大气湍流对象限探测器光斑检测的影响

Atmospheric turbulence effect on detecting spot of four-quadrant detector

大气湍流运动频率一般在几赫兹到几百赫兹之间变化,激光在大气中传输时将受到此种运动的调制,调制的结果将对接收到的光斑能量分布形式与光斑形状产生影响,光斑能量与形状的变化将对象限探测器(QD)的输出产生影响。设计了一种湍流环境下的光斑检测后续处理电路,该电路使用两级增益系统,初级增益主要抑制噪声,二级增益使用可变增益放大,实现对象限探测器输出信号的有效放大与处理。搭建实验系统来完成湍流环境下的器件性能测试,当测试距离为830m时,完成不同信噪比、光斑大小、调制信号对探测器影响的测试;当测试距离为12.5km时,象限探测器没有细分能力,噪声占据整个光敏面,失去光斑检测的能力,使用数字滤波可以提高其细分能力。

Movement frequency of atmospheric turbulence varies between a few Hz to hundreds Hz.When laser transmits in the atmospheric,some characteristis will be changed by turbulence modulation.The energy distribution form and shape of spot will varied with movement frequency of turbulence,mean while,output of detector will be effected.In order to test the effect of turbulence on detector and ensure output signal is amplified and processed effectively,a kind of spot detection circuit was designed in turbulent environment.Two bands amplification was used in system.The noise suppression was completed in the first band and variable gain amplifier was used in the second band to meet the requirement of light intensity.Testing system was set up to test the characteristic of quadrant detector in turbulence.Experiment of spot detection in field was carried out.Influence of detector on different SNR,spot size and modulated signal was tested at the distance of 830 m.And the ability to detect spot is invalid at the test distance of 12.5 km because photosensitive surface is occupied by noise from the impact of turbulence,which shows that subdivision of quadrant detector has been broken in a long distance when digital filter is uesd the subdivision can be improved.