塑料光纤激光打标散射点实验研究

塑料光纤（Plastic Optical Fiber，POF）纤芯散射点的形状和大小尺寸控制对基于半导体激光器（LD）和侧面发光POF的LCD背光源设计具有重要意义。研究了一种表面无损伤的POF纤芯散射点的激光打标方法，基于非成像光学的边缘光线原理分析了激光打标制作POF纤芯散射点的二次聚焦过程，推导出激光侧面入射在POF上表面时的焦点坐标的表达式计算式。实验研究了1.06 m波长激光在POF纤芯制作打标散射点时，激光光束半径（打标聚焦透镜高度）、激光功率和重复打标次数对POF散射点形状和体积尺寸的影响。纤芯内散射点的检测采用650 nm激光的散射光相对光强分布进行检测，通过显微照片的对比判断散射点的形状和尺寸。实验结果表明，POF纤芯散射点的形状决定于激光光束半径（打标聚焦透镜高度），当聚焦透镜高度激光光束半径为束腰半径透镜焦距时，可以得到光纤径向细而长的条散射点；。当聚焦透镜高度小于聚焦透镜焦距时，在POF上下两个表面附近形成漏斗状散射点。而随着激光功率增大和重复打标次数增加，散射点的体积尺寸随着增加。单次打标时POF的激光损伤阈值约为80 W/mm2，而要使POF散射点具有稳定的细长条状，激光功率密度应大于140 W/mm2。

Experimental study on laser marking for scattering points of plastic optical fiber

The controllable parameters of shape and size of the scattering points of the plastic optical fiber (POF) core are of great significance to the design of the LCD backlight based on the semiconductor laser diode (LD) and the side-glowing POF. A laser marking method for POF core scattering points with surface damage free was researched. Based on the principle of edge-ray in non-imaging optical theories, the secondary focusing at laser beam for marking POF core scattering points was analyzed, and the formulas for focal point coordinates of laser incident on the POF was derived. The effects of focusing lens height, laser power and marking repeat times on the shape and size of scattering points in the fiber core of POF were studied experimentally by using a 1.06 m laser marking system. Relative intensity distribution of the scattered laser at 650 nm was used to detect scattering points in fiber core,the shape and size of the scattering points are judged by comparison of their micrographs. The experimental results showed that the shape of scattering points in the fiber core was determined by focusing lens height.When the focusing lens height was the focal length of the lens, elongate scattering points along the radial direction can be obtained. With the increase of laser power or marking repeat times, the size of scattering points increased. The laser damage threshold of POF was about 80 W/mm2 under single laser marking. However, the laser power density should be greater than 140 W/mm2 in order to make the scattering points have steady elongated shapes.