Polymer microring resonators for high sensitivity, broadband, wide-directivity ultrasound detection and high-resolution imaging

Optical detection of ultrasound is an emerging technique based on the interaction of strain field and optical field, modulating the optical properties of the resonance cavity for sensitive detection. Such a detection scheme can have several unique advantages, such as broadband response and size-independent sensitivity, compared with conventional piezoelectric transducers. Detector's high sensitivity is essential for deep penetration depth, especially for high-resolution imaging because of the strong attenuation of high-frequency ultrasound. Besides, small element size has the advantage of realizing wide acceptance angle of ultrasound detection. Previously we have demonstrated optical-based ultrasound detectors using polymer microring resonators, showing flat spectral response from dc to high frequency, over 90 MHz at -3-dB. By improving the fabrication process, we are able to achieve a new generation device with higher sensitivity and smaller element size. An ultralow noise-equivalent pressure of 21.4 Pa over 1-75 MHz range has been achieved using a fabricated detector of 60 mu m diameter. We will mainly demonstrate its applications to photoacoustic imaging, including photoacoustic computed tomography and photoacoustic microscopy. The new generation device can also be applied to other ultrasound-related imaging and detection.