Recent Advances in Distributed Acoustic Sensing Based on Phase-Sensitive Optical Time Domain Reflectometry

Distributed acoustic sensing (DAS) using coherent Rayleigh backscattering in an optical fiber has become a ubiquitous technique for monitoring multiple dynamic events in real time. It has continued to constitute a steadily increasing share of the fiber-optic sensor market, thanks to its interesting applications in many safety, security, and integrity monitoring systems. In this contribution, an overview of the recent advances of research in DAS based on phase-sensitive optical time domain reflectometry (ϕ-OTDR) is provided. Some advanced techniques used to enhance the performance of ϕ-OTDR sensors for measuring backscattering intensity changes through reduction of measurement noise are presented, in addition to methods used to increase the dynamic measurement capacity of ϕ-OTDR schemes beyond conventional limits set by the sensing distance. Recent ϕ-OTDR configurations which significantly enhance the measurement spatial resolution, including those which decouple it from the probing pulse width, are also discussed. Finally, a review of recent advances in more precise quantitative measurement of an external impact based on frequency shift and phase demodulation methods using simple direct detection ϕ-OTDR schemes is given

Distributed Fiber Ultrasonic Sensor and Pattern Recognition Analytics

Ultrasound interrogation and structural health monitoring technologies have found a wide array of applications in the health care, aerospace, automobile, and energy sectors. To achieve high spatial resolution, large array electrical transducers have been used in these applications to harness sufficient data for both monitoring and diagnoses. Electronic-based sensors have been the standard technology for ultrasonic detection, which are often expensive and cumbersome for use in large scale deployments. Fiber optical sensors have advantageous characteristics of smaller cross-sectional area, humidity-resistance, immunity to electromagnetic interference, as well as compatibility with telemetry and telecommunications applications, which make them attractive alternatives for use as ultrasonic sensors. A unique trait of fiber sensors is its ability to perform distributed acoustic measurements to achieve high spatial resolution detection using a single fiber. Using ultrafast laser direct-writing techniques, nano-reflectors can be induced inside fiber cores to drastically improve the signal-to-noise ratio of distributed fiber sensors. This dissertation explores the applications of laser-fabricated nano-reflectors in optical fiber cores for both multi-point intrinsic Fabry–Perot (FP) interferometer sensors and a distributed phase-sensitive optical time-domain reflectometry (φ-OTDR) to be used in ultrasound detection. Multi-point intrinsic FP interferometer was based on swept-frequency interferometry with optoelectronic phase-locked loop that interrogated cascaded FP cavities to obtain ultrasound patterns. The ultrasound was demodulated through reassigned short time Fourier transform incorporating with maximum-energy ridges tracking. With tens of centimeters cavity length, this approach achieved 20kHz ultrasound detection that was finesse-insensitive, noise-free, high-sensitivity and multiplex-scalability. The use of φ-OTDR with enhanced Rayleigh backscattering compensated the deficiencies of low inherent signal-to-noise ratio (SNR). The dynamic strain between two adjacent nano-reflectors was extracted by using 3×3 coupler demodulation within Michelson interferometer. With an improvement of over 35 dB SNR, this was adequate for the recognition of the subtle differences in signals, such as footstep of human locomotion and abnormal acoustic echoes from pipeline corrosion. With the help of artificial intelligence in pattern recognition, high accuracy of events’ identification can be achieved in perimeter security and structural health monitoring, with further potential that can be harnessed using unsurprised learning

Fiber Optic Sensors and Fiber Lasers

The optical fiber industry is emerging from the market for selling simple accessories using optical fiber to the new optical-IT convergence sensor market combined with high value-added smart industries such as the bio industry. Among them, fiber optic sensors and fiber lasers are growing faster and more accurately by utilizing fiber optics in various fields such as shipbuilding, construction, energy, military, railway, security, and medical.This Special Issue aims to present novel and innovative applications of sensors and devices based on fiber optic sensors and fiber lasers, and covers a wide range of applications of optical sensors. In this Special Issue, original research articles, as well as reviews, have been published

Aplicações De Métodos De Sensoriamento De Vibração Baseados Em Técnicas

Orientadores: Fabiano Fruett, Claudio FloridiaTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: Sensores à fibra óptica distribuídos têm sido empregados para monitorar vários parâmetros, tais como temperatura, vibração, tensão mecânica, campo magnético e corrente elétrica. Quando comparados a outras técnicas convencionais, tais sensores são vantajosos devido a suas pequenas dimensões, imunidade a interferências eletromagnéticas, alta adaptabilidade, robustez a ambientes nocivos, dentre outros. Sensores acústicos distribuídos em particular são interessantes devido a sua capacidade em serem usados em aplicações tais como monitoração de saúde de estruturas e vigilância de perímetros. Através da análise em frequência da estrutura, por exemplo uma aeronave, uma ponte, um edifício ou mesmo máquinas em uma fábrica, é possível avaliar sua condição e detectar danos e falhas em um estágio primário. Tais soluções podem cobrir ambas as aplicações de detecção de intrusão e monitoração estrutural com mínimas adaptações no sistema sensor. Desta forma, vibrações e distúrbios pequenas estruturas com resolução de dezenas de centímetros e em grandes estruturas ou perímetros com alguns metros de resolução espacial e centenas de quilômetros de alcance podem ser detectadas. Outra característica útil desta solução baseada em fibra óptica é a possibilidade de ser combinada com técnicas de processamento digital de sinais, permitindo a detecção e localização de perturbações rápidas, reconhecimento de padrões de intrusão em tempo real e multiplexação de dados de superfícies estruturais para aplicações SHM. O principal objetivo desta tese é fazer uso desses recursos para empregar técnicas de DAS como soluções de tecnologias- chave para várias aplicações. Neste trabalho, as técnicas de phase-OTDR foram estudadas e as principais contribuições da tese focaram em trazer soluções inovadoras e validações para aplicações de vigilância e vigilância. Este doutorado teve um período sanduíche nas instalações da RISE Acreo AB, Estocolmo, Suécia, onde experimentos foram realizados e foi parte da 42ª Chamada CISB/Saab/CNPqAbstract: Distributed optical fiber sensors have been increasingly employed for monitoring several parameters, such as temperature, vibration, strain, magnetic field and current. When compared to other conventional techniques, these sensors are advantageous due to their small dimensions, lightweight, immunity to electromagnetic interference, high adaptability, robustness to hazardous environments, less complex data multiplexing, the feasibility to be embedded into structures with minimum invasion, the capability to extract data with high resolution from long perimeters using a single optical fiber and detect multiple events along the fiber. In particular, distributed acoustic sensors (DAS) based on optical time domain reflectometry (OTDR), are of high interest, due to their capability to be used in applications such as structural health monitoring (SHM) and perimeter surveillance. Through the frequency analysis of a structure, for instance an aircraft, a bridge, a building or even machines in a workshop, it is possible to evaluate its condition and detect damages and failures at an early stage. Also, OTDR based solutions for vibration monitoring can be easily adapted with minimum setup modifications to detect intrusion in a perimeter, a useful tool for surveillance of military facilities, laboratories, power plants and homeland security. The same OTDR technique can be used as a non-destructive diagnostic tool to evaluate vibrations and disturbances on both small structures with some dozens of centimeters¿ resolution and in big structures or perimeters with some meters of spatial resolution and hundreds of kilometers of reach. Another useful feature of this optical fiber based solution is the possibility to be combined with high-performance digital signal processing techniques, enabling fast disturbance detection and location, real-time intrusion pattern recognition and fast data multiplexing of structure surfaces for SHM applications. The main goal of this thesis is to make use of these features to employ DAS techniques as key enabling technologies solutions for several applications. In this work, OTDR based techniques were studied and the thesis main contributions were focused on bringing innovative solutions and validations for SHM and surveillance applications. This PhD had a sandwich period at Acreo AB, Stockholm, Sweden, where experimental tests were performed and it was part of the 42ª CISB/Saab/CNPq CalDoutoradoEletrônica, Microeletrônica e OptoeletrônicaDoutora em Engenharia Elétrica202816/2015-0CAPESCNP

Chirped-pulse phase-sensitive optical time domain reflectometry

El mundo actual funciona gracias a las grandes infraestructuras que dotan de energía y transporte seguros a sus ciudadanos. Dichas infraestructuras (presas, diques, gaseoductos, oleoductos, puentes, líneas de ferrocarril, carreteras…) típicamente presentan grandes dimensiones y es especialmente difícil monitorizar su buen funcionamiento y su salud estructural además de protegerlas de posibles amenazas. Los sensores distribuidos de fibra óptica son una solución fiable y rentable para esta problemática, ya que permiten medir vibraciones, deformaciones y temperatura a lo largo de todos los puntos de una fibra óptica estándar de comunicaciones. Los sensores de fibra óptica basados en scattering Rayleigh son particularmente útiles cuando las medidas deben ser realizadas en tiempo real, como por ejemplo en la detección y caracterización de vibraciones. En esta tesis, se ha realizado un estudio acerca de distintas soluciones y alternativas a las limitaciones de la tecnología OTDR. Se ha propuesto una nueva técnica, derivada de ésta, que ofrece unas prestaciones que superan notablemente a las de los sistemas OTDR tradicionales. Para ello, en primer lugar, se ha procedido a realizar un estudio en profundidad de los fundamentos y el estado del arte de las técnicas de monitorización basadas en Reflectometría Óptica en el Dominio del Tiempo (OTDR, por sus siglas en inglés) y, en particular, sobre la implementación sensible a la fase, también conocida como OTDR. Se ha estudiado la limitación en rango y resolución de los sistemas OTDR principalmente asociada a la aparición de efectos no lineales como la inestabilidad de modulación. Actualmente, un OTDR tradicional presenta una resolución máxima del orden de los 10 metros para un rango de medida del orden de pocas decenas de km (si no se aplica ningún tipo de técnica de amplificación distribuida). Además de estudiar esta limitación y a qué es debida, se han propuesto dos técnicas para mitigar los efectos perjudiciales de la MI. En primer lugar, se ha realizado un estudio del efecto de la forma de los pulsos ópticos empleados en el sensor en la traza retrodispersada en un OTDR. Se ha podido comprobar cómo los pulsos triangulares o gaussianos presentan mayor robustez que los pulsos rectangulares, tradicionalmente empleados, frente a la MI. En segundo lugar, se ha propuesto una técnica basada en el concepto de Amplificación de Pulsos Chirpeados (CPA, por sus siglas en inglés), que ha permitido desarrollar un OTDR con resoluciones milimétricas. Hasta el momento ningún OTDR había podido llegar a tales resoluciones, lo que abre un nuevo abanico de aplicaciones a la tecnología OTDR donde se requiera alta resolución espacial en la medida. También se ha estudiado la otra gran limitación de este tipo de sensores: su comportamiento no lineal ante una perturbación. Actualmente, salvo que se implementen técnicas de recuperación de fase o barridos en longitud de onda que implican más complejidad, coste y tiempo de medida, no es posible realizar medidas cuantificables de temperatura o deformaciones. Del mismo modo, tampoco se pueden realizar medidas acústicas reales. En este trabajo, en primer lugar, se propone emplear la técnica de Reconstrucción de Fase empleando Diferenciación Óptica Ultrarápida (PROUD, por sus siglas en inglés) para recuperar el campo complejo de una señal OTDR. Con esta medida, el sensor pasaría a comportarse de forma lineal sin la complejidad intrínseca de los métodos tradicionales de detección de fase. En segundo lugar, y de aquí viene el nombre de esta tesis doctoral, se propone el uso de pulsos chirpeados en los sensores OTDR. La nueva técnica llamada Chirped-Pulse OTDR, ha permitido la medida de forma lineal de cambios de temperatura y deformaciones, en un único disparo y sin la necesidad de realizar barridos en frecuencia o implementar detección coherente. A lo largo de este trabajo, se han alcanzado resoluciones de 0.5mK/4n y se ha demostrado la posibilidad de hacer medidas acústicas reales. También se han estudiado las limitaciones de esta técnica y propuesto varias soluciones. Se ha demostrado que el ruido de fase del láser empleado en el sistema, puede ser mitigado con esta nueva técnica. Además, se ha propuesto el uso de amplificación distribuida basada en scattering Raman estimulado para alcanzar rangos de medida mayores, hasta 75 km con una resolución espacial de 10 m

Contributions to the development of distributed sensors based on stimulated Brillouin scattering

RESUMEN: El objetivo principal de esta tesis es contribuir al desarrollo y la mejora del rendimiento de los sensores distribuidos basados en la dispersión Brillouin. Durante el desarrollo de este trabajo se han considerado diferentes áreas de mejora. En primer lugar, se han propuesto diversas configuraciones experimentales para superar algunas de las limitaciones típicas que tienen estos sensores, como son los efectos no locales en los sensores BOTDA o la aparición de sub-picos en el espectro de ganancia de Brillouin en sistemas basados en el dominio de frecuencia. Otro objetivo principal de este trabajo es aplicar diferentes enfoques de procesado para resolver problemáticas aún no resueltas, como la discriminación entre las medidas de temperatura y las de deformación obtenidas con los sensores Brillouin. Además, también se han estudiado algunos métodos alternativos al método tradicional basado en la aplicación de ajustes Lorentzianos para estimar el cambio de la frecuencia Brillouin. Finalmente, este trabajo también ha tratado de contribuir a la validación de los conocimientos adquiridos mediante la validación en escenarios reales, como aplicaciones de alta temperatura o detección de fugas en tuberías.ABSTRACT: The main objective of this thesis dissertation is to contribute to the development and improvement in the performance of distributed sensors based on Brillouin scattering. Different areas of improvement have been considered during the development of this work. First of all, various different experimental configurations have been proposed to overcome some traditional limitations of these sensors, such as non-local effects on Brillouin optical time domain analysis (BOTDA) sensors or appearance of sub-peaks on the Brillouin gain measured with systems based on the frequency domain. Another main objective of this work is applying different processing approaches in an attempt to solve open problems such as the discrimination between temperature and strain measurements obtained with Brillouin sensors. Additionally, it would be interesting to provide some faster and alternative methods to estimate the Brillouin shift in comparison to traditional method based on applying Lorentzian fittings. Finally, this work has also tried to contribute to the validation of the acquired knowledge by performing validations in real scenarios, such as high-temperature applications or leakage detection in pipelines.This work has been supported by the funding of the following entities and actions: • Universidad de Cantabria through the research grant Programa de Personal Investigador en Formación Predoctoral and research stays grants in Pamplona, Spain and in Aversa, Italy. • Agencia Estatal de Investigación through research project Sensores fotónicos para seguirdad y protección (TEC2016-76021-C2-2-R). • Ministerio de Economía y Competitividad through research project Sensores de fibra óptica para seguirdad y protección (TEC2013-47264-C2-1-R). • Gobierno de Cantabria through research project Detección de fugas en autovías del agua mediante sensores ópticos (FASO). • Fundación TTI through a research grant Patrocinio de actividades formativas en investigación científica y técnica. • Cost action td1001: Novel and reliable optical fibre sensor systems for future security and safety applications (OFSESA) through a research grant for a short term scientific mission to Aversa, Italy and through two grants for summer schools

Embedded fiber optic sensors for temperature monitoring of continuous casting mold

The continuous casting process has been widely used for most of the steel production in the world instead of conventional ingot casting/rolling. Traditionally, thermocouples are being widely used to monitor the mold temperature in the continuous casting which has the following drawbacks: large size, low spatial resolution, and single detection point. On the contrary, fiber optic sensors can be a promising solution to the continuous casting temperature monitoring owing to its advantage of compact size, high resolution, high-temperature survivability, etc. In this thesis, we successfully developed extrinsic Fabry-Perot interferometer (EFPI) sensor for point temperature sensing, and optical frequency domain reflectometry (OFDR) system for distributed temperature sensing. We embedded the optical fiber and fiber optic sensors in the copper slide using electrodeposition for continuous high-temperature sensing. The sensing principle and the fabrication of EFPI sensors was discussed. To verify the best method for sensor coating, three different coating methods were applied to optical fiber sensors before embedding. We observed that the sensitivity of embedded EFPI sensor with wax coating has been surprisingly enhanced more than 30 times. An experiment designed monitoring the casting process of aluminum was conducted, showing fast time response of the embedded EFPI sensor. Also the basic working principle, the nonlinear sweep compensation method and the data processing procedure of OFDR system. A calibration experiment of OFDR system was also demonstrated in this thesis. The OFDR system can achieve 1 cm spatial resolution --Abstract, page iii

A novel technique of optical frequency sweep linearization of a DFB laser for high resolution FMCW reflectometry

13301甲第4407号博士（学術）金沢大学博士論文本文Full 以下に掲載：1.Journal of Engineering and Applied Sciences (JEAS) 10(8) pp.3817-3522 MAY 2015. ARPN. 共著者：NOR AZLINAH BINTI MD LAZAM, Koichi Iiyama, Takeo Maruyama, Yosuke Kimura and Nguyen Van Tu 2.International Journal of Electrical and Electronics Engineering Research (IJEEER) 5(6) pp.1-10 DEC 2015. TRANS-STELLAR. 共著者：NOR AZLINAH BINTI MD LAZAM, Akihiro Igarashi, Nakamoto Atsushi, Takeo Maruyama and Koichi Iiyam