Distributed optical fiber sensors have the advantages of corrosion resistance, anti-electromagnetic interference and adaptability to extreme environments. They can be used in perimeter security, pipeline monitoring, seismic detection and other fields. A novel optical fiber sensor called microwave frequency fiber interferometer has been proposed for low frequency sensing applications such as submarine seismic monitoring. However, the MFFI can only achieve integrated sensing and cannot achieve distributed localization of disturbances. In order to solve the problem that MFFI cannot achieve distributed localization and make it more suitable for long distance sensing applications, we propose a dual wavelength MFFI system based on wavelength division multiplexing to achieve distributed localization through time delay estimation algorithm. Our proposed system and algorithm make up for the inability of MFFI to achieve distributed localization and can be used in more sensing applications.
The precision of frequency signal is constantly improving, and the application of high-precision frequency signals requires an equally high-precision transmission method. So in this paper, we demonstrate an optical carrier radiofrequency phase stabilization transfer system based on a phase lock loop (PLL), applied to a 20 km spooled fiber link. The phase noise induced by optical fiber is suppressed by the PLL, and the transfer stability improved from 7.2×10-13@1 s to 8.9×10-15@1 s. In addition, the phase difference of peak-to-peak with compensation is less than 10 ps in a measurement of about 1 day. The phase study in antenna is with the compensation mode, so this work will lay the foundation for the phase synchronization of distributed coherent antenna system.
In this paper, a research of PMMA optical fiber reflectivity changing along with the angle of tips has been studied. A type of integrated conical fiber probe is designed. Nine angles of cone fiber tips were fabricated and tested in 0.4 L /min continuous uniform bubble flow (air) in this study to validate the performance of each cone angle. A simulation model of PMMA optical fiber tip was established based on physical properties of fiber to simulate the reflectivity of different angle tips set into gas/liquid environment. The first and second high peaks of experimental data agree well with the positions of those calculated using the simulation.
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