Topology optimization of freeform large-area metasurfaces

Abstract

We demonstrate optimization of optical metasurfaces over 10 5 -10 6 degrees of freedom in two and three dimensions, 100-1000+ wavelengths (λ) in diameter, with 100+ parameters per λ 2 . In particular, we show how topology optimization, with one degree of freedom per high-resolution "pixel," can be extended to large areas with the help of a locally periodic approximation that was previously only used for a few parameters per λ 2 . In this way, we can computationally discover completely unexpected metasurface designs for challenging multi-frequency, multi-angle problems, including designs for fully coupled multi-layer structures with arbitrary per-layer patterns. Unlike typical metasurface designs based on subwavelength unit cells, our approach can discover both sub-and suprawavelength patterns and can obtain both the near and far fields.

Inverse Designed Metalenses with Extended Depth of Focus

“…Such design methodologies, often referred to as inverse design, have been employed to design high efficiency periodic gratings 11 , monochromatic lenses 12,13 , PSF-engineered optics 14 and achromatic lenses [15][16][17] . Till date, however, there are limited experimental demonstrations of inverse-designed aperiodic metasurfaces exhibiting superior performance to optics designed by traditional methods.…”

Computational inverse design for cascaded systems of metasurface optics

“…Such work has led to designs for polychromatic and high-incidenceangle metasurface lenses and gratings [29,[33][34][35], and has facilitated the exploration of novel fabrication platforms, such as arrangements of Mie-scattering dielectric spheres [36]. Notably, recent works have considered the optimization of metasurfaces composed of multilayer metaatoms [37][38][39]. In such designs, differently-shaped dielectric scatterers are stacked on top of each other within a subwavelength volume, in order to achieve superior performance to singlelayer meta-atoms.…”

Overlapping domains for topology optimization of large-area metasurfaces

“…However, early designs were limited to small devices, whereas many practical applications require diameters 1000λ [8] that would require enormous computational resources for full Maxwell simulations. More recently, new inverse-design techniques have become capable of large-area design, using either an interpolated library of offline simulation results for a few parameters [3] or freeform topology optimization (in which every "pixel" is a degree of freedom) with online Maxwell solvers [5]. The fundamental strategy to rapidly model a large-area metasurface is to divide it up into many unit cells and then simulate each cell independently.…”