| The Frequency-Modulated Continuous-Wave(FMCW)lidar can obtain the target distance information by processing the difference beat frequency signal between the received signal and the transmitted signal.Moreover,the performance used to measure the distance and velocity of the target is independent of the ambient light conditions,and no additional secondary light source is needed to provide illumination.The FMCW has sinusoidal wave、sawtooth wave and triangular wave,in which the triangular wave modulated continuous wave can measure the distance in the up-chirp and down-chirp,and use the positive and negative frequency-modulated slope to eliminate the coupling between distance and velocity information,so as to measure the target velocity.The FMCW lidar has the advantages of relatively simple structure、small size、light weight and low cost,so it has been widely used in military and civil fields.However,the measurement accuracy of FMCW lidar is easily affected by atmospheric interference and speckle noise on the surface of the object.The linewidth and modulation linearity of the laser source also affect the measurement accuracy of the target distance and velocity.In this thesis,the narrow-linewidth distributed feedback laser and the monolithic integrated dual-frequency laser are used as the light source of the lidar,respectively,to achieve the measurement of the target distance and velocity.The main research contents and results of this paper are as follows:(1)The research of FMCW lidar based on double-sideband modulation is realized,the ranging system of the double-sideband modulation lidar is built,and the experimental analysis is carried out.Double-sideband modulation lidar can use external modulation way,through the Mach-Zehnder modulator work in orthogonal offset points.The resulting ±1 order sideband with linear frequency modulation continuous performance.When the local carrier and ±1 order sideband beat frequency will produce a linear frequency variation of the microwave signal.The LFM triangular wave signal is loaded into the Mach-Zehnder modulator and the modulator to modulate the narrow linewidth laser with the linewidth of 0.8MHz.While the center frequency of 6 GHz、a modulation bandwidth of 2.4 GHz and a modulation period of 50μs is realized.The frequency-modulated continuous-wave ranging lidar based on double-sideband modulation has realized the measurement of different distances.In the experiment,the measurement distance is 50 m to 2935 m,and the maximum relative measurement error is 3.76% at 100 m.The relative error rate was maintained between 0.35% and 0.52%for distance measurement under different modulation bandwidths(0.8GHz-2.4 GHz).(2)The research of FMCW lidar based on linear frequency modulated dualfrequency laser is realized.The dual-frequency LFM lidar is built,and the experimental analysis is carried out.In the dual-frequency lidar system based on monolithic integrated dual-frequency distributed feedback laser,the dual-frequency laser frequency difference(i.e.beat frequency)is set to 15 GHz.According to the principle of sideband injection locking found dual-frequency laser lock range from 14.8 GHz to15.7 GHz and the maximum modulation bandwidth of 700 MHz linear frequency modulation continuous wave lidar is obtained.By loading the linear frequency modulation signal of the triangular wave into the laser,the dual-frequency LFM signal with a central frequency of 15 GHz and a bandwidth of 320 MHz,and a modulation period of 200 μs is realized.Dual-frequency LFM lidar can measure different distances and velocities.In the experiment,the distance of measurement is 55 m to 2935 m,and the maximum relative error of distance is 1.6% at 1105 m.The range of velocity measurement is 1.47 m/s to 5.05 mm/s,and the maximum relative error is 3.18% at1.47 m/s.By changing the length of the delay fiber or adjusting the resolution ratio of the oscilloscope,the distance resolution is 0.5 m and the velocity resolution is 1.02mm/s in the dual-frequency lidar system. |
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