Invited
Fibre-integrated Brillouin Micro-spectroscopy

Brillouin imaging for mechanical micro-characterisation of biomaterials has strong potential for medical diagnostics of disease-modified tissues. Here we explore fibre integration pathways towards Brillouin endoscopy, required to translate the technology from laboratory to clinics.

Micromechanical properties of tissues, cells and biomaterials contain key information for understanding their physiological function and for evaluation of pathologic conditions. Brillouin imaging (BI) is an optical technique for mapping the longitudinal elastic modulus in three-dimensions with micron resolution [1]. It is based on the principle of inelastic scattering of light by thermally-activated acoustic vibrations (phonons). Since the technique uses a light beam of relatively low power and requires no physical contact with the tissue, the measurement can be non-invasive and suitable for in vivo diagnostics [2, 3].

To date, the main technological developments in the field of BI have focused on improvements in spectral resolution, sensitivity and the acquisition time of Brillouin spectrometers. The sample-facing part of the optical setup was kept unchanged, relying on a confocal microscopy system. The instrument usually requires full-sized optical table and constant adjustment of the optical alignment, thus confining the use of this technology to a research laboratory rather than clinical practice. To realize the technique`s potential for in vivo and in situ biomedical imaging, it is necessary to reduce the setup complexity and size using flexible and miniature probes. Fibre-optical probes compatible with typical flexible endoscopes (1-2 mm) could be an ideal solution for achieving scalable and portable Brillouin imaging systems.

Here we discuss the main challenges in fibre-integration of Brillouin micro-spectroscopy setups and present several routes towards achieving this goal. Our results demonstrate the performance of a single-fibre and a dual-fibre Brillouin probe used in combination with virtually-imaged phase-array spectrometer to realise fibre-integrated Brillouin spectroscopy of liquid samples [4].

References

1. Koski, K. J. & Yarger, J. L. Appl. Phys. Lett. 87, 061903 (2005).
2. Scarcelli, G. & Yun, S. H. Nat. Photonics 2, 39–43 (2008).
3. Antonacci, G. et al. J R Soc. Interface 12, 20150843 (2015).
4. Kabakova, I. V. et. al. J Innov. Opt. Health Sci. 10, 1742002 (2017).