Ultrasound Detector – Optomechanical Silicon Photonics

A highly sensitive optomechanical ultrasound detector integrated into a silicon photonic chip has been developed by researchers. The device is 100 times more sensitive than state-of-the-art piezoelectric detectors of identical sizes. Their design could substantially improve the performance of ultrasound detectors in a wide variety of biomedical applications.

The researchers used a new optomechanical ultrasound sensor (OMUS). Their ultrasound detector design was based on a “split-rib” silicon photonic waveguide: containing the main part attached to a moveable membrane; and a thinner “rib” attached to a fixed substrate. This part of the waveguide was arranged in a ring shape, causing it to act as a photonic resonator. Both parts were separated by a tiny gap just 15 nm across, which contained an intense electric field.

When an ultrasound wave distorted the membrane even slightly, the electric field generated a large change in the waveguide’s refractive index – altering the resonant wavelength of the ring-shaped rib in turn. Using a tunable laser, the researchers could read out this wavelength in real-time, producing a highly accurate signal.

The researchers describe their sensor as a game changer in deep tissue imaging. Because of its low ultrasound detection limit, the OMUS is ideal for biomedical applications such as mammography and tumor detection. It could even be used in miniaturized catheters and to perform non-invasive brain imaging through the skull, which was previously impractical due to bone’s strong ultrasound attenuation.

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