Nanophotonic Devices for Nonlinear Optomechanics
AdvisorBarclay, Paul E.
Committee MemberFeder, David L.
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AbstractNanophotonic cavity optomechanical devices, structures with optical modes coupled to mechanical vibrations, enable ultrasensitive measurement and control of dynamics of nanoscale mechanical systems and their environment. Recent developments in cavity optomechanics are paving the way for experiments which reveal the quantum properties of mesoscopic mechanical systems. In particular, nonlinear cavity optomechanical systems show promise for observing mechanical energy eigenstates through quantum non-demolition (QND) measurements of single phonons. This thesis discusses several novel new cavity optomechanical devices, and the first studies of their nonlinear properties for use in these experiments. We present the systematic design, fabrication and initial characterization of paddle nanocavities (PNCs), consisting of a nanoscale photonic crystal cavity with a sub-picogram scale mechanical oscillator suspended within the centre of the optical modes. These devices in silicon and silicon nitride have record low mass compared with other nonlinear optomechanical systems, record nonlinear optomechanical coupling strength compared to other single mode systems, and THz optical mode spacing suppressing quantum tunneling between the optical modes. Measurements under ambient conditions of a silicon PNC demonstrate an optical mode with quality factor of approximately 6,000 near 1550 nm, and optomechanical coupling to several mechanical resonances with frequencies in the tens of MHz range. Theoretical analysis shows these PNC's have a quadratic optomechanical coupling coefficient 2π x 750 MHz/nm^2, and their nonlinear signal can be observed above system noise levels. Although silicon nitride PNC's have a lower coupling coefficient 2π x 10 MHz/nm^2, their mechanical frequency can be reduced with high aspect ratio supports to increase the prospect for QND measurements. We also show how silicon paddled double nanocavities (PDC's), two optical cavities in a single nanobeam with a paddle section in-between mediating their interactions, can have a coupling coefficient 2π x 350 GHz/nm^2, and how ensembles of mechanical resonators can be incorporated into a single nanobeam photonic crystal cavity. Finally, we discuss how phononic crystals and low-pressure measurements can be used to increase device characteristics. An experimental high-vacuum system is detailed, and measurements of a nanocavity torque sensor with record sensitivity, and first measurements of a hexagonal boron nitride optomechanical system are presented.
CitationHealey, C. (2019). Nanophotonic Devices for Nonlinear Optomechanics (Unpublished doctoral thesis). University of Calgary, Calgary, AB.
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