Abstract: To extend the depth of focus of a incoherent optical system becomes a hotspot problem in the domain of opticals.In this paper，based on the basic principle of cubic-phase-modulation phase mask，MTF is analyzed deeply.A lot of simulation testing is maken and how to set up an important parameter（a） is put forward.The MTF of incoherent optical imaging system show extremely insensitive to the larger scale of defocus(－20≤ψ≤20).So the arbitrary MTF in the scale of defocus can be used to restore the blurred image and the simulation results prove the feasibility of this method.

Key words: defocus, stationary phase method, cubic-phase-modulation phase mask, large depth of-focus imaging system

摘要： 扩大非相干光学成像系统的焦深已是应用光学领域热点问题。从相位掩膜板的基本原理出发，对其调制传递函数（MTF）的性质进行了深入分析，并从仿真实验结果中提出了一个重要参数a的设定方法，从而使得成像系统即使在前向离焦和后向离焦的较大范围内(－20≤ψ≤20)内传递函数仍表现出极不敏感性。这样可以用其最大离焦范围内中任意调制传递函数逆变化来还原图像。仿真实验证明了用该方法的可行性。

关键词: 离焦, 稳相法, 相位掩膜板, 大焦深成像系统