Tadayon Mohammad Amin, Baylor Martha-Elizabeth, Ashkenazi Shai
IEEE Trans Ultrason Ferroelectr Freq Control. 2014 Dec;61(12):2132-8. doi: 10.1109/TUFFC.2014.006505.
Piezoelectric technology is the backbone of most medical ultrasound imaging arrays; however, signal transduction efficiency severely deteriorates in scaling the technology to element size smaller than 0.1 mm, often required for high-frequency operation (>20 MHz). Optical sensing and generation of ultrasound has been proposed and studied as an alternative technology for implementing sub-millimeter size arrays with element size down to 10 μm. The application of thin polymer film Fabry-Perot resonators has been demonstrated for high-frequency ultrasound detection; however, their sensitivity is limited by light diffraction loss. Here, we introduce a new method to increase the sensitivity of an optical ultrasound receiver by utilizing a waveguide between the mirrors of the Fabry-Perot resonator. This approach eliminates diffraction loss from the cavity, and therefore the finesse is only limited by mirror loss and absorption. By applying this method, we have achieved noise equivalent pressure of 178 Pa over a bandwidth of 30 MHz or 0.03 Pa/Hz1/2, which is about 20-fold better than a similar device without a waveguide. The finesse of the tested Fabry-Perot resonator was around 200. This result is 5 times higher than the finesse measured in the same device outside the waveguide region.
压电技术是大多数医学超声成像阵列的核心；然而，在将该技术缩小到小于0.1毫米的元件尺寸时，信号转换效率会严重下降，而高频操作（>20兆赫兹）通常需要这种尺寸。作为实现元件尺寸低至10微米的亚毫米尺寸阵列的替代技术，光学超声传感与产生已被提出并得到研究。薄聚合物薄膜法布里-珀罗谐振器在高频超声检测中的应用已得到证实；然而，其灵敏度受光衍射损耗限制。在此，我们介绍一种通过在法布里-珀罗谐振器的反射镜之间利用波导来提高光学超声接收器灵敏度的新方法。这种方法消除了腔内的衍射损耗，因此精细度仅受反射镜损耗和吸收限制。通过应用该方法，我们在30兆赫兹带宽上实现了178帕的噪声等效压力或0.03帕/赫兹1/2，这比没有波导的类似器件高出约20倍。测试的法布里-珀罗谐振器的精细度约为200。该结果比在波导区域外同一器件中测得的精细度高5倍。
