相位调制激光多普勒频移测量方法的改进

本文对现有相位调制激光多普勒频移测量方法进行了改进,通过定义新的鉴频参量来同时利用相位调制信号直流和交流分量中的有用信息进行多普勒频移测量.由于相位调制信号直流分量中包含着调制信号光的Fabry-Perot干涉仪光强透过率,所以这一改进本质上是将基于Fabry-Perot干涉仪的边缘技术激光多普勒频移测量方法的优势引入到相位调制测量方法中,以提高其自身的性能.理论上证明改进后的相位调制激光多普勒频移测量方法无需对信号光的光强进行测量,所以可以进一步简化探测系统的结构和较少噪声混入的通道.另外,通过对改进前后鉴频和测量灵敏度曲线进行对比,还证明了其具有更高的测量灵敏度和动态范围.实验上对硬目标反射的频移可控信号光进行测量,不但证明了理论的正确性,而且证明了改进后的相位调制激光多普勒频移测量方法,测量动态范围提高约1倍,测量标准偏差降低约35%.

Improvement of phase modulation laser Doppler shift measurement method

Sinusoidal phase-modulated signal light through the Fabry-Perot interferometer can produce a beat signal. Moreover, its amplitude monotonically changes with the signal light frequency. So the beat signal amplitude can be used to measure laser-Doppler-shift. In addition to the beat signal, the phase-modulated signal also contains a direct current (DC) signal, and it still contains a large amount of Doppler-shift information, but the information is not utilized, resulting in the waste of Doppler information. In this paper, this kind of phase-modulated laser-Doppler-shift measurement method is improved to simultaneously utilize the useful information in the DC and beat signal for the Doppler-shift measurement. The specific method is to use the ratio of beat signal amplitude to DC signal amplitude to define a new parameter used in Doppler-shift measurement. The signal light intensity terms in DC and beat signal can be eliminated, so the improved phase-modulated laser-Doppler-shift measurement method does not need to measure the signal light intensity, which makes its structure further simplified and a noise channel eliminated. By comparing the frequency change curves between the newly defined parameter and the beat signal amplitude theoretically, we find that they have the same distribution rule. This theoretical result shows that the improved phase-modulated laser-Doppler-shift measurement method will keep the same working mode as un-improved one, and can inherit its advantages. In theory, by comparing the measurement sensitivity curves, it is proved that the improved phase-modulated laser-Doppler-shift measurement method has higher measurement sensitivity and dynamic range than the un-improved one. The useful information included in the DC signal is the modulated signal light intensity transmittance of Fabry-Perot interferometer. So the improvement is essential to introduce the advantages of edge-technique laser-Doppler-shift measurement method based on the Fabry-Perot interferometer into the phase-modulated method for achieving higher performance. Two phase-modulated laser-Doppler-shift measurement methods before and after improvement are separately used to measure the frequency-shifted controllable signal light reflected by a hard object. The experimental results are in accordance with the theoretical analysis results very well. The comparison of experimental result between the two methods shows that the improved phase-modulated laser-Doppler-shift measurement method can approximately double the measurement dynamic range and reduce about 35% measurement standard deviation compared with the un-improved one.