Impact of fabrication errors and refractive index on multilevel diffractive lens performance

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 analyse 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.

Field at sharp focusing of shifted single-ring Laguerre–Gauss modes with circular polarization

“…Misalignment [15][16][17][18] in the formation of vortex beams can lead to the "splitting" of high-order optical vortices into firstorder components 19,20 . Similar phenomena are observed with the deviation of the wavelength of the illuminating beam 21 from the base one for which the optical element was manufactured [22][23][24][25][26][27] , and with errors in the DOE relief height [28][29][30][31] . Note, at such deviations, the vortex beam of the first order becomes asymmetric 32 .…”

Экспериментальное Исследование Изображающего Объектива На Основе Дифракционных Линз, Корректирующих Аберрации

“…Минимизация размеров объектива является актуальной задачей, без решения которой невозможно дальнейшее сокращение размеров таких устройств. Минимизировать размеры объектива можно, использовав дифракционную или гармоническую линзу [1][2][3][4][5][6][7][8]. За счет особой формы таких линз можно уменьшить хроматизм, но все же относительно высокая хроматическая аберрация этих оптических элементов должна устраняться дополнительной цифровой обработкой [9].…”