Assembly of Optical Micro-Ring Resonator-Based Ultrasound Sensor for Photoacoustic Imaging

In the past couple of decades, optical coherence tomography (OCT) and photoacoustic imaging (PAI) have been developed and applied widely in biomedical and clinical research. Based on the interference of back-scattered light, OCT can reconstruct the sample in 3D with high resolution and high speed. Alternatively, PAI is another non-invasive imaging modality that combines optical excitation and ultrasonic detection. It can be used to visualize absorption differences in tissues to construct 3D images. In this work, we report on an assembly of an optical ultrasound detector for PAI. The sensor consists of an integrated optical micro-ring resonator (MRR) whose input and output waveguides are interfaced with optical fibers. These fibers are attached to specially developed miniature fiber holders, which enable automated manipulation and firm attachment of the fibers to the waveguides. The entire device assembly process is carried out with an automated setup for micro-positioning, active/passive precision alignment, attachment via welding, soldering, bonding, and automated optical inspection. This automated assembly station provides several significant advantages, such as positioning accuracy, short assembly time, and high reproducibility.