Design Of High Precision Ranging System Based On Mach Zehnder Fiber Interferometer

FMCW laser ranging technology has the advantages of non-contact measurement and does not rely on cooperative targets.It is one of the important methods to obtain large scale 3D object shape information,and has gradually become the main research content in the current measurement field.DFB laser can realize current tuning,has the advantages of fast sweep frequency,small package size,low price and so on,and has gradually become the preferred light source of FMCW laser ranging.However,it has the disadvantage of nonlinear frequency modulation when the driving current is injected linearly,which will lead to spectrum broadening of the output signal of the laser,and ultimately affect the ranging accuracy and measurement resolution of the whole ranging system.Aiming at the above problems,a high precision ranging system based on Mach-Zed fiber interferometer is designed in this paper.The system is composed of two parts: a semiconductor(DFB)laser frequency-modulated nonlinear correction subsystem and a frequency-modulated continuous wave(FMCW)high precision ranging subsystem.In this paper,the measuring principle of FMCW high precision range finder system and the influence of triangle wave frequency modulation on the vibration suppression of the range finder system are analyzed,and the influence of frequency modulation nonlinearity of DFB laser on the range finder accuracy is discussed.The method of correcting the nonlinear frequency modulation is studied.The open-loop correction algorithm and the nonlinear correction system based on optical fiber are designed.The open-loop correction algorithm mainly determines initial drive current waveform of the laser used in the system.The nonlinear correction system based on fiber realizes the tracking and phase locking of the standard signal,and then completes the frequency modulation nonlinear correction of DFB laser.Finally,the DFB laser signal with nonlinear correction is applied to the FMCW high precision ranging subsystem to carry out high precision ranging experiments.In this paper,the measurement results of the range finder system before and after calibration are compared,and it is proved that the range finder system has higher measurement accuracy under the locked state of DFB laser.The repeatability measurement of multiple target distances shows that the system has higher measuring accuracy and better repeatability when the measuring distance is less than 2m under the current experimental conditions.