A ring resonator of SiO2 is positioned on a thin membrane of Si. Acoustical waves cause oscillations of the membrane by which the ring deforms. This results in a change in optical resonance wavelength from the nominal value of 1.5 micron. The resonance shift is detected with an optical interrogator system. Prototype rings can measure acoustical frequencies around 1MHz with sensitivities and detection comparable to state of the art piezo-electric transducers. Research is in progress to realize ring resonators for the detection of higher acoustical frequencies.
Intravascular ultrasound imaging. Nondestructive testing of strength of materials. The ring resonators can be made in high volume at very low cost with standard CMOS processes.