All-optical transducer for ultrasound and photoacoustic imaging by dichroic filtering

The ultrasound (US) and photoacoustic (PA) multi-modality imaging has the advantages of combining good acoustic resolution with high optical contrast. An all-optical transducer for both imaging modalities can simplify the entire system design and miniaturize the imaging scanhead for intravascular imaging applications. In this study, we propose and demonstrate an all-optical US/PA transducer using a thin plate for optoacoustic generation for US imaging, a microring resonator for acoustic detection, and a dichroic filter to switch between the two imaging modes. In other words, a dichroic (i.e., a color filter) is used to selectively pass light depending on the imaging mode. When under US imaging, the light hits the color filter to generate US for US imaging. When under PA imaging, the light pass through the color filter and directly hits the image object. The experimental image results indicated that the US and PA imaging modes can be selected by switching the laser wavelengths using a dichroic filter. The imaging resolution and contrast were improved by applying the synthetic aperture focusing technique (SAFT). The axial and lateral resolutions of the implemented imaging system were 125μm and 2.52°, respectively, while application of the SAFT enhanced the contrast by about 5dB.