26 February

Light-motion interaction in disordered nanostructures

Friday 26 February 2021, 12:00pm

ICN2 Seminar Hall, ICN2 Building, UAB


PhDGuillermo Arregui 

Directors: ICREA Prof. Clivia M. Sotomayor Torres, Group Leader and Dr Pedro D. Garcia, Senior Researcher at  Phononic and Photonic Nanostructured at ICN2.

Short Abstract: This thesis focuses on understanding the coupling of confined light (photons) to collective mechanical degrees of freedom (phonons) in disordered periodic-on-average nanostructures. In particular, it explores how the spontaneous localization of the electromagnetic field due to disorder, i.e., Anderson localization, can serve as a local transducer to observe the analogous phenomena for mechanical excitations. While Anderson localization of light has been experimentally investigated in a large variety of systems and in a broad range of frequencies, the observation of its mechanical counterpart remains elusive at GHz frequencies and above. Here, I will discuss possible ways and platforms to achieve this seminal observation and identify the critical bottlenecks of the approach. The first difficulty encountered is that localized acoustic and optical modes appear at uncorrelated positions due to the random nature of the complex interference processes. This is circumvented by employing GaAs/AlAs superlattices where we numerically evidence a statistically enhanced optomechanical coupling in the Anderson-localization regime. Secondly, the transduced mechanical signals scale with the quality factor of the employed optical cavities, often low for Anderson-localized modes. We show here how silicon slotted photonic crystal waveguides with intrinsic fabrication disorder lead to high-Q Anderson modes with which both detection and actuation of low-frequency (less than 1 GHz) and high-frequency (~ 7 GHz) mechanical motion is demonstrated. The high-frequency guided modes are affected by fabrication disorder and will be used to further explore localization phenomena of phonons and of coupled excitations. Finally, I will tackle the flip side of the coin: how to avoid the effect of disorder. For that, I will numerically quantify the robustness of a topological edge state to fabrication imperfection and compare it to a conventional waveguide.