacture, and have other advantages. [ABSTRACT FROM AUTHOR]

Lightweight, stretchable, and wearable fiber strain sensors have recently been widely studied for the development of health monitoring systems, human-machine interfaces, and wearable devices. The interface interaction between the stretchable substrate and conducting materials plays a vital role in the performance of the fiber-based strain sensors. In this work, a scalable strategy using elastic yarn as a flexible substrate coated with a one-dimensional (1D) multiwalled carbon nanotube (MWCNT) and two-dimensional (2D) MXene (Ti 3 C 2 T x) mixed conductive layer was presented. The introduction of ultra-thin polyurethane (PU) bridge layer into the sensing system greatly improved the interfacial adhesion between the yarn and conductive layer. Therefore, the sensors obtained significantly enhanced performance, which exhibited the superstretchability up to 300% without evidently irreversible damaging the intrinsic conductive pathways (the maximum elongation reached 1218%), high sensitivity (maximum gauge factor is approximately 441.68 at 210%–300%), fast response time (about 70 ms), and excellent stability (low fatigue properties over 1500 stretch-release cycles). Furthermore, the fabricated fiber strain sensors were used to access the relevant physiological signals, including finger and joint movements, face gestures, and sitting posture detection. Such high mechanical performance fiber-based electronics can serve as the basis for future multifunctional smart wearable sensors for abundant existing and emerging applications. [Display omitted] • A water-based polyurethane was utilized for stretchable fiber strain sensors. • The polyurethane could enhance the interface interaction. • Fiber sensors with large strains and high stability were realized. • Physiological signals were acquired. [ABSTRACT FROM AUTHOR]