Ultrahigh-Sensitivity 3D-Printed Hollow Fabry-Perot Fiber Ultrasound Sensor for Photoacoustic Imaging

Photoacoustic imaging is an advanced imaging technique that requires highly sensitive ultrasonic detectors to capture weak high-frequency signals. Optical ultrasound sensors, particularly Fabry-Perot (FP) interferometers, offer a promising alternative with improved sensitivity, compact size, and electromagnetic immunity. However, traditional deposition-based FP fiber sensors, which rely on solid spacers, are mechanically constrained, limiting further sensitivity improvements. Existing printed structures are unable to achieve the high-frequency response required for photoacoustic imaging. In this work, we present an ultrahigh-sensitivity hollow FP fiber sensor fabricated by two-photon polymerization 3D printing and vapor deposition. The unique hollow design reduces the backing resistance limitations of the response film typically seen in solid FP sensors, resulting in improved displacement sensitivity with a high frequency response. The sensor achieves a total sensitivity of 797 mV/kPa, which is 22x higher than that of the conventional solid FP sensor, with a low noise-equivalent pressure of 2.8 Pa. It operates at a central response frequency of 1.5 MHz with a bandwidth of 1.2 MHz and features a wide response angle of 180 degrees, which minimizes blind spots. Additionally, we developed a photoacoustic imaging system based on this sensor, achieving a resolution of 117 mu m. This hollow FP fiber sensor offers a robust solution for high-precision ultrasound detection and imaging, enabling advanced photoacoustic imaging applications in the future.