Controlling phonons and photons at the wavelength scale: integrated photonics meets integrated phononics

Abstract

Radio-frequency communication systems have long used bulk- and\nsurface-acoustic-wave devices supporting ultrasonic mechanical waves to\nmanipulate and sense signals. These devices have greatly improved our ability\nto process microwaves by interfacing them to orders-of-magnitude slower and\nlower loss mechanical fields. In parallel, long-distance communications have\nbeen dominated by low-loss infrared optical photons. As electrical signal\nprocessing and transmission approaches physical limits imposed by energy\ndissipation, optical links are now being actively considered for mobile and\ncloud technologies. Thus there is a strong driver for wavelength-scale\nmechanical wave or "phononic" circuitry fabricated by scalable semiconductor\nprocesses. With the advent of these circuits, new micro- and nanostructures\nthat combine electrical, optical and mechanical elements have emerged. In these\ndevices, such as optomechanical waveguides and resonators, optical photons and\ngigahertz phonons are ideally matched to one another as both have wavelengths\non the order of micrometers. The development of phononic circuits has thus\nemerged as a vibrant field of research pursued for optical signal processing\nand sensing applications as well as emerging quantum technologies. In this\nreview, we discuss the key physics and figures of merit underpinning this\nfield. We also summarize the state of the art in nanoscale electro- and\noptomechanical systems with a focus on scalable platforms such as silicon.\nFinally, we give perspectives on what these new systems may bring and what\nchallenges they face in the coming years. In particular, we believe hybrid\nelectro- and optomechanical devices incorporating highly coherent and compact\nmechanical elements on a chip have significant untapped potential for\nelectro-optic modulation, quantum microwave-to-optical photon conversion,\nsensing and microwave signal processing.\n