Design of simplified long wavelength infrared imaging systems based on optical-digital joint optimization

Long-wavelength infrared systems offer strong penetration capabilities and can operate without external illumination, making them invaluable in a wide range of applications. However, their reliance on specialized and costly materials such as germanium and zinc selenide significantly increase system costs, which poses challenges to broader adoption and large-scale deployment. In this paper, we propose a joint optimization method that explicitly incorporates diffraction effects into the design process, effectively simplifying the system by reducing the number of elements while maintaining high imaging quality. Two design examples including a traditional coaxial system and an off-axis freeform system are presented to demonstrate the effectiveness of the proposed method. Additionally, we introduce a tolerance analysis approach based on the structural similarity index of the imaging results, enabling a quantitative evaluation of the system's robustness against manufacturing and assembly deviations. Experimental validations are conducted to confirm the practical applicability and performance of the proposed method.