An optomechanical ultrasound sensor on a silicon photonic chip provides unprecedented sensitivity due to an innovative optomechanical waveguide. Because of this high-sensitivity waveguide, the 20-μm sensor has a detection limit two orders of magnitudes better than piezoelectric elements of identical size. The low detection limit of the sensor enables new clinical and biomedical applications of ultrasonic and photoacoustic imaging such as deep-tissue mammography and the study of vascularization or innervation of potential tumorous tissue.
The sensor is based on a highly sensitive split-rib optomechanical waveguide fabricated using new CMOS-compatible processing. A low detection limit can improve the trade-off between imaging resolution and depth for ultrasound applications and is crucial for photoacoustic imaging, where pressures are up to three orders of magnitude lower than in conventional ultrasound imaging techniques. Furthermore, it may enable low-pressure applications like through-skull functional brain imaging, which suffers from the strong ultrasound attenuation of bone.
A fine-pitched (30 μm) matrix of these tiny sensors can be easily integrated on-chip with photonic multiplexers. This opens the possibility of new applications such as miniaturized catheters because the sensor matrices require only few optical fibers to be connected instead of one electrical connection per element in the case of piezoelectric sensors.
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