Breaking the sensitivity-frequency trade-off in a two-photon 3D-printed hollow-tympanic diaphragm Fabry–Perot fiber ultrasonic sensor

Developing ultra-sensitive miniature fiber sensors capable of detecting ultrasonic signals in the kilohertz range is of fundamental importance for a wide range of applications. However, current Fabry–Perot interferometric (FPI) fiber sensors face the main challenge of the intrinsic trade-off between sensitivity and resonant frequency, which hinders broadband ultrasonic detection. To break the sensitivity-frequency trade-off, we have proposed and demonstrated an FPI sensing diaphragm based on a hollow-tympanic diaphragm (HTD) structure. The HTD design integrates a centrally thinned tympanic-inspired region to enhance sensitivity and a peripheral hollow support to maintain the resonant frequency, effectively overcoming the trade-off between sensitivity and bandwidth. It is fabricated on the fiber end face using two-photon 3D printing technology for constructing an FPI acoustic fiber sensor. The obtained mechanical sensitivity reaches 1435 nm/kPa at the center frequency of 198 kHz, demonstrating that the HTD design effectively maintains high sensitivity within the high-frequency range. This result verifies that the proposed structure successfully mitigates the trade-off between the sensitivity and frequency response. Furthermore, the device successfully captures continuous pulsed ultrasonic signals generated by a spark discharge source, with demodulated results showing excellent agreement with the source frequency, confirming its potential for high-resolution acoustic field detection and transient ultrasonic measurement. Such a high-sensitivity probe capable of operating effectively in the high-frequency detection range holds great potential for applications in industrial ultrasonic monitoring, biomedical sensing, and structural health diagnostics.