Fiber optics, besides their great impact in telecommunications, are nowadays proving to become an interesting sensing solution for the real-time monitoring of both industrial environments and large infrastructure such as oil & gas pipelines, viaducts, dams and railways. The main peculiar feature of fiber optic sensors is that they can reconstruct, in a truly distributed way, the entire profile of parameters such as temperature, strain and vibrations, along the whole sensing fiber length. In particular, for short-range applications (few kms) where an extreme spatial resolution (down to cm) is required, Phase-Coded Brillouin Optical Correlation Domain Analysis (BOCDA) is, by far, the most promising solution. However, this high spatial resolution comes at the expense of a very high system complexity and a low measurement speed due to massive averaging time required to cope with a poor system signal-to-noise ratio (SNR). The goal of this work of thesis has been focused on addressing the aforementioned BOCDA issues in order to provide a competitive and cost-effective solution for a wide range of in-field applications. To this purpose, a systematic analysis has been carried out to identify and optimize the system parameters mostly affecting the overall SNR, leading to a 100-times improvement in measurement speed while maintaining a 2-cm spatial resolution along the whole sensing fiber. A Time-Gating approach has also been implemented to increase the maximum BOCDA sensing range while guaranteeing an adequate measurement SNR. Besides, the system layout has been upgraded including novel devices usually employed in high-bit rate optical communications, such as, small footprint 10GHz clock, PRBS generators and ADC acquisition boards for the development of a compact, portable and cost-effective BOCDA sensor. The feasibility of the proposed solution has been experimentally demonstrated by means of systematic measurements aimed at localizing hot-spot up to 250 °C along few hundreds meters of sensing fiber.
Le fibre ottiche, oltre al loro grande impatto nelle telecomunicazioni, stanno dimostrando oggigiorno di essere una soluzione interessante per il monitoraggio in tempo reale di ambienti industriali e di grandi infrastrutture come oleodotti e gasdotti, viadotti, dighe e ferrovie. La principale peculiarità dei sensori a fibra ottica è la possibilità di ricostruire in modo distribuito l'intero andamento di parametri come la temperatura, la deformazione e le vibrazioni, lungo tutta la fibra sensore. In particolare, per le applicazioni a breve distanza (pochi km) per le quali è richiesta una risoluzione spaziale accurata (fino a cm), Phase-Coded Brillouin Optical Correaltion Domain Analysis (BOCDA) è sicuramente la soluzione più promettente. Tuttavia, questa elevata risoluzione spaziale comporta una complessità di sistema molto elevata e una bassa velocità di misurazione a causa del tempo medio necessario per far fronte ad uno scarso rapporto segnale-rumore (SNR) del sistema. L'obiettivo di questo lavoro di tesi è stato quello di affrontare le suddette questioni per il BOCDA, al fine di fornire una soluzione competitiva ed economica per una vasta gamma di applicazioni. A tale scopo, è stata condotta un'analisi sistematica per identificare e ottimizzare i parametri del sistema che influenzano maggiormente l'SNR complessivo, portando ad un miglioramento di 100 volte della velocità di misurazione mantenendo una risoluzione spaziale di 2 cm lungo l'intera fibra sensore. É stato implementato un approccio Time-Gating per aumentare il range di rilevamento massimo del BOCDA, garantendo al tempo stesso un SNR di misura adeguato. Inoltre, il layout del sistema è stato aggiornato includendo nuovi dispositivi impiegati in comunicazioni ottiche a bit rate elevato, come ad esempio clock a 10 GHz di dimensioni ridotte, generatori PRBS e schede di acquisizione ADC per lo sviluppo di un sensore BOCDA compatto, portatile ed economico. La fattibilità della soluzione proposta è stata dimostrata sperimentalmente mediante misure sistematiche volte a localizzare hot-spot fino a 250 °C lungo alcune centinaia di metri di fibra sensore.
Phase-coded Brillouin optical correlation domain analysis for high-resolution distributed fiber sensing
CUSCINÀ, DANIELE
2017/2018
Abstract
Fiber optics, besides their great impact in telecommunications, are nowadays proving to become an interesting sensing solution for the real-time monitoring of both industrial environments and large infrastructure such as oil & gas pipelines, viaducts, dams and railways. The main peculiar feature of fiber optic sensors is that they can reconstruct, in a truly distributed way, the entire profile of parameters such as temperature, strain and vibrations, along the whole sensing fiber length. In particular, for short-range applications (few kms) where an extreme spatial resolution (down to cm) is required, Phase-Coded Brillouin Optical Correlation Domain Analysis (BOCDA) is, by far, the most promising solution. However, this high spatial resolution comes at the expense of a very high system complexity and a low measurement speed due to massive averaging time required to cope with a poor system signal-to-noise ratio (SNR). The goal of this work of thesis has been focused on addressing the aforementioned BOCDA issues in order to provide a competitive and cost-effective solution for a wide range of in-field applications. To this purpose, a systematic analysis has been carried out to identify and optimize the system parameters mostly affecting the overall SNR, leading to a 100-times improvement in measurement speed while maintaining a 2-cm spatial resolution along the whole sensing fiber. A Time-Gating approach has also been implemented to increase the maximum BOCDA sensing range while guaranteeing an adequate measurement SNR. Besides, the system layout has been upgraded including novel devices usually employed in high-bit rate optical communications, such as, small footprint 10GHz clock, PRBS generators and ADC acquisition boards for the development of a compact, portable and cost-effective BOCDA sensor. The feasibility of the proposed solution has been experimentally demonstrated by means of systematic measurements aimed at localizing hot-spot up to 250 °C along few hundreds meters of sensing fiber.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/147343