Measurement of Distance to Moving Target Using Frequency-Modulated Continuous-Wave Interference Technique

When a frequency-modulated continuous-wave interference technique is used to measure the distance to a moving target in real time, the Doppler effect causes deviations in the measurement results. To solve this problem, we propose a method that employs triangular wave modulation on the optical frequency of the laser light source. By generating two frequency-swept signals with opposite frequency-modulation directions in one modulation period, the Doppler effect can be eliminated using the opposite frequency shifts between the two frequency-modulation directions. Experimental results show that triangular wave modulation at a frequency of 2 Hz and an amplitude of 15.57 μm can overcome a 5-mm measurement deviation caused by the Doppler shift for single-direction motion; the standard deviation of the target distance measurement results is 0.035 mm. Simultaneously, we realize a distance measurement for a target moving with a velocity of 1 mm/s over a measurement range of 800 mm with good linearity. This technique also achieves a speed measurement of up to 9 mm/s at 800 mm, and the minimum relative error can reach 0.067%. The method can be used for real-time tracking measurement of the distance to the moving target, and it is useful for a wide range of applications of frequency-modulated continuous-wave interference-ranging technology. © 2019, Chinese Lasers Press. All right reserved.