Net on-chip Brillouin gain based on suspended silicon nanowires

Raphaël Van Laer,Bart Kuyken,Alexandre Bazin,Dries Van Thourhout,Roel Baets

doi:10.1088/1367-2630/17/11/115005

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 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.

Highlights

The interaction between photons and acoustic phonons has been investigated in bulk materials since the 1920s [1, 2]
In case the phonons are generated by optical forces, the interaction is often called stimulated Brillouin scattering (SBS) – a feedback loop in which energy flows from the optical waves to the mechanical oscillator
Through a novel opto-acoustic nanodevice, a series of suspended silicon wires, we demonstrate modest (0.5 dB) net Brillouin gain with high efficiencies

Summary

Introduction

The interaction between photons and acoustic phonons has been investigated in bulk materials since the 1920s [1, 2]. The removal of the bandwidth restriction and the accompanying optical versatility has motivated a great deal of SBS work in small-core waveguides, from photonic crystal [6,7,8], dual-web [9] and subwavelength [10] fibres to chalcogenide [11,12,13] and silicon waveguides [14,15,16]. Mass-manufacturable siliconon-insulator chips are an exciting platform for high-density optomechanical circuitry, perhaps even at the quantum level [19,20,21] Recent work on this front has demonstrated promising photon-phonon coupling efficiencies in all-silicon waveguides [16]. From a wider perspective and not limited to our system, such geometric disorder may hinder development of nanoscale phonon circuits quite generally [19,20,21, 23]

Theoretical background

TPA and tan φ

Optomechanical experiments

Conclusion