Research Of Optical Fiber Acoustic Vibration Sensing Demodulation Method Based On Dual Tunable Lasers

With high sensitivity,compact structure and excellent immunity to electromagnetic interference,fiber acoustic vibration Fabry-Perot sensor can be used widely in aviation,aerospace and other fields.It also has broad prospects for development and application value.In this paper,the demodulation method for fiber acoustic vibration Fabry-Perot sensor which is a kind of high sensitivity sensor is studied and the optical fiber Fabry-Perot acoustic vibration sensing demodulation method based on dual tunable lasers is provided.The major work of the paper is as follows:1.The research was carried out on existing optic fiber acoustic vibration sensor and its demodulation method.The principle of quadrature phase demodulation which is used for interference signal is discussed in detail.How to select the working wavelength of the quadrature phase demodulation is decided by theoretical analyzed.We studied the coupling loss of the Fabry-Perot cavity and calculated the range of initial cavity length which can be well fit for t he demodulation system considering the quardrature signal building theory.2.The influence of initial cavity length drift on signal demodulation is studied by simulation and experiment.Initial cavity length drift of 0~2.2?m is achieved by changing temperature and in this case traditional interference intensity direct demodulation method and quadrature phase demodulation method are compared and analyzed: relative change of demodulation signal amplitude by quadrature phase demodulation method is less than 5.3%;the stability of demodulation signal amplitude by quadrature phase demodulation method increases 12.4 times than that by traditional interference intensity direct demodulation method.The stable demodulation performance of optic fiber acoustic vibration sensor under wide range of temperature changing is realized.4.Method of wavelength tuning compensation is provided in order to solve the problem of initial Fabry-Perot cavity length dispersing.Initial cavity length of 55?m~130?m is realized by this method and relative change of demodulation signal amplitude is less than 4.9% which enhance the adaptability of the demodulation system to the sensor parameter changing.