采用双层Kinoform型衍射光学元件，设计了一种能够同时在红外中波(MWIR)3~5 μm和长波(LWIR)8~14 μm波段内工作的双波段光学系统。系统仅使用两种材料（ZnS和ZnSe）和四片透镜，实现了焦距100 mm、F数1.2的长焦距、大相对孔径光学系统设计。通过数值仿真运算，合理地选择双层衍射光学元件的两种基底材料及设计波长，衍射光学元件的带宽积分衍射效率超过96%。系统像差得到了很好的校正，成像质量良好，中波所有视场调制传递函数(MTF)(14.3 lp/mm)大于0.7，长波大于0.65，且接近衍射极限，同时分析了衍射效率对系统MTF的影响。最后利用Matlab软件绘制了衍射表面微结构仿真图，两个衍射面的最大闪耀深度分别为179.3 μm和159.4 μm，最小特征尺寸为1.41 mm，完全满足目前金刚石车削工艺的加工要求。

A dual-band infrared optical system working in both mid-wave infrared (MWIR) (3~5 μm) and long-wave infrared (LWIR) (8~14 μm) has been designed with the double-layer Kinoform diffractive optical elements (DOEs). The system is comprised of four lenses , two ZnS lenses and two ZnSe lenses, and its focal length is 100 mm with F number of 1.2. The average efficiency of double-layer DOEs made of ZnS and ZnSe is more than 96%. The aberration of the system has been improved perfectly. When the Nyquist frequency is less than 14.3 lp/mm, the modulation transfer function (MTF) in MWIR is more than 0.7, which approaches to the diffraction limit. The MTF in LWIR is more than 0.65 in the same frequency. The effect of the efficiency for the MTF has been analysed. Due to the high diffraction efficiency, efficiency is not the main effect element for the performance of the system. A figure generated by the Matlab software shows the curves of the profile of DOEs. The blazed depths of the two kinoform surface have been calculated by the same software, which is 179.3 μm amd 159.4 μm, respectivly. The minimum feature size of the DOEs is 1.41 mm. It can be manufactured by the single-point diamond tuning (SPDT) technology easily and precisely.