Large evanescently-induced Brillouin scattering at the surrounding of a nanofibre

TL;DR

This paper reports the first observation of highly efficient evanescently-induced Brillouin scattering near a nanofibre, with a gain coefficient significantly surpassing that of traditional fibers, opening new possibilities in free-space optoacoustics and sensing.

Contribution

It demonstrates, for the first time, strong Brillouin scattering driven by evanescent fields around a nanofibre, with a gain coefficient much higher than in conventional fibers.

Findings

Maximum gain coefficient of 18.90 m$^{-1}$W$^{-1}$.

Gain is 11 times higher than in hollow-core fibre.

Enables new applications in spectroscopy, microscopy, and optomechanics.

Abstract

Brillouin scattering has been widely exploited for advanced photonics functionalities such as microwave photonics, signal processing, sensing, lasing, and more recently in micro- and nano-photonic waveguides. So far, all the works have focused on the opto-acoustic interaction driven from the core region of micro- and nano-waveguides. Here we observe, for the first time, an efficient Brillouin scattering generated by an evanescent field nearby a sub-wavelength waveguide embedded in a pressurised gas cell, with a maximum gain coefficient of $18.90 \pm 0.17$ m$^{-1}$W$^{-1}$. This gain is 11 times larger than the highest Brillouin gain obtained in a hollow-core fibre and 79 times larger than in a standard single-mode fibre. The realisation of strong free-space Brillouin scattering from a waveguide benefits from the flexibility of confined light while providing a direct access to the opto-acoustic interaction, as required in free-space optoacoustics such as Brillouin spectroscopy and microscopy. Therefore, our work creates an important bridge between Brillouin scattering in waveguides, Brillouin spectroscopy and microscopy, and opens new avenues in light-sound interactions, optomechanics, sensing, lasing and imaging.