Contribution to the development of new photonic systems for fiber optic sensing applications

En este trabajo de doctorado se presentan nuevos sistemas y subsistemas de sensores de fibra óptica. Así, se proponen y desarrollan nuevas técnicas, componentes y tecnologías basadas en láseres de fibra con espejos distribuidos (random), fibras de cristal fotónico, estructuras de luz lenta, multiplexores de inserción y extracción (add and drop), conmutadores tele-alimentados por luz, reflectometría óptica tanto en el dominio del tiempo como de la frecuencia o filtros ópticos reconfigurables. También se han demostrado nuevas aplicaciones para estructuras de sensores tradicionales y técnicas de medida ya conocidas. Todas ellas dirigidas a la mejora del funcionamiento de los actuales transductores, redes de sensores y aplicaciones de monitorización de salud estructural. De este modo, y en primer lugar, se han desarrollado nuevos transductores puntuales. En concreto, dos sensores interferométricos basados en fibras de cristal fotónico y otro basado en una estructura resonante en anillo. También se han realizado diferentes redes de sensores utilizando OTDRs comerciales. Por un lado, se han multiplexado diferentes sensores utilizando una red en forma de bus y, por el otro, se ha interrogado de manera remota un sensor FLM/LPG a una distancia de 253 km sin necesidad de amplificación. Se han estudiado láseres basados en efecto de realimentación distribuida random (RDFB) para su uso en interrogación de sensores. Para ello, se han demostrado dos nuevos láseres multi-longitud de onda y también, por primera vez, se ha modulado un laser random. Después, se han demostrado experimentalmente varias redes de sensores de fibra óptica teniendo en cuenta los principales desafíos que estas presentan: multiplexar varios sensores en una misma red y permitir su monitorización de manera remota. En primer lugar, se han multiplexado sensores basados en la modulación de la intensidad óptica utilizando técnicas de multiplexación en dominio del tiempo. En segundo lugar, se han multiplexado sensores basados en fibras de cristal fotónico. En tercer lugar, se presentan tres nuevos métodos para la medida remota de sensores. Por último, se incluye la demostración de un conmutador de fibra óptica tele-alimentado a través de luz. Éste se utiliza en tres redes diferentes para añadir robustez e incrementar la versatilidad en la multiplexación. Finalmente, se han realizado tres pruebas de campo para aplicaciones de monitorización de salud estructural.In this PhD work, different new photonic systems and subsystems for fiber optic sensing are presented. The aim of this thesis has been to contribute to the fiber optic sensors field using modern techniques, components and technologies such as random fiber lasers, photonic crystal fibers, slow light structures, add and drop multiplexers, powered by light switches, optical frequency and time domain reflectometry or reconfigurable optical filters, among others. New applications of traditional sensing structures or techniques have been also demonstrated. All of them focused on improving the performance of current sensors transducers, multiplexing networks and structural health monitoring applications. Thus, new point transducers have been developed: two of them are interferometric sensors based on photonic crystal fibers; and another one is based on a fiber ring resonator structure. Fiber optic sensor networks using commercial OTDRs have been also explored. On the one hand, different sensors have been successfully multiplexed in the same bus network. And, on the other hand, a FLM/LPG sensor was remotely interrogated at a distance of 253 km without using amplification. Random distributed feedback (RDFB) lasers have been explored for sensors interrogation. Two multi-wavelength Raman fiber lasers suitable for sensors interrogation have been demonstrated. Also, a random fiber laser has been internally modulated for the first time. Then, some experimental demonstrations of fiber optic sensors networks have been carried out taking into account the principal challenges they pose: multiplexing a number of optical sensors in a single networks, and enabling the possibility of remote sensing. Firstly, intensity sensors using TDM technology have been multiplexed. Secondly, PCF sensors have been successfully multiplexed. Thirdly, three new approaches to enable remote sensing are presented. Finally, a remote powered by light fiber optic switch have been included in three networks in order to add robustness and multiplexing versatility.Este trabajo se ha llevado a cabo gracias a las aportaciones económicas recibidas de los siguientes organismos, entre otros: - Secretaría de Estado de Investigación, Desarrollo e Innovación, Ministerio de Economía y Competitividad de España a través del programa de Formación del Personal Investigador y asociado al proyecto de investigación TEC2010-20224-C02-01. - Universidad Pública de Navarra mediante las ayudas a tesis doctorares. - Acción Europea COST- TD1001: Novel and Reliable Optical Fibre Sensor Systems for Future Security and Safety Applications (OFSeSa) - También se ha recibido financiación del Proyecto de Investigación de la Secretaría de Estado de Investigación, Desarrollo e Innovación, Ministerio de Economía y Competitividad de España TEC2013-47264-C2-2-R, de Innocampus, del Proyecto Europeo SUDOE-ECOAL-Intereg Project ECOAL-MGT y de los Fondos FEDER.Programa Oficial de Doctorado en Tecnologías de las Comunicaciones (RD 1393/2007)Komunikazioen Teknologietako Doktoretza Programa Ofiziala (ED 1393/2007

Optical fibre-based sensors for oil and gas applications.

Oil and gas (O&G) explorations moving into deeper zones for enhanced oil and gas recovery are causing serious safety concerns across the world. The sensing of critical multiple parameters like high pressure, high temperature (HPHT), chemicals, etc., are required at longer distances in real-time. Traditional electrical sensors operate less effectively under these extreme environmental conditions and are susceptible to electromagnetic interference (EMI). Hence, there is a growing demand for improved sensors with enhanced measurement capabilities and also sensors that generates reliable data for enhanced oil and gas production. In addition to enhanced oil and gas recovery, the sensing technology should also be capable of monitoring the well bore integrity and safety. The sensing requirements of the O&G industry for improved sensing in deeper zones include increased transmission length, improved spatial coverage and integration of multiple sensors with multimodal sensing capability. This imposes problems like signal attenuation, crosstalks and cross sensitivities. Optical fibre-based sensors are expected to provide superior sensing capabilities compared to electrical sensors. This review paper covers a detailed review of different fibre-optic sensing technologies to identify a feasible sensing solution for the O&G industry

Jacquard-woven photonic bandgap fiber displays

We present an overview of photonic textile displays woven on a Jacquard loom, using newly discovered polymer photonic bandgap fibers that have the ability to change color and appearance when illuminated with ambient or transmitted light. The photonic fiber can be thin (smaller than 300 microns in diameter) and highly flexible, which makes it possible to weave in the weft on a computerized Jacquard loom and develop intricate double weave structures together with a secondary weft yarn. We demonstrate how photonic crystal fibers enable a variety of color and structural patterns on the textile, and how dynamic imagery can be created by balancing the ambient and emitted radiation. Finally, a possible application in security ware for low visibility conditions is described as an example

Optical fiber sensors and sensing networks: overview of the main principles and applications

Optical fiber sensors present several advantages in relation to other types of sensors. These advantages are essentially related to the optical fiber properties, i.e., small, lightweight, resistant to high temperatures and pressure, electromagnetically passive, among others. Sensing is achieved by exploring the properties of light to obtain measurements of parameters, such as temperature, strain, or angular velocity. In addition, optical fiber sensors can be used to form an Optical Fiber Sensing Network (OFSN) allowing manufacturers to create versatile monitoring solutions with several applications, e.g., periodic monitoring along extensive distances (kilometers), in extreme or hazardous environments, inside structures and engines, in clothes, and for health monitoring and assistance. Most of the literature available on this subject focuses on a specific field of optical sensing applications and details their principles of operation. This paper presents a more broad overview, providing the reader with a literature review that describes the main principles of optical sensing and highlights the versatility, advantages, and different real-world applications of optical sensing. Moreover, it includes an overview and discussion of a less common architecture, where optical sensing and Wireless Sensor Networks (WSNs) are integrated to harness the benefits of both worlds.This work was supported by FCT—Fundação para a Ciência e Tecnologia within the R&D Units Project Scope: UIDB/00319/2020

Suspended-core fibers for sensing applications

A brief review on suspended-core fibers for sensing applications is presented. A historical overview over the previous ten years about this special designed microstructure optical fiber is described. This fiber presents attractive optical properties for chemical/biological or gas measurement, but it can be further explored for alternative sensing solutions, namely, in-fiber interferometers based on the suspended-core or suspended-multi-core fiber, for physical parameter monitoring.info:eu-repo/semantics/publishedVersio

Investigations towards the development of a novel multimodal fibre optic sensor for oil and gas applications.

Oil and gas (O&G) explorations are moving into deeper zones of earth, causing serious safety concerns. Hence, sensing of critical multiple parameters like high pressure, high temperature (HPHT), chemicals, etc., are required at longer distances. Traditional electrical sensors operate less effectively under these extreme environmental conditions and are susceptible to electromagnetic interference (EMI). Compared to electrical sensors, fibre optic sensors offer several advantages like immunity to EMI, electrical isolation, ability to operate in harsh environmental conditions and freedom from corrosion. Existing fibre optical sensors in the O&G industry, based on step index single mode fibres (SMF), offer limited performance, as they operate within a narrow wavelength window. A novel multimodal sensor configuration, based on photonic crystal fibre (PCF) and utilising a multiwavelength approach, is proposed for the first time for O&G applications. This thesis reports computational and experimental investigations into the new multimodal sensing methodology, integrating both optical phase-change and spectral-change based approaches, needed for multi-parameter sensing. It includes investigations to improve the signal-to-noise ratio (SNR) by enhancing the signal intensity attained through structural, material and positional optimisations of the sensors. Waveguide related, computational investigations on PCF were carried out on different fibre optic core-cladding structures, material infiltrations and material doping to improve the signal intensity from the multimodal sensors for better SNR. COMSOL Multiphysics simulations indicated that structural and material modifications of the PCF have significant effects on light propagation characteristics. The propagation characteristics of the PCF were improved by modifying the geometrical parameters, and microstructuring the fibre core and cladding. Studies carried out on liquid crystal PCF (LCPCF) identified its enhanced mode confinement characteristics and wavelength tenability features (from visible to near infrared), which can be utilised for multi-wavelength applications. Enhancing core refractive index of the PCF improved the electric field confinements and thereby the signal intensity. Doping rare earth elements into the PCF core increases its refractive index and also provides additional spectroscopic features (photoluminescence and Raman), leading to a scope for multi-point, multimodal sensors. Investigations were carried out on PCF-FBG (Fibre Bragg grating) hybrid configuration, analysing their capabilities for optical phase-change based, multipoint, multi-parameter sensing. Computational investigations were carried out using MATLAB software, to study the effect of various fibre grating parameters. These studies helped in improving understanding of the FBG reflectivity-bandwidth characteristics, for tuning the number of sensors that can be accommodated within the same sensing fibre and enhancing the reflected signal for improved SNR. A new approach of FBG sensor positioning has been experimentally evaluated, to improve its strain sensitivity for structural health monitoring (SHM) of O&G structures. Further, experimental investigations were carried out on FBGs for sensing multiple parameters like temperature, strain (both tensile and compressive) and acoustic signals. Various spectroscopic investigations were carried out to identify the scope of rare earth doping within the PCF for photoluminescence and Raman spectroscopy based multimodal sensors. Rare earth doped glasses (Tb, Dy, Yb, Er, Ce and Ho) were developed using melt-quench approach and excitation- photoluminescence emission studies were carried out. The studies identified that photoluminescence signal intensity increases with rare earth concentration up to an optimum value and it can be further improved by tuning the excitation source characteristics. Photoluminescence based temperature studies were carried out using the rare earth doped glasses to identify their suitability for O&G high temperature conditions. Raman spectroscopic investigations were carried out on rare earth (Tb) doped glasses, developed using both melt-quench and sol-gel based approaches. Effect of 785 nm laser excitation on Raman signatures and suitability of rare earth doped materials for fibre-based Raman distributed temperature sensing (DTS) were also studied. Finally, a novel multimodal fibre optic sensor configuration is proposed for the O&G applications, consisting of rare earth doped photonic crystal fibre integrating Bragg gratings and operating in multiple wavelength regimes in a multiplexed fashion. The integrated sensor combination is expected to overcome the limitations of existing sensors with regards to SNR, sensing range and multimodal sensing capability

Femtosecond Laser Micromachining of Advanced Fiber Optic Sensors and Devices

Research and development in photonic micro/nano structures functioned as sensors and devices have experienced significant growth in recent years, fueled by their broad applications in the fields of physical, chemical and biological quantities. Compared with conventional sensors with bulky assemblies, recent process in femtosecond (fs) laser three-dimensional (3D) micro- and even nano-scale micromachining technique has been proven an effective and flexible way for one-step fabrication of assembly-free micro devices and structures in various transparent materials, such as fused silica and single crystal sapphire materials. When used for fabrication, fs laser has many unique characteristics, such as negligible cracks, minimal heat-affected-zone, low recast, high precision, and the capability of embedded 3D fabrication, compared with conventional long pulse lasers. The merits of this advanced manufacturing technique enable the unique opportunity to fabricate integrated sensors with improved robustness, enriched functionality, enhanced intelligence, and unprecedented performance. Recently, fiber optic sensors have been widely used for energy, defense, environmental, biomedical and industry sensing applications. In addition to the well-known advantages of miniaturized in size, high sensitivity, simple to fabricate, immunity to electromagnetic interference (EMI) and resistance to corrosion, all-optical fiber sensors are becoming more and more desirable when designed with characteristics of assembly free and operation in the reflection configuration. In particular, all-optical fiber sensor is a good candidate to address the monitoring needs within extreme environment conditions, such as high temperature, high pressure, toxic/corrosive/erosive atmosphere, and large strain/stress. In addition, assembly-free, advanced fiber optic sensors and devices are also needed in optofluidic systems for chemical/biomedical sensing applications and polarization manipulation in optical systems. Different fs laser micromachining techniques were investigated for different purposes, such as fs laser direct ablating, fs laser irradiation with chemical etching (FLICE) and laser induced stresses. A series of high performance assembly-free, all-optical fiber sensor probes operated in a reflection configuration were proposed and fabricated. Meanwhile, several significant sensing measurements (e.g., high temperature, high pressure, refractive index variation, and molecule identification) of the proposed sensors were demonstrated in this dissertation as well. In addition to the probe based fiber optic sensors, stress induced birefringence was also created in the commercial optical fibers using fs laser induced stresses technique, resulting in several advanced polarization dependent devices, including a fiber inline quarter waveplate and a fiber inline polarizer based on the long period fiber grating (LPFG) structure

Lab-on-fiber technology: a new avenue for optical nanosensors

The "lab-on-fiber" concept envisions novel and highly functionalized technological platforms completely integrated in a single optical fiber that would allow the development of advanced devices, components and sub-systems to be incorporated in modern optical systems for communication and sensing applications. The realization of integrated optical fiber devices requires that several structures and materials at nano- and micro-scale are constructed, embedded and connected all together to provide the necessary physical connections and light-matter interactions. This paper reviews the strategies, the main achievements and related devices in the lab-on-fiber roadmap discussing perspectives and challenges that lie ahead

Coaxial cable Bragg grating

In order to ensure the continued safe and reliable operation of various civil structures, such as dams, bridges, and buildings, in situ strain monitoring is of great importance, especially for structures that may experience large strains. A new coaxial cable Bragg grating (CCBG) is developed as a strain sensor and the sensor\u27s capacity for large range strain measurement is demonstrated for the first time. The sensor device is comprised of regularly spaced periodic discontinuities along a coaxial cable. The discontinuities are fabricated using a computer numerical controlled (CNC) machine to drill holes in the cable. Each discontinuity generates a weak reflection to the electromagnetic wave propagating inside the cable. Superposition of these weak reflections produces a strong reflection at discrete frequencies that can be explained by Bragg grating theory. A positive feedback oscillation system is also developed to enhance the measurement accuracy. The Q-factor was enhanced by 3500 times in this case. By monitoring the resonant frequency shift of the sensor\u27s reflection or transmission spectra using the oscillation system, strain measurement sensitivity of 20με and a dynamic range of 50000με (5%) were demonstrated for axial strain measurements. The temperature responses of various types of CCBGs have also been investigated. The experimental results show that the CCBG sensors perform well for large strain measurement needed in structural health monitoring (SHM) --Abstract, page iii

Experimental and theoretical analysis of polarization-maintaining fibre for sensing applications

Fibre optic sensors have been developed extensively over the past several decades, showing their potential and suitability for real-time measurement and thus meeting various industrial challenges. This has been achieved through the continuous innovation both in the fibre structural design and in the exploration of a variety of sensing mechanisms employed. Optical fibre sensors have shown advantages over conventional electrical counterparts by being of small size, immunity to electromagnetic interference and resistance to chemical attack, thus revealing their potential for a range of industrial applications. High-birefringence (Hi-Bi) optical fibres represent an important type of specialist fibres that have been explored widely by researchers. The focus of this thesis is to explore their potential for different sensing applications as the birefringence of these polarization maintaining (PM) fibres varies in response to the change in the surrounding environment, such as force and pressure. Extensive evaluation of high-birefringence optical fibres, such as those with an elliptical core or elliptical inner cladding, Bow-Tie, Panda and Hi-Bi Photonic Crystal Fibres (PCFs), has been made both experimentally and theoretically, using numerical or analytical techniques. In this thesis, the material birefringence of Polarization-Maintaining fibres, e.g. PM side hole fibre(s) with one or two hole(s) located in its cladding, is calculated using a thermo-elastic displacement potential method through the superposition of sectional displacement potentials. These PM fibres have shown the potential for pressure/force measurement based on their birefringence characteristics when exposed to a transverse force. The methodology used is generic and thus applicable to any one-hole fibre structures, should the hole diameter or position vary in the fibre cladding, or the fibre hole be empty or filled in with any material. This enables the analysis to be applied more widely in a range of optical fibre sensor applications. Direct measurement of transverse force through the interrogation of induced birefringence variation has also been investigated in this thesis by using two specialist single mode Polarisation-Maintaining (PM) side-hole(s) fibres and four different types of Hi-Bi and low-Bi PCFs. The variation in the pressure sensitivity of these PM fibres has been investigated both theoretically and experimentally and it was confirmed that they are dependent upon several key parameters of the system, including the fibre structure, the magnitude and the direction of the applied external force, the fibre length used and the birefringence of the fibre. The theoretical data obtained have shown a good agreement with those from experiments, confirming the suitability of the use of such PM fibres for the measurement of pressure, force and mass of an object, applied in different directions, over a wide range and in real time. It is concluded based on the theoretical and experimental data obtained that PCFs of low birefringence are more sensitive than those of high birefringence (Hi-Bi) although the former require a longer length to achieve a similar level of birefringence. Compared to conventional Hi-Bi fibres (e.g. Panda and Bow-Tie fibres), PCFs have demonstrated much lower temperature sensitivity and this suggests that they are well suited to measure pressure, force, and mass in real time when temperature varies by using a fibre loop mirror (FLM) configuration. To solve the length problem in the low birefringence PCFs, a joint PCF approach can be used by fusion-splicing a short length of Low-Bi with a short section of a Hi-Bi PCF and their sensitivity to lateral pressure has been investigated and reported in detail in this thesis