Guided-wave Brillouin scattering in air

TL;DR

This paper reports the discovery of stimulated forward Brillouin scattering in air within hollow-core fibers, providing a new optomechanical interaction that is tunable and useful for sensing applications.

Contribution

The study introduces a new form of gas-based Brillouin scattering in hollow-core fibers, supported by an analytical model and numerical simulations, expanding optomechanical interaction understanding.

Findings

Observed a resonance at 35 MHz corresponding to axial-radial acoustic mode.

Developed an analytical model predicting Brillouin coupling strength and frequency.

Identified potential applications in sensing and limitations for certain optical systems.

Abstract

Here we identify a new form of optomechanical coupling in gas-filled hollow-core fibers. Stimulated forward Brillouin scattering is observed in air in the core of a photonic bandgap fiber. A single resonance is observed at 35 MHz, which corresponds to the first excited axial-radial acoustic mode in the air-filled core. The linewidth and coupling strengths are determined by the acoustic loss and electrostrictive coupling in air, respectively. A simple analytical model, refined by numerical simulations, is developed that accurately predicts the Brillouin coupling strength and frequency from the gas and fiber parameters. Since this form of Brillouin coupling depends strongly on both the acoustic and dispersive optical properties of the gas within the fiber, this new type of optomechanical interaction is highly tailorable. These results allow for forward Brillouin spectroscopy in dilute gases, could be useful for sensing and will present a power and noise limitation for certain applications.