Research On Key Technology Of Fiber Grating Hydrophone Array Based On Matched Interference

Fiber optic underwater acoustic detection system has the characteristics of high sensitivity and wide dynamic range.It has important applications in underwater early warning detection,marine resources development and other military and civil fields.Fiber Bragg Grating hydrophone based on matched interference has the advantages of simple wet-end structure and large-scale light and small-size wet-end arrays.In this paper,the technology of fiber Bragg grating hydrophone array based on matching interference is studied.The key problems such as wavelength matching,probe design and array structure design are mainly solved to support the application and development of fiber Bragg grating hydrophone array.The main contents and innovations of this paper are as follows:1.The drift characteristics of grating temperature and pressure in fiber Bragg grating hydrophone array are analyzed,and the adaptability of the array to underwater environment is evaluated.During the underwater operation of the array,the combined effect of temperature and depth on the central wavelength offset of the FBG is less than 0.265 nm in the depth range of 1 000 m,and the central wavelength of the light source need not be changed.2.A miniaturized fiber Bragg grating hydrophone probe with an outer diameter of less than 9.5mm was designed and wound.Within the test frequency range of 80Hz～1.25 kHz,the average acoustic pressure phase sensitivity was-149.74 dB,and the frequency response fluctuation was less than that.3.A four-element fiber Bragg grating hydrophone thin linear array with a diameter of 20 mm was designed and fabricated.The phase sensitivity of each element and the crosstalk between each channel were tested.The average phase sensitivity of each channel was-149.63 dB,-151.61 dB,-150.37 dB and-151.8 dB,respectively.Before the array was fitted with PU tube,the time crosstalk between one channel and the following channels was lower than-40 dB.The time-division crosstalk between 1 channel and subsequent channel is lower than-35 dB after putting PU tube on the array,which is worse than before putting PU tube on the array.The reason is that the sound signal transmitted through PU tube and air will lead to the increase of time-division crosstalk between channels,and the channel closer to the signal source will be affected more.