A highly sensitive optomechanical ultrasound detector integrated onto 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 then read out this wavelength in real-time, producing a highly accurate signal.