【作者】 段啊丽；

【导师】 韩道福；

【作者基本信息】 南昌大学 ， 光学工程， 2012， 硕士

【摘要】 出射激光照射在粗糙物体表面上,被粗糙面反射或散射的部分光会按原路返回,重新进入激光腔内与原光混合,调制激光器的输出光功率,形成自混合散斑。输出光探头与粗糙物面的距离不同,或粗糙面的粗糙度不同,或粗糙面非静止时,速度不同等都会引起自混合散斑信号的改变。利用自混合散斑传回的信息来分析被测物面的相关属性是近几年光纤激光器传感研究的热点之一。选择一定粗糙度的待测物面,固定激光输出探头与被测物面的距离,控制被测面移动的速度,利用光电探测器探测不同速度下的散斑信号,在计算机上对信号进行分析处理,可以得出速度与散斑信号的属性值相关关系,利用二者的这种关系可以组建自混合散斑速度传感系统。本文首先介绍了目前对1550nm的环形掺铒光纤激光器已有的理论基础,并基于此对光纤激光器进行了改进,分别提出了等效F-P腔光纤激光器和Q型腔光纤激光器。同时对不同腔型输出的光功率作了理论推导,得到了输出光功率的表达式。然后,基于不同的掺铒光纤激光器搭建了两套自混合散斑速度传感系统,分别采用两种不同的信号处理方法----频谱能量密度法和分形盒数法对不同系统采集的自混合散斑信号分析处理,得出散斑频谱能量密度与被测目标速度成近似的线性关系,散斑信号的分形盒数与速度成近似的指数关系。利用实验中的经验公式,基于Labview软件编写虚拟仪器,实现自混合散斑信号的快速采集,实时处理,及被测目标速度的实时测量。接着,利用Matlab语言编写了滤波程序,采用自适应滤波器对信号进行滤波,提高了测速的精度。最后,通过编程对速度传感系统进行了优化,实现了速度实时测量结果的自动存档,速度大小的实时监控及报警系统,并且通过以太网实现了速度传感系统的远程监控。更多还原

【Abstract】 When light out from laser illuminates the rough surface of the measured target, part of light reflected or scattered reenter the laser cavity, mixing with the original one. Then the laser output power is modulated, and self-mixed speckle can be detected. The amplitude and the frequency of speckle is influenced on the different distance between measured target and the laser fan-out, the dissimilar roughness of measured target, and the distinct velocity the target moved at. Studing objects’ property by self-mixing speckle is one hotspot in recent years. If our target of certain roughness is chosen, and the distance detected is fixed, changing the velocity of target, analyzing the self-mixing speckle output, a relationship between speckle and velocity can be obtained. Based on this, a velocity measured system of self-mixed speckle will be built.In this paper, the basic theory of a ring cavity laser with1550nm erbium-doped fiber (EDF) is reviewed firstly. Grounded on this, two new fiber lasers are showed: the equivalent Fabry-Perot cavity fiber laser and the Q cavity fiber laser. The theory about the new cavities is studied, and the power expression of output laser is gained. Secondly, two velocity measured systems of different EDF laser are built. Self-mixed speckle signal which is collected from two systems is processed by two ways--energy density of speckle frequency spectrum and the number of box-counting (NBC). In our study, the linear dependence between energy density of speckle frequency spectrum and velocity is received. The index relationship between NBC and velocity is obtained. According to the experiential formula, a program is wrote by labview, where the signal is fastly collected and processed, and the target velocity is showed real time. Thirdly, to improve the measured precision, a programme of adaptive noise caceller is wrote by matlab to filter. Finally, some melioration is taken for our velocity measured system by additional program:the velocity measured real time can be saved automatically; the value of velocity is inspected real time, and if it exceeds the bound set at the beginning the system will give an alarm; the measured system can be controlled remotely by Ethernet.更多还原