Silicon-photonics focused ultrasound detector for minimally invasive optoacoustic imaging

Abstract

One of the main challenges in miniaturizing optoacoustic technology is the low sensitivity of sub-millimeter piezoelectric ultrasound transducers, which is often insufficient for detecting weak optoacoustic signals. Optical detectors of ultrasound can achieve significantly higher sensitivities than their piezoelectric counterparts for a given sensing area but generally lack acoustic focusing, which is essential in many minimally invasive imaging configurations. In this work, we develop a focused sub-millimeter ultrasound detector composed of a silicon-photonics optical resonator and a micro-machined acoustic lens. The acoustic lens provides acoustic focusing, which, in addition to increasing the lateral resolution, also enhances the signal. The developed detector has a wide bandwidth of 84 MHz, a focal width smaller than 50 µm, and noise-equivalent pressure of 37 mPa/Hz1/2 – an order of magnitude improvement over conventional intravascular ultrasound. We show the feasibility of the approach and the detector’s imaging capabilities by performing high-resolution optoacoustic microscopy of optical phantoms with complex geometries.

Silicon photonic acoustic detector (SPADE) using a silicon nitride microring resonator

“…In the case of intravascular imaging [41] , acoustic focusing capabilities would need to be added to MRR-SPADE, which may be achieved by bonding the sensor to an acoustic lens, as demonstrated in Refs. [42] , [43] , or by utilizing larger microrings, which exhibit a needle-shaped focus [44] , [45] , [46] .…”