Because the acoustic wave is capable of propagating at a long-distance in water, the hydrophone plays a key role in the underwater acoustic sensing all the time. The hydrophone based on fiber optic interferometry has an extremely high sensitivity and large dynamic range. In addition, the electrically passive, immunity to electromagnetic interference, and multiplexing properties of fiber optic sensor offer great advantages over traditional piezoelectric hydrophone.
Due to the complete path-balance between the two counterpropagating waves, a Sagnac interferometric configuration can employ a low-coherent light source to reduce the cost. This configuration can easily route optical paths and replace sensor heads to compare with each other. But, the sensitivity varying with frequency and the polarization-induced signal fading problem make it unsuitable for applications in need of detecting correct amplitude of signals. The Michelson interferometric configuration with Farady rotator mirror (FRM) has a constant sensitivity and solves the polarization-induced signal fading problem. But, this configuration uses a high-coherent light source and expensive FRMs, and be difficult to route. In this paper, we use the polarization-insensitive Michelson fiber optic sensor to adjust the demodulation circuits we design.
In this paper, we establish the interferometric hydrophones. The fiber optic coil of the sensor head is embedded with the special materials in order to acoustic impedance matching and waterproofing. We employ phase generated carrier demodulation technology to get the acoustic signal of interest from the output of the interferometer. In our experiment, the dual Sagnac configuration has a dynamic range of 23 dB and a sensitivity of -226 dB re V/1uPa, the Michelson configuration with FRMs has a dynamic range of 25 dB and a sensitivity of -204 dB re V/1uPa.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0908104-145822 |
| Date | 08 September 2004 |
| Creators | Huang, Guo-ting |
| Contributors | Meng-en Lee, Yan-kuin Su, Yaw-dong Wu, Wuu-wen Lin, Mao-hsiung Chen |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0908104-145822 |
| Rights | unrestricted, Copyright information available at source archive |
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