衍射聚焦器件轴向光强分布的焦深和焦移特性,直接决定着系统接收面的装配误差和获得最佳的能量利用率。当器件的口径和面型特征尺寸可与照射波长比拟时,必须考虑光波与衍射器件的电磁作用。利用严格电磁分析方法――时域有限差分法,对有限口径衍射微柱透镜的轴向光强分布进行了严格分析,并且与传统的标量分析方法进行详细比较。分析比较了TE和TM极化波入射情况下,不同面型分布(8台阶,16台阶量化面型和连续面型)的衍射微柱透镜焦深和焦移特性与透镜F数的关系。结果表明透镜轴向光强最大点向透镜面偏移,焦移量的严格计算结果要大于标量计算结果,表明透镜的快聚焦特性,而二者得到的焦深量基本一致,同时两种理论方法都表明透镜焦深和焦移随F数的增加而增加。

It is necessary to study characteristics of axial intensity distributions, such as focal depth and focal shift, which influence the maximum energy efficiency obtained and the assembling error at the receiving plane. The rigorous electromagnetic characteristic must be considered for diffractive optical elements (DOEs) whose features are on the order of or smaller than the wavelength of the incidence illumination. The rigorous electromagnetic analysis of diffractive micro-cylindrical lenses that are finite in extent using a two dimensional finite-difference time-domain (FDTD) method is presented. Compared with the scalar theory, the axial intensity distributions of lenses with different F-numbers are analyzed rigorously, considering different incidence polarizations (transverse electric polarization and transverse magnetic polarization) and different profile structures (continuous profile, 16-level profile and 8-level profile) of lenses, respectively. It is shown that focal shifts calculated by the rigorous method are larger than those made by the scalar theory, and focal depths calculated by these two methods are consistent basically, furthermore, focal depth and focal shift increase when F-number increases for both the rigorous electromagnetic method and the scalar method.