Broadband highly amplified ultrasound in antiresonant hollow core fibers for optoacoustic sensing and neurostimulation

[Preprint] High frequency broadband ultrasound in nested antiresonant hollow core fibers (NANFs) is investigated for the first time. NANFs have remarkable features to enable high resolution microscale optoacoustic imaging sensors and neurostimulators. Solid optical fibers have been successfully employed to measure and generate ultrasonic signals, however facing relevant attenuation, limited frequency range, bandwidth, and spatial resolution. Here, we numerically demonstrate highly efficient ultrasonic propagation in NANFs from 10 to 100 MHz. The induced pressures and sensing responsivity are evaluated in detail, and important parameters for the development of ultrasonic devices are reviewed. High pressures (up to 234 MPa) and sensing responsivities (up to -207 dB) are tuned over 90 MHz range by changing the diameters of two distinct NANF geometries. To the best of our knowledge, this is widest bandwidth reported using similar diameter fibers. The results point out significant advance for fiber-based ultrasonic sensors and transmitters, contributing to improve their efficiency and microscale spatial resolution to detect, diagnose and treat diseases in biomedical applications.