Cascaded hollow FP cavities on fiber end-face for ultrasonic and photoacoustic detection

For photoacoustic (PA) detectors, compact form factor, exceptional sensitivity, broad bandwidth, and omnidirectional responsiveness are crucial performance indicators. In this research, we introduce what we believe to be a novel cascaded hollow Fabry-Pérot (CH-FP) interferometric PA sensor fabricated via two-photon polymerization (TPP), which is based on single-mode optical fiber architecture. Featuring a micron-scale transverse dimension of 120μm, the device demonstrates a bandwidth exceeding 30 MHz, minimum detectable pressure of 0.58 Pa/Hz^(1/2) at 1 MHz, and an -3 dB angular response uniformity within ±90. The monolithic integration of optical readout and microfabrication scalability positions this technology as a promising candidate for next-generation PA tomography and endoscopy applications.