Design of compact wide-band optical system based on double-layer diffractive elements

Diffractive optical elements (DOEs) have obvious advantages in wide-band achromatization and athermalization, and are widely used in wide-band optical systems. Based on the bandwidth-integrated average diffraction efficiency (BIADE) model, a double-layer diffractive optical element (D-DOE) suitable for wide-band applications was designed using BaF₂ and Sapphire materials. By combining it with refractive elements, a wide-band optical system with an F-number of 4.9 and a focal length of 24 mm for the ultraviolet-shortwave infrared range (0.35 µm~2 µm) was designed, which could achieve athermalization within the temperature range of −40 ℃~80 ℃. At the Nyquist cutoff frequency of 41 lp/mm, the modulation transfer function (MTF) of all fields of view in the ultraviolet-visible bands (0.35 µm~0.78 µm) and near-infrared-shortwave infrared bands (0.78 µm~2 µm) is greater than 0.65 and 0.5, respectively, while maintaining an ultra-compact form factor measuring just 30 mm×11 mm with a total weight of only 2.35 g. This system has significant advantages in terms of imaging quality, miniaturization and lightweight of the optical system.