Majumder Apratim, Meem Monjurul, Stewart Robert, Menon Rajesh
Opt Express. 2022 Jan 17;30(2):1967-1975. doi: 10.1364/OE.443338.
We utilized inverse design to engineer the point-spread function (PSF) of a low-f-number, freeform diffractive microlens in an array, so as to enable extended depth of focus (DOF). Each square microlens of side 69 µm and focal length 40 µm (in a polymer film, n∼1.47) generated a square PSF of side ∼10 µm that was achromatic over the visible band (450 to 750 nm), and also exhibited an extended DOF of ∼ ± 2 µm. The microlens has a geometric f/# (focal length divided by aperture size) of 0.58 in the polymer material (0.39 in air). Since each microlens is a square, the microlens array (MLA) can achieve 100% fill factor. By placing this microlens array (MLA) directly on a high-resolution print, we demonstrated integral imaging with applications in physical security. The extended DOF preserves the optical effects even with expected film-thickness variations, thereby increasing robustness in practical applications. Since these multi-level diffractive MLAs are fabricated using UV-nanoimprint lithography, they have the potential for low-cost large volume manufacturing.
我们利用逆向设计来设计阵列中低f数自由形式衍射微透镜的点扩散函数（PSF），以实现扩展焦深（DOF）。每个边长为69 µm、焦距为40 µm（在聚合物薄膜中，n约为1.47）的方形微透镜产生一个边长约为10 µm的方形PSF，该PSF在可见光波段（450至750 nm）是消色差的，并且还表现出约±2 µm的扩展焦深。该微透镜在聚合物材料中的几何f/#（焦距除以孔径尺寸）为0.58（在空气中为0.39）。由于每个微透镜都是方形的，微透镜阵列（MLA）可以实现100%的填充因子。通过将此微透镜阵列（MLA）直接放置在高分辨率打印件上，我们展示了其在物理安全应用中的积分成像。即使存在预期的薄膜厚度变化，扩展焦深也能保留光学效果，从而提高实际应用中的稳健性。由于这些多级衍射MLA是使用紫外纳米压印光刻制造的，它们具有低成本大批量制造的潜力。
