John and Marcia Price College of Engineering
8 Comparing the Performances of Multilevel Diffractive Lenses and Fresnel Zone Plates of High Numerical Aperture.
Jack Doughty; Rajesh Menon; and Apratim Majurnder
Faculty Mentor: Rajesh Menon (Electrical and Computer Engineering, University of Utah)
Abstract
This study investigates the performance of Multilevel Diffractive Lenses (MDLs) in comparison to Fresnel Zone Plates (FZPs) under identical geometric and fabrication constraints, focusing on high numerical apertures (NAs) of 0.7, 0.9, and 0.99. By employing the direct binary search inverse design algorithm, MDLs were optimized starting from the FZP design. Simulations were conducted at a wavelength of 0.532 μm using MEEP and RSoft to validate the designs. The results indicate that MDLsexhibit superior efficiency, intensity, and reduced aberrations compared to FZPs. At an NA of 0.99, the MDL demonstrated a Figure of Merit (FoM) of 16.0350, a 59.52% improvement over the FZP’s FoM of 10.0516. Both lenses showed identical Full-Width at Half Maximum (FWHM) values of 0.29287 μm, indicating similar resolving power. However, the MDL’s depth of field (DOF) was 17.65% shorter than that of the FZP, implying a tighter focus capability. Despite the minimal difference in DOF, the MDL’s higher efficiency and intensity distribution make it a promising alternative to FZPs in advanced optical applications. This study supports the potential of MDLs to enhance imaging systems, miniaturized optical devices, laser beam shaping, and fiber optics, paving the way for future innovations in thee fields.
Background
Diffractive optical elements (DOEs) have revolutionized the field of optics by offering compact, lightweight, and highly efficient solutions for precise light manipulation [1]. These characteristics make DOEs particularly suitable for applications where weight and space constraints are critical, such as microscopy, beam shaping, and fiber optics. Among the various types of DOEs, the Fresnel Zone Plate (FZP) has been one of the most popular and widely utilized lenses. The FZP consists of concentric rings that alternate between transparent and opaque regions, focusing light through the principle of diffraction. It’s simple yet effective design has made it a staple in numerous optical applications [2].
Advancements in micro-fabrication techniques, including imprint lithography and electron-beam lithography, have enabled the creation of even more compact, complex, and precise optical structures. This progress has led to the development of the Multilevel Diffractive Lens (MDL), which leverages the ability to pattern multiple discrete phase levels on a flat surface. Unlike the binary phase steps of the FZP, the MDL can manipulate light with higher efficiency and greater design flexibility [3][5]. Additionally, the MDL’s more compact design allows for more efficient use of space, which is beneficial in applications requiring miniaturized optical components.
The potential