Role of Fabrication Errors and Refractive Index on Multilevel Diffractive Lens Performance

TL;DR

This study investigates how fabrication errors and refractive index variations impact the focusing efficiency of multilevel diffractive lenses, especially in the THz regime, to inform better design and manufacturing practices.

Contribution

It provides a statistical simulation analysis of fabrication imperfections and refractive index changes on MDL performance, highlighting the importance of initial parameter selection.

Findings

Fabrication errors reduce focusing efficiency significantly.

Refractive index variations also impact lens performance.

Number of ring height levels influences sensitivity to errors.

Abstract

Multilevel diffractive lenses (MDLs) have emerged as an alternative to both conventional diffractive optical elements (DOEs) and metalenses for applications ranging from imaging to holographic and immersive displays. Recent work has shown that by harnessing structural parametric optimization of DOEs, one can design MDLs to enable multiple functionalities like achromaticity, depth of focus, wide-angle imaging, etc. with great ease in fabrication. Therefore, it becomes critical to understand how fabrication errors still do affect the performance of MDLs and numerically evaluate the trade-off between efficiency and initial parameter selection, right at the onset of designing an MDL, i.e., even before putting it into fabrication. Here, we perform a statistical simulation-based study on MDLs (primarily operating in the THz regime) to analyze the impact of various fabrication imperfections (single and multiple) on the final structure as a function of the number of ring height levels. Furthermore, we also evaluate the performance of these same MDLs with the change in the refractive index of the constitutive material. We use focusing efficiency as the evaluation criterion in our numerical analysis; since it is the most fundamental property that can be used to compare and assess the performance of lenses (and MDLs) in general designed for any application with any specific functionality.