# Polarization Control via Artificial Optical Nonlinearity in Dielectric Metasurfaces

## TL;DR

This paper explores how dielectric metasurfaces can control light polarization through artificial optical nonlinearity, enabling new applications in nonlinear imaging and light generation.

## Contribution

The study introduces a model for designing metasurfaces with tailored third-order nonlinear optical properties, focusing on polarization control.

## Key findings

- An effective nonlinear medium model was developed for amorphous silicon-based metasurfaces.
- Quantitative values of artificial nonlinear susceptibility tensor elements were extracted.
- Functional devices demonstrated control over amplitude, phase, and polarization of emitted light.

## Abstract

Nonlinear optical
phenomena are generally governed by geometry
in matter systems, as they depend on the spatial arrangement of atoms
within materials or molecules. Metasurfaces, through precisely designed
geometries on a subwavelength scale, allow the optical response of
a material to be tailored far beyond its natural properties. Therefore,
metasurfaces are highly appealing for enabling the engineering of
nonlinear optical interactions. Current studies of nonlinear metasurfaces
predominantly focus on the phase control of the generated light. Nonetheless,
investigating the tensorial nature of the nonlinearity of metasurfaces
and its effect on the polarization of the generated light is critical
to fully unlocking a range of applications, such as nonlinear vector
beam generation and nonlinear polarization imaging. Here, we study
the artificial optical nonlinearity of a dielectric metasurface originating
from its meta-atom symmetry and describe the third-order nonlinear
behavior by considering the polarization degree of freedom. We establish
an effective nonlinear medium model that serves as a design toolbox
for developing amorphous silicon-based geometric metasurfaces with
customizable features for third-harmonic generation. We further extract
quantitative values of the artificial nonlinear susceptibility tensor
elements related to the investigated nonlinear process and geometry.
The implemented functional devices demonstrate the versatility of
dielectric metasurfaces in shaping the emitted light in terms of amplitude,
phase, and polarization for the precise engineering of advanced nonlinear
architectures targeting applications in nonlinear imaging and complex
light generation.