Large-Area, Broadband Multi-Level Diffractive Lens of Achromatic Imaging from Visible to Near-Infrared

The Multiorder Diffractive Lens (MDL) plays a crucial role in imaging systems due to its advantages of small size, light weight, and easy integration. Currently, both domestic and international analyses of MDL imaging performance indicate certain constraints between lens aperture, lens thickness, and the transmission band, which affect the application of MDL to some extent. This paper combines genetic algorithms (GA) and the Hook-Jeeves algorithm (HJA) to transform the MDL design problem into a mathematical optimization problem, solving for the height to improve the constraint relationship between the lens aperture and the transmission band. While ensuring a 5cm aperture, a wide spectral range focusing from 0.4 to 1.1[[EQUATION]] is achieved. Additionally, the processing of grayscale exposure has been optimized, achieving breakthroughs in large aperture fabrication technology. A 5cm aperture MDL is fabricated with an average measured radius of the large aperture MDL rings at 1.99[[EQUATION]] (designed ring width is 2[[EQUATION]]), and the deviation between the designed and processed values of step height is within 1%. This demonstrates high precision and uniformity in MDL fabrication. An optical test path compatible with a 10cm aperture is designed and built, to verify its focusing characteristics and imaging performance. The root mean square (RMS) focal length of MDL in the visible and near-infrared bands is found to be 22.90cm, with an RMS spot size of 24.94[[EQUATION]], and an average focusing efficiency of 42% from 0.4 to 1.1[[EQUATION]]. The line pair resolution is measured at 20.1 lp/mm. Furthermore, in terms of off-axis imaging performance, when inclined at [[EQUATION]], the MDL maintains consistent spot size and focal length with on-axis incidence, with a focusing efficiency of 53.57%, and a corresponding line pair resolution of 16 lp/mm. Experimental results demonstrate that the large aperture wide-band MDL exhibits good focusing performance and imaging effects in the visible to near-infrared spectrum, showing broad application prospects in fields such as microscopy analysis, photoelectric detection, and medical imaging.