Fabrication of Nanostructures for Diffractive Optical Elements on Polyimide Membranes

Planar meta-lenses fabricated on flexible materials have changed the traditional view of diffractive optics by enabling compact, lightweight, and flexibility optical components. However, achieving high focusing efficiency and resolution remains a significant challenge in both design and fabrication. In this work, a nanofabrication approach combining photolithography and polyimide casting is employed to realize membrane-based multilevel phase-type Fresnel zone plates (FZPs) with high focusing efficiency. Computational and experimental results indicate that the focusing efficiency at the primary focus increases with the number of phase levels. FZPs with 16-level phase structure on polyimide membrane achieve 91.6% focusing efficiency (≈9.5× better than conventional amplitude-type FZPs). These lenses produced diffraction-limited focal spots with minimal side-lobes and significantly reduce unwanted diffraction orders, resulting in extremely low background signals. The lightweight and flexible design of these high-efficiency meta-lenses holds strong potential for a wide range of applications and techniques, including astronomy, free-space optical communications, spectroscopy, remote sensing and space instruments, where compact and adaptable optical systems are essential.