title: Optical racetrack resonator transduction of nanomechanical cantilevers.
abstract: Optomechanical transduction has demonstrated its supremacy in probing nanomechanical displacements. In order to apply nano-optomechanical systems (NOMS) as force and mass sensors, knowledge about the transduction responsivity (i.e. the change in measured optical transmission with nanomechanical displacement) and its tradeoffs with system design is paramount. We compare the measured responsivities of NOMS devices with varying length, optomechanical coupling strength gom, and optical cavity properties. Cantilever beams 1.5 to 5 μm long are fabricated 70 to 160 nm from a racetrack resonator optical cavity and their thermomechanical (TM) noise signals are measured. We derive a generic expression for the transduction responsivity of the NOMS in terms of optical and mechanical system parameters such as finesse, optomechanical coupling constant, and interaction length. The form of the expression holds direct insight as to how these parameters affect the responsivity. With this expression, we obtain the optomechanical coupling constants using only measurements of the TM noise power spectra and optical cavity transmission slopes. All optical pump/probe operation is also demonstrated in our side-coupled cantilever-racetrack NOMS. Finally, to assess potential operation in a gas sensing environment, the TM noise signal of a device is measured at atmospheric pressure.
authors.affiliation: National Institute for Nanotechnology, 11421 Saskatchewan Drive, T6G 2M9, Edmonton, Canada. Department of Electrical and Computer Engineering, University of Alberta, Edmonton, T6G 2V4, Canada.
authors.forename: V T K
authors.initials: VT
authors.lastname: Sauer
authors.forename: Z
authors.initials: Z
authors.lastname: Diao
authors.forename: M R
authors.initials: MR
authors.lastname: Freeman
authors.forename: W K
authors.initials: WK
authors.lastname: Hiebert