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A self-powered in-nostril sensor based on the PVA thermoelectric hydrogel fiber was developed for long-term non-irritant anti-interference respiratory monitoring by discerning the temperature differences between the exhaled gas and skin in the nasal cavity. Owing to its slender structure and excellent pliability, the fiber sensor can be easily inserted into the nasal cavity without causing any discomfort. With the assistance of deep learning, the gel fiber-based respiratory monitoring strategy can actively identify seven respiratory patterns with an accuracy of 97.1%, providing a promising paradigm for early detection of respiratory diseases based on wearable bioelectronics. [Display omitted] Direct and consistent monitoring of respiratory patterns is crucial for disease prognostication. Although the wired clinical respiratory monitoring apparatus can operate accurately, the existing defects are evident, such as the indispensability of an external power supply, low mobility, poor comfort, and limited monitoring timeframes. Here, we present a self-powered in-nostril hydrogel sensor for long-term non-irritant anti-interference respiratory monitoring, which is developed from a dual-network binary-solvent thermogalvanic polyvinyl alcohol hydrogel fiber (d = 500 μm, L=30 mm) with Fe2+/Fe3+ ions serving as a redox couple, which can generate a thermoelectrical signal in the nasal cavity based on the temperature difference between the exhaled gas and skin as well as avoid interference from the external environment. Due to strong hydrogen bonding between solvent molecules, the sensor retains over 90 % of its moisture after 14 days, exhibiting great potential in wearable respiratory surveillance. With the assistance of deep learning, the hydrogel fiber-based respiration monitoring strategy can actively recognize seven typical breathing patterns with an accuracy of 97.1 % by extracting the time sequence and dynamic parameters of the thermoelectric signals generated by respiration, providing an alert for high-risk respiratory symptoms. This work demonstrates the significant potential of thermogalvanic gels for next-generation wearable bioelectronics for early screening of respiratory diseases. [ABSTRACT FROM AUTHOR]

In this work, a high performance surface plasmon resonance (SPR) fiber sensor based on metallic elliptical nanohole and circular nanodisk binary array has been theoretically designed and investigated. The binary array structure is integrated on the end facet of optical fiber to excite SPR and generate three optical resonance dips in reflection spectra in the near-infrared region. The first resonance dip not only fits the characteristics of narrow linewidth, but also has the advantages of high peak-to-dip signal ratio and sensitivity. When the external environment changes in the refractive index (RI) range of 1.33 ~ 1.40, a high RI sensitivity of 669 nm/RIU, a narrow FWHM of 5.8 nm, and a high FOM value of 115.3 are yielded simultaneously for the first dip. Compared to unitary nanostructure arrays, the composite plasmonic structure of nanodisk and elliptical nanohole array demonstrated here can generate SPR modes with sharper spectral feature which is crucial to high sensitivity and precision detection technology. These features make our proposed plasmonic fiber tip sensor highly promising in terms of high-performance biosensing applications. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel side polished PCF-based SPR sensor with shifted core region employing gold as a plasmonic layer for sensing analytes of refractive index ranging from 1.33 to 1.39. For the ease of plasmonic excitation, we shift the core region towards the edge of the polished cladding. Upon optimizing the sensor structure by varying the geometrical parameters for the sensing range of 1.33–1.39, the proposed PCF sensor structure exhibits a maximum wavelength sensitivity of 24,200 nm/RIU with the resolution of 4.13 × 10−6 RIU. Also, this sensor exhibits a maximum amplitude sensitivity of 432 RIU−1 with a resolution of 2.3 × 10−6 RIU. The proposed sensor exhibits linearity with the R2 value of 0.98791 for the refractive index ranging between 1.33 and 1.39. Furthermore, we carry out perturbation analysis to ensure that the proposed sensor withstands the fabrication tolerance. Therefore, the proposed sensor holds good as a potential contender for sensing in chemical and biological applications. [ABSTRACT FROM AUTHOR]

Kidneys are one of the most important organs in the body. They cleanse the blood and convert waste and excess water into urine. If the kidneys are unable to perform their functions, dialysis is prescribed to assist the patient. Clean and healthy water, as well as accurate evaluation of dissolved substances in water, play a key role in the dialysis process to ensure the patient's safety and well-being. As the dissolved substances change the refractive index of pure water, a refractive index biosensor can be a useful system. In this research, a fiber optic sensor based on surface plasmon resonance with a coating of nanocomposite layers has been studied theoretically. In the numerical simulation, water is used as the sensing medium. The aim of this simulation is to test the sensors that detect impurities in water for dialysis. The simulation is conducted for nanocomposites of nickel-tellurium oxide, platinum-tellurium oxide, and cobalt-tellurium oxide with thicknesses of 50 nm, 70 nm, 90 nm, 110 nm, and 130 nm. The simulation also considers various volume filling factors, including 0.55, 0.65, 0.75, and 0.85. The comparison of the results showed that Ni-TeO2 (with a thickness of 110 nm and a volume filling factor of 0.85) has the highest quality and is considered the winning structure. The graphene layers are tested on the nanocomposites to enhance the quality of the final structure. The results of the simulations show that adding 50 layers of graphene can improve the sensor figure of merit from 80.603 (RIU−1) to 85.522 (RIU−1), while the refractive index of the aqueous media changes from 1.33 to 1.34. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper proposes a novel optical fiber sensor for highly sensitive Hg2+ detection based on Mach–Zehnder interference (MZI) structure and thiophene–chitosan hydrogel (TCH). We obtained the MZI structure by splicing the coreless fiber (CLF), thin core fiber, and CLF. And then, we etched the thin-core optical fiber cladding and assembled the TCH to produce a Hg2+ sensitive sensor. According to theoretical derivation and experimental verification, the detection sensitivity of the sensor to Hg2+ can reach 1.008 × 1011 mol l−1, and the detection limit is 5 × 10−13 mol l−1. The sensor also has performance stability within 24 h for concentration measurement, with an average standard deviation of 3.2 × 10−13 mol l−1 within an hour of observation. In addition, the sensor has the advantages of specificity, simple preparation, and low cost, and it is suitable for monitoring the concentration of Hg2+ in complex water systems. [ABSTRACT FROM AUTHOR]

Although microwave photonic approaches have been used for fiber sensing applications before, most contributions in the past dealt with evaluating the sensor signal's amplitude. Carrying this topic on, the authors previously presented a scheme for the interrogation of fiber sensors that was based on a fiber Bragg grating's phase response for the electrical signal. However, neither has the measurement setup been analyzed nor have the amplitude and phase-based approaches been compared in detail before. Hence, this paper picks up the previously proposed setup, which relies on an amplitude modulation of the optical signal and investigates for sources of signal degradation, an aspect that has not been considered before. Following the incorporation of the microwave signal, the setup is suitable not only for an amplitude-based evaluation of fiber Bragg gratings but also for a phase-based evaluation. In this context, the signal-to-noise ratios are studied for the conventional amplitude-based evaluation approach and for the recently developed phase-based approach. The findings indicate a strong advantage for the signal-to-noise ratio of the phase response evaluation; an 11 dB improvement at the least has been found for the examined setup. Further studies may investigate the consequences and additional benefits of this approach for radio-over-fiber sensing systems or general performance aspects such as achievable sensitivity and sampling rates. [ABSTRACT FROM AUTHOR]

An ultrasonic sensor based on extrinsic Fabry–Pérot interference (EFPI) has been designed and demonstrated to detect the ultrasonic wave signal. The sensitivity and natural frequency of fiber Fabry–Pérot (F-P) sensor with different structure parameter have been simulated by COMSOL. The simulation results illustrate that the sensitivity is up to 1.737 nm/kPa and the natural frequency is 2.1 MHz, when the silica diaphragm thickness is 2 μm, the radius is 90 μm, and the cavity length is 18 μm. The most suitable parameters have been selected and the F-P sensor has been fabricated. When the ultrasonic signals with the frequencies of 40 kHz and 1.2 MHz are respectively applied to the sensor, the frequencies detected by the EFPI ultrasonic sensor are 39 kHz and 1.21 MHz based on a partial discharge detection experiment for the designed demodulation system. The experimental results show that the sensor can accurately detect ultrasonic signals. As an excellent platform for ultrasonic signal sensing, this EFPI ultrasonic sensing system has great potential applications in partial discharge detection field. [ABSTRACT FROM AUTHOR]

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]

Herein a gold nanosphere (AuNS)-coated wavelength-mode localized surface plasmon resonance (LSPR) fiber sensor was fabricated by a simple and time-saving electrostatic self-assembly method using poly(allylamine hydrochloride). Based on the localized enhanced coupling effect between AuNSs, the LSPR spectrums of the AuNS monolayer with good dispersity and high density exhibited a favourable capability for refractive index (RI) measurement. Based on the results obtained from the optimization for AuNS distribution, sensing length, and RI range, the best RI sensitivity of the fiber modified by 100 nm AuNS reached up to about 2975 nm/RIU, with the surrounding RI range from 1.3322 to 1.3664. Using an 80 nm AuNS-modified fiber sensor, the RI sensitivity of 3953 nm/RIU was achieved, with the RI range increased from 1.3744 to 1.3911. The effect of sensing length to RI sensitivity was proven to be negligible. Furthermore, the linear relationship between the RI sensitivity and plasma resonance frequency of the bulk metal, which was dependent on the interparticle plasmon coupling effect, was quantified. Additionally, the resonance peak was tuned from 539.18 nm to 820.48 nm by different sizes of AuNSs-coated fiber sensors at a RI of 1.3322, which means the spectrum was extended from VIS to NIR. It has enormous potential in hypersensitive biochemistry detection at VIS and NIR ranges. [ABSTRACT FROM AUTHOR]

In sensors utilizing the traditional harmonic Vernier effect, it is imperative to isolate the reference interferometer to mitigate the impact of external environmental fluctuations on the reference spectrum, thereby averting measurement inaccuracies. However, achieving such isolation between interferometers in compact fiber optic sensors poses significant challenges. We propose a fiber optic strain sensor based on the enhanced harmonic Vernier effect. In the enhanced harmonic Vernier effect, two interferometers are simultaneously involved in sensing. Hence, the isolation of interferometers is no longer a concern. Furthermore, the two interferometers exhibit responses with opposite signs, leading to a greater displacement of the envelope. Consequently, the sensitivity of the sensor is further enhanced without altering the harmonic order. Firstly, we conducted numerical simulations to analyze the enhanced harmonic Vernier effect. Secondly, we fabricated a Fabry–Perot interferometer (FPI) and a Mach–Zehnder interferometer (MZI) with strain sensitivity of opposite signs, generating a first-order harmonic. The experimental results indicate that the sensor's sensitivity is 15.1 pm/ μ ϵ , which is 1.41 and 2.80 times higher than the traditional harmonic Vernier effect using FPI and MZI as sensing interferometers, respectively. The proposed sensor and enhancement method hold promising potential for applications in high-sensitivity measurement fields. • High sensitivity fiber optic strain sensor. • Enhanced Harmonic Vernier Effect for improved sensitivity. • Hybrid interferometer design, eliminating the need for a reference interferometer. • Mitigation of external environmental fluctuations without the need for isolation. • Sensitivity enhancement without altering the harmonic order. [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]

The development of reliable, lightweight, and effective sensors is a vital step in effectively monitoring critical parameter changes. This review focuses on the utilization of tapered optical fiber as a material sensing platform. The fundamental concept of the tapered fiber sensor is based on the interaction of strong evanescent waves caused by the fiber's dimensional change. The primary goal of this review is to explore the potential of tapered optical fiber for biosensing applications. A number of tapered optical fiber configurations and operations have been reviewed in order to propose appropriate optical sensor designs for biosensing applications. Hence, this analysis could serve as a benchmark for a more thorough study of biosensing device development. [ABSTRACT FROM AUTHOR]

Nitrogen-vacancy (NV) centers in diamonds play a large role in advanced quantum sensing with solid-state spins for potential miniaturized and portable application scenarios. With the temperature sensitivity of NV centers, the temperature fluctuations caused by the unknown environment and the system itself will mix with the magnetic field measurement. In this research, the temperature-sensitive characteristics of different diamonds, alongside the temperature noise generated by a measurement system, were tested and analyzed with a homemade NV magnetometer in a fiber-optic scheme. In this work, a multi-frequency synchronous manipulation method for resonating with the NV centers in all axial directions was proposed to compensate for the temperature fluctuations in a fibered NV magnetic field sensing scheme. The symmetrical features of the resonance lines of the NV centers, the common-mode fluctuations including temperature fluctuations, underwent effective compensation and elimination. The fluorescence change was reduced to 1.0% by multi-frequency synchronous manipulation from 5.5% of the single-frequency manipulation within a ±2 °C temperature range. Additionally, the multi-frequency synchronous manipulation improved the fluorescence contrast and the magnetic field measurement SNR through an omnidirectional manipulation scheme. It was very important to compensate for the temperature fluctuations, caused by both internal and external factors, to make use of the NV magnetometer in fiber-optic schemes' practicality. This work will promote the rapid development and widespread applications of quantum sensing based on various systems and principles. [ABSTRACT FROM AUTHOR]

Liquid-level sensors are required in modern industrial and medical fields. Optical liquid-level sensors can solve the safety problems of traditional electrical sensors, which have attracted extensive attention in both academia and industry. We propose a distributed liquid-level sensor based on optical frequency domain reflectometry and with no-core fiber. The sensing mechanism uses optical frequency domain reflectometry to capture the strong reflection of the evanescent field of the no-core fiber at the liquid–air interface. The experimental results show that the proposed method can achieve a high resolution of 0.1 mm, stability of ±15 μm, a relatively large measurement range of 175 mm, and a high signal-to-noise ratio of 30 dB. The sensing length can be extended to 1.25 m with a weakened signal-to-noise ratio of 10 dB. The proposed method has broad development prospects in the field of intelligent industry and extreme environments. [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 paper, a gold/graphene/Ti3C2Tx-MXene hybrid layered D-type photonic crystal fiber (PCF) design based on surface plasmon resonance (SPR) sensors is proposed for cancer cell detection. This design uniquely combines gold, graphene, and Ti3C2Tx-MXene materials to achieve a synergistic effect, significantly enhancing the sensitivity and specificity of the sensor. The full vector finite element method (FVFEM) is used for the entire numerical analysis of the proposed biosensor. The cladding of the D-type PCF has a hexagonal arrangement of air holes. In the first cladding, the two air holes closest to the metal layer are narrowed down to enhance the plasma wave and provide an efficient leakage channel. The last two air holes closest to the metal layer in the same layer are enlarged to limit light scattering and couple more energy to the surface plasmon polariton (SPP) mode. The sensitivity of the sensor improves by using these different diameter air holes and coating the D-type PCF surface with a hybrid gold/graphene/Ti3C2Tx-MXene layer. The geometrical parameters are optimized to obtain higher sensor sensitivity. The corresponding wavelength sensitivities are 3000 nm/RIU for Basal cells, 5000 nm/RIU for HeLa cells (Henrietta Lacks cells), 5714 nm/RIU for Jurkat cells (Human T lymphocyte cells), 7143 nm/RIU for PC12 cells (Pheochromocytoma cells), 8571 nm/RIU for MDA-MB-231 cells (Breast cancer cells), and 9286 nm/RIU for MCF-7 cells (Michigan Cancer Foundation-7, a breast cancer cell line), respectively, confirming the excellent performance of the proposed sensor. The sensor proposed paves the way for efficient, simple, low-cost, and highly sensitive cancer detection techniques that could replace surgical and chemical techniques. [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 fiber-optic refractometer for various liquids with refractive indices in the range from 1.33 to 1.43 has been manufactured and tested. The sensor is based on a thin silicon oxynitride (Si3N4-xOx) film coated thinned optic fiber section (taper) obtained in a multimode all-silica optical fiber by chemical etching of the reflective cladding. The film was deposited on the cylindrical surface of the thinned fiber by the surface plasma chemical vapor deposition method (SPCVD). Lossy mode resonance (LMR) was observed in the transmission spectrum of the coated taper at a wavelength dependent on the refractive index of the liquid in which the taper was immersed. We tested the obtained sensors in distilled water, isopropyl alcohol, dimethylformamide, and their aqueous solutions. It was found that with the help of the SPCVD, one can obtain a set of sensors in a single deposition run with the dispersion of sensitivity and spectral position of LMR no more than 5%. Maximum sensitivity of the manufactured sensors to surrounding media refractive index (SMRI) variation exceeds 1090 nm/RIU, which is the highest value recorded to date for a sensor with a non-oxide coating. [ABSTRACT FROM AUTHOR]

A kind of novel and compact magnetic field sensor has been proposed and investigated experimentally. The proposed sensor consists of a tapered single mode fiber coupled with a nanostructured magnetic fluid-infiltrated photonic crystal fiber, which is easy to be fabricated. The response of magnetic fluid to magnetic field is used to measure the intensity of magnetic field via whispering gallery mode. The magnetic field-dependent shift in resonance wavelength is observed. The maximum magnetic field intensity sensitivity is 53 pm/mT. The sensor sensitivity is inversely proportional to the thickness of the photonic crystal fiber cladding. [ABSTRACT FROM AUTHOR]

For decades, optical fiber interferometers have been extensively studied and applied for their inherent advantages. With the rapid development of science and technology, fiber sensors with higher detection sensitivity are needed on many occasions. As an effective way to improve measurement sensitivity, Vernier effect fiber sensors have drawn great attention during the last decade. Similar to the Vernier caliper, the optical Vernier effect uses one interferometer as a fixed part of the Vernier scale and the other as a sliding part of the Vernier scale. This paper first illustrates the principle of the optical Vernier effect, then different configurations used to produce the Vernier effect are classified and discussed. Finally, the outlook for Vernier effect fiber sensors is presented. [ABSTRACT FROM AUTHOR]

In the chain and rope hoist systems of large cranes, instant and monitoring of the strain caused by different loads is of great importance. Strain is a size that cannot be measured directly and whose effect can be measured. Strain can be measured point by point with the help of electronic sensors. However, increasing the number of measuring points causes complexity in electronic systems. Thanks to distributed fiber sensors, this problem has been overcome and standard SMF has been used as tens of thousands of measuring points. In this study, a model of the pulley system used in large cranes is created and the strain occurring at a certain point of a SMF was experimentally measured using the BOTDA technique. SNR was improved by using the wavelet noise reduction technique in the processing of the received signals. In order to monitor the measured strain, a user‐friendly interface was designed. [ABSTRACT FROM AUTHOR]

This paper proposed a fiber sensor based on a Silicon core fiber incorporated with a fused silica grating design. The proposed structure has a high sensitivity in refractive index and temperature variation through theoretical calculation and finite element method simulation. The sensitivities of the refractive index in different polarization directions are 1838.7 and 1949.8 nm/RIU, respectively, within the index range from 1.28 to 1.38 RIU. The temperature range within 15–40 °C has the sensitivity up to 1.6 nm/°C by using ethanol analyte. The proposed fiber sensor can provide a method or a solution for intelligent sensing systems. [ABSTRACT FROM AUTHOR]

A plasmonic structure using gold nanorods (GNRs) on the surface of a tapered fiber was developed. The structure was used to study the Raman spectra of Rhodamine 6G (R6G) and zinc oxide (ZnO) adsorbed on the tapered optical fiber covered with the GNRs, respectively. The tapered optical fiber was manufactured by a dynamic etching process. The tapered fiber had a tip diameter in the nanometer range. The optical tweezing phenomenon was used to develop the plasmonic structure along the length of the tapered fiber surface. The density of GNRs varied as the diameter of the fiber in the tapered region changed. Raman spectra for R6G and ZnO were recorded and analyzed at different fiber locations with and without GNRs. We could obtain the SERS spectrum of a R6G solution of concentration 10−7 M using the developed substrate. [ABSTRACT FROM AUTHOR]

Single-crystal fiber (SCF) is a fibrous crystalline material, which possesses broad application prospects in the fields of national defense and people's livelihood due to its excellent physical and chemical properties and large aspect ratio. With the maturity and development of the edge-defined film-fed growth technique, laser-heated pedestal growth technique and micro-pulling down technique, SCF ushers in a boom period with various materials and diversified applications. Among them, high melting point oxide SCF for high-temperature sensing has shown great potential for application in harsh environments such as strong oxidation, strong radiation, strong corrosion and strong electromagnetic interference by virtue of its high temperature resistance, oxidation resistance and compact structure. In recent years, researchers have combined optical and acoustic sensing technologies with SCF to broaden the operating temperature of conventional glass fiber sensors while maintaining the structural flexibility, and to compensate for the low lifetime of traditional contact temperature sensing tecniques such as thermocouples in harsh environments. Here, following the development process of the single crystal fiber, the technical characteristics and the research status of the growth techniques as well as the temperature sensing techniques are summarized in detail. [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]

• We designed a fiber sensor system comprising fused silica fiber Bragg grating and silicon core fiber-based fiber Bragg grating. • A hybrid fiber Bragg grating sensor system was proposed, employing only two sensing devices to detect three different environmental targets. • Our focus was solely on addressing the connection between two distinct fibers, namely fused silica and silicon core fiber. We discussed the associated loss and spectral distortion issues. In this article, we introduce a multi-parameter fiber sensor system that utilizes a hybrid FBG design. The design combines a fused silica fiber Bragg grating and a fiber Bragg grating based on a silicon core fiber. This combination enables the sensor to detect surrounding temperature, water level, and refractive index. The sensor successfully measured temperature within the range of 10 to 40 °C, water level within the range of 40 to 140 cm, and refractive index within the range of 1.2 to 1.4. These ranges exhibit a high level of linearity within the proposed sensing range. Additionally, we discuss the challenges associated with connecting the fused silica fiber and the silicon core fiber. [ABSTRACT FROM AUTHOR]

A surface plasmon resonance (SPR) sensor based on a photonic crystal fiber (PCF) is proposed for low refractive index (RI) detection. The core of PCF is formed by two-layer air walls and either layer is composed of six identical sector rings with negative curvature. Plasmonic material gold (Au) is coated on the external cladding surface. Finite element method (FEM) is applied to investigate the performance of the SPR sensor. Results show that the sensor is independent of polarization due to the coincident coupling properties of the two polarized modes. Additionally, in low RI ranging from 1.20 to 1.33, the sensor keeps a high spectral sensitivity with an average value of 7738 nm/RIU. When RI varies from 1.32 to 1.33, the resolution reaches to its maximum of 8.3 × 10−6. The proposed sensor shows much significance in low RI detection, which is promising in real-time measurement for medical, water pollution, and humidity. [ABSTRACT FROM AUTHOR]

The paper presents the study of the possibilities of optical monitoring of the fluid flow velocity. An optical fiber with an array of Bragg fiber gratings, the central wavelengths of which varied depending on the velocity of the transmitted stream, was used as a sensitive element. The advantage of the developed method lies in the possibility of additional simultaneous measurement of the temperature of the liquid—which allows us to produce hot-wire anemometers, or to exclude the influence of temperature on measurements of the flow velocity. The sensitivity of the developed method was 697 pm/(m/s). [ABSTRACT FROM AUTHOR]

A fast interrogation scheme for fiber Bragg grating (FBG) using Kalman filter (KF) algorithm is presented. The resolution of the system using KF algorithm is tested, and the dynamic interrogation of the system is verified using vibration signals. Meanwhile, different degrees of static pressure were applied to the FBG, and the static interrogation of the system is verified. Experimental verification shows that the Bragg wavelength resolution of the proposed algorithm can reach 0.3 pm and is relatively stable as the wavelength resolution of the system decreases. In addition, the antinoise performance of KF algorithm is compared with that of direct peak search algorithm. Compared with other commonly used FBG peak search algorithms, the innovative algorithm has the characteristics of low computational cost, high sensitivity, and stability. [ABSTRACT FROM AUTHOR]

• Formed a F-P interferometer on a 45° polished side hole eccentric core fiber. • Can be used as an RI sensing probe for solutions, which is easy to operate. • Can be used as sensors for other parameters, such as temperature by filling suitable materials. A Fabry-Pérot interferometer on the tip of a microstructured fiber and its sensing application was demonstrated. The microstructured side hole eccentric core fiber was fabricated using the drilling hole method. The fiber end face was polished to 45° which could reflect the light transverse to the fiber, utilizing the side wall of the air hole as the reflection surface. Sensing abilities of the interferometer were investigated in the experiment. It can work as a probe for liquid RI sensing by simply plunging the fiber tip into the solution being tested, in addition, it can become sensors for different parameters by filling functional materials into the air hole. An example of filling UV curable adhesive into the fiber to be a temperature sensor was demonstrated in the experiment. The sensing structure on the fiber tip shows the advantages of high linearity, easy fabrication and good reproducibility, as a sensor it is also convenient to operate. [ABSTRACT FROM AUTHOR]

• Wearable Optical Fiber Sensor based macro-bending loss for Biomechanical Motion Evaluation. • A U-shaped fiber sensor has been integrated into elbow and knee joint phantoms and measuring its response to various elbow and knee joint movements in the range of 0°-90°. • The recorded sensing data revealed an extra sensitivity of −0.457 nm/° with linear regression coefficients of more than 98.7 % for elbow flexion angle and a 0.506 nm/° sensitivity with a high linear regression coefficient of ∼ 99.6 % for knee flexion angle. • The proposed sensor exhibits a high sensitivity which it significantly improves the optical sensing signal to more than 5.5 times in correspondence with many previous published works. The biocompatibility and other unique physical properties of optical fibers reflect their potential for use in biomechanical motion sensing. In this paper, a wearable macro-bending structure fiber sensor has been fabricated and its potential is demonstrated for observing key motions during physical therapy for patients with joint stiffness. The sensor's performance has been evaluated by integrating it into elbow and knee joint phantoms and measuring its response to various elbow and knee joint movements in the range of 0°-90°. The recorded sensing data revealed the extra sensitivity of −0.457 nm/° with linear regression coefficients (R2) of more than 98.7 % for elbow flexion angle and a 0.506 nm/° sensitivity with a high linear regression coefficient (R2) of ∼ 99.6 % for knee flexion angle. Additionally, good reproducibility and swift response facility were demonstrated during the experiment, indicating that the designed sensor possesses enormous potential in terms of different body motion monitoring applications, even subtle ones. The results show that the sensor's high sensitivity leads to a very good correlation between the sensor's output and the actual elbow joint movement. [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]

Common gaseous fuels are mixtures of several components. As the properties of the fuels can vary with the composition, but combustion needs to be stable, reliable analytical methods are highly sought after. Raman spectroscopic methods have proved their suitability for the characterization of diverse gaseous mixtures. They have the potential to overcome existing limitations of established technologies, since they are fast, non-consumptive, and accurate. Here, we demonstrate a gas sensor based on fiber-enhanced Raman spectroscopy (FERS) for fuel gas monitoring. Online detection of all gas components, including alkanes, carbon dioxide (CO2), nitrogen (N2), and hydrogen sulfide (H2S), for varying concentration ranges from tens of vol% down to the ppm level enables a comprehensive characterization of the fuels. The developed sensor system features a pinhole assembly which sufficiently reduces the background signal from the fiber to enable the detection of C2–C4 alkanes occurring in low concentrations. Detection limits in the low ppm region were achieved for the minor components of fuel gases, which allow the online monitoring of necessary purification steps, e.g., for biogas. The obtained results indicate that fiber-enhanced Raman sensors have the potential for comprehensive online and onsite gas sensing for fuel gas quality control. [ABSTRACT FROM AUTHOR]

We demonstrate a DNA-based optical fiber device that uses an in-fiber grating, a light absorbing coating with surface anchored DNA, and a built-in optical thermometer. This device is used for precisely thermal cycling surface DNA spots bound by a simple UV cross-linking technique. Near-infrared light of wavelengths near 1550 nm and guided power near 300 mW is coupled out of the fiber core by a tilted fiber Bragg grating inscribed in the fiber and absorbed by the coating to increase its temperature to more than 95 °C. A co-propagating broadband light signal (also in the near-infrared region) is used to measure the reflection spectrum of the grating and thus the temperature from the wavelength shifts of the reflection peaks. The device is capable of sensitive DNA melt analysis and can be used for DNA amplification. [ABSTRACT FROM AUTHOR]

Complex monolithic Si MEMS can be created using a single mask by extending the empty-space-in-silicon (ESS) or silicon-on-nothing (SON) technology. The fabrication combines isotropic and anisotropic etching with selective removal of passivation layers followed by hydrogen annealing. The resulting expanded design space includes multilayer structures and embedded cavities. The MEMS formation by the hydrogen annealing is simulated both at large scales and microscopic scales that together predict the shape of the finished MEMS. We demonstrate the accuracy of our process and simulations by fabricating single- and double-layer evacuated silicon voids that form Fabry-Perot optical pressure sensors with the sealed voids as pressure references. We also create multi-layered sensors with an integrated photonic crystals sensing diaphragm for improved optical readout. The sensors have a calculated 6.7 $\mu \text{V}$ /Pa sensitivity and low noise over a dynamic range of over 70.9 kPa. [2019-0091] [ABSTRACT FROM AUTHOR]

A polydimethylsiloxane (PDMS) packaged microfiber knot ring (MKR) resonator was used as a load-sensing probe. Based on the large Young's modulus and low elastic effect of the silica, the load-sensing characteristic of the bare MKR was experimentally verified with a sensitivity of 6 pm/N. The sensitivity and stability were improved significantly after the MKR was encapsulated in the PDMS film. When the load was applied, the PDMS deformed due to the elastic effect, which in turn changed the length of the MKR. When the microfiber and ring diameter were 7.20 μm and 4.0 mm, respectively, a load sensitivity of 90 pm/N was experimentally demonstrated in the working range from 10 to 50 N. The corresponding strain sensitivity was 0.038 pm/με. The impacts from both the microfiber diameter and ring length on the load-sensing performance were analyzed as well. The experimental results show that the higher sensitivity needs a smaller ring diameter but is independent on the microfiber diameter. This MKR load-sensing probe is promising for exploring miniature sensor chips, due to advantages of low cost, simple and rapid fabrication, and the compact structure. [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]

The inclinometer is one of the most important instruments used in geotechnical engineering. The inclinometer is installed into a borehole to monitor the angle of inclination at regular intervals along the borehole to profile the land/soil displacement. In this paper, a novel design of an in-place inclinometer utilizing fiber Bragg grating (FBG) sensor technology is presented. The presented inclinometer is highly sensitive and has an angle measurement resolution of 0.006°. The conventional inclinometers may be twisted involuntarily due to the force that they experience during installation. This twisting may hamper the measurement accuracy of inclinometers. The performance of the proposed FBG-based in-place inclinometer is independent of twisting; hence, its accuracy remains intact even if it is twisted. [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]

Wavefront shaping (WFS) techniques have been used as a powerful tool to control light propagation in complex media, including multimode fibers. In this paper, we propose a new application of WFS for multimode fiber-based sensors. The use of a single multimode fiber alone, without any special fabrication, as a sensor based on the light intensity variations is not an easy task. The twist effect on multimode fiber is used as an example herein. Experimental results show that light intensity through the multimode fiber shows no direct relationship with the twist angle, but the correlation coefficient (CC) of speckle patterns does. Moreover, if WFS is applied to transform the spatially seemingly random light pattern at the exit of the multimode fiber into an optical focus. The focal pattern correlation and intensity both can serve to gauge the twist angle, with doubled measurement range and allowance of using a fast point detector to provide the feedback. With further development, WFS may find potentials to facilitate the development of multimode fiber-based sensors in a variety of scenarios. [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]

In this article, the novel low‐cost and simple intensity‐modulated Sagnac loop based temperature sensor setup is presented. The sensor head consists of a short length of polarization‐maintaining fiber (PMF), which is spliced to a single‐mode fiber optic coupler. Due to the short section of PMF, the spectrum has wide separation between adjacent interferometer dips. This idea ensures that transmission of a broadband light source has different losses after propagation through Sagnac loop whether temperature changes and causes shift of interferometer dips. Therefore, tracking of wavelength shift of interferometer dip is not required in this setup as it relies on direct optical power measurement. Instead of using spectral analysis instruments, we present the novel intensity‐modulated optical fiber temperature sensor based on Sagnac loop created of short section of PMF. This particular sensor was experimentally investigated for a temperature range of 25‐50.5°C and exhibited the sensitivity of 0.066 mW/1°C with resolution of 0.34°C. The setup could be easily applied in order to create fiber optic sensor network for temperature monitoring. [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]

An all-fiber magnetic-field sensor combining a multicore fiber taper and magnetic fluid is proposed and experimentally demonstrated. The magnetic-field sensing mechanism is investigated theoretically and experimentally. Experimental results demonstrate that the dip-wavelength of the proposed sensor regularly varies with the changes of the applied magnetic field. The measuring sensitivity is achieved to be ~34 pm/Gs in the magnetic induction intensity range of 50–300 Gs. Moreover, the sensor responding to the 50-Hz alternating magnetic field is also experimentally investigated, and a minimal detectable magnetic induction intensity of ~23.7 Gs is successfully achieved. The proposed magnetic field sensor is attractive due to its compact size, low cost, and immunity to electromagnetic interference. [ABSTRACT FROM AUTHOR]

• An ADCF is designed with large pressure-induced difference of the refractive indices of the two fiber cores up to 10−5/MPa. • A hydraulic pressure sensing system is designed without using a costly optical spectrum analyzer. • The hydraulic pressure sensor has sensing range from 0 to 900 MPa, sensitivity of 0.3 mm/MPa, and resolution of 0.22 MPa. We propose a novel asymmetric double-core fiber (ADCF) which provides an ADCF-based hydraulic pressure sensing system without using optical spectrum measurement based on a costly optical spectrum analyzer. The ADCF is designed with asymmetric double fiber cores and two side air holes, which ensure the asymmetric pressure-induced phase change for the guiding light in the two fiber cores. Based on the finite element method, optical properties of the ADCF under hydraulic pressure are investigated considering the fiber parameters such as the refractive index, the distance of two holes or two fiber cores, the size of two fiber cores and the fiber length. A hydraulic pressure sensing system based on the ADCF and a low-cost linear array charge coupled device (CCD) is proposed, where the hydraulic pressure demodulation is achieved by measuring the movement of the spatial interference pattern of the light from the double fiber cores of the ADCF. Numerical simulation shows that the hydraulic pressure sensor based on a 10-cm ADCF and a 2.867-cm CCD has a sensing range from 0 to 900 MPa and a sensitivity of 0.3 mm/MPa. In this paper, a low-cost CCD is used instead of a costly spectrometer, which greatly reduces the cost of the sensing system. The proposal for the ADCF and the solution for hydraulic pressure sensing are of great significance to promote the wide application of the hydraulic pressure fiber sensor. [ABSTRACT FROM AUTHOR]