We design a cavity optomechanical system in which a localized GHz frequency mechanical mode of a nanobeam resonator is evanescently coupled to a high quality factor (Q > 10^6) optical mode of a separate nanobeam optical cavity. Using separate nanobeams provides flexibility in independently designing the optics and mechanics of the system. In addition, the small gap ( approx. 25 nm) between the two resonators gives rise to a slot mode effect that enables a large zero-point optomechanical coupling strength to be achieved, with g=2pi > 300 kHz in a Si3N4 system at 980 nm and g/2pi approx. 900 kHz in a Si system at 1550 nm. The ability to achieve large coupling strengths to GHz frequency mechanics in Si3N4 is important due to its low intrinsic mechanical dissipation rate and broad optical transparency window, which allows operation throughout the visible and near-infrared. As an application of this platform, we consider wide-band optical frequency conversion between 1300 nm and 980 nm, using two optical nanobeam cavities coupled on either side to the breathing mode of a mechanical nanobeam resonator.
Citation: Optics Express
Pub Type: Journals
Optomechanics, photonic crystals, phononic crystals