Boosting SNR of cascaded FBGs in a sapphire fiber through a rapid heat treatment.

This Letter reports the performance of femtosecond (fs) laser-written distributed fiber Bragg gratings (FBGs) under high-temperature conditions up to 1600°C and explores the impact of rapid heat treatment on signal-to-noise ratio (SNR) enhancement. FBGs are essential for reliable optical sensing in extreme temperature environments. Comprehensive tests demonstrate the remarkable performance and resilience of FBGs at temperatures up to 1600°C, confirming their suitability for deployment in such conditions.

Miniaturized 7-in-1 fiber-optic Raman probe.

This Letter reports a miniature 7-in-1 fiber-optic Raman probe that eliminates the inelastic background Raman signal from a long-fused silica fiber. Its foremost purpose is to enhance a method for investigating extraordinarily tiny substances and effectively capturing Raman inelastic backscattered signals using optical fibers. We successfully used our home-built fiber taper device to combine seven multimode fibers into a single fiber taper with a probe diameter of approximately 35 µm.

Calculations of adsorption-dependent refractive indices of metal-organic frameworks for gas sensing applications.

Detection of volatile organic compounds (VOCs) is one of the most challenging tasks in modelling breath analyzers because of their low concentrations (parts-per-billion (ppb) to parts-per-million (ppm)) in breath and the high humidity levels in exhaled breaths. The refractive index is one of the crucial optical properties of metal-organic frameworks (MOFs), which is changeable via the variation of gas species and concentrations that can be utilized as gas detectors. Herein, for the first time, we used Lorentz-Lorentz, Maxwell-Ga, and Bruggeman effective medium approximation (EMA) equations to compute the percentage change in the index of refraction (Δn%) of ZIF-7, ZIF-8, ZIF-90, MIL-101(Cr) and HKUST-1 upon exposure to ethanol at various partial pressures.

Thermally robust and highly stable method for splicing silica glass fiber to crystalline sapphire fiber.

This research reports an advancement in splicing silica glass fiber to sapphire single-crystal optical fiber (SCF) using a specialized glass processing device, including data that demonstrate the thermal stability of the splice to 1000°C. A filament heating process was used to produce a robust splice between the dissimilar fibers. A femtosecond laser is used to inscribe a fiber Bragg gratings sensor into the SCF to measure the high-temperature capabilities and signal attenuation characteristics of the splice joint.

Identification of Volatile Organic Liquids by Combining an Array of Fiber-Optic Sensors and Machine Learning.

In this paper, we report an array of fiber-optic sensors based on the Fabry-Perot interference principle and machine learning-based analyses for identifying volatile organic liquids (VOLs). Three optical fiber tip sensors with different surfaces were included in the array of sensors to improve the accuracy for identifying liquids: an intrinsic (unmodified) flat cleaved endface, a hydrophobic-coated endface, and a hydrophilic-coated endface. The time-transient responses of evaporating droplets from the optical fiber tip sensors were monitored and collected following the controlled immersion tests of 11 different organic liquids.

A Fiber-Optic Sensor-Embedded and Machine Learning Assisted Smart Helmet for Multi-Variable Blunt Force Impact Sensing in Real Time.

Early on-site diagnosis of mild traumatic brain injury (mTBI) will provide the best guidance for clinical practice. However, existing methods and sensors cannot provide sufficiently detailed physical information related to the blunt force impact. In the present work, a smart helmet with a single embedded fiber Bragg grating (FBG) sensor is developed, which can monitor complex blunt force impact events in real time under both wired and wireless modes.

Metal-organic Framework Materials Coupled to Optical Fibers for Chemical Sensing: A Review.

Metal-organic frameworks (MOFs), a newer class of crystalline nanoporous materials, have been in the limelight owing to their exceptional tunability for structures and physicochemical properties, and have found successful applications in gas storage, gas separation, and catalysis. The mesmerizing properties of MOFs, especially the extensive and tunable porosity and chemical selectivity, also make them an excellent candidate class as chemo-sensory materials. Moreover, MOF-based sensors have attracted considerable attention in the past decade.

Micromachined Optical Fiber Sensors for Biomedical Applications.

Optical fibers revolutionized the rate of information reception and transmission in telecommunications. The revolution has now extended to the field of physicochemical sensing. Optical fiber sensors (OFSs) have found a multitude of applications, spanning from structural health monitoring to biomedical and clinical measurements due to their unique physical and functional advantages, such as small dimensions, light weight, immunity to electromagnetic interference, high sensitivity and resolution, multiplexing, and remote operation.

Machine learning identifies liquids employing a simple fiber-optic tip sensor.

We proposed an extremely simple fiber-optic tip sensor system to identify liquids by combining their corresponding droplet evaporation events with analyses using machine learning techniques. Pendant liquid droplets were suspended from the cleaved endface of a single-mode fiber during the experiment. The optical fiber-droplet interface and the droplet-air interface served as two partial reflectors of an extrinsic Fabry-Perot interferometer (EFPI) with a liquid droplet cavity.

Gas sensing materials roadmap.

Gas sensor technology is widely utilized in various areas ranging from home security, environment and air pollution, to industrial production. It also hold great promise in non-invasive exhaled breath detection and an essential device in future internet of things. The past decade has witnessed giant advance in both fundamental research and industrial development of gas sensors, yet current efforts are being explored to achieve better selectivity, higher sensitivity and lower power consumption.

Fiber optic sensor embedded smart helmet for real-time impact sensing and analysis through machine learning.

Background: Mild traumatic brain injury (mTBI) strongly associates with chronic neurodegenerative impairments such as post-traumatic stress disorder (PTSD) and mild cognitive impairment. Early detection of concussive events would significantly enhance the understanding of head injuries and provide better guidance for urgent diagnoses and the best clinical practices for achieving full recovery.

New Method: A smart helmet was developed with a single embedded fiber Bragg grating (FBG) sensor for real-time sensing of blunt-force impact events to helmets.

Microwave device inspired by fiber-optic extrinsic Fabry-Perot interferometer: a novel ultra-sensitive sensing platform.

The fiber-optic extrinsic Fabry-Perot interferometer (EFPI) is one of the simplest sensing configurations and is widely used in various applications. Inspired by the EFPI, we report a novel and universal ultra-sensitive microwave sensing platform based on an open-ended hollow coaxial cable resonator. Two highly-reflective microwave reflectors were fabricated in a coaxial cable to form a microwave Fabry-Perot etalon.

NMR studies of materials loaded into porous-wall hollow glass microspheres.

Porous-wall hollow glass microspheres (PWHGMs) are a form of glass materials that consist of 1-μm-thick porous silica shells, 20-100 μm in diameter, with a hollow cavity in the center. Utilizing the central cavity for material storage and the porous walls for controlled release is a unique combination that renders PWHGMs a superior vehicle for targeted drug delivery. In this study, loaded PWHGMs were characterized for the first time employing proton nuclear magnetic resonance (H NMR) spectroscopy.

A Spatially Distributed Fiber-Optic Temperature Sensor for Applications in the Steel Industry.

This paper presents a spatially distributed fiber-optic sensor system designed for demanding applications, like temperature measurements in the steel industry. The sensor system employed optical frequency domain reflectometry (OFDR) to interrogate Rayleigh backscattering signals in single-mode optical fibers. Temperature measurements employing the OFDR system were compared with conventional thermocouple measurements, accentuating the spatially distributed sensing capability of the fiber-optic system.

Chemical Detection Using a Metal-Organic Framework Single Crystal Coupled to an Optical Fiber.

The quantitative detection and real-time monitoring of target chemicals in the liquid phase are made possible by combining the tailored adsorption properties of metal-organic framework (MOF) material and the precise measuring capabilities of an optical fiber (OF) Fabry-Pérot interferometer (FPI) device. As the single-crystal MOF host adsorbs target analyte guests from the environment, its dielectric properties change causing the reflection spectrum derived from the FPI device to shift. A single crystal of HKUST-1 was attached to the end-face of an OF to form the sensor OF∪MOF (∪, union).

Capillary-tube package devices for the quantitative performance evaluation of nuclear magnetic resonance spectrometers and pulse sequences.

With the increased sensitivity of modern nuclear magnetic resonance (NMR) spectrometers, the minimum amount needed for chemical-shift referencing of NMR spectra has decreased to a point where a few microliters can be sufficient to observe a reference signal. The reduction in the amount of required reference material is the basis for the NMR Capillary-tube Package (CapPack) platform that utilizes capillary tubes with inner diameters smaller than 150 m as NMR-tube inserts for external reference standards. It is shown how commercially available electrophoresis capillary tubes with outer diameters of 360 m are filled with reference liquids or solutions and then permanently sealed by the arc discharge plasma of a commercially available fusion splicer normally employed for joining optical fibers.

Probing changes in tilt angle with 20 nanoradian resolution using an extrinsic Fabry-Perot interferometer-based optical fiber inclinometer.

In this paper, we introduce and demonstrate a novel optical fiber extrinsic Fabry-Perot interferometer (EFPI) for tilt measurements with 20 nrad resolution. Compared with in-line optical fiber inclinometers, an extrinsic sensing structure is used in the inclinometer reported herein. Our design greatly improves on the tilt angle resolution, the temperature stability, and the mechanical robustness of inclinometers with advanced designs.

An Optical Interferometric Triaxial Displacement Sensor for Structural Health Monitoring: Characterization of Sliding and Debonding for a Delamination Process.

This paper presents an extrinsic Fabry-Perot interferometer-based optical fiber sensor (EFPI) for measuring three-dimensional (3D) displacements, including interfacial sliding and debonding during delamination. The idea employs three spatially arranged EFPIs as the sensing elements. In our sensor, the three EFPIs are formed by three endfaces of three optical fibers and their corresponding inclined mirrors.

EXponentially Converging Eradication Pulse Train (EXCEPT) for solvent-signal suppression in investigations with variable T(1) times.

Selective presaturation is a common technique for suppressing excessive solvent signals during proton NMR analysis of dilute samples in protic solvents. When the solvent T1 relaxation time constant varies within a series of samples, parameters for the presaturation sequence must often be re-adjusted for each sample. The EXCEPT (EXponentially Converging Eradication Pulse Train) presaturation pulse sequence was developed to eliminate time consuming pulse-parameter re-optimization as long as the variation in the solvent's T1 remains within an order of magnitude.

Dual lithium insertion and conversion mechanisms in a titanium-based mixed-anion nanocomposite.

The electrochemical reaction of lithium with a vacancy-containing titanium hydroxyfluoride was studied. On the basis of pair distribution function analysis, NMR, and X-ray photoelectron spectroscopy, we propose that the material undergoes partitioning upon initial discharge to form a nanostructured composite containing crystalline Li(x)TiO(2), surrounded by a Ti(0) and LiF layer. The Ti(0) is reoxidized upon reversible charging to an amorphous TiF(3) phase via a conversion reaction.