Abstract

A compact fiber ultrasound-sensing device comprised of a Barium Titanate (BaTiO₃) microsphere coupled to an open cavity off-core Fabry-Perot (FP) fiber sensor fabricated through lateral offset splicing single mode fiber (SMF-28) is proposed and demonstrated. The multiple passes of the FPI enabled by the high refractive index microsphere brought a 40dB enhancement of finesse. The broadband ultrasound sensing over 0.1- 45 MHz is achieved by selecting whispering gallery modes (WGMs) via varying microsphere position. The scattering and internal reflection of light in the microsphere is enabled by multibeam interference, leading to an increase in passages and WGMs at specific resonant wavelengths, and hence the high contrast and quality factor of the transmission spectrum are obtained for broadband ultrasound detection at high sensitivity. The optimized lateral offset is governed by the diameter of the microsphere to maximize the frequency response of the acoustic wave of a piezoelectric transducer centered at 3.7 MHz.

© 2022 The Author(s)