Optical design of a cascade airborne spectral imaging system with wide FOV and compactness

Abstract

In response to the demands of light weight, small size, wide field of view (FOV) and real time airborne spectral imaging, a novel spectral imaging system with lightweight and compactness is designed based on fold cascade structure. A concentric cascade spectral imaging system is studied. It mainly consists of two optics, a front fold monocentric objective and an Offner spectral imaging array. The front fold monocentric objective achieves an intermediate curved image with wide FOV, then the Offner spectral imaging array divides the intermediate image into sub-images and obtains spectral sub images through dispersion and reimaging. Based on the first-order theory and aberration characteristics, the cascade spectral imaging system is optimized. The optimized cascade spectral imaging system is with a real time full FOV of 110°, focal length of 110mm, F number of 4.8 and a working wavelength band of 480nm to 760nm. After performance evaluation, both its smile and keystone are well balanced. The spectral resolution is about 0.6nm, the maximum RMS radius on image plane is less than 3μm, and the MTF value is over 0.5@85 lp/mm. The tube length of the optimized system is only 85mm. The obtained cascade spectral imaging system not only achieves a real time spectral imaging in a wide FOV, but also realizes the miniaturization and lightness. It has a great potential application for airborne remote sensing and will make profound theorical value in this field.