基于相干激光雷达的激光微多普勒探测

Laser Detection on Micro-Doppler Effect in Coherent Ladar

利用相干激光雷达探测目标微动特性技术是一种以单频激光为光源,用外差探测的方式实现对低速、低频多个运动物体进行微多普勒信息提取和识别的技术。以波长为1.064μm的窄线宽单块激光器为光源,发射激光经过模拟长距离传输的4 km的光纤延迟,照射到以扬声器的发声单元和电动平移台为目标的微动物体上,目标反射的激光会聚进入单模光纤,参考光与信号光通过3 dB光纤合束器线性耦合进入同一根光纤,并在探测器表面进行相干。用于接收相干信号的探测器的接入方式为光纤输入,带宽为3.5 GHz。利用时间-频率域联合描述的方法对数/模(A/D)采样后的数据进行分析。在4 km光纤延迟时,本系统最低探测速度为0.5 mm/s,速度分辨率达到毫米每秒量级,频率分辨率达到千赫兹量级。利用微多普勒信息探测技术,实现了探测物体表面的微动状态信息和识别运动状态的目的。

A coherent ladar system for detecting vibration of a moving target was demonstrated. Micro-Doppler information was obtained to identify moving targets. Single frequency laser at 1. 064 μm was input to a 4 km long single mode fiber to simulate the translation of long distance. A loudspeaker was used as the target with micromotion. Back-scattered light from the target was collected by the receiving optics and coupled into a single mode fiber. A 3 dB fiber coupler was used to combine the received signal and the master oscillation, the output of the coupler was detected by a photodiode detector with 3.5 GHz bandwidth. The electrical signals of detector＇s output were sampled by a high speed A/D card. The information of micro-motion can be extracted through the arithmetic of time-frequency analysis. With the delay of 4 km fiber, the lowest speed that the system can detect was 0.5 mm/s, the resolution of speed detection was in the order of mm/s, the resolution of frequency was in the order of kHz. Utilizing the technology of micro Doppler detection, the targets of different motion dynamics can be classified and identified.