Ultrabroad Bandwidth and Highly Sensitive Optical Ultrasonic Detector for Photoacoustic Imaging

We demonstrate an ultrasonic detector with unprecedented broad bandwidth and high sensitivity, based on an imprinted polymer optical microring. It has an acoustic response of up to 350 MHz at -3 dB and noise-limited detectable pressure as low as 105 Pa in this frequency range. Application of such a detector in photoacoustic imaging leads to improved axial resolving ability compared with using the conventional ultrasound detector, and sub-3 mu m axial resolution is achieved, which is more than a 2-fold improvement with respect to the reported record. The device's miniaturized cavity height guarantees its broadband response, and at the same time, its high optical quality factor ensures the detection sensitivity. Our work suggests that the polymer-based miniature microring resonator works as a high-performance ultrasound detector and has potential for acquiring volumetric photoacoustic images with cellular/subcellular resolution in three dimensions.