Broadband ultrasound sensing based on fused dual-core chalcogenide-PMMA microfibers

High-frequency ultrasound sensors are essential for high-resolution medical ultrasonic imaging and industrial ultrasonic non-destructive monitoring. In this paper, we propose highly sensitive broadband ultrasound sensors based on fused dual-core chalcogenide-polymethyl methacrylate (As₂Se₃-PMMA) microfibers. We demonstrate that ultrasound response is determined by the differential slope of transmission spectra in the dual-core microfiber, which is verified by detecting the acoustic response in various microfibers of different tapering parameters. A broadband ultrasound frequency range with a high signal-to-noise ratio (SNR) is achieved in the fused dual-core microfiber (DCM) with a sub-micron core diameter and a close core separation due to the large spectral slope at the quadrature points of the transmission spectrum. In addition, we experimentally demonstrate the sensing of ultrasound waves propagating with and without an aluminum plate in the DCM sensor. An ultrasound sensor with a broadband frequency range from 20 kHz to 80 MHz and an average SNR of 31 dB is achieved in a compact fused dual-core As₂Se₃-PMMA microfiber when it is directly placed on a piezoelectric transducer (PZT).