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Small-scale robots capable of remote active steering and navigation offer great potential for biomedical applications. However, the current design and manufacturing procedure impede their miniaturization and integration of various diagnostic and therapeutic functionalities. Here, we present a robotic fiber platform for integrating navigation, sensing, and therapeutic functions at a submillimeter scale. These fiber robots consist of ferromagnetic, electrical, optical, and microfluidic components, fabricated with a thermal drawing process. Under magnetic actuation, they can navigate through complex and constrained environments, such as artificial vessels and brain phantoms. Moreover, we utilize Langendorff mouse hearts model, glioblastoma microplatforms, and in vivo mouse models to demonstrate the capabilities of sensing electrophysiology signals and performing localized treatment. Additionally, we demonstrate that the fiber robots can serve as endoscopes with embedded waveguides. These fiber robots provide a versatile platform for targeted multimodal detection and treatment at hard-to-reach locations in a minimally invasive and remotely controllable manner.

We study the point-by-point inscription of sapphire parallel fiber Bragg gratings (sapphire pFBGs) in a fully multimode system. A parallel FBG is shown to be critical in enabling detectable and reliable high-order grating signals. The impacts of modal volume, spatial coherence, and grating location on reflectivity are examined. Three cascaded seventh-order pFBGs are fabricated in one sapphire fiber for wavelength multiplexed temperature sensing. Using a low-cost, fully multimode 850-nm interrogator, reliable measurement up to 1500°C is demonstrated.

Previously, a fused-quartz acoustic waveguide named the suspended core waveguide with tight-field confinement in a small diameter was developed and its sensing potential in harsh environment was demonstrated with the fabricated periodic acoustic fiber Bragg grating. In this paper, the acoustic sensor was exposed to around 70 Gy/h gamma radiation at room temperature for 3550 h at Oak Ridge National Laboratory. For comparisons, a thermocouple and two optical fiber Bragg gratings were tested under the same conditions. The central frequency reading of the acoustic sensor was found to encounter a relatively fast decrease of 0.5 kHz in the first 800 hours. The reading then became stable, centering at 478.5 kHz with a fluctuation of ±0.2 kHz, and responded to small environmental temperature variations less than 1.2 °C. The major effect to the fluctuation was concluded to be radiation-induced material compaction and expansion. For optical fiber Bragg gratings, the same one-directional fast change of readings in the first 500 hours were observed as well. Although the optical gratings were able to track temperature changes, they also showed continuous drifts. The survivability and consistency of the acoustic sensor under long-term gamma radiation could lead to new sensing methods in nuclear applications.

A fused quartz acoustic waveguide structure was reported as the suspended core waveguide. The waveguide featured good acoustic wave confinement within the core and a relatively small diameter. Consistent high-temperature sensing was also demonstrated with the waveguide after a temperature sensor was fabricated inside. The waveguide was fabricated by suspending its core rod in the middle of the hollow cladding tube by discrete thin supporting disks. It was found that the characteristics of acoustic propagation in the waveguide was similar to that in a bare core rod and that the waveguide was largely insensitive to lossy surface perturbations. The diameter of the waveguide was relatively small, little more than the bulk longitudinal acoustic wavelength. For sensing, the periodic structure, the acoustic fiber Bragg grating, was fabricated on the core of the suspended core waveguide. A temperature test up to 1000 °C was performed. The central frequency of the reflected acoustic wave was found to change unidirectionally and consistently with changes in temperature. With its good field confinement and consistent sensing capabilities, the suspended core waveguide could find vast potential in many applications.

We present the generation of 12.1 ns frequency chirped pulses from a distributed feedback laser diode via injection current modulation and demonstrate its application to absorption-based methane sensing at 1650.9 nm. The chirp spectral distribution is found to be significantly impacted by the transient dynamics of these short pulses. A simplified, two-part model is used to evaluate the chirp property, suggesting spectral mixing and oscillation. The chirp enables intra-pulse self-calibrated gas sensing by taking the amplitude ratio between the absorption peak and a reference, which is demonstrated for methane concentrations from 0 to 22.6% with a detection limit of 25 ppm. It also provides resistance to power fluctuation from various sources. These short pulses offer high spatial and temporal resolution and can potentially enable reflection-based, highly multiplexed gas sensing systems.

High temperature sensor with robust performance, minimum footprint, and fast response is desirable for many applications in extreme environments. This article introduces a miniature high temperature sensor based on fiber Fabry-Perot interferometer. The interferometric cavity is directly fabricated on the tip of a 125 μm single-crystal sapphire fiber through femtosecond laser micromachining and CO2 laser welding with the sapphire fiber as a light-guiding element. The sensor has an all-sapphire structure to ensure both physical and chemical stability. The sensor was tested in the lab from room temperature up to 1455 °C and shows an excellent temperature response with 1.32 nm/ °C at room temperature and full-range average resolution of 0.68 °C. The thermal response of the sensor is evaluated via both numerical simulation and experiment. Owing to the small size and fast thermal diffusivity of sapphire, the thermal response time of ∼1.25 ms has been experimentally demonstrated.

An in-fiber twist sensor based on point-by-point-inscribed off-centered FBG in a two-mode fiber is demonstrated. Twist sensing over a range of -180° to 180° is achieved with a reflection-based system.

We report a flexible method to integrate 3D optical resonators inside optical fibers. A prism-coupled cylindrical resonator and a free-space-coupled asymmetric resonator cavity are demonstrated in optical fibers with a quality factor up to 3.53×105.

This paper presents parallel FBGs in sapphire fiber to significantly boost the signal intensity of high order FBGs. Cascaded parallel FBGs are fabricated and achieve multi-point high temperature sensing.

False-positive 131I accumulation in patients with thyroid carcinoma could be due to various etiologies. Herein, we reported a case of papillary thyroid carcinoma in a 36-year-old woman. She underwent a 131I radiotherapy after a transareola endoscopic total thyroidectomy. 131I scintigraphy showed a high uptake in the thyroid bed. Surprisingly, increased activity was also noted in the right areola area. This activity corresponding to the entry site of endoscope revealed on the following SPECT/CT.

Non-destructive acoustic structural sensing is an imperative technology, applicable to many different fields such as aerospace and civil engineering. To maintain a high sensitivity or to mitigate acoustic loss, it is important to increase the signal-to-noise ratio by improving coupling efficiency from acoustic sources to the object under test, such as an acoustic waveguide. Here, a fully integrated fused quartz horn design is combined with a fused quartz acoustic waveguide. The resulting system is intended to demonstrate a high accuracy low cost alternative to current sensing systems and the present article report on the viability of using a merged acoustic horn and waveguide.

Acoustic sensors and acoustic measurements receive much attention in various applications. Because waveguides are commonly used in sensor design, theoretical means to study acoustic propagation and interaction in waveguides are necessary. However, current methods for elastic wave coupling, including the transfer matrix method and coupled mode theory in planar 2D waveguides, are not satisfactory. In this work, a coupled mode analysis for acoustic waves in 3D stress-free elastic waveguides is proposed. Similar to the coupled mode theory in optical waveguides, the analysis is presented by the evolution of modal amplitudes. It can solve various modal conversion and scattering problems in elastic waveguides with small changes of cross sections and stress-free boundaries. To demonstrate the practicability, the coupled mode analysis is used to calculate the reflection spectrum of the newly proposed structure, the acoustic fiber Bragg grating. In a notch-based grating fabricated on a thin cylindrical waveguide, the results from coupled mode analysis are in good agreement with those from the transfer matrix method, which has been already validated experimentally. The coupled mode analysis is a promising method to solve various scattering problems.

The goal of non-destructive acoustic sensing is to passively monitor innate structural parameters such as temperature, strain, and pressure. Intended for use in harsh structural environments, a distributed acoustic sensing system has been created using a single mode, radiation hardened, fused-silica core rod and a high-resolution acoustic sensor. This study aims to enhance the capabilities of the acoustic sensor by manipulating the fused-silica core rod, geometrically, to induce and control additional acoustic reflections. Here, two geometries are demonstrated to markedly improve upon previous fiber designs and result in a consistent acoustic profile.

Aedes aegypti is a major vector of arboviruses that cause dengue, chikungunya, yellow fever and Zika. Although recent success in reverse genetics has facilitated rapid progress in basic and applied research, integration of forward genetics with modern technologies remains challenging in this important species, as up-to-47% of its chromosome is refractory to genetic mapping due to extremely low rate of recombination. Here we report the development of a marker-assisted-mapping (MAM) strategy to readily screen for and genotype only the rare but informative recombinants, drastically increasing both the resolution and signal-to-noise ratio. Using MAM, we mapped a transgene that was inserted in a >100 Mb recombination desert and a sex-linked spontaneous red-eye (re) mutation just outside the region. We subsequently determined, by CRISPR/Cas9-mediated knockout, that cardinal is the causal gene of re, which is the first forward genetic identification of a causal gene in Ae. aegypti. This study provides the molecular foundation for using gene-editing to develop versatile and stable genetic sexing methods by improving upon the current re-based genetic sexing strains. MAM does not require densely populated markers and can be readily applied throughout the genome to facilitate the mapping of genes responsible for insecticide- and viral-resistance. By enabling effective forward genetic analysis, MAM bridges a significant gap in establishing Ae. aegypti as a model system for research in vector biology. As large regions of suppressed recombination are also common in other plant and animal species including those of economic significance, MAM will have broad applications beyond vector biology.

A chirped pulse-based gas sensing technique was developed. With a short, 11.2 ns frequency chirped pulse generating differential absorption within the pulse duration, inter- pulse calibrated methane sensing up to 20.5% was demonstrated.

The 27th International Conference on Optical Fiber Sensors was to be held on June 8th 2020 in Alexandria, Virginia USA. By March of 2019, over 330 papers had been scheduled for presentation with eight invited speakers, two workshops and eight.

This paper presents a miniature all-sapphire-fiber Fabry-Perot temperature sensor and its evaluation in the exhaust flow of a Honeywell turbofan engine. The sensor demonstrates reliable and fast response as compared to a commercial thermocouple.

Off-axis Bragg gratings with varied horizontal and vertical distances off the center in a step-index two-mode fiber were fabricated by 800 nm infrared-femtosecond laser pulses through a point-by-point technique. In this article, we experimentally investigate these gratings via measuring the transmitted power and the reflected intensity profiles under different input polarization, with multiple characteristics reported for the first time to the best of our knowledge. To highlight, we find that the birefringence induced to the LP01 reaches its maximum magnitude at an intermediate offset, followed by the fast and slow axes switching at a further slightly increased offset. We also show that the peak reflectivity of the LP11 exhibits strong polarization dependence, with the much stronger peak reflectivity constantly corresponding to the polarization perpendicular to the damage-point-to-center line, whereas the peak reflectivity of the LP01 has almost no polarization dependence. Moreover, we report that the reflected mode patterns of the cross-coupling of the LP01 and LP11 are linked to the direction of linear polarization, through which one can selectively excite an arbitrarily oriented LP11 by merely altering the polarization.

Understanding the cytoarchitecture and wiring of the brain requires improved methods to record and stimulate large groups of neurons with cellular specificity. This requires miniaturized neural interfaces that integrate into brain tissue without altering its properties. Existing neural interface technologies have been shown to provide high-resolution electrophysiological recording with high signal-to-noise ratio. However, with single implantation, the physical properties of these devices limit their access to one, small brain region. To overcome this limitation, we developed a platform that provides three-dimensional coverage of brain tissue through multisite multifunctional fiber-based neural probes guided in a helical scaffold. Chronic recordings from the spatially expandable fiber probes demonstrate the ability of these fiber probes capturing brain activities with a single-unit resolution for long observation times. Furthermore, using Thy1-ChR2-YFP mice we demonstrate the application of our probes in simultaneous recording and optical/chemical modulation of brain activities across distant regions. Similarly, varying electrographic brain activities from different brain regions were detected by our customizable probes in a mouse model of epilepsy, suggesting the potential of using these probes for the investigation of brain disorders such as epilepsy. Ultimately, this technique enables three-dimensional manipulation and mapping of brain activities across distant regions in the deep brain with minimal tissue damage, which can bring new insights for deciphering complex brain functions and dynamics in the near future., Existing neural interfaces are limited in accessing one, small brain region. Here, the authors introduce a scaffold with helix hollow channels, which direct multisite multifunctional fibre probes into the brain at different angles, allowing for simultaneous recording and stimulation across distant regions.

The LACMTA HR4000 heavy rail vehicle was designed to meet the ASME RT-2 Safety Standard for Structural Requirements for Heavy Rail Transit Vehicles. The crash energy management (CEM) structures designed for this vehicle also provide unique performance characteristics through use of a staged combination of CEM technologies. The resulting design, using easily replaceable components, provides reduced repair costs for lower speed collisions, minimizes the number of cars damaged during a collision, while exceeding the RT-2 standard for safety to the operator. None of the CEM technologies used are novel, but their integrated design provides a unique performance in heavy rail vehicle design. This paper provides an overview of the CEM design development. First, a general description of the CEM system function is provided, including the various CEM technologies used and how they interact during a collision. Then the 1-dimensional and 3-dimensional nonlinear dynamic models developed for optimizing the design are discussed. The CEM test program performed to demonstrate the system function and validate the modeling is described. Finally, the performance of the CEM system in train-to-train collision analyses is presented. Underframe testing was conducted for validation of the simulations.

The ASME RT-2 Safety Standard for Structural Requirements for Heavy Rail Transit Vehicles requires that crashworthiness analyses be performed for two primary collision scenarios. Both scenarios use a moving train colliding into a stopped train in their ready-to-run loading condition where no passenger mass is included in the analysis. This standard is now frequently cited in technical specifications for new vehicles by transit agencies in North America. When evaluating a collision scenario, it is a logical extension to consider including passenger weights. A collision has a greater risk of injury if more passengers are onboard. In addition, additional passenger weight increases the kinetic energy at a specific collision speed, which can contribute to the collision severity. The difficulty of including the passenger load is that the passengers are loosely coupled to the train collision response and have independent collision behaviors based on the passenger configurations relative to the vehicle interior. The corresponding occupant decelerations can occur over different time frames than the vehicle deceleration. This paper describes a 1-dimensional lumped mass method for incorporating passenger weight into crashworthiness analysis. Each car in the train, the large car body mass is given the ready-to-run weight. The additional passenger load is divided into separate masses that are coupled to the car body using nonlinear springs. The separate passenger masses and attributes for the springs are derived from the specific seating layout of a car. Passengers are grouped by the various seating configurations with different timescales for coupling their mass into the car body. Several collision analyses were performed with this 1D model for the LACMTA HR4000 heavy rail vehicle at the speeds specified in ASME RT-2 (24 and 40 km/h) at both the ready-to-run weight and at the maximum passenger weight. The influence on the crash dynamics and overall permanent stroke of the crash energy management (CEM) structures at each car interface is discussed. For the seating configuration used, a small fraction of the passenger mass is seen to influence the crash dynamics. This is because of the relatively long time it takes to couple much of the passenger mass into the car body relative to the short duration of the primary crash pulse on a car. Consequently, the addition of a large passenger weight did not require a commensurate increase in energy absorption capacity for the CEM structures of vehicle.

This paper reports a miniature all-sapphire high temperature fiber sensor based on fiber Fabry-Perot interferometer fabricated by femtosecond laser micromachining and CO2 laser welding. The sensor was tested to 1455°C with up to 5.38 nm/°C sensitivity.

A novel concept of acoustic fiber Bragg grating (AFBG) was conceived and experimentally validated as an effective technique for high-temperature sensing. Similar to the well-known optical fiber Bragg grating, the AFBG employs interactions between waves and periodic structures on an elongated waveguide. Acoustic waves reflected from periodic structures interfere with each other and result in the emergence of resonance frequency when acoustic wavelength matches with pitch length of the periodic structures. When the single-mode operation condition is satisfied, the resonance frequency location can be accurately resolved and thus be used as an effective indicator for temperature sensing. To demonstrate this concept, an AFBG sample was fabricated on a telecommunication optical fiber (125- $\mu \text{m}$ diameter) with femtosecond laser micromachining setup, and it demonstrated sensing capability up to 700 °C, which was limited by the fiber material (fused silica) and could be over 1400 °C if other material, such as sapphire, was used as the waveguide. With the features of various applicable material, low system cost, and potential multiplexing capability, this AFBG technology is a promising candidate for high-temperature sensing, even in a distributed manner.

Modern high-temperature processes, such as fossil energy production, nuclear reactors, and chemical reactors lack robust, distributed sensing systems to map temperatures in these high-value harsh-environment systems. Regular silica-fiber-based distributed temperature sensing systems usually only operate at temperatures below about 800 °C. In this paper, we present the design, implementation, and testing of a distributed ultra-high temperature sensing system using Raman scattering intensity, which operates from room temperature to above 1400 °C. Consideration is given to the impacts of thermal radiation, fluorescence, and the multimode nature of unclad single-crystal fiber to optimize the system. Results from picosecond and sub-nanosecond lasers were compared. Measurements were taken with a ∼2 m sapphire optical fiber, which represents the longest commercially available length. A spatial resolution of 12.4 cm and position standard deviation of 0.28 mm were achieved up to the maximum testing temperature of 1400 °C, which is a new record for distributed temperature sensing systems.

Using adaptive optics, we experimentally demonstrate the ability to control linearly polarized modes in 4- and 17-mode fibers, where feedback is provided by the correlation between the experimentally captured intensity distribution and the theoretical profile of the desired mode. Selective excitations of high-order mixed orbital angular momentum modes are also shown.

By using few-mode fibers (FMFs), it is possible to simultaneously determine the values of multiple parameters such as temperature and strain. In this work, we extend this capability to the case of mode-based reconstruction of the distribution of a continuous variable function. As a specific example, we theoretically demonstrate that by measuring the mode-dependent losses of multiple guided modes in an FMF, it is possible to determine the spatial distributions of chemicals diffused within the fiber.

In this study, we fabricated a highly flexible fiber-based capacitive humidity sensor using a scalable convergence fiber drawing approach. The sensor&rsquo, s sensing layer is made of porous polyetherimide (PEI) with its porosity produced in situ during fiber drawing, whereas its electrodes are made of copper wires. The porosity induces capillary condensation starting at a low relative humidity (RH) level (here, 70%), resulting in a significant increase in the response of the sensor at RH levels ranging from 70% to 80%. The proposed humidity sensor shows a good sensitivity of 0.39 pF/% RH in the range of 70%&ndash, 80% RH, a maximum hysteresis of 9.08% RH at 70% RH, a small temperature dependence, and a good stability over a 48 h period. This work demonstrates the first fiber-based humidity sensor fabricated using convergence fiber drawing.

Readily available temperature sensing in boilers is necessary to improve efficiencies, minimize downtime, and reduce toxic emissions for a power plant. The current techniques are typically deployed as a single-point measurement and are primarily used for detection and prevention of catastrophic events due to the harsh environment. In this work, a multi-point temperature sensor based on wavelength-multiplexed sapphire fiber Bragg gratings (SFBGs) were fabricated via the point-by-point method with a femtosecond laser. The sensor was packaged and calibrated in the lab, including thermally equilibrating at 1200 &deg, C, followed by a 110-h, 1000 &deg, C stability test. After laboratory testing, the sensor system was deployed in both a commercial coal-fired and a gas-fired boiler for 42 days and 48 days, respectively. The performance of the sensor was consistent during the entire test duration, over the course of which it measured temperatures up to 950 &deg, C (with some excursions over 1000 &deg, C), showing the survivability of the sensor in a field environment. The sensor has a demonstrated measurement range from room temperature to 1200 &deg, C, but the maximum temperature limit is expected to be up to 1900 &deg, C, based on previous work with other sapphire based temperature sensors.

This study reports on the temperature dependent behavior of silica based optical fibers upon exposure to high temperatures in hydrogen and ambient air. The hydroxyl absorption bands in the wavelength range of 1000–2500 nm of commercially available multimode fibers with pure silica and germanium doped cores were examined in the temperature range of 20–800 °C. Two hydroxyl-related infrared absorption bands were observed: ∼2200 nm assigned to the combination of the vibration mode of Si-OH bending and the fundamental hydroxyl stretching mode, and ∼1390 nm assigned to the first overtone of the hydroxyl stretching. The absorption in the 2200 nm band decreased in intensity, while the 1390 nm absorption band shifted to longer wavelengths with an increase in temperature. The observed phenomena were reversible with temperature and suspected to be due, in part, to the conversion of the OH spectral components into each other and structural relaxation.

A high-speed quasi-distributed fiber optic sensing technique is proposed. A sensing link consisting multiple identical fiber Bragg gratings (FBGs) was interrogated by a pulsed light source, and a dispersive unit at the receiver end was used to convert the wavelength shifts of the reflected pulses into time-delay changes. This Bragg wavelength-dependent time delay can be accurately calculated by a fast cross-correlation-based algorithm, enabling distributed high-speed sensing. This technique is experimentally demonstrated using a sensing link containing 2014 FBGs with a reflectance of about −35 dB. A wavelength resolution of 9.03 pm was achieved without any data averaging. Dynamic strain was applied to one of the FBGs, and corresponding wavelength variation was measured at a sampling rate of 20 kHz, obtaining a dynamic resolution of $\surd $ Hz.

A novel technique of liquid-surface-level sensing using a transverse pulse train is reported. Liquid level was detected by the reflection time of pulse train propagation on vertical, straight hollow wire partially immersed in liquid using two kinds of reflections. One is the echo from the liquid surface and the other is from the end of the sensing wire in which propagation speed is influenced by the liquid. Both the signals can be detected in a single measurement. In this paper, the standard deviation of the interface echo method and the end echo method is 26 and 199 $\mu \text{m}$ , respectively. To the best of our knowledge, the error of the interface echo method is the lowest among all acoustic-based liquid-surface-level sensors in the current market. The attenuation coefficient of the interface echo method and the end echo method in water is 0.19 and 3.77 dB/m, respectively. The combination of the end echo and the interface echo techniques and low attenuation make it suitable for long distance and highly accurate liquid-surface-level sensing.

In this paper, we report a novel high-speed white light interferometry (WLI) demodulation algorithm for multiplexed low-finesse Fabry–Perot interferometers (FPIs). The dependence of the demodulation speed on the number of multiplexed sensors was characterized through simulations. An experimental demonstration of 70-kHz real-time WLI demodulation of two extrinsic FPIs was conducted. Sub-nanometer spatial resolution was well achieved for both channels. The crosstalk between the two channels was characterized with respect to the cavity modulation frequency.

In the era of the internet of things (IoTs), it is desired to equip the decentralized electronics with distributed power sources. The fiber-based triboelectric nanogenerator (FTENG) provides one of the soundest solutions due to its high efficiency, easy deployment, excellent wearability, low cost, and eco-friendliness. Compared with other forms of TENGs, it can be woven into fabrics as wearable devices, offering good compactness and comfortability. However, the industrial-loom-compatible FTENGs have yet to be fabricated; the fiber diameter and length are typical challenges in the large scale weaving. In this paper, the thermal drawing process (TDP) is introduced to produce FTENGs that are compatible with industrial looms. The diameter of the polymer-cladding and metal-core fiber has been reduced to ~350 μm, and the length of a single fiber has been scaled up to sub-kilometer. Both hand-woven and loom-woven swatches are demonstrated, showing good flexibility, stretchability, power density, stability, washability, and breathability. Besides serving as power sources, such swatches have been used as self-powered sensors for body motion monitoring and communication. These applications show that the thermally drawn FTENGs can serve as powerful and reliable wearable devices in modern electronics.

A high-temperature all-fiber non-destructive multi-parameter sensing system is developed. The system can operate consistently in a wide range of temperature changes by specially designed active signal generation and detection units. It is capable of monitoring temperature up to 600°C and cracks on metal pipes with an acoustic wave generation unit and an acoustic detection unit. A gold-coated multi-mode fiber is used to deliver a laser pulse for acoustic excitation while minimizing parasitic acoustic signals at high temperature. An in-fiber Fabry–Perot fiber Bragg grating (FP-FBG) is fabricated in another single-mode fiber and bonded to the test object for acoustic detection. The FP-FBG avoids strain redistribution inside the bonder at high temperature to ensure consistent operation. The feasibility of the system for temperature monitoring and crack detection in real-world applications is also demonstrated on an industry-standard P91 pipe.