Research On The Filtered Generalized Lock-in Amplifier Demodulation Algorithm For Fiber-optic Vibration Measurement

With the continuous development of fiber optic sensing technology,fiber optic vibration sensors are widely used in the field of vibration measurement.Phase Generated Carrier(PGC)demodulation algorithm is widely used in interferometric fiber optic sensors.Because of its large dynamic range,high measurement accuracy and other advantages.Its accuracy is affected by many aspects,and the drift of the modulation depth is one of the factors that seriously affect the demodulation accuracy.The demodulation accuracy is affected by many aspects,and the drift of modulation depth is one of the factors affecting accuracy.This dissertation introduces the filtered Generalized Lock-in Amplifier(fGLIA)to the field of optical fiber vibration measurement,and improve it to make it more suitable for dynamic signal demodulation.Theoretically,the algorithm has better robustness to the modulation depth due to the special carrier structure.In the existing demodulation schemes that calculate the modulation depth and directly eliminate the influence of the modulation depth,the zero poles in the middle of the algorithm will lead to demodulation distortion.The improved PGC-fGLIA algorithm can demodulate stably in a wide range of modulation depths under experimental conditions.The main work of this dissertation includes:(1)The significance of seismic observation is explained.The mainstream interferometric optical fiber sensor is introduced in optical fiber vibration sensing.The principle of interferometric optical fiber sensing is analyzed.The existing PGC demodulation algorithm to solve the influence of modulation depth is summarized.The PGC demodulation algorithm is theoretically analyzed and the selection principles of parameters are given,and the calculation scheme of carrier phase delay and modulation depth is theoretically deduced.(2)The fGLIA algorithm is introduced and improved to make it suitable for dynamic signal demodulation.The principle of the PGC-fGLIA algorithm is deduced.It theoretically avoids the problem that the PGC-Arctan algorithm cannot be demodulated normally at a specific modulation depth.The PGC-Arctan algorithm and PGC-fGLIA algorithm are realized through simulation,and the influence of modulation depth and calculation error is analyzed on different demodulation algorithms.In addition,the simulation verifies the calculation scheme of phase delay and modulation depth,and lay the foundation for vibration measurement experiments.(3)The optical fiber optical path experimental platform and the optical fiber vibration sensor experimental platform were built.The phase delay in the experimental platform were analyzed.The modulation depth of the phase modulator Y waveguide in different experimental optical paths was calibrated.The calibration signals and vibration signals with different modulation depths were collected through the experimental platform,and the demodulation results of the PGC-Arctan algorithm and the PGC-fGLIA algorithm were compared to verify that the PGC-fGLIA algorithm can demodulate stably at different modulation depths.In the vibration experiment,the total harmonic distortion of the PGC-fGLIA algorithm demodulated signal can be maintained at-52 d B to-48 d B,which proves the practicability of the algorithm in the field of optical fiber vibration measurement.Through the above work,the influence of PGC algorithm demodulation parameter selection on the demodulation results is studied.The feasibility of PGC-fGLIA algorithm demodulation under different modulation depths is verified,and the PGC-fGLIA algorithm can be applied to optical fiber vibration measurement.It is hoped that it can provide a reference for the subsequent research work on the PGC demodulation algorithm.