Hydrophone Based On The Feedback Effect Of Optical Fiber Laser

As optical fiber gratings and erbium-doped fiber being greatly improved with thedevelopment of optical fiber technology, the fiber lasers have been widely used in the sensorfield such as measuring temperature, pressure and sound for its stable performance, and themeasurement of underwater sound signals fiber laser hydrophone has also been greatlydeveloped. Fiber hydrophone sensor takes distributed feedback (DFB) or distributed braggreflector (DBR) fiber laser which is formed by gratings and doped fiber as its sensing unit.We can demodulate the output of fiber laser using intensity demodulation and phasedemodulation when modulated by the underwater accoustic. The research of sensing unit anddemodulation method is essential to the application and development of fiber hydrophonesensor.The thesis focuses on the fiber laser hydrophone based on the feedback effect. Firstly,the thesis shows the background and development of fiber laser hydrophone. Secondly, weanalyze the DBR fiber laser characteristics by theory and experiment. Then the analysis ofDBR fiber laser is shown as taking the coherent and incoherent feedback into fiber laser, andwe calculate the largest Lyapunov exponent to determine the system stablity at differentfeedback. Finally, we test the feedback system by experiment.After the theroy and test, the fiber laser hydrophone system based on feedback is set up.Single-mode fiber twisted round the a flexible silica gel column is connected with the fiberlaser to achieve the system. Instead of being the sensing unit, the fiber laser is separated fromthe sensing unit, so the system is cheaper, more simple, and longer lifetime than the trandionalone. The system includes sensing unit, DBR fiber laser, detection part, signal acquisition andprocessing part, and real-time display part. Using intensity and phase demodulation method,we can measure the acoustic with different feedback, and we can achieve the fiber laserhydrophone based on feedback.