| Summary: | 碩士 === 國立中山大學 === 電機工程學系研究所 === 94 === An interferometer is used for phase detection. Thus, the hydrophone which is based on interferometric optic fiber sensor has extremely high sensitivity. Sagnac interferometric hydrophone has low noise of marine environment, which is more suitably used to detect underwater acoustic signal than that of a Mach-Zehnder interferometer. In this paper, a configuration of dual Sagnac interferometer was proposed. The mathematical model was derived and analyzed.
The fiber optic sensor head contains mandrel type and planar one. The acoustic window are made of silicon rubbers. It was should that we can increase their sensitivities by increase number of wrapping fiber coils.
In our experiment, the result shows that among all the mandrel sensor heads, the most highest dynamic range is up to 37.6±1.4 dB, and its sensitivity is -223.3±1.7 dB re V/1µPa ; while the dynamic range of the planar sensor head is 42.1±1.5 dB, and its sensitivity is -213.8±1.3 dB re V/1µPa。
As for the configuration of the optical interferometers, the intensity of the dual Sagnac interferometer is 20 dB larger than its Sagnac counterpart. Its dynamic range is above 66 dB, which is 24 dB larger than that of the Sagnac interferometer with the sensitivity of -192.0 dB re
V/1µPa. In addition, by using software simulation to design optimal lengths of delay fibers , we can increase interferometer’s the dynamic range of underwater acoustic detection. This paper verify that, by means of adjusting the length of these two delay fibers, we can actually increase the dynamic range of acoustic signal detection.
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