Using mechanics to convert between microwave and optical frequencies

Abstract

We demonstrate unique piezoelectric optomechanical devices able to coherently transfer microwave electrical signals to modulated optical signals, and vice versa, transferring modulated optical signals to microwave electrical signals. This coherent bilateral transfer, demonstrated most recently in a single device design, holds promise for the eventual demonstration of coherent transfer in the quantum domain. The basis of design for the devices with which this was accomplished is an optomechanical crystal that supports co-located optical and mechanical resonant modes, coupled to one other via moving boundary (index of refraction) modulation, either induced by motion from energy in the mechanical mode, or by optical pressure due to energy in the optical mode. The basis for coupling microwave mechanical motion to microwave electrical signals is via the use of a piezoelectric material for the entire device, where transduction itself is accomplished using metal transducers remote from the optomechanical structure. This remote design minimizes the lossy interaction of any optical signals with the metal electrode structures, but introduces the need to couple the electromechanical transducer to the optomechanical transducer via itinerant phonons, which presents a new challenge.