Study On Frequency Modulated Continuous Wave Laser Interference Fiber-optic Distance Measurement Technology

Frequency modulated continuous wave(FMCW)laser interference distance measurement is a new type of coherent detection technology.By demodulating the interference beat signal carrying distance information,it can achieve non-contact,high precision and large dynamic distance.However,due to the frequency modulation nonlinearity of the tunable laser source in the measurement system,the frequency spectrum of the beat signal is wide,which seriously restricts the accuracy of the measurement system.Therefore,this paper mainly studies two aspects of FMCW interferometric beat signal demodulation algorithm and laser frequency modulation nonlinear correction method.A frequency capture algorithm based on phase calculation is written.First,according to the principle of FMCW laser interference distance measurement,the fiber-optic FMCW interference distance measurement system is designed and built,and the acquisition of the beat signal is realized.Then,by performing amplitude correction and sliding filtering on the beat signal,a beat signal with consistent amplitude and higher signal noise is obtained,and the position and size of the signal extremum points are determined.The phase calculation of the beat signal is realized by combining the formula of the anti-cosine trigonometry function.Finally,according to the linear relationship between the phase-frequency-distance and the characteristics of phase segmentation,the high-precision demodulation of the beat signal is realized.The simulation and experiments verify the correctness and feasibility of the demodulation method,avoid the effect of quantitative error,and reduce the measurement blind zone.A frequency modulation nonlinear correction method for DFB semiconductor lasers is proposed.First,the static frequency modulation characteristics of DFB semiconductor lasers are tested,including the drive current-output optical power relationship,drive current-output optical frequency relationship,and the effect of frequency modulation nonlinearity on distance measurement is analyzed.Then,by establishing the relationship between the signal extreme point position and the laser modulation current,the drive current node parameters are compensated.The corrected current parameters are fed back into the measurement system,and the nonlinear correction of the laser is realized,and the linearity of the beat signal is increased by about 90 times after correction.Experiments show that the method is simple and easy to implement,and ensures the compactness of the system,which can effectively improve the measurement resolution of the system.Through the experimental calibration of the key coefficients in the distance measurement system,the distance measurement at different locations within the distance of 4.3m are realized,and the accuracy can be up to 58?m at 1.3m.In addition,the experiments prove that the triangular wave modulation can overcome the Doppler frequency shift produced when the target moves at a uniform speed,and achieves the distance-speed decoupling measurement of the moving target.The linear fitting result of the distance measurement is 0.9999,and the relative accuracy of the speed reaches 0.18%,which indicates that the system has good distance measurement linearity and speed accuracy.