Imprinted high-Q polymer micro-ring resonator array for high-resolution photoacoustic tomography

We present the first demonstration of a polymer-based micro-ring resonator array with over 40 elements fabricated using nanoimprint lithography (NIL), and its application for photoacoustic tomography imaging. By precisely varying the radius of each micro-ring at the nanometer scale and maintaining its high-quality factor, we achieved distinguishable resonances within a free spectral range of only 2.19 nm. The micro-ring array was used to perform photoacoustic tomography (PAT), achieving lateral and axial resolutions of 40 µm and 38 µm, respectively, and an ultrasound response bandwidth of 173.5 MHz, and a noise equivalent pressure (NEP) of 13.5 Pa. PAT images of ex vivo mouse prostates were acquired by the micro-ring array, showing a high correlation with biological tissue structures and regions of blood vessels. Further spectral analysis of the PAT images can differentiate the prostate cancers from the normal prostates. This work highlights the significant advantages of using NIL-fabricated micro-ring resonator arrays made from polymer materials, demonstrating their potential for advanced applications in biomedical imaging as well as optical communications and integrated photonic systems.