University of Minnesota
School of Physics & Astronomy

Academic Calendar

Thursday, January 21st 2016
10:00 am:
Thesis Defense in 334 PAN
Speaker: Semere Tadesse, University of Minnesota
Subject: "Nano-Optomechanical System based on Microwave Frequency Surface Acoustic Waves"
This is the pulbic portion of Mr. Tadesse's thesis defense. His advisor is Mo Li, ECE

Cavity optomechnics studies interaction of cavity confined photons with nanomechanical motion. Many of the studies reported so far are focused on interaction of photons with localized mechanical modes. In my doctoral research, I did experimental investigations to extend this study to propagating phonons. We used surface travelling acoustic wave as mechanical element of the optomechanical system. The system constitutes microwave frequency surface acoustic wave transducers co-intergrated with optical cavities on piezoelectric aluminum nitride film. Acousto-optic modulation with the acoustic wavelength significantly below the optical wavelength and modulation speed over 10GHz was demonstrated. The phase and modal matching conditions in this paradigm were investigated for efficient optmechanical coupling. This system was used to demonstrate optomecahnically induced transparency and absorption, which are dynamical consequences of the optomechanical coupling. Phase coherent interaction of the acoustic wave with multiple nanocavities was also explored, highlighting the scalability of the optomechanical system. In a related experiment, a photonic nanoscavity was placed inside an acoustic echo-chamber, and interaction of a phonon pulse with the photonic cavity was investigated. One limitation of our system is that the surface generated acoustic wave leaks into the supporting silicon substrate depriving the optical cavities the strain field necessary for strong optomechanical coupling. This limitation was addressed by realizing the optomechanical system on suspended aluminum nitride membrane. The membrane confines both the acoustic and optical fields and led to a strong optmechanical coupling.

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