We demonstrate a nanoscale device platform in GaAs that establishes a link between the radio frequency (RF) and optical domains through acoustic waves, mediated by the piezoelectric and photoelastic effects. First, interdigitated transducers (IDTs) convert 2.4 GHz RF photons into 2.4 GHz propagating surface acoustic waves. These acoustic waves are routed through phononic crystal waveguides and are coupled to a nanobeam optomechanical cavity that supports both a highly localized 2.4 GHz breathing mechanical mode and a high quality factor 1550 nm optical mode. In contrast to non-resonant excitation of photonic structures with IDTs, here the phononic waveguide preferentially excites a localized mechanical mode, which in turn strongly interacts with the optical mode through the photoelastic effect. Finally, the optical mode can be out-coupled or excited via an optical fiber taper waveguide. Using this platform, we demonstrate preparation of the breathing mode in a coherent state at any location in phase space, and optically read out an average coherent intracavity phonon number as small as one-twentieth of a phonon. In the time-domain, we show that RF pulses are mapped to optical pulses, forming a resonant acousto-optic modulator with a sub-Volt half-wave voltage. We also observe a novel acoustic wave interference effect in which RF-driven motion is completely cancelled by optically-driven motion, enabling the demonstration of interferometric opto-acoustic modulation in which acoustic wave propagation is gated by optical pulses. Efforts to improve upon the efficiency of the different transduction processes and integration with quantum dot gain media will be discussed.
Kartik Srinivasan, "Piezo-optomechanical transducers as a link between radio frequency, optical, and acoustic waves (Conference Presentation)," Proc. SPIE 10090, Laser Resonators, Microresonators, and Beam Control XIX, 100900Q (Presented at SPIE LASE: January 31, 2017; Published: 21 April 2017); https://doi.org/10.1117/12.2251504.5387835774001.
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