Optical transduction and routing of microwave phonons in cavity-optomechanical circuits

Abstract

Going beyond the canonical cavity-optomechanical system consisting of a Fabry–Perot cavity with a movable end mirror, here we explore a new paradigm in which phononic crystal waveguides are used to wire together local cavity elements to form interacting microcircuits of photons and phonons. Single cavity-waveguide elements, fabricated in the device layer of a silicon-on-insulator microchip, are used to optically excite and detect C-band (∼6 GHz) microwave phonons propagating in phononic-bandgap-guided acoustic waveguides. Interconnecting a pair of optomechanical cavities via a phonon waveguide is then used to demonstrate a tunable delay and filter for microwave-over-optical signals in the 1,500 nm wavelength band. Finally, we realize a tight-binding form of mechanical coupling between distant optomechanical cavities, leading to direct phonon exchange without dissipation in the waveguide. These initial demonstrations indicate the potential of cavity-optomechanical circuits for performing coherent signal processing as well as for realizing new modalities of optical readout in distributed micromechanical sensors.