Ultra sensitive NO2 gas detection using the reduced graphene oxide coated etched fiber Bragg gratings

We report a simple and highly sensitive methodology for the room temperature NO2 gas sensing using reduced graphene oxide (RGO) coated clad etched fiber Bragg grating (eFBG). A significant shift (>10 pm) is observed in the reflected Bragg wavelength (lambda(B)) upon exposing RGO coated on the surface of eFBG to the NO2 gas molecules of concentration 0.5 ppm. The shift in Bragg wavelength is due to the change in the refractive index of RGO by charge transfer from the adsorbing NO2 molecules. The range of NO2 concentration is tested from 0.5 ppm to 3 ppm and the estimated time taken for 50% increase in Delta lambda(B) ranges from 20 min (for 0.5 ppm) to 6 min (for 3 ppm). (C) 2015 Elsevier B.V. All rights reserved.

Fiber Bragg Grating Sensor Package for Submicron Level Displacement Measurements

In this article, the design and development of a Fiber Bragg Grating (FBG) based displacement sensor package for submicron level displacement measurements are presented. A linear shift of 12.12 nm in Bragg wavelength of the FBG sensor is obtained for a displacement of 6 mm with a calibration factor of 0.495 mu m/pm. Field trials have also been conducted by comparing the FBG displacement sensor package against a conventional dial gauge, on a five block masonry prism specimen loaded using three-point bending technique. The responses from both the sensors are in good agreement, up to the failure of the masonry prism. Furthermore, from the real-time displacement data recorded using FBG, it is possible to detect the time at which early creaks generated inside the body of the specimen which then prorogate to the surface to develop visible surface cracks; the respective load from the load cell can be obtained from the inflection (stress release point) in the displacement curve. Thus the developed FBG displacement sensor package can be used to detect failures in structures much earlier and to provide an adequate time to exercise necessary action, thereby avoiding the possible disaster.

光纤Bragg光栅液氦环境下温度传感特性的研究

进行了液氦温度（4．2K）到室温（298K）温区内光纤Bragg光栅（FHG）温度传感性能的实验研究。重点分析了液氦温度（4．2K）到液氮温度（77K）FBG的温度传感特性。实验表明：FHG传感特性与温度相关。在50K以下，温度响应基本没有变化；50K-77K，波长偏移量随温度上升变化不规律；150K-298K传感特性近似成线性。对比裸光栅与涂敷光栅，涂敷光栅的温度灵敏度远大于裸光栅的温度灵敏度。选用外加热膨胀系数大的聚合物封装，可以显著提高FHG的温敏系数和线性度。

光纤Bragg光栅在77K环境下的温度传感性能研究

进行了从液氮温度(77 K)到室温(286 K)的光纤Bragg光栅(FBG)温度传感性能的实验研究。结果表明,FBG的温敏系数与温度相关。低于210 K,FBG的温敏系数变小,这将限制低温环境下FBG作为温度传感器的使用。通过在裸FBG外部涂敷热膨胀系数为61×10-6的丙烯酸脂材料,可以显著提高FBG的温敏系数和线性度。80 K时,有丙烯酸脂包层材料的FBG温敏系数为0.01526 nm/K,而同温度条件下裸FBG的温敏系数仅为0.00449 nm/K。

液氮温度光纤Bragg光栅的应变传感特性

对光纤Bragg光栅（FBG）液氮（77 K）下的应变传感技术及应变特性进行了研究.实验和分析表明：常温下FBG反射谱中的单个中心峰在低温下会劈裂为多峰,它产生于光纤、粘贴胶和金属基底热膨胀系数间的差异引起的强烈非均匀热弹性应变,使常温下均匀的光栅变啁啾化.建立了多种技术手段,成功消除了低温多峰现象,并测得了FBG低温和常温下的应变传感特性.实验结果表明：FBG的应变灵敏系数与温度无关.

Proof of Concept of Impact Detection in Composites Using Fiber Bragg Grating Arrays

Impact detection in aeronautical structures allows predicting their future reliability and performance. An impact can produce microscopic fissures that could evolve into fractures or even the total collapse of the structure, so it is important to know the location and severity of each impact. For this purpose, optical fibers with Bragg gratings are used to analyze each impact and the vibrations generated by them. In this paper it is proven that optical fibers with Bragg gratings can be used to detect impacts, and also that a high-frequency interrogator is necessary to collect valuable information about the impacts. The use of two interrogators constitutes the main novelty of this paper.

Fiber Bragg Gratings, IT Techniques and Strain Gauge Validation for Strain Calculation on Aged Metal Specimens

This paper studies the feasibility of calculating strains in aged F114 steel specimens with Fiber Bragg Grating (FBG) sensors and infrared thermography (IT) techniques. Two specimens have been conditioned under extreme temperature and relative humidity conditions making comparative tests of stress before and after aging using different adhesives. Moreover, a comparison has been made with IT tecniques and conventional methods for calculating stresses in F114 steel. Implementation of Structural Health Monitoring techniques on real aircraft during their life cycle requires a study of the behaviour of FBG sensors and their wiring under real conditions, before using them for a long time. To simulate aging, specimens were stored in a climate chamber at 70 degrees C and 90% RH for 60 days. This study is framed within the Structural Health Monitoring (SHM) and Non Destructuve Evaluation (NDE) research lines, integrated into the avionics area maintained by the Aeronautical Technologies Centre (CTA) and the University of the Basque Country (UPV/EHU).

Influence of Humidity on Fiber Bragg Grating Sensors

We demonstrate the influence of the relative humidity (RH) on the wavelength of fiber Bragg grating sensors (FBGS), performing tests with five FBGS at different humidity and temperature conditions. These tests were performed in a climate chamber whose RH changes according to a scheduled profile from 30% to 90%, in steps of 10%. These profiles were repeated for a wide range of temperatures from to , in steps of . Two different types of instrumentation methods have been tested, spot welding and epoxy bonding, in two different materials, steel and carbon fiber reinforced polymer (CFRP). We discuss the results for each type of sensor and instrumentation method by analyzing the linearity of the Bragg wavelength with RH and temperature.

Fabricación de una boya marina en biocomposite de fibra y resina naturales

En el presente TFG se ha construido una boya marina con fibras de lino y resina de origen natural. Para ello en el TFG se ha seguido el esquema para un estudio experimental dividido principalmente en tres puntos: Memoria ( Introducción, Estado del arte, Objetivos, Parte experimental, Conclusiones, Futuros estudios), Presupuesto (Fabricación del molde y de la boya) y Anexos (Fichas técnicas y de seguridad de los materiales). La idea de fabricar una boya marina en biocomposites surge de la diversidad de aplicaciones que estas tienen y como visión medioambiental, siendo esta una alternativa al uso de polimeros dependientes del petróleo. Para su construcción primero se ha fabricado un molde con fibra de vidrio, mediante el método de moldeo por contacto a mano, a partir de una boya de polietileno. Y sobre este molde, mediante el método de infusión, se ha fabricado la mitad de la boya marina con biocomposites.

Aperiodic structures in optics and integrated optics and the transverse Bragg reflector laser

The first part of this work describes the uses of aperiodic structures in optics and integrated optics. In particular, devices are designed, fabricated, tested and analyzed which make use of a chirped grating corrugation on the surface of a dielectric waveguide. These structures can be used as input-output couplers, multiplexers and demultiplexers, and broad band filters.

Next, a theoretical analysis is made of the effects of a random statistical variation in the thicknesses of layers in a dielectric mirror on its reflectivity properties. Unlike the intentional aperiodicity introduced in the chirped gratings, the aperiodicity in the Bragg reflector mirrors is unintentional and is present to some extent in all devices made. The analysis involved in studying these problems relies heavily on the coupled mode formalism. The results are compared with computer experiments, as well as tests of actual mirrors.

The second part of this work describes a novel method for confining light in the transverse direction in an injection laser. These so-called transverse Bragg reflector lasers confine light normal to the junction plane in the active region, through reflection from an adjacent layered medium. Thus, in principle, it is possible to guide light in a dielectric layer whose index is lower than that of the surrounding material. The design, theory and testing of these diode lasers are discussed.