150 MHz polymer resonator for optoacoustic mesoscopy based on a tapered optical fiber

Optical ultrasound detection enables greater miniaturization than conventional piezoelectric transducers while preserving high sensitivity. Although sub-micron silicon photonics detectors have been demonstrated, image artifacts caused by surface acoustic waves interference remain a key challenge. Polymer detectors offer better acoustic coupling, yet they have been limited to tens of micrometers in size because of optical confinement requirements. Here we overcome that limit with the smallest polymer resonator built on an optical fiber, using a 6 µm thick polymer cavity on a tapered single mode fiber tip. The detector achieved a bandwidth of about 150 MHz and a noise equivalent pressure density of about 1.5 mPa.Hz^-1/2. Imaging experiments yielded 7 µm axial and 17 µm lateral resolution, with high fidelity performance that surpassed piezoelectric and state of the art optical detectors. This combination of broad bandwidth, artifact free imaging, and manufacturability makes the detector ideal for optoacoustic mesoscopy (OptAM) applications.