A Transparent Acoustic Lens for Integrated Ultrasound-Optical Systems

Transparent ultrasound transducers (TUT) enable integration of ultrasound with optical techniques such as photoacoustic and fluorescence imaging. However, due to fabrication difficulty, most existing TUTs are flat and unfocused, which limits acoustic efficiency and precision. Conventional acoustic lenses using clear materials provide focusing but their curved geometry distorts the optical images. Here, we introduce a transparent acoustic lens based on a dual-sided binary Fresnel lens design, which maintains a flat optical interface while providing acoustic focusing. The lens was fabricated using PMMA and mineral oil, two materials with nearly matched refractive index but different speed of sound. Due to the mineral oil, we fabricated both glass-sealed and PET-sealed versions of the lens. The glass-sealed lens provided the clear optical results, while the PET-sealed lens demonstrated acoustic focusing. This work provides a pathway toward integrated ultrasound-optical systems that combine enhanced acoustic focusing with preserved optical image quality.