Ultrasensitive and broadband micro-ring based optomechanical ultrasound sensor for photoacoustic imaging

This is the authors' abstract. We don't add key points for this paper.

Recent advances in ultrasonography and photoacoustic tomography call for ultrasound sensors with high sensitivity, broad bandwidth, miniaturized footprint, and scalability. A conventional piezoelectric transducer is fundamentally constrained by limited sensitivity, element density, and system integration complexity. In this work, we introduce a micro-ring based optomechanical ultrasound sensor using a SiN/Si hybrid waveguide structure with a 30 nm air gap engineered within the sensing region. The micro-ring resonator exhibits a high-quality factor of 4.8 × 10 4 and a free spectral range (FSR) of 18 nm at the wavelength of 1580 nm. With a compact diameter of 18 µm, the sensor achieves a low noise-equivalent pressure below 0.64 mPa Hz −1/2 over a frequency range of 2–30 MHz, which is two orders of magnitude better than piezoelectric devices of the same size. Furthermore, the device enables photoacoustic signal detection at a depth up to 10 cm and offers a wide acceptance angle of ±20° for frequencies up to 20 MHz. High-resolution photoacoustic tomography of a graphite pencil lead is demonstrated, revealing sub-millimetric structural details. With its exceptional sensitivity, broad bandwidth, and inherent compatibility with chip-scale multiplexing, this platform offers a promising solution for minimally invasive photoacoustic endoscopy, high-resolution imaging systems, and highly dense ultrasound sensor networks.