Light-sound interactions have long been exploited in various acousto-opticdevices based on bulk crystalline materials. Conventionally these devicesoperate in megahertz frequency range where the acoustic wavelength is muchlonger than the optical wavelength and a long interaction length is required toattain significant coupling. With nanoscale transducers, acoustic waves withsub-optical wavelengths can now be excited to induce strong acousto-opticcoupling in nanophotonic devices. Here we demonstrate microwave frequencysurface acoustic wave transducers co-integrated with nanophotonic resonators onpiezoelectric aluminum nitride substrates. Acousto-optic modulation of theresonance modes at above 10 GHz with the acoustic wavelength significantlybelow the optical wavelength is achieved. The phase and modal matchingconditions in this scheme are investigated for efficient modulation. The newacousto-optic platform can lead to novel optical devices based on nonlinearBrillouin processes and provides a direct, wideband link between optical andmicrowave photons for microwave photonics and quantum optomechanics.
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