# Nonlinear anisotropic dielectric metasurfaces for ultrafast nanophotonics

## TL;DR

This paper demonstrates broadband ultrafast optical modulation using anisotropic silicon nanobrick metasurfaces, revealing how nonlinear processes can be engineered for polarization control and ultrafast nanophotonic devices.

## Contribution

It develops a quantitative model to disentangle nonlinear effects in anisotropic nanostructures and demonstrates ultrafast, polarization-dependent optical switching with potential applications in photonic devices.

## Key findings

- Ultrafast transmission modulation achieved within 20 ps.
- Distinct nonlinear processes identified and modeled.
- Potential for polarization-multiplexed nanophotonic devices.

## Abstract

We report on the broadband transient optical response from anisotropic nanobrick amorphous silicon particles, exhibiting Mie-type resonances. A quantitative model is developed to identify and disentangle the three physical processes that govern the ultrafast changes of the nanobrick optical properties, namely two-photon absorption, free-carrier relaxation, and lattice heating. We reveal a set of operating windows where ultrafast all-optical modulation of transmission is achieved with full return to zero in 20 ps. This is made possible due to the interplay between the competing nonlinear processes and despite the slow (nanosecond) internal lattice dynamics. The observed ultrafast switching behavior can be independently engineered for both or- thogonal polarizations using the large anisotropy of nanobricks thus allowing ultrafast anisotropy control. Our results categorically ascertain the potential of all-dielectric resonant nanophotonics as a platform for ultrafast optical devices, and reveal the pos- sibility for ultrafast polarization-multiplexed displays and polarization rotators.