Quantitative measurements of the vibrational eigenmodes in ultra-high-Q silica microspheres are reported. The modes are efficiently excited via radiation-pressure induced dynamical back-action of light confined in the optical whispering-gallery modes of the microspheres (i.e. via the parametric oscillation instability). Two families of modes are studied and their frequency dependence on sphere size investigated. The measured frequencies are in good agreement both with Lambs theory and numerical finite element simulation and are found to be proportional to the spheres inverse diameter.
A tunable, all-optical, coupling method has been realized for a high-textit{Q} silica microsphere and an optical waveguide. By means of a novel optical nanopositioning method, induced thermal expansion of an asymmetric microsphere stem for laser powe
rs up to 171~mW has been observed and used to fine tune the microsphere-waveguide coupling. Microcavity displacements ranging from (0.612~$pm$~0.13) -- (1.5 $pm$ 0.13) $mu$m and nanometer scale sensitivities varying from (2.81 $pm$ 0.08) -- (7.39 $pm$ 0.17) nm/mW, with an apparent linear dependency of coupling distance on stem laser heating, were obtained. Using this method, the coupling was altered such that different coupling regimes could be explored for particular samples. This tunable coupling method, in principle, could be incorporated into lab-on-a-chip microresonator systems, photonic molecule systems, and other nanopositioning frameworks.
We demonstrated the tuning of whispering gallery modes (WGMs) of a silica microsphere during optical levitation through the annealing process. We determined the annealing temperature from the power balance between the CO2 laser light heating and seve
ral cooling processes. Cooling caused by heat conduction through the surrounding air molecules is the dominant process. We achieved a blue shift of the WGMs as large as 1 %, which was observed in the white-light scattering spectrum from the levitated microsphere.
We report on the experimental observation of coherent cavity soliton frequency combs in silica microspheres. Specifically, we demonstrate that careful alignment of the microsphere relative to the coupling fiber taper allows for the suppression of hig
her-order spatial modes, reducing mode interactions and enabling soliton formation. Our measurements show that the temporal cavity solitons have sub-100-fs durations, exhibit considerable Raman self-frequency shift, and generally come in groups of three or four, occasionally with equidistant spacing in the time domain. RF amplitude noise measurements and spectral interferometry confirm the high coherence of the observed soliton frequency combs, and numerical simulations show good agreement with experiments.
Plasmonic nanostructures hold promise for the realization of ultra-thin sub-wavelength devices, reducing power operating thresholds and enabling nonlinear optical functionality in metasurfaces. However, this promise is substantially undercut by absor
ption introduced by resistive losses, causing the metasurface community to turn away from plasmonics in favour of alternative material platforms (e.g., dielectrics) that provide weaker field enhancement, but more tolerable losses. Here, we report a plasmonic metasurface with a quality-factor (Q-factor) of 2340 in the telecommunication C band by exploiting surface lattice resonances (SLRs), exceeding the record by an order of magnitude. Additionally, we show that SLRs retain many of the same benefits as localized plasmonic resonances, such as field enhancement and strong confinement of light along the metal surface. Our results demonstrate that SLRs provide an exciting and unexplored method to tailor incident light fields, and could pave the way to flexible wavelength-scale devices for any optical resonating application.
Systems with low mechanical dissipation are extensively used in precision measurements such as gravitational wave detection, atomic force microscopy and quantum control of mechanical oscillators via opto- and electromechanics. The mechanical quality
factor ($Q$) of these systems determines the thermomechanical force noise and the thermal decoherence rate of mechanical quantum states. While the dissipation rate is typically set by the bulk acoustic properties of the material, by exploiting dissipation dilution, mechanical $Q$ can be engineered through geometry and increased by many orders of magnitude. Recently, soft clamping in combination with strain engineering has enabled room temperature quality factors approaching one billion ($10^9$) in millimeter-scale resonators. Here we demonstrate a new approach to soft clamping which exploits vibrations in the perimeter of polygon-shaped resonators tethered at their vertices. In contrast to previous approaches, which rely on cascaded elements to achieve soft clamping, perimeter modes are soft clamped due to symmetry and the boundary conditions at the polygon vertices. Perimeter modes reach $Q$ of 3.6 billion at room temperature while spanning only two acoustic wavelengths---a 4-fold improvement over the state-of-the-art mechanical $Q$ with 10-fold smaller devices. The small size of our devices makes them well-suited for near-field integration with microcavities for quantum optomechanical experiments. Moreover, their compactness allows the realization of phononic lattices. We demonstrate a one-dimensional Su-Schrieffer-Heeger chain of high-$Q$ perimeter modes coupled via nearest-neighbour interaction and characterize the localized edge modes.