提出了一种基于分数傅里叶变换的多平面成像方法。由空间光调制器给出时序加载全息图的同步信号到外部控制电路，外部控制电路根据时序信号控制聚合物分散液晶屏的开关，使非成像位置的聚合物分散液晶屏为开态，让光通过；使成像位置的屏为关态，接收图像。时序加载不同的全息图，在不同屏上得到了不同的像，利用人眼的视觉暂留效应，实现了多平面全息成像的三维显示。该投影方法可以通过控制光学系统参数和计算全息图时的采样条件调节深度范围，系统简单，易于实现。

A method of imaging on multiple focal planes based on fractional Fourier transformation is presented. It is used to compute the holograms, so that different images are projected at different depths in the same system. By using synchronization information sent by the spatial light modulator, the circuits control the switch of the polymer doped liquid crystal screens. That means only the one with the right depth is switched off corresponding to the projected image, others let light pass through. With the sequential loaded holograms on the spatial light modulator, different holographic images are presented on multiple focal planes. Three-dimensional (3D) display by holographic display imaging on multiple focal planes is realized as a result of visual staying phenomenon. The imaging depth can be adjusted according to parameters of the optical system and sampling conditions. Besides, the system is simple and easy to carry out.