Design of a wide-band zoom optical system with a three-layer diffractive optical element

Current optical lenses for security are challenged by achieving high-resolution imaging across a wide spectrum and a large field of view while maintaining a compact structure with a high zoom ratio. Although the system's resolution can be improved through the introduction of a diffractive element, it concurrently poses the challenge of the system's low diffraction efficiency. In this paper, a zoom diffractive-refractive hybrid optical system is proposed by introducing a three-layer diffractive optical element (TLDOE). First, the relationships between the diffraction efficiency of the TLDOE and the Abbe number of its materials are studied, yielding material selection and matching methods for achieving high diffraction efficiency under wideband conditions, and the diffraction efficiency of wide-field system influenced by the microstructure heights of the TLDOE is further analyzed. Thus, a comprehensive design method for the TLDOE to achieve high diffraction efficiency over a broad spectrum and a large field of view is obtained. Moreover, based on the zoom differential equation, the conditions for a four-group three-trajectory zoom system to achieve a high zoom ratio within a compact structure are studied. Within a volume of only 145×46×46mm³, the system attains a diffraction efficiency exceeding 89% and a 20× zoom ratio, encompassing a spectrum from 450 to 1700 nm. It offers a significant reference approach for the realization of military security applications, with extensive application prospects.