Net on-chip Brillouin gain based on suspended silicon nanowires

TL;DR

This paper demonstrates high-efficiency continuous-wave Brillouin gain in suspended silicon nanowires, advancing on-chip phononic amplification, but highlights geometric disorder as a key challenge for nanoscale phonon technologies.

Contribution

It reports the highest Brillouin gain efficiency in silicon nanowires and explores the impact of geometric disorder on phononic device performance.

Findings

Achieved Brillouin gain exceeding optical losses in silicon beams.

Attained record efficiencies up to 10^4 W^{-1}m^{-1}.

Identified geometric disorder as a major challenge.

Abstract

The century-old study of photon-phonon coupling has seen a remarkable revival in the past decade. Driven by early observations of dynamical back-action, the field progressed to ground-state cooling and the counting of individual phonons. A recent branch investigates the potential of traveling-wave, optically broadband photon-phonon interaction in silicon circuits. Here, we report continuous-wave Brillouin gain exceeding the optical losses in a series of suspended silicon beams, a step towards selective on-chip amplifiers. We obtain efficiencies up to $10^{4} \, \text{W}^{-1}\text{m}^{-1}$, the highest to date in the phononic gigahertz range. We also find indications that geometric disorder poses a significant challenge towards nanoscale phonon-based technologies.