Design And Research Of Fiber Laser Hydrophone

Fiber optic hydrophone is a new type of transducer that can convert underwater acoustic signals into optical signals.It plays a very important role in the fields of national defense,military affairs and national economy.With the development of science and technology,the requirements of hydrophone performance in various fields are getting higher and higher.Fiber laser hydrophone uses fiber laser as the sensing unit and unbalanced interferometer for demodulation.It has the characteristics of light weight,small size,high sensitivity,simple structure and so on.Becaues of its great research value,it has received extensive attention and has been rapid development in recent years.Based on the principle of fiber laser,the sensing system of fiber laser hydrophone is studied in this paper.The main contents are as follows:(1)The significance and wide application prospect of fiber optic hydrophone was described,as well as the classification and principle of it.On this foundation,the advantages of fiber laser hydrophone were summarized.Finally,the research status at home and abroad was sorted out,and the current development trend of hydrophone was introduced.(2)A variety of principles related to the fiber laser hydrophone sensing system was concluded,including:output principle and sensing principle of fiber laser,demodulation principle of phase generated carrier method,principle of differential cross multiplication algorithm and tangent cut algorithm.Finally,the related parameters of differential cross multiplication algorithm were analyzed and selected.(3)The sensing part of fiber laser hydrophone was studied in detail.Firstly,the characteristics of fiber laser are analyzed.The type of doped fiber used for fiber laser was Yb/Er co-doped fiber.The influence of phase shift position,phase shift volume,grating length and refractive index variation on phase-shifting grating's transmission spectrum in fiber laser was analyzed by using transfer matrix theory,and the change trend of the transmission peak's transmittance and bandwidth was also obtained.Then a sensitizing structure based on double ended elastic diaphragms for fiber laser hydrophone was designed.The influence of diaphragm's size change on its performance was obtained.The simulation analysis of the sensitizing structure was carried out by using COMSOL simulation software.The sensitivity of sound pressure can be improved by about 60dB(re rad/?Pa)in theory.(4)The interference demodulation system of fiber laser hydrophone was studied.Firstly,the advantages of Michelson interferometer were expounded.Then,in order to achieve better signal modulation,a fiber optic phase modulator was designed.The device can achieve high precision adjustment and high frequency adjustment of the phase,that is,the realization of carrier.Finally,the demodulation system was simulated by using MATLAB simulation software.The phenomena in the demodulation results were analyzed and the corresponding improvements were made.The demodulation system was proved to be feasible.(5)The sensing characteristics of optical fiber laser hydrophone were experimentally investigated.Firstly,the temperature and strain sensing experiments of fiber laser were carried out.The temperature sensitivity was 10.25pm/?,and the strain sensitivity was 0.7pm/?m.It was proved that the fiber laser can be used for strain sensing.Then,the signal generator was used to simulate the interference signal to verify the feasibility of the PGC demodulation system.Finally,the experiment system of fiber laser hydrophone in air was built.The sound was produced by loudspeaker,and the signal was collected by oscilloscope and processed by fast Fourier transform(FFT).The experimental results showed that the response amplitude of fiber laser hydrophone was increased by 12dB and the fluctuation range was reduced by nearly 15dB,which proved that the sensitizing structure has the sensitization effect and can make the frequency response flatter.The innovation of this paper is as follows:(1)A sensitizing structure based on double end elastic diaphragm is designed,which has a certain effect in improving the sensitivity and flatting the frequency response.(2)A optical fiber phase modulation device is designed to achieve high precision and high frequency regulation of the phase.This paper is a preliminary exploration of fiber laser hydrophone sensing system.The experimental system needs to be improved,and the multiplexing array of hydrophone needs further study.