# Gigahertz optomechanical modulation by split-ring-resonator nanophotonic meta-atom arrays

## TL;DR

This paper demonstrates gigahertz-frequency ultrafast optical modulation using nanophotonic split-ring resonator arrays, revealing complex vibrational dynamics and acousto-plasmonic interactions with potential applications in ultrafast modulation and sensing.

## Contribution

It introduces a novel nanophotonic metasurface with split-ring resonators that achieve gigahertz modulation via ultrafast mechanical vibrations and detailed numerical analysis of their nanomechanical dynamics.

## Key findings

- Gigahertz oscillations in reflected infrared light induced by visible pump pulses.
- Multimodal vibrational response involving opening and closing motions of split rings.
- Acousto-plasmonic interactions dominate the ultrafast optical modulation.

## Abstract

Using polarization-resolved transient reflection spectroscopy, we investigate the ultrafast modulation of light interacting with a metasurface consisting of coherently vibrating nanophotonic meta-atoms in the form of U-shaped split-ring resonators, that exhibit co-localized optical and mechanical resonances. With a two-dimensional square-lattice array of these resonators formed of gold on a glass substrate, we monitor the visible-pump-pulse induced gigahertz oscillations in intensity of reflected linearly-polarized infrared probe light pulses, modulated by the resonators effectively acting as miniature tuning forks. A multimodal vibrational response involving the opening and closing motion of the split rings is detected in this way. Numerical simulations of the associated transient deformations and strain fields elucidate the complex nanomechanical dynamics contributing to the ultrafast optical modulation, and point to the role of acousto-plasmonic interactions through the opening and closing motion of the SRR gaps as the dominant effect. Applications include ultrafast acoustooptic modulator design and sensing.