John Zehnpfennig

Stimulated optomechanical excitation of surface acoustic waves in a microdevice

Stimulated Brillouin interaction between sound and light, known to be the strongest optical nonlinearity common to all amorphous and crystalline dielectrics, has been widely studied in fibres and bulk materials but rarely in optical microresonators. The possibility of experimentally extending this principle to excite mechanical resonances in photonic microsystems, for sensing and frequency reference applications, has remained largely unexplored. The challenge lies in the fact that microresonators inherently have large free spectral range, whereas the phase-matching considerations for the Brillouin process require optical modes of nearby frequencies but with different wave vectors. Here we rely on high-order transverse optical modes to relax this limitation and report the experimental excitation of mechanical resonances ranging from 49 to 1,400 MHz by using forward Brillouin scattering. These natural mechanical resonances are excited in ∼100 μm silica microspheres, and are of a surface-acoustic whispering-gallery type.

Surface optomechanics: calculating optically excited acoustical whispering gallery modes in microspheres

Stimulated Brillouin scattering recently allowed experimental excitation of surface acoustic resonances in micro-devices, enabling vibration at rates in the range of 50 MHz to 12 GHz. The experimental availability of such mechanical whispering gallery modes in photonic-MEMS raises questions on their structure and spectral distribution. Here we calculate the form and frequency of such vibrational surface whispering gallery modes, revealing diverse types of surface vibrations including longitudinal, transverse, and Rayleigh-type deformations. We parametrically investigate these various modes by changing their orders in the azimuthal, radial, and polar directions to reveal different vibrational structures including mechanical resonances that are localized near the interface with the environment where they can sense changes in the surroundings.

Surface optomechanics: Calculation of love surface acoustic waves on microresonators

We calculate optomechanically excited Love waves on the surface of a silica whispering-gallery microresonator surrounded by air and pollutants. We show a method for sensing and distinguishing type or concentration of pollutant via frequency shift.

Characterization of surface acoustic wave optomechanical oscillators

We describe and experimentally demonstrate an optomechanical oscillator where light drives a surface mechanical mode of a spherical resonator, using a combination of photoelastic scattering and optical electrostriction. These oscillators are shown to have discretely-selectable frequencies ranging from 50 MHz to 1.5 GHz on a single silica microsphere device. We also report on initial measurements of phase noise and continuous frequency tuning of these oscillators.

Surface Optomechanics: Observation of Surface Acoustic Resonances

We experimentally demonstrate excitation by light of a mechanical Rayleigh surface mode. The acoustical mode is small in volume and high in mechanical Q, related to the small material dissipation for such waves and to the unique geometry in which the acoustical wave is circumferentialy circulating while not leaking through the device support.

Surface Optomechanics: Analytic Solution of Detection Limits of Surface Acoustic Waves in Various Fluids

We derive the detection limits of SAW resulting from Brillouin scattering in a WGR. We calculate the absolute concentration limits for detection of chemicals in fluids surrounding the WGR. Give general equations for velocity, linewidth, and detectability.

Surface optomechanics: Observation of surface acoustic resonances in whispering gallery resonators

We experimentally demonstrate the excitation of a mechanical Rayleigh surface mode through optical electrostriction in a silica microsphere resonator. These modes have applications in optomechanical photonic oscillators and surface acoustic wave based sensing.

Surface optomechanics: Mechanical whispering-gallery modes in microspheres

We analyze circumferentially circulating mechanical whispering-gallery modes [WGM] resonating in a micron scaled silica sphere. We recently showed that such modes can be excited optically [1]. A variety of modes are calculated in which the deformation is polar, radial or azimuthal. Additionally, we calculate Rayleigh WGMs for which points on the surface follow a circular path.