Nature Commun. 5, 4452 (2014)

Credit: NPG

Cavity optomechanics explores the interactions that occur between electromagnetic and mechanical waves when they are tightly confined within a resonator. One kind of structure that supports simultaneous localization of light and vibration is an optomechanical crystal — a periodic structure that exhibits a bandgap for both photons and phonons. Now, an international team from Spain, France and Morocco report a one-dimensional silicon optomechanical crystal with a complete phononic bandgap and demonstrate for the first time experimentally the excitation of acoustic modes at a frequency 4 GHz. The optical and mechanical Q-factors of the structure are on the order of 104 and 103, respectively. The team observed six confined optical modes with wavelengths between 1,470 nm and 1,600 nm within their structure with vacuum coupling rates ranging from kHz to MHz. The advantage of this scheme is that it is compatible with on-chip integration and that the optical and mechanical properties of the design originate from different geometric features of the structure and thus can be designed independently.