2 research outputs found

    Microwave Photonics for Distributed Sensing

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    In the past few years, microwave-photonics technologies have been investigated for optical fiber sensing. By introducing microwave modulation into the optical system, the optical detection is synchronized with the microwave modulation frequency. As a result, the system has a high SNR and thus an improved detection limit. In addition, the phase of the microwave-modulated light can be obtained and Fourier transformed to find the time-of-arrival information for distributed sensing. Recently, an incoherent optical-carrier-based microwave interferometry (OCMI) technique has been demonstrated for fully distributed sensing with high spatial resolution and large measurement range. Since the modal interference has little influence on the OCMI signal, the OCMI is insensitive to the types of optical waveguide. Motivated by the needs of distributed measurement in the harsh environment, in the first part of this paper, several OCMI-based sensing systems were built by using special multimode waveguides to perform sensing for heavy duty applications. Driven by an interest on the high-resolution sensing, in the second part of the paper, I propose a coherence-gated microwave photonics interferometry (CMPI) technique, which uses a coherent light source to obtain the optical interference signal from cascaded weak reflectors. The coherence length of the light source is carefully chosen or controlled to gate the signal so that distributed sensing can be achieved. The experimental results indicate that the strain resolution can be better than 0.6 脗碌蔚 using a Fabry-Perot interferometer (FPI) with a cavity length of 1.5 cm. Further improvement of the strain resolution to the 1 n蔚 level is achievable by increasing the cavity length of the FPI to over 1m. The CMPI has also been utilized for distributed dynamic measurement of vibration by using a new signal processing method. The fast time-varying optical interference intensity change induced by the sub-scan rate vibration is recorded in the frequency domain. After Fourier transform, distinctive features are shown at the vibration location in the time domain signal, where the vibration frequency and intensity can be retrieved. The signal processing method supports vibration measurement of multiple points with the measurable frequency of up to 20 kHz

    Dise帽o, fabricaci贸n y caracterizaci贸n de sensores basados en fibras 贸pticas de m煤ltiples n煤cleos

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    [ES] La fibra 贸ptica ha supuesto una gran revoluci贸n en el mundo de las telecomunicaciones debido a su alta capacidad de transmisi贸n y sus bajas p茅rdidas. Hoy en d铆a no ser铆a posible transportar la cantidad de tr谩fico que se genera en internet si no fuera por sis- temas de comunicaciones basados en fibras 贸pticas. Sin embargo, el n煤mero de dispo- sitivos conectados a internet es cada vez mayor, por lo que la capacidad de la fibra 贸ptica est谩ndar de un solo n煤cleo se puede ver limitada en un futuro no muy lejano. Una forma de aumentar dicha capacidad es utilizar fibras 贸pticas con varios n煤cleos. Actualmente existe un gran inter茅s sobre la investigaci贸n en este tipo de fibras para aplicaciones de telecomunicaciones, por lo que no es dif铆cil encontrar fibras multin煤- cleo comerciales. Aunque el uso m谩s com煤n de la fibra 贸ptica es para telecomunicaciones, tambi茅n se puede utilizar como sensor. Uno de los m茅todos m谩s comunes para la implementa- ci贸n de sensores es la inscripci贸n de redes de difracci贸n en fibras 贸pticas de un solo n煤cleo. Sin embargo, la inscripci贸n de redes de direcci贸n en fibras de m煤ltiples n煤cleos abre nuevas l铆neas de investigaci贸n para el desarrollo de sensores avanzados. En esta tesis se ha estudiado distintos tipos de redes de difracci贸n inscritas en una fibra de siete n煤cleos para su aplicaci贸n en la implementaci贸n de sensores. En primer lugar, se describe el sistema de fabricaci贸n que permite inscribir distintos tipos de redes de difracci贸n en la fibra multin煤cleo de forma selectiva, es decir, permite seleccionar en que n煤cleos se va a inscribir la red. Mediante este sistema se han inscrito redes de periodo largo y posteriormente se han caracterizado como sensor de deformaci贸n, tor- si贸n y curvatura. Despu茅s, se han inscrito redes de Bragg inclinadas para aumentar de forma intencionada la diafon铆a entre los n煤cleos de la fibra mediante el acoplo de luz entre ellos. Adem谩s, se ha demostrado experimentalmente que esta diafon铆a es sensible a la deformaci贸n de la fibra, a la curvatura, a la temperatura y al 铆ndice de refracci贸n que rodea la fibra. Por otro lado, se ha demostrado que las redes de Bragg inscritas en fibras multin煤cleo se pueden utilizar para implementar sensores de curvatura capaces de operar en entornos radioactivos. Finalmente se han fabricado redes de Bragg rege- neradas capaces de operar a altas temperaturas, estas redes se han caracterizado como sensor de temperatura, deformaci贸n y curvatura.[CAT] La fibra 貌ptica ha suposat una gran revoluci贸 en el m贸n de les telecomunicacions a causa de la seua alta capacitat de transmissi贸 i les seues baixes p猫rdues. Hui en dia no seria possible transportar la quantitat d'informaci贸 que es genera en internet si no fos pels sistemes de comunicacions basats en fibres 貌ptiques. No obstant aix貌, el nombre de dispositius connectats a internet es cada vegada m茅s gran, per la qual cosa la capacitat de la fibra 貌ptica est脿ndard d'un sol nucli es pot veure limitada en un futur no gaire lluny脿. Una manera d'augmentar aquesta capacitat es utilitzar fibres 貌ptiques amb diversos nuclis. Actualment existeix un gran inter猫s sobre la investigaci贸 en aquesta mena de fibres per a aplicacions de telecomunicacions, per la qual cosa no es dif铆cil trobar fibres de m煤ltiples nuclis comercials. Encara que l'煤s mes com煤 de la fibra 貌ptica es per a telecomunicacions, tamb茅 es pot utilitzar com a sensor. Un dels m猫todes m茅s comuns per a la implementaci贸 de sensors es la inscripci贸 de xarxes de difracci贸 en fibres 貌ptiques d'un sol nucli. No obstant aix貌, la inscripci贸 de xarxes de difracci贸 en fibres de m煤ltiples nuclis obri noves l铆nies d'investigaci贸 per al desenvolupament de sensors m茅s complexos. En aquesta tesi s'ha estudiat diferents tipus de xarxes de difracci贸 inscrites en una fibra de set nuclis per a la seua aplicaci贸 en la implementaci贸 de sensors en fibra 貌ptica. En primer lloc, es descriu el sistema de fabricaci贸 de xarxes de difracci贸 que permet inscriure diferents tipus de xarxes de difracci贸 en la fibra de m煤ltiples nuclis de manera selectiva, es a dir, permet seleccionar en que nuclis s'inscriur脿 la xarxa. Mitjan莽ant aquest sistema s'han inscrit xarxes de per铆ode llarg i posteriorment s'han caracteritzat com a sensor de deformaci贸, torsi贸 i curvatura. Despr茅s, s'han inscrit xarxes de Bragg inclinades per a augmentar de manera intencionada la diafonia entre els nuclis de la fibra mitjan莽ant l'acoblament de llum entre ells. A m茅s d'aix貌, s'ha demostrat experimentalment que aquesta diafonia es sensible a la deformaci贸 de la fibra, a la curvatura, a la temperatura i a l'铆ndex de refracci贸 que envolta la fibra. D'altra banda, s'ha demostrat que les xarxes de Bragg inscrites en fibres m煤ltiples nuclis es poden utilitzar per a implementar sensors de curvatura que poden operar en entorns radioactius. Finalment s'han fabricat xarxes de Bragg regenerades que suporten altes temperatures, aquestes xarxes s'han caracteritzat com a sensor de temperatura, deformaci贸 i curvatura.[EN] Optical fiber has been a great revolution in the world of telecommunications due to its high transmission capacity and low attenuation. Today it would not be possible to transport the amount of traffic that is generated on the Internet without communication systems based on optical fibers. However, the number of devices connected to the Internet is increasing, so the capacity of standard single-core fiber optics may be limited so far in the future. One way to increase this capacity is to use multi-core optical fibers. Nowadays is a great interest in research in this type of fibers for telecommunications applications, so it is not difficult to find commercial multicore fibers. Although the most common use of fiber optics is for telecommunications, it can also be used as a sensor. One of the most common methods for sensor implementation is the inscription of diffraction gratings on single-core optical fibers. However, the enrollment of steering networks in multi-core fibers opens new lines of research for the development of advanced sensors. In this thesis, different types of diffraction gratings inscribed in a seven-core fiber have been studied for their application in the implementation of sensors. In the first place, the diffraction grating manufacturing system is described that allows to inscribe different types of diffraction gratings in the multicore fiber selectively, that is, it allows to select in which cores the grating is going to be inscribed. By means of this system, long-period networks have been inscribed and subsequently they have been characterized as a deformation, torsion, and curvature sensor. Then, slanted Bragg gratings have been inscribed to intentionally increase the crosstalk between the fiber cores by coupling light between them. Furthermore, this crosstalk has been experimentally shown to be sensitive to fiber deformation, curvature, temperature, and the index of refraction surrounding the fiber. On the other hand, it has been shown that Bragg networks inscribed in multicore fibers can be used to implement curvature sensors capable of operating in radioactive environments. Finally, regenerated Bragg nets capable of operating at high temperatures have been manufactured. These nets have been characterized as a temperature, deformation, and curvature sensor.Agradezco a la Universitat Polit猫cnica de Val猫ncia la beca FPI (PAID-01-18) que me fue concedida para realizar est谩 tesis.Madrigal Madrigal, J. (2022). Dise帽o, fabricaci贸n y caracterizaci贸n de sensores basados en fibras 贸pticas de m煤ltiples n煤cleos [Tesis doctoral]. Universitat Polit猫cnica de Val猫ncia. https://doi.org/10.4995/Thesis/10251/180806TESI
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