High spatiotemporal resolution optoacoustic sensing with photothermally induced acoustic vibrations in optical fibres

Yizhi Liang,Bai-Ou Guan,Long Jin,Linghao Cheng,Huojiao Sun

doi:10.1038/s41467-021-24398-w

Abstract

Optoacoustic vibrations in optical fibres have enabled spatially resolved sensing, but the weak electrostrictive force hinders their application. Here, we introduce photothermally induced acoustic vibrations (PTAVs) to realize high-performance fibre-based optoacoustic sensing. Strong acoustic vibrations with a wide range of axial wavenumbers kz are photothermally actuated by using a focused pulsed laser. The local transverse resonant frequency and loss coefficient can be optically measured by an intra-core acoustic sensor via spectral analysis. Spatially resolved sensing is further achieved by mechanically scanning the laser spot. The experimental results show that the PTAVs can be used to resolve the acoustic impedance of the surrounding fluid at a spatial resolution of approximately 10 μm and a frame rate of 50 Hz. As a result, PTAV-based optoacoustic sensing can provide label-free visualization of the diffusion dynamics in microfluidics at a higher spatiotemporal resolution.

Highlights

Optoacoustic vibrations in optical fibres have enabled spatially resolved sensing, but the weak electrostrictive force hinders their application
The canÀ be monochromatic Árepresented as acÀoustic φ x; y; z; wtÁav1⁄4esAiφn?aðxu;nyiÞfoÁerimðkz optical fibre zÀωtÞ, where φ? x; y is the transverse mode profile (R0n or TR2n modes in this bcoynct2aeÁx∇t)2?, φw?hÀixch; ydÁe1⁄4terωm2reisnÁeφs?tÀhxe; rÁesonant y, where angular frequency ωres A denotes the complex amplitude and ca the acoustic velocity
By taking into account the loss coefficient b, the axial profile of the acoustic vibration can be expressed as φðzÞ

Summary

Introduction

Optoacoustic vibrations in optical fibres have enabled spatially resolved sensing, but the weak electrostrictive force hinders their application. A radar-inspired random access approach was demonstrated in which two phase-randomly modulated counterpropagating pump light beams created a localized acoustic vibration[26] This technique could resolve over 2 million independent sensing points in backward SBS-based distributed fibre sensors[27]. Two detuned counterpropagating light beams can create localized correlation peaks at particular fibre positions according to Brillouin optical correlation-domain analysis[29] This method was employed in a silicon–chalcogenide photonic waveguide with a resolution of hundreds of microns when measuring the Brillouin frequency shift[30,31], which can hopefully be used in acoustic impedance measurements based on the strong photon-phonon interactions in nanoscale waveguides[32]. Electrostriction creates a refractive index change of only 10-9, and it usually requires optical fibres tens or hundreds of metres long to retrieve the sensing signal

Methods

Results

Conclusion