Research On Key Technologies Of Distributed Optical Fiber Hydrophone System

China has a vast coastline and abundant marine resources.With the development of marine exploration,optical fiber hydrophones have brought out its important strategic significance and application value.Distributed optical fiber sensing systems show great potential in building long-distance,high-precision,and large-capacity fiber-optic sensing systems,and in disaster prediction,resource exploration,and defense of earthquake warning,anti-submarine warfare,underwater defense,and oil and gas exploration.The security field has an indispensable position.This thesis focuses on the application of distributed fiber detection systems in the field of weak underwater acoustic signal detection.It combines interferometric fiber optic hydrophones with distributed fiber acoustic sensing systems to design signal circuits and water in distributed fiber optic hydrophone systems.Key technologies such as priming technology were studied.The principle of distributed optical fiber acoustic sensing system is introduced in detail.A dual-channel signal generation circuit is designed.The hydrophone element of the elastic layer sensitization structure and the hydrophone element of the single diaphragm structure are designed.The specific research content is as follows:1.Introduction to Distributed Fiber Acoustic Sensor System.Starting from the theory of optical time domain reflectometry,the feasibility of long-distance real-time quantitative measurement of the system is proved theoretically;the demodulation algorithm used in the system—the principle of phase-generated carrier algorithm is introduced in detail;the system solution and working principle are introduced.The key technical indicators of the system were tested through experiments.The maximum detection distance of the system was 12.5 Km,the spatial sampling resolution was 0.4 m,the spatial resolution was 10 m,the frequency response flatness was 3.9 dB,and the linear goodness of fit was greater than 99.5%.2.Dual channel signal generation circuit design.Based on the principle of direct digital frequency synthesis technology,a circuit solution based on direct digital frequency synthesis technology is designed to analyze the spurious of direct digital frequency synthesis technology.Two DDS chips are used in combination with the design of a single chip,and the circuit after debugging is adopted.Can synchronously output all the way 2KHz sine signal and all the way 8KHz TTL signal,the sine signal amplitude is adjustable between 0-3V,the TTL signal pulse width is adjustable between 10-100ns,the signal frequency error is smaller than lOppm.3.Sensitive primitive design.A theoretical analysis model for the elastic sensitized layer structure hydrophone element was established,and the sound pressure sensitivity calculation formula of the primitive element was deduced.The influence of various parameters on the sound pressure sensitivity was analyzed,and the hydrophone base was finally produced.Yuan conducted a test experiment to verify the theoretical analysis.The experimentally measured sound pressure sensitivity level of the hydrophone element was around-141.6dB different from the theoretical analysis value by 0.2dB,the frequency response flatness was less than 5 dB,and the signal-to-noise ratio was about 40dB.This verifies the correctness of the theoretical analysis.The vibrational mechanics analysis was performed on the single-diaphragm hydrophone element,the formula for the sound pressure sensitivity of the element was deduced,and the hydrophone element was tested to verify the theoretical analysis.The hydrophone was experimentally measured.The sound pressure sensitivity of the primitive is different by 0.4dB from the theoretical analysis value of-123.8dB,and the frequency response flatness is less than 6dB.