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Harnessing optical forces in integrated photonic circuits


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.

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Figure 1: The substrate coupled waveguide gradient force.
Figure 2: Schematics of the experimental set-up and device system.
Figure 3: Device characterization and experimental demonstration of the waveguide gradient force.
Figure 4: Measurement of the thermal response of the device.


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We thank J. Chen and B. Penkov for contributions at the early stage of this project. W.H.P.P. acknowledges support from the Alexander von Humboldt postdoctoral fellowship programme. The devices were fabricated at Yale University Microelectronics Center and the NSF-sponsored Cornell Nanoscale Facility. M.H. acknowledges support from the Air Force Office of Scientific Research Young Investigator Program and the NSF STC MDITR Center. H.X.T. thanks M. Roukes, A. Scherer, J. Harris and S. Girvin for discussions.

Author Contributions H.X.T. planned and supervised the project; M. L. and H.X.T. conceived the experiment; M.L. fabricated the devices, and did the measurements; W.H.P.P. conducted the force calculation and simulation; C.X. helped with the automation of the pattern generation; M.L., W.H.P.P. and H.X.T. analysed the data and wrote the manuscript; and T.B.-J. and M.H. provided the layout of the couplers and waveguide, and assisted with fabrication of devices.

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Correspondence to H. X. Tang.

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This file contains Supplementary Methods with Supplementary Figures S1-S2 and Supplementary References, and Supplementary Discussion with Supplementary Figures 1-10, Supplementary Table 1 and Supplementary References. (PDF 2146 kb)

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Li, M., Pernice, W., Xiong, C. et al. Harnessing optical forces in integrated photonic circuits. Nature 456, 480–484 (2008).

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