High-sensitivity and wide-directivity ultrasound detection using high Q polymer microring resonators

Small size ultrahigh Q polymer microrings working at near visible wavelength have been experimentally demonstrated as ultralow noise ultrasound detectors with wide directivity at high frequencies $\left(>20\text{MHz}\right)$ . By combining a resist reflow and a low bias continuous etching and passivation process in mold fabrication, imprinted polymer microrings with drastically improved sidewall smoothness were obtained. An ultralow noise-equivalent pressure of 21.4 Pa over 1–75 MHz range has been achieved using a fabricated detector of $60\mu \text{m}$ diameter. The device’s wide acceptance angle with high sensitivity considerably benefits ultrasound-related imaging.