In this Letter, we report on a simple, but highly sensitive sensor based on two intrinsic Fabry–Perot interferometers (FPIs) inscribed in a standard single-mode optical fiber. A brief theoretical study on the Vernier effect is presented, in which a simulation of the sensitivity magnification factor dependence on the FPI’s length is performed. Based on the simulation results, the FPIs were fabricated using a custom micromachining setup that integrates a near-infrared femtosecond laser and a motorized XYZ platform. Using the Vernier effect, sensitivities of 145 pm/με and 927 pm/°C were obtained for strain and temperature, respectively. The sensor’s performance combined with its versatile and customizable configuration allows real-time and in situ strain and temperature monitoring under harsh environments.

In this paper, a network of 37 fiber Bragg grating (FBG) sensors is proposed for real-time, in situ, and operando multipoint monitoring of the surface temperature distribution on a pack of three prismatic lithium polymer batteries (LiPBs). Using the network, a spatial and temporal thermal mapping of all pack interfaces was performed. In each interface, nine strategic locations were monitored by considering a three-by-three matrix, corresponding to the LiPBs top, middle and bottom zones. The batteries were subjected to charge and discharge cycles, where the charge was carried out at 1.0 C, whereas the discharge rates were 0.7 C and 1.4 C. The results show that in general, a thermal gradient is recognized from the top to the bottom, but is less prominent in the end-of-charge steps. The results also indicate the presence of hot spots between two of the three batteries, which were located near the positive tab collector. This occurs due to the higher current density of the lithium ions in this area. The presented FBG sensing network can be used to improve the thermal management of batteries by performing a spatiotemporal thermal mapping, as well as by identifying the zones which are more conducive to the possibility of the existence of hot spots, thereby preventing severe consequences such as thermal runaway and promoting their safety. To our knowledge, this is the first time that a spatial and temporal thermal mapping is reported for this specific application using a network of FBG sensors.

We present the first Bragg gratings fabricated in two, three and five rings undoped PMMA microstructured polymer optical fibres (mPOFs) with relative low cost 266 nm Nd:YAG laser in the 850 nm region. The fibers were connectorised with commercial ferrules for easy coupling with silica patch cables. Temperature, humidity and strain sensitivities are measured and also the impact of ring structure and the diameter of POF on the characterization measurements are studied for potential applications. We also analyzed the effect of the number of hexagonal rings structure in gratings fabrication, noticing that larger number of rings lead to more difficulties to obtain strong gratings, where we consider this performance due to the scattering effects. We demonstrate Bragg gratings fabrication in 5-rings structure mPOF after 6 min by using 266 nm Nd:YAG laser whereas no Bragg gratings have been fabricated so far using 325 nm He-Cd laser system. Up to 30 dB relative reflected power gratings are obtained in two rings mPOF, showing good time stability and promising results for undoped mPOF applications.

We propose an optical fiber hydrostatic pressure sensor based on micro-cavities generated by the fiber fuse effect. The presented sensor is manufactured through the recycling of optical fiber destroyed by the fiber fuse effect, being, therefore, a cost-effective solution, when compared with other similar micro-cavity-based solutions. The developed sensor was characterized for pressures up to 20 kPa, showing a linear sensitivity coefficient of 0.47 ± 0.03 nm · kPa ^-1 , for pressure values below 8 kPa. Furthermore, we propose a new theoretical model to describe the behavior of the microcavities embedded in optical fibers. This allows us to solve the discrepancies, already identified by other authors, between the experimental results and the ones attained with the flat mirrors Fabry-Perot model. By this way, we were able to describe the sensor response, within the full dynamic range.

In this work, a fiber Bragg grating (FBG) based sensing system for wheelchair pressure ulcer prevention was developed. Six FBGs were strategically positioned in a wheelchair to monitor the more prominent bone areas, namely scapulas (right (SR) and left (SL)), ischiatic zone (right (IR) and left (IL)), and heels (right (HR) and left (HL)). The sensing architecture was tested by a female user during pressure relief exercises, to verify its effectiveness on pressure monitoring. The proposed system proves to be a compact and reliable solution for wheelchair pressure ulcer prevention, making it a suitable alternative to existing conventional electronic sensors, with the advantage of being immune to electromagnetic interferences and usable in humid environments. In addition to the pressure, the breathing rate was also monitored. By combining the proposed sensing architecture with a wheelchair user detection software, it is possible to create alerts for the user to know when a new position should be adopted, in order to relieve the pressure in a specific area, thus avoiding one of the biggest problems for such patients, pressure ulcers.