提出了一种具有增大焦深特性的改进型分形波带片(FZP)。分析并推导了改进型分形波带片基于优化参数w的周期公式；计算了改进型分形波带片在菲涅耳近似下的衍射光场分布以及对应的横向光场分布特性因子，包括分辨率因子（G），施特雷尔比(S)以及旁瓣强度因子(M)；同时分析了在不同的径向坐标r和r2下的改进型分形波带片的焦深特性，结果证明在径向坐标r下，改进型分形波带片的焦深是常规分形波带片焦深的1.5倍以上。分别从横向和纵向两个方面分析了改进型分形波带片的光场分布，结果表明，在宽带光照明下，改进型分形波带片的焦深也大于常规的分形波带片。

A modified fractal zone plate (FZP) with the character of extending the focal depth is proposed. Through calculating, the period and the structure of modified FZP with the parameter w are obtained. Within the Fresnel approximation, the diffractive field distribution and the corresponding factors of the transverse field distribution such as superresolution factor G, Strehl ratio S and sidelobe strength M have been studied using the numerical method. The properties of modified FZP in different radial coordinates (r and r2) also have been studied. The study shows that the modified FZP in r coordinate have a great improvement of focal depth than conventional FZP. The analysis of the lateral and axial properties shows that the focal depth of the modified FZP is larger than the FZP under the broadband lighting.