Modal spectroscopy of optoexcited vibrations of a micron-scale on-chip resonator at greater than 1 GHz frequency.

We analyze experimentally and theoretically >1 GHz optoexcited mechanical vibration in an on-chip micron-scaled sphere. Different eigen-mechanical modes are excited upon demand by the centrifugal radiation pressure of the optical whispering-gallery-mode, enabling an optomechanical modal spectroscopy investigation of many vibrational modes. Spectral analysis of the light emitted from the device enables deduction of its natural vibrational modes in analogy with spectroscopy of a molecule's vibrational levels, and its eccentricity perturbation is shown to induce spectral splitting.