Harnessing optical forces in integrated photonic circuits

ature 456, 480-484 (27 November 2008) doi:10.1038/nature07545; Received 26 August 2008; Accepted 14 October 2008
Harnessing optical forces in integrated photonic circuits
Mo Li1,2, W. H. P. Pernice1,2, C. Xiong1,2, T. Baehr-Jones3, M. Hochberg3 & H. X. Tang1,2
Department of Electrical Engineering,
Department of Mechanical Engineering, Yale University, New Haven, Connecticut 06511, USA
Department of Electrical Engineering, University of Washington, Seattle, Washington 98195, USA
Correspondence to: H. X. Tang1,2 Correspondence and requests for materials should be addressed to H.X.T. (Email: hong.tang@yale.edu).
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The force exerted by photons is of fundamental importance in light–matter interactions. For example, in free space, optical tweezers have been widely used to manipulate atoms and microscale dielectric particles1, 2. This optical force is expected to be greatly enhanced in integrated photonic circuits in which light is highly concentrated at the nanoscale3, 4. Harnessing the optical force on a semiconductor chip will allow solid state devices, such as electromechanical systems, to operate under new physical principles. Indeed, recent experiments have elucidated the radiation forces of light in high-finesse optical microcavities5, 6, 7, but the large footprint of these devices ultimately prevents scaling down to nanoscale dimensions. Recent theoretical work has predicted that a transverse optical force can be generated and used directly for electromechanical actuation without the need for a high-finesse cavity3. However, on-chip exploitation of this force has been a significant challenge, primarily owing to the lack of efficient nanoscale mechanical transducers in the photonics domain. Here we report the direct detection and exploitation of transverse optical forces in an integrated silicon photonic circuit through an embedded nanomechanical resonator. The nanomechanical device, a free-standing waveguide, is driven by the optical force and read out through evanescent coupling of the guided light to the dielectric substrate. This new optical force enables all-optical operation of nanomechanical systems on a CMOS (complementary metal-oxide-semiconductor)-compatible platform, with substantial bandwidth and design flexibility compared to conventional electrical-based schemes.