Inverse design of large-area metasurfaces

TL;DR

This paper introduces a fast, approximate computational framework for the inverse design of large-area metasurfaces, enabling multi-parameter and multi-wavelength optimization with high flexibility and validation against full Maxwell solutions.

Contribution

It extends previous metasurface design methods by employing a locally periodic approximation for efficient large-scale inverse design, including non-subwavelength structures.

Findings

Validated the approximation against brute-force Maxwell solutions.

Enabled optimization of large-area metasurfaces with thousands of parameters.

Extended applicability beyond subwavelength regimes to include additional diffracted orders.

Abstract

We present a computational framework for efficient optimization-based "inverse design" of large-area "metasurfaces" (subwavelength-patterned surfaces) for applications such as multi-wavelength and multi-angle optimizations, and demultiplexers. To optimize surfaces that can be thousands of wavelengths in diameter, with thousands (or millions) of parameters, the key is a fast approximate solver for the scattered field. We employ a "locally periodic" approximation in which the scattering problem is approximated by a composition of periodic scattering problems from each unit cell of the surface, and validate it against brute-force Maxwell solutions. This is an extension of ideas in previous metasurface designs, but with greatly increased flexibility, e.g. to automatically balance tradeoffs between multiple frequencies, or to optimize a photonic device given only partial information about the desired field. Our approach even extends beyond the metasurface regime to non-subwavelength structures where additional diffracted orders must be included (but the period is not large enough to apply scalar diffraction theory).