Optical Ultrasound Resonators for Biomedical Photoacoustic Imaging: A Review

Photoacoustic imaging (PAI) stands out for reconstructing target objects with high resolution, which demands optimized acoustic performance. Unlike piezoelectric sensors, which face an inherent tradeoff between sensitivity and miniaturization, optical ultrasound sensors can achieve both high sensitivity and wide bandwidth with compact designs. In particular, optical resonance-based ultrasound sensors demonstrate exceptional performance due to the resonant cavity, which enhances the acoustic signal amplification. This review comprehensively summarizes the working principles and critical performance parameters of optical ultrasound sensors, along with the primary metrics for evaluating acoustic detection and imaging capabilities. We focus on three optical ultrasound resonator modalities with their latest discoveries and PAI implementations, analyzing the strengths and weaknesses. Furthermore, we discuss the emerging trends toward miniaturization, improved acquisition quality, and clinical implementation, which offer unprecedented opportunities for all-optical high-resolution, real-time visualization in PAI.