Dynamic Range Of A Novel Interferometric Fiber-Optic Hydrophone And Its Application In Underwater Measurement

With the development of ocean science, the application of fiber-optic hydrophone is more and more wide. Compared with traditional hydrophone, acousto-optic interferometric fiber-optic hydrophone can emit detection laser in the aerial platform, coupling the underwater sound field information on the water surface, remote sensing the underwater sound field by detecting the re-flected laser. Acousto-optic fiber-optic hydrophone not only has high sensitivity, but also can take the task in the hostile environment by non-contact measurement, thus this is a sensor with high potential application value;At the beginning of this paper, we briefly introduced the developed history of fiber-optic hy-drophone and the application of acousto-optic fiber-optic hydrophone. Then analyzed a kind of acousto-optic interferometric fiber-optic hydrophones based on π/2 phase modulation, introduced the principle of using this method to obtain two channels of orthogonal signals; two most common-ly used fiber-optic hydrophone digital demodulation algorithms, the differentiate-cross-multiply al-gorithm and the arctangent algorithm were introduced in detail, the dynamic range and the reason the dynamic range was limited were analyzed, the advantages and the disadvantages were com-pared, respectively; the concept of distortionless dynamic range of differentiate-cross-multiply algorithm was proposed, the dynamic range is found to be linearly increasing with sampling fre-quency by theoretically analyzing its demodulation principle; the dynamic range influenced by the detection signal amplitude, frequency and the sampling rate is researched by Matlab simula-tion; the influence to these two demodulation algorithms when the two channels of signals are not orthogonal is analyzed.The π/2 phase modulation interferometric experiment setup based on piezoelectric transducer (PZT) is built to demodulate vibrating signal, the experimental result demonstrates a minimum phase shift of 2.4 x 10-5 rad can be detected, the dynamic range of the system is influenced by the signal frequency and sampling rate, the distortionless dynamic range is improved from 87 dB to 102 dB when signal frequency goes from 5 kHz to 1 kHz. The acousto-optic interferometric fiber-optic hydrophone experiment setup is built for pool experiment, the reflected acoustic signal of the aluminum plate which is 10 m under the water is detected. According to the analysis of the experimental result, the maximum detectable depth of the acousto-optic interferometric fiber-optic hydrophone is 36 m.At the end of this paper, we proposed a method using laser-induced sound source and acousto-optic interferometric fiber-optic hydrophones array to detect underwater object location and size, analyzing its operating principle. The principle of using differential positioning algorithm and deconvolution algorithm to estimate the underwater target location and size is introduced. Finally, the numerical simulation was carried on to verify the feasibility of this method.