All-fiber Sensor Research Articles

Respiratory rate monitoring based on all-fiber strain-induced humidity sensor

In this paper, an agarose coated-fiber Bragg grating (AG-FBG) based respiratory rate (RR) sensor for evaluating respiratory function and health status by all-fiber strain-induced humidity-sensitive material is proposed and experimentally demonstrated. The variation of the environment humidity leads to changes in the film morphology of AG, i.e., expansion and contraction, which impose strains on FBG to dynamically shift the central wavelength. In the experiment, the average sensitivity of the proposed AG-FBG-based RR sensor is 23.6 pm/%RH in the range of 30 %RH–90 %RH. Under the monitoring of a commercial FBG demodulator with a wavelength resolution of 1 pm, rich human breathing information is collected. The RR monitoring under different human postures and breathing patterns are respectively measured. In one breathing cycle, the response time and recovery time are 778 ms and 762 ms, respectively. The proposed sensor is simple and low-cost, shows easy signal demodulation, stable signal wavelength variation, and high repeatability, which has potential applications in vital signs monitoring and medical treatment.

All-Fiber Flexible Electrochemical Sensor for Wearable Glucose Monitoring.

Wearable sensors, specifically microneedle sensors based on electrochemical methods, have expanded extensively with recent technological advances. Today's wearable electrochemical sensors present specific challenges: they show significant modulus disparities with skin tissue, implying possible discomfort in vivo, especially over extended wear periods or on sensitive skin areas. The sensors, primarily based on polyethylene terephthalate (PET) or polyimide (PI) substrates, might also cause pressure or unease during insertion due to the skin's irregular deformation. To address these constraints, we developed an innovative, wearable, all-fiber-structured electrochemical sensor. Our composite sensor incorporates polyurethane (PU) fibers prepared via electrospinning as electrode substrates to achieve excellent adaptability. Electrospun PU nanofiber films with gold layers shaped via thermal evaporation are used as base electrodes with exemplary conductivity and electrochemical catalytic attributes. To achieve glucose monitoring, gold nanofibers functionalized by gold nanoflakes (AuNFs) and glucose oxidase (GOx) serve as the working electrode, while Pt nanofibers and Ag/AgCl nanofibers serve as the counter and reference electrode. The acrylamide-sodium alginate double-network hydrogel synthesized on electrospun PU fibers serves as the adhesive and substance-transferring layer between the electrodes. The all-fiber electrochemical sensor is assembled layer-by-layer to form a robust structure. Given the stretchability of PU nanofibers coupled with a high specific surface area, the manufactured porous microneedle glucose sensor exhibits enhanced stretchability, superior sensitivity at 31.94 μA (lg(mM))-1 cm-2, a broad detection range (1-30 mM), and a significantly low detection limit (1 mM, S/N = 3), as well as satisfactory biocompatibility. Therefore, the novel electrochemical microneedle design is well-suited for wearable or even implantable continuous monitoring applications, thereby showing promising significant potential within the global arena of wearable medical technology.

All-fiber light intensity sensor employing a three-core fiber taper integrated by magnetic fluids

An all-fiber optic light intensity sensor employing a three-core fiber (TCF) taper integrated by magnetic fluids (MFs) is proposed and fabricated. The three-beam interference and evanescent field characteristic of the TCF taper are combined with the laser-generated photothermal effect of the MFs for the first time. The effect of irradiation laser intensity on the interference spectrum of the proposed sensor is investigated experimentally. According to the experimental results, the interferential transmission spectrum is susceptible to the irradiation laser intensity. Under 473 nm laser irradiation, the maximum laser intensity sensitivity reaches −1.64425 nm/(mW/mm2). Moreover, the modal coupling processes of the TCF before and after tapering are investigated experimentally and by simulation. The proposed sensor is attractive because of its sensitive light response, simple structure, easy fabrication, and compact size. This work gives a significant reference for the manufacture and application of optically controlled microfluidic devices integrated by MFs.

A nanonewton force sensor using a U-shape tapered microfiber interferometer.

Nanomechanical measurements, especially the detection of weak contact forces, play a vital role in many fields, such as material science, micromanipulation, and mechanobiology. However, it remains a challenging task to realize the measurement of ultraweak force levels as low as nanonewtons with a simple sensing configuration. In this work, an ultrasensitive all-fiber nanonewton force sensor structure based on a single-mode-tapered U-shape multimode-single-mode fiber probe is proposed and experimentally demonstrated with a limit of detection of ~5.4 nanonewtons. The use of the sensor is demonstrated by force measurement on a human hair sample to determine the spring constant of the hair. The results agree well with measurements using an atomic force microscope for the spring constant of the hair. Compared with other force sensors based on optical fiber in the literature, the proposed all-fiber force sensor provides a substantial advancement in the minimum detectable force possible, with the advantages of a simple configuration, ease of fabrication, and low cost.

3D-Printed Ultracompact Multicore Fiber-Tip Probes for Simultaneous Measurement of Nanoforce and Temperature.

Optical fiber force sensing has attracted considerable interest in biological, materials science, micromanipulation, and medical applications owing to its compact and cost-efficient configuration. However, the glass fiber has an intrinsic high Young's modulus, resulting in force sensors being generally less sensitive. While hyperelastic polymer materials can be utilized to enhance the force sensitivity, the thermodynamic properties of the polymer may weaken the sensing accuracy and reliability. Herein, we demonstrate ultracompact three-dimensional (3D)-printed multicore fiber (MCF) tip probes for simultaneous measurement of nanoforce and temperature with high sensitivity. The sensor is highly sensitive to force-induced deformation due to the special geometric features of the polymer microcantilever, and the high-temperature sensitivity can be implemented through the poly(dimethylsiloxane) (PDMS) microcavity on the same fiber facet. Moreover, the sensitivities of the fiber interferometers are remarkably enhanced by introducing the optical analogue of the Vernier effect. Such a device exhibits a force sensitivity of 56.35 nm/μN, which is more than 103 times that of all-silica fiber force sensors. The PDMS microcavity provides a temperature sensitivity of 1.447 nm/°C, measuring the local temperature of the probe and compensating for temperature crosstalk of the force detection. The proposed compact MCF-tip sensor can simultaneously measure nanoforce and temperature with high sensitivity, facilitating multiparameter sensing in a restricted space environment and showing the potential in miniaturized all-fiber multiparameter sensors.

Simultaneous bending and temperature measurement based on a superimposed fiber grating sensor

A compact and novel superimposed fiber grating (SI-FG) sensor for simultaneous measurement of temperature and bending based on UV-induced FBG cascaded with a multimode fiber (MMF) embedded ultra-long period fiber grating (MMF-EULPFG) has been proposed and experimentally validated. The MMF-EULPFG acts as a temperature and bending sensing unit and was fabricated by periodically splicing a non-UV-non-photosensitive MMF and a UV-photosensitive single-mode fiber (SMF) which is so called cleaving-splicing method. Due to the periodic refractive index modulation, the 6-period SMF-MMF structure based MMF-EULPFG with a total length of 2.7 mm forms transmission spectra with a −17 dB dip. The proposed SI-FG sensor exhibits high bending and temperature sensitivities of 17.096 nm/m−1 and −0.238 nm/℃, respectively. The UV-induced FBG is fabricated in the initial segment of UV-sensitive fibers within EULPFG by UV exposure method. The dip of FBG transmission spectra also shows response to bending and temperature. By utilizing a matrix obtained from the experimental results, simultaneous measurement of temperature and bending can be achieved. Due to its compact structure and high sensitivity, the proposed novel SI-FG sensor can be used as a competitive all-fiber sensor for structural health monitoring and 3D-shape sensing.Index Terms: Optical fiber sensor, long period fiber grating, superimposed fiber grating, simultaneous measure.

The Spectral Numerical Mode Matching Method for Simulating Concentric All-Fiber Sensor Structures With Metallic Films

The Spectral Numerical Mode Matching Method for Simulating Concentric All-Fiber Sensor Structures With Metallic Films

Compact refractive index sensor based on offset splicing long-period fiber grating

Long-period fiber grating (LPFG) is one of the most important passive fiber devices. They work by coupling light from the fundamental core mode to the forward-propagating cladding mode, creating a series of resonant peaks in the transmission spectrum. In this paper, a series of no-core fiber (NCF) sections were periodically misaligned and embed in the single-mode fiber (SMF), to form a LPFG through the periodic refractive index (RI) modulation along the fiber axis. This fabricating method enhances the RI modulation to shorten the length of the proposed sensor to 2.82 mm. Experimental result shows that the highest RI sensitivity for the sensor reaches −4460.83 nm/RIU in a measuring range of 1.33–1.40 RIU at room temperature. Hopefully, the proposed study can lay some implementation methods for the design of the all-fiber compact RI sensor.

Integrated All-Fiber Sensor for Simultaneous Measurements of Curvature and Temperature

Integrated All-Fiber Sensor for Simultaneous Measurements of Curvature and Temperature

Ultra-sensitive and stable All-Fiber iontronic tactile sensors under high pressure for human movement monitoring and rehabilitation assessment

Interfacial capacitance sensing technology shows great potential in the fields of flexible electronics and healthcare. However, further advancements are necessary to enhance the sensitivity and mechanical stability of all-fiber iontronic tactile sensors (ITSs), especially under high pressure. This study addresses these challenges by optimizing the electrode structure and composition, incorporating hydrophilic cotton fibers as the dielectric layer framework. As a result, the ITSs exhibit ultrahigh sensitivity (58853 kPa−1), rapid response times (below 2 ms), and improved mechanical stability, enduring 10,000 cycles at 195.2 kPa. Moreover, these sensors have proven effective in detecting human motion and physiological signals in both air and aquatic environments. Integration into a motion state recognition system demonstrates potential applications in sports injury recovery, stroke rehabilitation, and chronic pain management.

Near-Infrared Dual Greenhouse Gas Sensor Based on Hollow-Core Photonic Crystal Fiber for Gas-Cell In-Situ Applications.

A greenhouse gas sensor has been developed to simultaneously detect multiple gas species within a hollow-core photonic bandgap fiber (HC-PBF) structure entirely composed of fibers. To enhance sensitivity, the gas cell consists of HC-PBF enclosed between two single-mode fibers fused with a reflective end surface to double the absorption length. The incorporation of side holes for gas diffusion allows for analysis of the relationship between gas diffusion speed, number of drilled side holes, and energy loss. As the number of drilled holes increases, the response time decreases to less than 3 min at the expense of energy loss. Gas experiments demonstrated detection limits of 0.1 ppm for methane and 2 ppm for carbon dioxide, with an average time of 50 s. In-situ testing conducted in rice fields validates the effectiveness of the developed gas detection system using HC-PBF cells, establishing all-fiber sensors with high sensitivity and rapid response.

Mid-infrared all-fiber light-induced thermoelastic spectroscopy sensor based on hollow-core anti-resonant fiber

In this article, a mid-infrared all-fiber light-induced thermoelastic spectroscopy (LITES) sensor based on a hollow-core anti-resonant fiber (HC-ARF) was reported for the first time. The HC-ARF was applied as a light transmission medium and gas chamber. The constructed all-fiber structure has merits of low loss, easy optical alignment, good system stability, reduced sensor size and cost. The mid-infrared transmission structure can be utilized to target the strongest gas absorption lines. The reversely-tapered SM1950 fiber and the HC-ARF were spatially butt-coupled with a V-shaped groove between the two fibers to facilitate gas entry. Carbon monoxide (CO) with an absorption line at 4291.50 cm−1 (2.33 µm) was chosen as the target gas to verify the sensing performance. The experimental results showed that the all-fiber LITES sensor based on HC-ARF had an excellent linear response to CO concentration. Allan deviation analysis indicated that the system had excellent long-term stability. A minimum detection limit (MDL) of 3.85 ppm can be obtained when the average time was 100 s

High sensitivity Sagnac interferometric temperature sensor using stress region refractiveindex modulation.

An all-fiber temperature sensor employing intentional refractive index modulation is experimentally demonstrated. The sensor consists of four sections of polarization maintaining fiber (FPMF) sandwiched between multi-mode fiber (MMF). The stress region of two sections of polarization maintaining fibers (PMFs) is aligned and then anti-clockwise rotates one PMF in 10deg angles while the other keeps still. Finally, the discharge proceeds. The remaining two PMFs are fusion spliced with the same method. Then the prepared FPMF-MMF structure is connected to the 3dB coupler to construct a Sagnac loop. The temperature sensitivity reaches 1.49nm/°C for a temperature range from 16°C to 55°C. The proposed temperature sensor with easy fabrication and good linearity in measuring temperature can be a promising candidate for various applications in environmental monitoring and industrial production.

All-Fiber Bimodal Interferometric Sensor With Inline Femtosecond Laser Ablated Cavity for Refractive Index Sensing

All-Fiber Bimodal Interferometric Sensor With Inline Femtosecond Laser Ablated Cavity for Refractive Index Sensing

Experimental study on temperature-insensitive curvature sensor based on reflective all-fiber structure

In the paper, a reflective all-fiber sensor for curvature measurement has been proposed, which is composed of Mach-Zehnder interferometer (MZI) and Fabry-Pérot interferometer (FPI). The MZI section acts as curvature sensing unit and is made by splicing a section of twin-hole and dual-core fiber (THDCF) between two sections of seven-core fiber (SCF). The FPI section is made by introducing an FPI cavity between two segments of single mode fibers inside a hollow core capillary through using UV-curable resins and used to reflect the energy. The reflection spectrum information tuned by MZI has respond to bending change. The experiment results show the reflective sensor exhibits a high curvature sensitivity and low temperature sensitivity of −1.19 nm/m−1 and −1 pm/°C in the range of 0–5.7778 m−1 and 30–100 °C, respectively. With the advantages of reflective structure, compact size, easy fabrication, and low temperature crosstalk, our sensor could be widely used in practical applications.

Ultra-compact temperature-compensated all-fiber ultraviolet sensor based on CdZnSe/ZnSe/ZnS quantum dots sealed in liquid-cavity

Ultra-compact temperature-compensated all-fiber ultraviolet sensor based on CdZnSe/ZnSe/ZnS quantum dots sealed in liquid-cavity

Three-core fiber-based temperature-insensitive twist sensor

We have experimentally proposed an all-fiber temperature-insensitive twist sensor, which is fabricated by splicing a three-core fiber (TCF) section and two parts of single-mode fibers (SMFs). Because of the special structure of TCF, the fundamental core mode and cladding mode can interfere with each other. The experimental results show that the maximum twist sensitivity is −0.250 nm/(rad/m) in the range of 0–50 rad/m, and 0.109 nm/(rad/m) in the range of −50–0 rad/m. The sensor has features of all-fiber structure, low-cost, easy-fabricated, and temperature insensitive, which makes it a competitive candidate for harsh environment sensing application.

All-fiber cascade system for high-sensitive temperature monitoring: An exploration of the tunability of Ti3C2-MKRs

A tunable all-fiber optical cascade temperature system is demonstrated with two microfiber knot resonators (MKRs) as sensing device (MKR_s) and reference device (MKR_r), respectively. The temperature monitoring device is prepared by depositing Ti3C2 onto MKR_s by optical deposition. Sufficient experimental evidence for temperature sensing sensitivity of the dual sensor device cascade system (MKR_r + Ti3C2-MKR_s) is 4.33 nm/°C, which is a 10.13-fold increase in sensitivity compared with the temperature sensing sensitivity of 0.427 nm/°C of the Ti3C2-MKR_s. After depositing Ti3C2 materials (∼400 μm) on the bare MKR_r, we further improve the sensitivity of the cascade system (Ti3C2-MKR × 2) to 9.20 nm/°C, which represents a significant 21.5 times improvement in sensitivity compared to Ti3C2-MKR_s. The sensitivity of cascade fiber optic sensors is controlled by varying the modified length of Ti3C2 materials optically deposited on the MKR_r surface. Overall, this study not only enhances device utilization but also provides a new research direction for the preparation of all-fiber sensors with tunable sensitivity.

All-fiber MZI hydrostatic pressure sensor

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.

Intelligent soft self-twisted shape sensor

This paper introduces an all-fiber flexible soft sensor that combines machine learning methods to acquire the ability to recognize its own twisted shape. The sensor is twisted into various shapes, the recognition accuracy of the shapes can reach 100 %. Unlike existing sensors, which require multiple sensors to form an array, such sensor requires only a single optical fiber MZI (Mach-Zehnder interferometer) embedded inside the flexible material, which makes the sensing structure and wiring connection very simple. At the same time, the sensor presents very good reliability, bend sensitivity and repeatability. Its temperature performance is also investigated. All above highlighting its great potential in intelligent robots, medical rehabilitation, surgical endoscopes, and object recognition.