Research On Acoustic Detection Technology Based On All-fiber Mach-zehnder Interferometer And Fiber Grating

Sound waves are the carrier of information and energy of many natural phenomena in nature.Through sound wave detection,these natural laws can be better grasped.Acoustic wave detection is an important research technology.Compared with traditional electronic acoustic wave sensors,fiber-optic acoustic wave sensing can work in a special environment where traditional electronic acoustic wave sensors are difficult to work properly.It can complete the work that traditional electronic acoustic wave sensors are difficult to complete,using modern A variety of multiplexing technologies for communication can form a large-scale acoustic wave detection array and sensor network.In addition to all the advantages of fiber-optic sensors,the fiber-grating(FBG)sensor has the most significant advantage of using intrinsic wavelength coding for sensing information,as well as intensity fluctuation with light source and polarization of light.Unrelated advantages,based on FBG is a research design with low transmission loss,high sensitivity,high signal to noise ratio,wide frequency response,large dynamic range,strong anti-electromagnetic interference capability,easy reuse,long-distance transmission and array.One of the important technologies of all-fiber acoustic wave sensors.At present,due to the difficulty in demodulation of wavelength-encoded signals,the demodulation equipment is complicated and the cost is too high,which is difficult to accept in the general field.How to improve detection sensitivity,accuracy,simplify detection methods,and reduce cost is an important research direction.Research shows that the all-fiber Mach-Zehnder(MZI)interferometer has the advantages of low polarization-dependent loss,low additional loss,stable output waveform,etc.,and the output waveform is a function of wavelength,and FBG completes information acquisition with wavelength change.Sensing.In this paper,based on the all-fiber MZI and FBG are all wavelength-dependent all-fiber devices,combining the characteristics of the two,focus on how to convert the change of FBG reflection wavelength into a demodulation method of light intensity change.The main research work includes:(1).Based on Maxwell's electromagnetic field theory,the mechanism of FBG reflection spectrum formation is analyzed in detail,and the analytical expression is given.The basic principle of FBG is used to measure the change of physical parameters.The FBG-based acoustic wave sensing is designed.Lay the theoretical foundation.(2).According to the vibration equation of the elastic diaphragm,the acoustic response characteristics of the elastic diaphragm are deeply analyzed,and the theoretical support for improving the sound and light conversion efficiency is made.(3).For the bare FBG strain sensitivity is low,can not meet the application requirements of high-sensitivity sound wave detection,and explore the method to improve the sensitivity of FBG detection.(4).Using the conventional MZI and resonant cavity MZI output spectrum as the acoustic wave detection source,using different structures of single FBG and double FBG,it is theoretically proved that the detection of light intensity changes instead of the traditional detection of FBG reflection wavelength changes reflects the changes of acoustic signals.The method of self-demodulation and mutual demodulation based on FBG is discussed separately.