为提高成像光谱仪的工作波长范围，提出了基于双波段焦平面探测器(FPAs)的双衍射级次全共路Offner成像光谱仪结构。该结构中凸面光栅的一级衍射光和二级衍射光完全重叠共路传输，并可由焦平面处的双波段红外焦平面探测器IR FPAs实现级次的自然分离和同时探测。分析了该结构的工作原理和设计方法，基于几何光线追迹法仿真了谱线弯曲和色畸变特性，基于Huygens点扩散函数(PSF)仿真了光谱响应函数(SRF)并导出了光谱带宽。实验显示: 双衍射级次共路Offner成像光谱仪的工作波段为3~6 μm(二级衍射)和6~12 μm(一级衍射)，谱线弯曲和色畸变均小于0.5个像元宽度，光谱带宽分别为13.2~14.3 nm(二级衍射)和28.3~33.3 nm(一级衍射)，两个工作波段内的衍射效率均大于或等于20%。整个系统结构简单紧凑、光谱范围宽，满足对地物或深空目标的中等分辨率的中远红外光谱探测需求。

An Offner imaging spectrometer based on Infrared Focal Plane Arrays(IR FPAs) operated in two common-path diffraction orders was proposed to extend the spectrometer wavelength coverage. The overlapped rays from the first order and the second order of convex grating could be naturally separated and simultaneously detected by the dual-band IR FPAs on the focal plane. The basic principles and design cautions were discussed in detail. Through geometrical ray tracing, the spectral smile and keystone were evaluated. Based on Huygens Point Spread Function(PSF), the Spectral Response Function (SRF) was also simulated, from which the spectral bandpass was derived as well. The dual-band Offner imaging spectrometer covers the wavelength range of 3 to 6 μm in the second order and 6 to 12 μm in the first order with bandpasses of 13.2-14.3 nm and 28.3-33.3 nm respectively. The two diffraction orders have the same spectral smile and keystone characteristics by both within half of a pixel width. The grating efficiencies are not lower than 20% over the full wavelength ranges. For its compact construction and wide spectral coverage, the instrument is competent for the measurements of the earth surface or deep space objects in the middle- and long- wave infrared (MWIR/LWIR) regions with moderate resolutions.