The Analysis About Probe And Demodulation System On Fiber-optic Acoustic Sensor

The 21st century is the information age, and the development of science and technology keep rapid speed. It is of great significance studying about the sound field information for defense and national economy. Fiber-optic acoustic sensors have many advantages, such as high sensitivity, large dynamic range and wide detection frequency band, so there are many countries paying great attention to it. Various parts of fiber-optic acoustic sensor system are studied through theoretical analysis and finite element analysis based on laboratory research results. Comparing the results of theoretical analysis and finite element analysis with experimental data, then explaining the phenomena found in experiments, and putting forward some advice about the fiber optic acoustic sensor system. The main contents include the following.Firstly:the history and research trends of foreign country and our country about fiber-optic acoustic sensor are introduced after consulting lots of related papers and articles. The principle of fiber phase modulation is described clearly. The basic principium of fiber-optic acoustic sensor is vividly depicted based on the Michelson-type interferometer.Secondly:the thought of finite element analysis and the method using software named ANSYS are introduced. Fiber probes of planar and mandrel structure are simulated with statics analysis through ANSYS. The results of theory analysis and the displacement contour maps from static simulation are discussed. The strongpoint and the flaw of two kinds of fiber-optic acoustic sensor probes are proposed, and also the direction to improve and optimize the fiber probe is put forward. The first order natural frequency of the elastic membrane in reflective optical sensor is acquired through theory analysis. And then the consistency of natural frequency between theory analysis and software simulation is validated. The elastic layer and fiber layer of two kinds of fiber-optic acoustic sensor probes are simulated with modal analysis. The differ about natural frequency of the two kinds of fiber probes is discussed, and then the peculiarity about frequency response curve of the two kinds of fiber probes is Explained in detailAnd also:the basic principle and the process of homodyne demodulation scheme for fiber optic sensors using phase generated carrier are introduced. The method to select qualified amplitude of the phase generated carrier is analyzed, and which is depended on the difference of the amplitude of generated carrier frequency and threefold frequency. And then the method is validated through experiment from side face.Another thing:the nonlinear character of optical fiber is simulated by software optic wave after doing theory analysis about the nonlinearity of optical fiber. Then the nonlinearity of optical fiber is used in the technology of phase controlling in fiber optic acoustic sensor, and then a novel method measuring optical fiber nonlinear coefficient based on nonlinearity is put forward.Lastly:all the results of fiber optic acoustic sensor studied in foreparts are summed up, and also the complexity, existent problems and future trend of development about fiber optic acoustic sensor are put forward.