Application of Raman and Brillouin Scattering Phenomena in Distributed Optical Fiber Sensing

We present a review of the basic operating principles and measurement schemes of standalone and hybrid distributed optical fiber sensors based on Raman and Brillouin scattering phenomena. Such sensors have been attracting a great deal of attention due to the wide industrial applications they offer, ranging from energy to oil and gas, transportation and structural health monitoring. In distributed sensors, the optical fiber itself acts as a sensing element providing unique measurement capabilities in terms of sensing distance, spatial resolution and number of sensing points. The most common configuration exploits optical time domain reflectometry, in which optical pulses are sent along the sensing fiber and the backscattered light is detected and processed to extract physical parameters affecting its intensity, frequency, phase, polarization or spectral content. Raman and Brillouin scattering effects allow the distributed measurement of temperature and strain over tens of kilometers with meter-scale spatial resolution. The measurement is immune to electromagnetic interference, suitable for harsh environments and highly attractive whenever large industrial plants and infrastructures have to be continuously monitored to prevent critical events such as leakages in pipelines, fire in tunnels as well as structural problems in large infrastructures like bridges and rail tracks. We discuss the basic sensing mechanisms based on Raman and Brillouin scattering effects used in distributed measurements, followed by configurations commonly used in optical fiber sensors. Hybrid configurations which combine Raman and Brillouin-based sensing for simultaneous strain and temperature measurements over the same fiber using shared resources will also be addressed. We will also discuss advanced techniques based on pulse coding used to overcome the tradeoff between sensing distance and spatial resolution affecting both types of sensors, thereby allowing measurements over tens of kilometers with meter-scale spatial resolution, and address recent advances in measurement schemes employing the two scattering phenomena

Novel Specialty Optical Fibers and Applications

Novel Specialty Optical Fibers and Applications focuses on the latest developments in specialty fiber technology and its applications. The aim of this reprint is to provide an overview of specialty optical fibers in terms of their technological developments and applications. Contributions include:1. Specialty fibers composed of special materials for new functionalities and applications in new spectral windows.2. Hollow-core fiber-based applications.3. Functionalized fibers.4. Structurally engineered fibers.5. Specialty fibers for distributed fiber sensors.6. Specialty fibers for communications

Optimization of multicore optical fibers with fiber Bragg gratings towards bend and shape sensing

A shape sensor based on fiber Bragg gratings (FBGs) in multicore fibers is a complex device with multiple factors which have to be accounted for a successful measure- ment system. In this dissertation, I considered several aspects of such shape and curvature sensors

Generation and characterization of cylindrical vector beams in few-mode fiber

For the past many decades, the Gaussian laser beam has driven major scientific discoveries that revolutionized the world of optics and photonics. In recent years, there is a burgeoning transformation where significant research has been dedicated in discovering the complex properties of cylindrical vector beams (CVBs). Increasingly, a beam of light with its intensity profile taking the shape of a single doughnut ring has attracted attention of several researchers the world over. Particularly, the so-called CVBs exhibit unique properties when focused owing to their radial and azimuthal distribution of polarization. In comparison to conventional (Gaussian-like) beams inheriting homogeneous polarization, CVBs provide unique light-matter interactions. For example, a radially polarized beam can enhance the imaging resolution of the system significantly with their spatial inhomogeneous polarization by imparting a symmetric and high numerical aperture focus. Moreover, CVBs with their phase and intensity singularities have found broad applications in quantum optics, optical micro/nano-manipulation, surface plasmon polariton, super-resolution imaging, and high-capacity fiber-optic communication. The studies of most widely used CVBs have been explored both in free space optics as well as in guided fiber optics. Further developments will require reliable techniques to generate these CVBs with strong coupling efficiency, high mode purity and high-power handling. For the past few years, the design, fabrication and study of optical fibers that supports CVBs, vortex and orbital angular momentum (OAM) beams have come to the forefront of research in this area. This is true in a sense that mode division multiplexing (MDM) is considered as a preeminent solution to the data capacity limitations faced by the standard single-mode fiber. In addition, vector beams in optical fibers constitute the fundamental basis set of linearly polarized (LP) modes (within the scalar approximation) as well as modes carrying OAM which represent another potential approach for implementing MDM based communications. Therefore, fundamental information and control over the vector beams is key to unravel future fiber communication links and CVB based fiber-optic sensors. For this purpose, it is essential to develop efficient methods to generate these CVBs. Some of the current methods reported for the generation of CVBs employ spiral phase plate, spatial light modulator (SLM), and offset fiber coupling. This thesis elucidates the generation as well as the optical characterization of such propagating cylindrical vector beams in a few-mode fiber. The ultimate purpose would be to develop simple, flexible and cost-effective photonic devices that will allow the efficient generation and stable propagation of the CVB while reducing the overall losses incurred by the system. Most of the methods reported earlier were limited to the measurements of the scalar LP mode groups of a FMF, thus neglecting the underlying vector beams that require delicate spectral and spatial control in order to be detected. In this thesis, three different techniques have been utilized for the generation of CVBs and OAM beams with high output purity. Initially, a tunable mechanical mode converter has been fabricated to demonstrate the generation of cylindrical vector beams supported by FMF in the telecom spectral range. This photonic device is utilized to demonstrate the non-destructive nonlinear characterization of CVB by utilizing the phenomenon of stimulated Brillouin scattering for the first time. We showed how the Brillouin gain spectra of the vector beams in some specialty fibers can be independently identified, measured, and subsequently exploited to probe the corresponding effective refractive indices of the vector beam retrieved from the data. This new characterization method of individual vector beam will have an impact in both light-wave and FMF-based optical sensing applications, which at present, mostly rely on the scalar LP modes. Further, a simple and low-cost technique to generate CVBs via long period fiber grating (LPFG) with very small grating pitch is reported. This work demonstrates that the cost-effective electric arc writing method for the fabrication of LPFGs is open to specialty few-mode fiber that often calls for very small pitch values. Finally, the generation of perfect cylindrical vector beams (PCVB) is demonstrated whose beam profile (i.e. transverse intensity profile) can be easily and precisely controlled. The latter novel method was used in-order to increase the free space coupling efficiency demanded by some specialty FMFs. The tailoring of the beam width and radius is performed via an iris and a diffractive phase mask implemented on a programmable SLM. The technique proposed towards the generation of PCVBs is highly adaptable for its robust nature to generate any arbitrary PCBs as well as perfect vortex beams with any topological order, using the same experimental setup. This experimental analysis is supported and validated via a rigorous theoretical framework that is in concordance with the results obtained

Optical Fiber Based Sensors for Harsh Environments

The primary objective of this study is to develop optical fiber-based sensors that are capable of operating in extreme conditions. Silica-based optical fibers are well known for their resilience to harsh environments. Whether they are integrated into distributed sensing schemes or as point sensors, optical fibers offer low-costs, highly accurate sensing platforms for various physical quantities. In this dissertation, state-of–the-art Al-doped radiation sensitive optical fibers for distributed ionizing radiation measurements are presented for the first time. This optical fiber sensor, coupled with a Rayleigh scattering-based optical frequency domain reflectometry (OFDR) scheme, was used to monitor and quantitate ionizing gamma radiation from a 60Co radioactive isotope. An alternative multi-core optical fiber was deployed to simultaneously monitor two different parameters. The dual-core fiber has been fabricated with two distinct optical cores to allow for differences between the cores’ temperature and strain coefficients. With such differences, temperature and strain changes were discriminated using a Brillouin scattering time domain analyzer (B-OTDA). Ultrafast lasers are commonly used to inscribe thermally stable nanostructures on optical fibers’ cores. IR laser-induced structures inscribed on low-loss, radiation-hard silica fibers were used to develop point and distributed sensors for in-pile nuclear reactor measurements. The sensors were subjected to, arguably the most challenging of artificial environments, with temperatures above 600°C, and high neutron fluxes at levels above 1.2×1014 n/s/cm2. The sensors were also used to monitor the temperature distribution inside of a solid oxide fuel cell (SOFC). The information obtained from the operational SOFC can be used to prolong its lifetime and increase its efficiency. Lastly, additive manufacturing embedding of optical fibers into metallic parts were attempted. A nickel-iron alloy, Invar-36, was investigated as a coating material for silica. The coefficient of thermal expansion (CTE) of Invar-36 can be carefully engineered to be close to that of silica. With a reduced CTE mismatch at the glass-metal interface, problems of adhesion and delamination can be deterred to extreme conditions. The proposed sensor designs and implementations would allow monitoring complex structures, and harsh environments like in SOFCs, gas turbines, robotics, or in high performance machinery, with minimal invasiveness

Distributed optical fibre sensing system for civil and geotechnical Infrastructures

Les capteurs à fibre optique distribués (DFS) tirant parti des mécanismes de diffusion se produisant dans l’élément détecteur de fibre, à savoir la diffusion de Rayleigh, Raman et Brillouin, ont été un sujet de recherche intense au cours des trois dernières décennies. Ils offrent de nombreuses applications pratiques classées en raison des avantages inhérents, tels que la petite taille, le poids léger, la sensibilité élevée, les performances excellentes, la durabilité intrinsèque dans des environnements difficiles, l’immunité aux interférences électromagnétiques (EMI), etc. En particulier, le DFS basé sur le processus de diffusion stimulée de Brillouin (SBS), appelé analyse temporelle optique de domaine de Brillouin (BOTDA), présente la capacité potentielle de réaliser la télédétection sur de longues distances, typiquement des dizaines de kilomètres et des centaines de kilomètres récemment. La fibre optique servant non seulement d’élément de détection, mais également de moyen de guidage de la lumière, est capable de détecter divers paramètres physiques d’intérêt, tels que la température, les contraintes, les pressions et les champs acoustiques. Ces measurandes peuvent être détectés directement ou indirectement le long de la fibre entière. Les systèmes de pergélisol dans le Nord canadien sont fortement perturbés par les changements climatiques dus au réchauffement de la planète; le dégel du pergélisol affecte à son tour les environnements et les communautés. Afin de réaliser une surveillance en temps réel de la stabilité des infrastructures, un réseau de détection BOTDA doté d'un nouveau transducteur à fibre optique est proposé pour surveiller les modifications physiques, notamment les pressions interstitielles, la température et le déplacement dans le pergélisol. Le principal défi consiste à mesurer simultanément les pressions d’eau interstitielle positive et négative, et à faire la distinction entre ces measurandes au sein d’un même transducteur. Lors de la première tentative, un polymère d'hydrogel est utilisé pour construire le transducteur, qui peut se dilater ou se contracter du fait de l'absorption ou de la libération d'eau par le matériau afin de détecter les pressions positives et négatives dans la plage cible de -100 kPa à +100 kPa le long d'un pergélisol système. Une fibre multi-cœur (MCF) bien conçue, incorporée dans le transducteur polymère, sera développée dans le but ultime de disposer de fonctionnalités de détection simultanée de plusieurs paramètres.Distributed optical fibre sensors (DOFS) taking advantage of the scattering mechanisms occurring within the fibre sensing element, i.e. Rayleigh, Raman and Brillouin scattering, have been an intense research subject over the last three decades. They offer widespread practical in-filed applications due to the inherent advantages possessed, such as small size, light weight, high sensitivity, excellent performance, intrinsic durability to harsh environment, immunity to electromagnetic interference (EMI), and so on. Particularly, the one based on stimulated Brillouin scattering (SBS) process, so-called Brillouin optical time-domain analysis (BOTDA), presents the potential capability to perform remote sensing over long distance, typically tens of kilometres and extended to hundreds of kilometres recently. Optical fibre acting as not only a sensing element but also as a light guidance medium is able to detect a variety of physical parameters of interest, such as temperature, strain, pressure and acoustic fields to name a few. These measurands can be sensed either by directly or indirectly along the whole fibre. Permafrost systems in Northern Canada are strongly disturbed by the climate changes due to global warming; the thawing permafrost is in turn affecting the environments and communities. In order to achieve real-time surveillance of the stability of infrastructures, a BOTDA sensing network with novel fibre transducer is proposed to monitor the physical changes including positive/negative pore water pressures, temperature and displacement along permafrost environments. The main challenge is to measure simultaneously the positive and negative pore water pressures and to discriminate among those measurands within a single transducer. As an initial attempt, a hydrogel polymer is deployed to build the transducer, which can expand or shrink due to water absorption or release by the material to detect positive and negative pressures in the target range of -100 kPa to +100 kilopascal along a permafrost system. A well-designed multi-core fibre (MCF) incorporated into the polymer tran

Recent developments in fibre optic shape sensing

This paper presents a comprehensive critical review of technologies used in the development of fibre optic shape sensors (FOSSs). Their operation is based on multi-dimensional bend measurements using a series of fibre optic sensors. Optical fibre sensors have experienced tremendous growth from simple bend sensors in 1980s to full three-dimensional FOSSs using multicore fibres in recent years. Following a short review of conventional contact-based shape sensor technologies, the evolution trend and sensing principles of FOSSs are presented. This paper identifies the major optical fibre technologies used for shape sensing and provides an account of the challenges and emerging applications of FOSSs in various industries such as medical robotics, industrial robotics, aerospace and mining industry

application of raman and brillouin scattering phenomena in distributed optical fiber sensing

We present a review of the basic operating principles and measurement schemes of standalone and hybrid distributed optical fiber sensors based on Raman and Brillouin scattering phenomena. Such sensors have been attracting a great deal of attention due to the wide industrial applications they offer, ranging from energy to oil and gas, transportation and structural health monitoring. In distributed sensors, the optical fiber itself acts as a sensing element providing unique measurement capabilities in terms of sensing distance, spatial resolution and number of sensing points. The most common configuration exploits optical time domain reflectometry, in which optical pulses are sent along the sensing fiber and the backscattered light is detected and processed to extract physical parameters affecting its intensity, frequency, phase, polarization or spectral content. Raman and Brillouin scattering effects allow the distributed measurement of temperature and strain over tens of kilometers with meter-scale spatial resolution. The measurement is immune to electromagnetic interference, suitable for harsh environments and highly attractive whenever large industrial plants and infrastructures have to be continuously monitored to prevent critical events such as leakages in pipelines, fire in tunnels as well as structural problems in large infrastructures like bridges and rail tracks. We discuss the basic sensing mechanisms based on Raman and Brillouin scattering effects used in distributed measurements, followed by configurations commonly used in optical fiber sensors. Hybrid configurations which combine Raman and Brillouin-based sensing for simultaneous strain and temperature measurements over the same fiber using shared resources will also be addressed. We will also discuss advanced techniques based on pulse coding used to overcome the tradeoff between sensing distance and spatial resolution affecting both types of sensors, thereby allowing measurements over tens of kilometers with meter-scale spatial resolution, and address recent advances in measurement schemes employing the two scattering phenomena

Monitoring of strain and temperature in an open pit using brillouin distributed optical fiber sensors

Marble quarries are quite dangerous environments in which rock falls may occur. As many workers operate in these sites, it is necessary to deal with the matter of safety at work, checking and monitoring the stability conditions of the rock mass. In this paper, some results of an innovative analysis method are shown. It is based on the combination of Distributed Optical Fiber Sensors (DOFS), digital photogrammetry through Unmanned Aerial Vehicle (UAV), topographic, and geotechnical monitoring systems. Although DOFS are currently widely used for studying infrastructures, buildings and landslides, their use in rock marble quarries represents an element of peculiarity. The complex morphologies and the intense temperature range that characterize this environment make this application original. The selected test site is the Lorano open pit which is located in the Apuan Alps (Italy); here, a monitoring system consisting of extensometers, crackmeters, clinometers and a Robotic Total Station has been operating since 2012. From DOFS measurements, strain and temperature values were obtained and validated with displacement data from topographic and geotechnical instruments. These results may provide useful fundamental indications about the rock mass stability for the safety at work and the long-term planning of mining activities

Design of optical fiber sensors and interrogation schemes

[ES] Las fibras ópticas son dispositivos muy utilizados en el campo de las telecomunicaciones desde su descubrimiento. En las últimas décadas, las fibras ópticas comenzaron a utilizarse como sensores fotónicos. Los primeros trabajos se centraron en la medición de unas dimensiones físicas en un punto específico. Posteriormente, surgió la posibilidad de medir las propiedades de la fibra óptica en diferentes puntos a lo largo de la fibra. Este tipo de sensores se definen como sensores distribuidos. Los componentes optoelectrónicos fueron desarrollados e investigados para telecomunicaciones. Los avances en las telecomunicaciones hicieron posible el desarrollo de sistemas de interrogación para sensores de fibra óptica, creciendo en paralelo con los avances de las telecomunicaciones. Se desarrollaron sistemas de interrogación de fibra óptica que permiten el uso de una única fibra óptica monomodo estándar como sensor que puede monitorear decenas de miles de puntos de detección al mismo tiempo. Los métodos que extraen la información de detección de la señal reflejada en la fibra óptica son los más empleados debido a la facilidad de acceso al sensor y la flexibilidad de estos sistemas. Los más estudiados son la reflectometría en dominios de tiempo y frecuencia. La reflectometría óptica en el dominio del tiempo (OTDR) fue la primera técnica utilizada para detectar la posición de los fallos en las redes de comunica-ción de fibra óptica. El OTDR sensible a la fase hizo posible detectar la elongación y la temperatura en una posición específica. Paralelamente, los gratings de Bragg (FBG) se convirtieron en los dispositivos más utilizados para implementar sensores en fibra óptica discretos. Se desarrollaron técnicas de multiplexación para realizar la detección en múltiples puntos utilizando FGBs. La reflectometría realizada interrogando arrays de FBG débiles demuestra que mejora el rendimiento del sistema en comparación al uso de una fibra monomodo. Los sistemas de interrogatorio actuales tienen algunos inconvenientes. Algunos de ellos son velocidad de interrogatorio limitada, grandes dimensiones y alto costo. En esta tesis doctoral se desarrollaron nuevos sistemas de interrogación y sensores de fibra óptica para superar algunos de estos inconvenientes. Los sensores de fibra óptica de plástico demuestran ser una plataforma innovadora para desarrollar nuevos sensores y sistemas de interrogación de bajo costo y fáciles de implementar para fibras de plástico comerciales. Se investigó la reflectometría en el dominio del tiempo y las técnicas fotónicas de microondas para la interrogación de una matriz de rejillas débiles que permitieron simplificar el sistema de interrogación para la detección de temperatura y vibración.[CA] Les fibres òptiques són dispositius molt utilitzats en el camp de les telecomunica-cions des del seu descobriment. En les últimes dècades, les fibres òptiques van començar a utilitzar-se com a sensors fotònics. Els primers treballs es van centrar en el mesurament d'unes dimensions físiques en un punt específic. Posteriorment, va sorgir la possibilitat de mesurar les propietats de la fibra òptica en diferents punts al llarg de la fibra. Aquest tipus de sensors es defineixen com a sensors distribüits. Els components optoelectrònics van ser desenvolupats i investigats per a telecomunicacions. Els avanços en les telecomunicacions van fer possi-ble el desenvolupament de sistemes d'interrogació per a sensors de fibra òptica, creixent en paral·lel amb els avanços de les telecomunicacions. Es van desenvolupar sistemes d'interrogació de fibra òptica que permeten l'ús d'una única fibra òptica monomodo estàndard com a sensor que pot monitorar desenes de milers de punts de detecció al mateix temps. Els mètodes que extreuen la informació de detecció del senyal reflectit en la fibra òptica són els més utilitzats a causa de la facilitat d'accés al sensor i la flexibilitat d'aquests sistemes. Els més estudiats són la reflectometría en dominis de temps i freqüència. La reflectometría òptica en el domini del temps (OTDR) va ser la primera tècnica utilitzada per a detectar la posició de les fallades en les xarxes de comunicació de fibra òptica. El OTDR sensible a la fase va fer possible detectar l'elongació i la temperatura en una posició específica. Paral·lelament, els gratings de Bragg (FBG) es van convertir en els dispositius més utilitzats per a implementar sensors en fibra òptica discrets. Es van desenvolupar tècniques de multiplexació per a realitzar la detecció en múltiples punts utilitzant FGBs. La reflectometría realitzada interrogant arrays de FBG febles demostra que millora el rendiment del sistema en comparació a l'ús d'una fibra monomodo. Els sistemes d'interrogatori actuals tenen alguns inconvenients. Alguns d'ells són velocitat d'interrogatori limitada, voluminositat i alt cost. En aquesta tesi doctoral es van desenvolupar nous sistemes d'interrogació i sensors de fibra òptica per a superar alguns d'aquests inconvenients. Els sensors de fibra òptica de plàstic demostren ser una plataforma innovadora per a desenvolupar nous sensors i siste-mes d'interrogació de baix cost i fàcils d'implementar per a fibres de plàstic comercials. Es va investigar la reflectometría en el domini del temps i les tècniques fotòniques de microones per a la interrogació d'una matriu de reixetes febles que van permetre simplificar el sistema d'interrogació per a la detecció de temperatura i vibració.[EN] Optical fibers are devices largely used in telecommunication field since their discovery. In the last decades, optical fibers started to be used as photonic sensors. The first works were focused on the measurement of physical dimensions to a specific point. Afterward, emerged the possibility to measure the optical fiber properties at different locations along the fiber. These kinds of sensors are defined as distributed sensors. The optoelectronic components were developed and investigated for telecommunications. The progress in telecommunication made possible the development of optical fiber sensors interrogation systems, growing in parallel with the advances of telecommunications. Optical fiber interrogation systems were developed to use a single standard monomode optical fiber as a sensor that can monitor tens of thousands of sensing points at the same time. The methods that extract the sensing information from the backscattered signal in the optical fiber are widely employed because of the easiness of access to the sensor element and the flexibility of these systems. The most studied are the reflectometry in time and frequency domains. The optical time domain reflectometry (OTDR) was the first technique used to detect the position of the failures in the optical fiber communication networks. Using phase sensitive OTDR it is possible to sense strain and temperature at a specific position. In parallel, fiber Bragg gratings (FBGs) became the most widely used devices to implement discrete optical fiber sensors. Multiplexing techniques were developed to perform multi points sensing using these gratings. The reflectometry performed interrogating weak FBGs arrays demonstrate to improve the performance of the system employing a single mode fiber. The interrogation systems nowadays have some drawbacks. Some of them are limited speed of interrogation, bulkiness, and high cost. New interrogation systems and optical fiber sensors were developed in this doctoral thesis to overcome some of these drawbacks. Plastic optical fiber sensors demonstrate to be an innovative platform to develop both new sensors and low cost, easy to implement interrogation systems for commercial plastic fibers. Reflectometry in time domain and microwave photonic techniques were investigated for the interrogation of weak gratings array allowed to simplify the interrogation system for the sensing of temperature and vibration.I would like to greatly thank the European Union’s Horizon 2020 Research and Innovation Program that funded the research described in this thesis under the Marie Sklodowska-Curie Action Grant Agreement 722509.Sartiano, D. (2021). Design of optical fiber sensors and interrogation schemes [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/161357TESI