基于矢量衍射理论，计算了径向偏振光束在焦点处光强分布。在径向偏振光束的聚焦过程中，焦斑大小主要取决于视场边缘的光线。根据这一特点，设计了以视场角正切值为自变量的连续型相位滤波函数。利用非线性规化算法，以缩小焦平面上横向宽度为目标，在不同的斯特尔比的约束条件下，优化得到一组相位滤波参数。计算结果表明，径向偏振光束通过此种相位滤波器再聚焦后，在保持相同斯特尔比的条件下，可获得更小的聚焦光斑。

Based on vectorial diffraction theory, the intensity distribution of radially polarized beam (RPB) at focal point is calculated. In the focusing process of the RPB, the size of focus spot is mainly decided by the light at the verge of field. According to this characteristic, a continuous phase filter function with the tangent of the field angle as independent variable is designed. A group of optimized phase filter parameters is acquired by non linear rules algorithms, targeting on a smaller focal spot and constrained by several Strehl ratios. The results show that the focused RPB through the proposed a phase filter, a shaper focus could be obtained with the same Strehl ratio.