Research On Phase Demodulation Technique For All Fiber Laser Doppler Signal

All fiber laser Doppler measurement is a precise measurement technology based on laser Doppler effect and optical mixing principle,combined with fiber and optical passive device technology.It has many advantages,such as non-contact measurement,high measurement precision,fast response speed,high time resolution and displacement resolution,etc.The velocity measurement is used in the field of aeronautics and astronautics and detonation physics,and it is the frontier technology in the field of displacement measurement.Interference fringe counting and interference fringe phase analysis are commonly used to demodulate the laser Doppler signal.The displacement measurement resolution of fringe counting method is ? /2.The accuracy of phase analysis method can break through the limitation of wavelength,and reach nanoscale.At present,the fringe counting method is usually used in the all fiber Doppler measurement,it has two disadvantages,which are that the displacement resolution is too low and displacement direction cannot be distinguished.In this paper,the following works are carried out for all fiber laser Doppler phase demodulation:1.Focusing on the phase demodulation and motion direction discrimination,an all fiber optical path and phase demodulation algorithm is designed with a 3×3 fiber coupler as the core device.Three common phase demodulation algorithms: Hilbert phase demodulation algorithm,sinusoidal fitting algorithm and 3×3 fiber coupler phase demodulation algorithm,are analyzed and studied respectively.The main contents of the study are as follows: the effects of the signal sampling rate,signal-to-noise ratio and periodic sampling number and other parameters on three phase demodulation algorithm calculation accuracy are studied.Then 3×3 optical fiber coupler phase demodulation algorithm is selected to demodulate the all fiber Doppler signal,also the all fiber laser Doppler signal phase demodulation system design and signal processing are briefly analyzed.2.For the 3×3 fiber coupler phase demodulation system,the hardware circuit and software program based on FPGA chip are designed.Three Doppler signals are collected at high speed through A/D,the phase solution of signal is realized via FPGA,and real time detec tion of digital-to-analog conversion on oscilloscope is realized by DA.Or the communication between the displacement and the upper computer through W5300.3.An experimental system is built,and the feasibility of the experimental device and algorithm is verified by taking the movement of piezoelectric ceramics as the object.The experimental results show that the displacement measurement range of the system is 5nm~18.34 ?m,the phase measurement error of is 32.2?,and the measurement error of displacement is 0.023%.