Análise da influência do monitoramento OTDR em WDM-PON: um estudo baseado em simulação

Redes Ópticas Passivas estão cada vez mais difundidas como rede de acesso de banda larga. Devido à sua importância, tais redes necessitam constantemente de supervisão. Diversas técnicas vêm sendo empregadas para supervisão de redes ópticas, dentre as quais se destacam as que utilizam reflectometria, pois agregam vantagens, tais como: baixo custo, em comparação com outros métodos de supervisão, e não exigência de intervenção na casa do usuário. Esta dissertação apresenta uma estratégia capaz de quantificar, por meio de simulações, o impacto que a técnica de reflectometria no domínio do tempo gera como interferência em transmissões típicas de uma rede WDM-PON.

Estudio teórico y simulación de un OTDR para sistemas de comunicaciones por fibra óptica

El reflectómetro óptico en el dominio del tiempo, conocido por sus siglas en inglés como OTDR, es un dispositivo muy utilizado en sistemas de comunicaciones por fibra óptica para conocer de una manera rápida y sencilla como varía la potencia óptica a lo largo de la fibra óptica, siendo otro de sus usos frecuentes la localización de fallos y roturas en un enlace. Este proyecto fin de carrera, consiste en la realización mediante Matlab de una interfaz gráfica que permite simular un OTDR para distintos tipos de fibras, conectores y empalmes visualizándose por pantalla la variación de la potencia óptica en función de la distancia, pudiendo ampliar cualquier tramo del enlace que se desee visualizar con mayor detalle. Los objetivos del proyecto podemos establecerlos en dos partes. Primero, realizar una interfaz que nos permita diseñar un enlace de fibra óptica de forma sencilla, permitiendo además medir desde la atenuación de la fibra a la de un empalme. En segundo lugar, emplear la interfaz desarrollada para comprobar conceptos teóricos, haciendo hincapié en los principales errores de un enlace de fibra óptica real. Para una mejor visualización y concepción de lo implementado, es necesario revisar los principios básicos de funcionamiento de la fibra óptica y las principales características de un enlace, así como, los distintos dispositivos que lo componen, para después explicar el funcionamiento del OTDR y sus usos; por ello, en los capítulos segundo y tercero, se explican estas nociones básicas, necesarias para un mejor entendimiento del proyecto. Para poder utilizar la interfaz gráfica de usuario, el capítulo cuarto muestra la descripción de las funciones con parámetros, así como el manual de usuario de la interfaz gráfica. En el capítulo quinto se hace una recopilación y estudios de resultados para distintas simulaciones comprobando desde casos sencillos a casos extremos en los que se debe prestar una especial atención a los elementos que componen el enlace, siendo finalmente, en el sexto capítulo donde se presentan distintas conclusiones así como posibles trabajos futuros, a partir de lo realizado. ABSTRACT. The optical time domain reflectometer, known as OTDR, is a widely used device in systems for fiber optic communications used to know quick and simply how the optical power its varying along the fiber, with particular emphasis to another of its frequent uses in troubleshooting on a link. This final project consists in carrying through a graphical interface in Matlab to simulate an OTDR for different types of fibers, connectors and splices, visualizing the variation of optical power as a function of the distance. It is possible to zoom in specific sections to view them with greater detail. The project objectives can be set in two parts: - Make an interface that allows us to design a fiber optic link easily and measuring from the fiber attenuation to a splice one. - Use the interface developed to test theoretical concepts, emphasizing the most important mistakes of a real optical fiber link. For better visualization and understanding of what it’s been implemented, it is necessary to review the basic operating principles of fiber optics and the main characteristics of a fiber link, and also the different types of devices that comprise it, and then explaining also how the OTDR works and its uses, therefore, in second and third chapters, explains these basics needed for a better understanding of the project. To use the GUI, the fourth chapter shows the description of the functions with parameters and the user manual of the GUI. The fifth chapter is a compilation and study of some simulation results for simple cases to check from simply to extreme cases putting special attention to the elements that make up the link. To sum up, in the sixth chapter will appear different conclusions and possible future works for improving the graphical interface or making a new one.

SNR enhanced distributed vibration fiber sensing system employing polarization OTDR and ultraweak FBGs

A distributed fiber sensing system based on ultraweak FBGs (UWFBGs) assisted polarization optical time-domain reflectometry (POTDR) is proposed for load and vibration sensing with improved signal-to-noise ratio (SNR) and sensitivity. UWFBGs with reflectivity higher than Rayleigh scattering coefficient per pulse are induced into a POTDR system to increase the intensity of the back signal. The performance improvement of the system has been studied. The numerical analysis has shown that the SNR and sensitivity of the system can be effectively improved by integrating UWFBGs along the whole sensing fiber, which has been clearly proven by the experiment. The experimental results have shown that by using UWFBGs with 1.1 x 10-5 reflectivity and 10-m interval distance, the SNR is improved by 11 dB, and the load and vibration sensitivities of the POTDR are improved by about 10.7 and 9 dB, respectively.

An OTDR and gratings assisted multifunctional fiber sensing system

We report a distributed multifunctional fiber sensing network based on weak-fiber Bragg gratings (WFBGs) and long period fiber grating (LPG) assisted OTDR system. The WFBGs are applied for temperature, strain, and vibration monitoring at key position, and the LPG is used as a linear filter in the system to convert the wavelength shift of WFBGs caused by environmental change into the power change. The simulation results show that it is possible to integrate more than 4472 WFBGs in the system when the reflectivity of WFBGs is less than {10}^{-5}. Besides, the back-Rayleigh scattering along the whole fiber can also be detected which makes distributed bend sensing possible. As an experimental demonstration, we have used three WFBGs UV-inscribed with 50-m interval at the end of a 2.6-km long fiber, which part was subjected for temperature, strain, and vibration sensing, respectively. The ratio of the intensity of output and input light is used for temperature and strain sensing, and the results show strain and temperature sensitivities are 4.2 \times {10}^{-4}{/\mu \varepsilon } and 5.9 \times {10}^{-3}{{/ {^{\circ }}\textrm {C}}} , respectively. Detection of multiple vibrations and single vibration with the broad frequency band up to 500 Hz are also achieved. In addition, distributed bend sensing which could be simultaneously realized in this system has been proposed.

A distributed and key-position fiber sensing system based on LPFG and WFBG assisted OTDR

An enhanced fiber sensing system used for distributed bending and key-position sensing is reported by integrating WFBGs, LPFG and OTDR, which also achieves strain and temperature sensitivities up to 0.047mv/με and 0.675mv/°C respectively. © 2014 OSA.

基于光时域反射计的全分布式光纤漏油传感器

报道了一种基于光时域反射计的全分布式光纤漏油传感器,该传感器能实现分布式实时监测长输油管道,及时发现小型的漏油事件.传感器沿管道铺设,利用光时域反射计实时测量光纤在长度上的损耗变化特点,及时发现并定位管道上的每一处泄漏事件.模拟实验证明了其实际操作的可行性,长期使用的稳定性和各种抗干扰性,能在15min内发现并定位漏油事件,且定位准确度为3m.

Wavelength Coded Optical Time-Domain Reflectometry

This paper presents a wavelength coded optical timedomain reflectometry based on optical heterodyne technique. In this scheme, the probe and reference optical pulses have different wavelengths. This enables optical heterodyne detection to be used to improve the system performances significantly. We demonstrate a spatial resolution of 2.5 m within a range of 60 km in weak-reflection signal detection and direct observation of Brillouin scattering over a long optical fiber, suggesting online fiber sensing possible. The principle of wavelength coding is applicable to other systems like lidar and radar to increase receiver sensitivity and simplify system structure.

Distributed water ingress and water potential measurements using fibre optics

We report on a distributed moisture detection scheme which uses a cable design based on waterswellable hydrogel polymers. The cable modulates the loss characteristic of light guided within a multi-mode optical fibre in response to relative water potentials in the surrounding environment. Interrogation of the cable using conventional optical time-domain reflectometry (OTDR) instruments allows water ingress points to be identified and located with a spatial resolution of 50 cm. The system has been tested in a simulated tendon duct grouting experiment as a means of mapping the extent of fill along the duct during the grouting process. Voided regions were detected and identified to within 50 cm. A series of salt solutions has been used to determine the sensor behaviour over a range of water potentials. These experiments predict that measurements of soil moisture content can be made over the range 0 to – 1500 kPa. Preliminary data on soil measurements have shown that the sensor can detect water pressure changes with a resolution of 45 kPa. Applications for the sensor include quality assurance of grouting procedures, verification of waterproofing barriers and soil moisture content determination (for load-bearing calculations).

Sensores de pressão em fibra óptica para o estudo dos fenómenos da percolação da água em solos

Dada a necessidade de obtermos sistemas monitorizados com elevada precisão, de grande durabilidade e resistentes às condições atmosféricas, surgiu a possibilidade de aplicação das fibras ópticas como sensores para monitorização de pressão. Nesse contexto, as fibras “hetero-core” (fibra óptica composta por uma fibra multimodo entre duas fibras ópticas monomodo) e a utilização de lentes GRIN (“GRaded INdex”) em conjunto com superfícies reflectoras permitem a determinação da pressão e são objecto de estudo desta dissertação. Em termos de aplicação, o objectivo principal desta tese de mestrado foi de proporcionar o projecto e desenvolvimentos da medida de pressão em 48 pontos para um tanque de estudo dos fenómenos de percolação da água nos solos e que é pertencente à Secção de Geotecnia do Departamento de Engenharia Civil da Faculdade de Engenharia da Universidade do Porto. Inicialmente, foi caracterizado um sistema contendo uma fibra “hetero-core” à qual foi aplicada uma curvatura, com auxílio de uma carruagem micrométrica. Este sistema permitiu a simulação do mesmo efeito de aplicação de pressão à fibra “hetero-core”. Na configuração seguinte, usou-se um OTDR (“Optical Time Domain Reflectometer”) para visualização e registo das perdas encontradas durante o processo de dobrar e esticar da fibra “hetero-core”. Ao longo deste registo, várias configurações foram testadas até ser encontrada a cabeça sensora com melhor comportamento para monitorizar a pressão. A multiplexagem foi conseguida ao colocar dois sensores em série, sendo cada um deles constituído por uma fibra “hetero-core” colocada no fundo de um tubo de água disposto verticalmente. Com a adição da água no tubo de água, a curvatura na fibra “hetero-core” aumentava, notando-se claramente que as perdas também subiam. Os resultados obtidos nesta configuração foram bastante satisfatórios permitindo a independência entre os dois sensores dispostos em série. Posteriormente, foi testada uma nova configuração sensora, o sensor de fibra óptica para monitorização de pressão foi construído com recurso a uma lente GRIN e uma superfície reflectora. Esta lente, disposta diante de um espelho, permitiu emitir e captar luz de um determinado comprimento de onda devido à reflexão do sinal luminoso no espelho. Com sucessivos incrementos, afastou-se e aproximou-se a lente ao espelho, registando-se e observando-se as perdas de potência obtidas com auxílio do OTDR. Também para esta configuração foi testada a multiplexagem de vários sensores, tendo sido utilizadas as seguintes opções: um acoplador de 2:1; um acoplador 4:1 e um comutador óptico. Verificou-se que a utilização de um comutador óptico é o melhor caso para a monitorização de pressão de múltiplos sensores. A multiplexagem com recurso ao comutador foi possível, uma vez que permitia a medição independente de cada sensor de pressão num determinado tempo. Com este resultado, é possível monitorizar 48 sensores com recurso ao OTDR, multiplexados temporalmente. Toda esta implementação prática da dissertação foi realizada nas instalações da Unidade de Optoelectrónica e Sistemas Electrónicos no INESC Porto, onde foram caracterizados e estudados sensores com diferentes características que poderão ser lidas neste documento. A componente teórica foi efectuada na Universidade da Madeira.

Modulation instability-induced fading in phase-sensitive optical time-domain reflectometry

Phase-sensitive optical time-domain reflectometry (?OTDR) is a simple and effective tool allowing the distributed monitoring of vibrations along single-mode fibers. We show in this Letter that modulation instability (MI) can induce a position-dependent signal fading in long-range ?OTDR over conventional optical fibers. This fading leads to a complete masking of the interference signal recorded at certain positions and therefore to a sensitivity loss at these positions. We illustrate this effect both theoretically and experimentally. While this effect is detrimental in the context of distributed vibration analysis using ?OTDR, we also believe that the technique provides a clear and insightful way to evidence the Fermi?Pasta?Ulam recurrence associated with the MI process.

Estudio y desarrollo de sensores de fibra óptica para detección de vibraciones en ductos ascendentes submarinos

En esta tesis doctoral se describe el trabajo de investigación enfocado al estudio y desarrollo de sensores de fibra óptica para la detección de presión, flujo y vibraciones en ductos ascendentes submarinos utilizados en la extracción y transporte de hidrocarburos, con el objetivo de aplicarlos en los campos de explotación de aguas profundas en el Golfo de México pertenecientes a la Industria Petrolera Mexicana. El trabajo se ha enfocado al estudio y desarrollo de sensores ópticos cuasi distribuidos y distribuidos. En especial se ha profundizado en el uso y aplicación de las redes de Bragg (FBG) y de reflectómetros ópticos en el dominio del tiempo sensible a la fase (φ-OTDR). Los sensores de fibra óptica son especialmente interesantes para estas aplicaciones por sus ventajosas características como su inmunidad a interferencias electromagnéticas, capacidad de multiplexado, fiabilidad para trabajar en ambientes hostiles, altas temperaturas, altas presiones, ambientes salino-corrosivos, etc. Además, la fibra óptica no solo es un medio sensor sino que puede usarse como medio de transmisión. Se ha realizado un estudio del estado del arte y las ventajas que presentan los sensores ópticos puntuales, cuasi-distribuidos y distribuidos con respecto a los sensores convencionales. Se han estudiado y descrito los interrogadores de redes de Bragg y se ha desarrollado un método de calibración útil para los interrogadores existentes en el mercado, consiguiendo incertidumbres en la medida de la longitud de onda menores de ± 88 nm e incertidumbres relativas (la mas interesante en el campo de los sensores) menores de ±3 pm. Centrándose en la aplicación de las redes de Bragg en la industria del petróleo, se ha realizado un estudio en detalle del comportamiento que presentan las FBGs en un amplio rango de temperaturas de -40 ºC a 500 oC. Como resultado de este estudio se han evaluado las diferencias en los coeficientes de temperatura en diversos tramos de mas mismas, así como para diferentes recubrimientos protectores. En especial se ha encontrado y evaluado las diferencias de los diferentes recubrimientos en el intervalo de temperaturas entre -40 ºC y 60 ºC. En el caso del intervalo de altas temperaturas, entre 100 ºC y 500 ºC, se ha medido y comprobado el cambio uniforme del coeficiente de temperatura en 1pm/ºC por cada 100 ºC de aumento de temperatura, en redes independientemente del fabricante de las mismas. Se ha aplicado las FBG a la medición de manera no intrusiva de la presión interna en una tubería y a la medición del caudal de un fluido en una tubería, por la medida de diferencia de presión entre dos puntos de la misma. Además se ha realizado un estudio de detección de vibraciones en tuberías con fluidos. Finalmente, se ha implementado un sistema de detección distribuida de vibraciones aplicable a la detección de intrusos en las proximidades de los ductos, mediante un φ-OTDR. En este sistema se ha estudiado el efecto negativo de la inestabilidad de modulación que limita la detección de vibraciones distribuidas, su sensibilidad y su alcance. ABSTRACT This thesis describes the research work focused for the study and development of on optical fiber sensors for detecting pressure, flow and vibration in subsea pipes used in the extraction and transportation of hydrocarbons, in order to apply them in deepwater fields in the Gulf of Mexico belonging to the Mexican oil industry. The work has focused on the study and development of optical sensors distributed and quasi distributed. Especially was done on the use and application of fiber Bragg grating (FBG) and optical reflectometers time domain phase sensitive (φ-OTDR). The optical fiber sensors especially are interesting for these applications for their advantageous characteristics such as immunity to electromagnetic interference, multiplexing capability, reliability to work in harsh environments, high temperatures, high pressures, corrosive saline environments, etc. Furthermore, the optical fiber is not only a sensor means it can be used as transmission medium. We have performed a study of the state of the art and the advantages offered by optical sensors point, quasi-distributed and distributed over conventional sensors. Have studied and described interrogators Bragg grating and has developed a calibration method for interrogators useful for the existing interrogators in the market, resulting uncertainty in the measurement of the wavelength of less than ± 0.17 nm and uncertainties (the more interesting in the field of sensors) less than ± 3 pm. Focusing on the application of the Bragg gratings in the oil industry, has been studied in detail the behavior of the FBGs in a wide range of temperatures from -40 °C to 500 oC. As a result of this study we have evaluated the difference in temperature coefficients over various sections of the same, as well as different protective coatings. In particular evaluated and found the differences coatings in the range of temperatures between -40 º C and 60 º C. For the high temperature range between 20 ° C and 500 ° C, has been measured and verified the uniform change of the temperature coefficient at 1pm / ° C for each 100 ° C increase in temperature, in networks regardless of manufacturer thereof. FBG is applied to the non-intrusive measurement of internal pressure in a pipeline and measuring flow of a fluid in a pipe, by measuring the pressure difference between two points thereof. Therefore, has also made a study of detecting vibrations in pipes with fluids. Finally, we have implemented a distributed sensing system vibration applied to intrusion detection in the vicinity of the pipelines, by φ-OTDR. In this system we have studied the negative effect of modulation instability limits the distributed vibration detection, sensitivity and scope.

Mode control in multimode optical fibre and its applications

This thesis describes an investigation into methods for controlling the mode distribution in multimode optical fibres. The major contributions presented in this thesis are summarised below. Emerging standards for Gigabit Ethernet transmission over multimode optical fibre have led to a resurgence of interest in the precise control, and specification, of modal launch conditions. In particular, commercial LED and OTDR test equipment does not, in general, comply with these standards. There is therefore a need for mode control devices, which can ensure compliance with the standards. A novel device consisting of a point-load mode-scrambler in tandem with a mode-filter is described in this thesis. The device, which has been patented, may be tuned to achieve a wide range of mode distributions and has been implemented in a ruggedised package for field use. Various other techniques for mode control have been described in this work, including the use of Long Period Gratings and air-gap mode-filters. Some of the methods have been applied to other applications, such as speckle suppression and in sensor technology. A novel, self-referencing, sensor comprising two modal groups in the Mode Power Distribution has been designed and tested. The feasibility of a two-channel Mode Group Diversity Multiplexed system has been demonstrated over 985m. A test apparatus for measuring mode distribution has been designed and constructed. The apparatus consists of a purpose-built video microscope, and comprehensive control and analysis software written in Visual Basic. The system may be fitted with a Silicon camera or an InGaAs camera, for measurement in the 850nm and 130nm transmission windows respectively. A limitation of the measurement method, when applied to well-filled fibres, has been identified and an improvement to the method has been proposed, based on modelled Laguerre Gauss field solutions.

Long-range and high-resolution correlation optical time-domain reflectometry utilizing an all optical chaotic source

A high resolution optical time domain reflectometry (OTDR) based on an all-fiber chaotic source is demonstrated. We analyze the key factors limiting the operational range of such an OTDR, e.g., integral Rayleigh backscattering and the fiber loss, which degrade the optical signal to noise ratio at the receiver side, and then the guideline for counter-act such signal fading is discussed. The experimentally demonstrated correlation OTDR presents ability of 100km sensing range and 8.2cm spatial resolution (1.2 million resolved points), as a verification of the theoretical analysis. To the best of our knowledge, this is the first time that correlation OTDR measurement is performed over such a long distance with such high precision.

High resolution optical time-domain reflectometry based on correlation utilizing an all-fiber chaotic source

We propose a high-resolution optical time domain reflectometry (OTDR) based on an all-fiber supercontinuum source. The source simply consists of a laser with moderate power and a section of fiber which has a zero dispersion wavelength near the laser's central wavelength. Spectrum and time domain properties of the source are investigated, showing that the source has great capability in nonlinear optics, such as correlation OTDR. We analyze one of the key factors limiting the operational range of such an OTDR, i.e., sampling time. Finally, we experimentally demonstrate a correlation OTDR with 25km sensing range and 5.3cm spatial resolution, as a verification of theoretical analysis.

Long-range and high-precision correlation optical time-domain reflectometry utilizing an all-fiber chaotic source

We propose a long range, high precision optical time domain reflectometry (OTDR) based on an all-fiber supercontinuum source. The source simply consists of a CW pump laser with moderate power and a section of fiber, which has a zero dispersion wavelength near the laser's central wavelength. Spectrum and time domain properties of the source are investigated, showing that the source has great capability in nonlinear optics, such as correlation OTDR due to its ultra-wide-band chaotic behavior, and mm-scale spatial resolution is demonstrated. Then we analyze the key factors limiting the operational range of such an OTDR, e. g., integral Rayleigh backscattering and the fiber loss, which degrades the optical signal to noise ratio at the receiver side, and then the guideline for counter-act such signal fading is discussed. Finally, we experimentally demonstrate a correlation OTDR with 100km sensing range and 8.2cm spatial resolution (1.2 million resolved points), as a verification of theoretical analysis.