An all-optical fiber-optic photoacoustic transducer

A highly sensitive fiber-optic Fabry-Perot photoacoustic transducer is proposed in this work. The transducer will consist of separate transmit and receive fibers. The receiver will be composed of a Fabry-Perot Ultrasound sensor with a selfwritten waveguide with all-optical ultrasound detection with high sensitivity. In previous work, we have shown an increase in resonator Q-factor from 1900 to 3200 for a simulated Fabry-Perot ultrasound detector of 45 mu m thickness upon including a waveguide to limit lateral power losses. Subsequently, we demonstrated a prototype device with 30nm gold mirrors and a cavity composed of the photosensitive polymer Benzocyclobutene. This 80 mu m thick device showed an improvement in its Q-factor from 2500 to 5200 after a self-aligned waveguide was written into the cavity using UV exposure. Current work uses a significantly faster fabrication technique using a combination of UV-cured epoxies for the cavity medium, and the waveguide within it. This reduces the fabrication time from several hours to a few minutes, and significantly lowers the cost of fabrication. We use a dip-coating technique to deposit the polymer layer. Future work will include the use of Dielectric Bragg mirrors in place of gold to achieve better reflectivity, thereby further improving the Q-factor of the device. The complete transducer presents an ideal solution for intravascular imaging in cases where tissue differentiation is desirable - an important feature in interventional procedures where arterial perforation is a risk. The final design proposed comprises the transducer within a guidewire to guide interventions for Chronic Total Occlusions - a disease state for which there are currently no invasive imaging options.