Multilevel diffractive lens in the MWIR with extended depth-of-focus and wide field-of-view
Tina M. Hayward, Syed N. Qadri, Nicole Brimhall, Freddie Santiago, M. Christophersen, Christopher Dunay, Richard L. Espinola, Héctor García Martín, C. C. Cheung, Rajesh Menon
Abstract
Optics in the mid-wave-infra-red (MWIR) band are generally heavy, thick and expensive. Here, we demonstrate multi-level diffractive lenses; one designed using inverse design and another using the conventional propagation phase (the Fresnel zone plate or FZP) with diameter = 25 mm and focal length = 25 mm operating at λ =4 μ m. We fabricated the lenses by optical lithography and compared their performance. We show that the inverse-designed MDL achieves larger depth-of-focus and better off-axis performance when compared to the FZP at the expense of larger spot size and reduced focusing efficiency. Both lenses are flat with thickness ≤0.5 mm and weigh ≤3.63 g, which are far smaller than their conventional refractive counterparts.