Research On The Demodulation Technology Of Laser Interference Detection Signal Of Water Surface Acoustic Wave

With the development of science and technology, the scope of activities of underwater target becomes deeper and deeper, the movement speed is more and more quickly, and concealment performance is getting better and better. The capture and recognition of noise information of submarines and other underwater target is becoming more and more difficulty. The traditional sonar technology is hard to meet the requirements of target detection. Laser interference technique is applied to the detection of water surface acoustic wave. By the demodulation of the laser interference signal, the information of underwater target can be restored rapidly. The technique can effectively realize the precision of detection,identification and position of the military targets, and it is also play an important role in the detection and utilization of the Marine resources. In the subject, laser interferometry technique was applied to the detection of water surface acoustic wave based on the principle of laser interferometry. By using the demodulation method based on 3×3 coupler and differential cross-multiplication method(DCM)technology, DSP system that can demodulate sensing signal from laser interference detection of water surface acoustic wave has been developed to recover the relation information with underwater target from demodulated signal in time. The main contents of this paper are shown as following:The principle that detection of water surface acoustic wave by laser interference technology caused by the vibration of underwater sound source and phase demodulation of detected signal has been studied. The lack of the spectrum analysis in the signal demodulation method has been analyzed, and a new phase demodulation scheme was proposed that 3×3 coupler method was applied to the demodulation of interference detection signal of water surface acoustic wave.The principle of 3×3 coupler demodulation method was deeply studied. The algorithm that the water surface acoustic wave signal was demodulated from optical signal of coupler output terminal has been processed. And it can realize phase demodulation algorithm of the Doppler detection signal based on DCM method.In accordance with the design of the optical path of laser Doppler detection,the fiber-optic detection path of interference based on the acousto-optic coupling has been set up. The hardware demodulation circuit has been designed. And the program of DSP was written, which based on DCM demodulation algorithm.By using the demodulation system, the demodulation experiments wereaccomplished. And the demodulation results has been analysed. Experimental results indicate that the absolute value of maximum relative error was 0.67% in accordance with the results of measuring each frequency for 3 times. Under the condition of sound pressure was constant, the change tendency between the frequency and amplitude of water surface acoustic wave signal was consistent with theoretical analysis. According to data above, it is preliminary proven that the demodulation system are feasible to recover the information of water surface acoustic wave in time.