Theoretical And Experimental Investigations On Underwater Acoustic Low-Pass Filtering Fiber-Optic Hydrophones

Signal aliasing induced by high frequency jam is one of the key cases which affect the properties of fiber-optic hydrophone systems. To eliminate the aliasing effectively, in this paper the scheme of underwater acoustic low-pass filtering is proposed. The model and theories of underwater acoustic low-pass filters are given based on those of air acoustic low-pass filters. Several simple acoustic low-pass filtering fiber-optic hydrophones are designed, and the acoustic pressure phase sensitivity frequency response properties are investigated in terms of theories, simulations and experiments. The main work is provided as follows:1. The theories and models of small underwater acoustic low-pass filters are investigated. Considering the elasticity of the filters and the radiation impedance, improved model and theories of underwater acoustic low-pass filters are given based on those of conventional air acoustic low-pass filters.2. Underwater acoustic low-pass filtering fiber-optic hydrophones of second-order, forth-order, and with side cavity are designed based on the model and theories given in this paper. And the acoustic pressure phase sensitivity frequency response properties are investigated in terms of theories, simulations and experiments. Results testify the correctness of the theories and models.3. To eliminate the signal aliasing in fiber-optic hydrophone systems, the novel scheme of underwater acoustic low-pass filtering is proposed in the paper. The anti-aliasing properties of the underwater acoustic low-pass filtering fiber-optic hydrophone systems are tested. Results show that this novel method will be an effective scheme used to eliminate the signal aliasing in modern optical fiber sonar systems.4. A novel passive working-point control wideband signal detection method by tuning the laser frequency is proposed for wideband detection requiments of fiber-optic hydrophone systems. The wideband detection properties of the fiber-optic hydrophone systems, which are based on laser frequency modulation, can be tested by this new detection method.The studies of this paper offer an effective technological method to improve the properties of fiber-optic hydrophone systems, especially the detection performance under the condition of underwater acoustic antagonizing by wideband jam.