Optical design of athermalized infrared dual-band annular folded lens with multilayer imaging diffractive optical elements

Abstract

In order to realize the miniaturization of the infrared dual-band imaging system, a common optical path annular folded lens (AFL) with multilayer imaging diffractive optical element (MIDOE) is designed in this paper. The design principle of the AFL is studied, and the relationship between the obscuration ratio and the field of view is given. For the wide temperature range, the theoretical model of the optimal substrate materials selection for the MIDOE is established to achieve the high diffraction efficiency. According to theory analysis, the infrared dual-band AFL with IRG26-ZNS MIDOE is designed in the mid-wave infrared (MWIR) 3∼5 μm and long-wave infrared (LWIR) 8∼12 μm. The focal length is 50 mm, the equivalent F number is 1, and the full field of view is 14 ° The modulation transfer function (MTF) curves of each field of view are close to the diffraction limit when the spatial frequency is 20lps/mm, and the MTF values are greater than 0.61 and 0.28 in MWIR and LWIR, respectively. When the ambient temperature ranges from -40 °C to 80 °C, the high image quality is achieved in dual-band. In addition, the tolerance analysis is performed to verify machinability of the system. The research in this paper has important significance for the realization of a new generation of the low-cost, integrated dual-band imaging system.