A Cavity Optomechanical Platform for GHz Phonon Amplification via Anderson-Localized Optical Modes

We explore [1] Anderson-localized cavity optomechanics in a two-dimensional optomechanical platform: a waveguide etched in a suspended silicon membrane that incorporates a slotted line air defect. Inherent and unavoidable fabrication imperfections are adequate to induce sufficient backscattering to realize Anderson-localization of optical modes. The introduction of an air slot allows for a strong confinement of the electromagnetic field that is guided along the slot, and enhances the ability for light to couple to in-plane mechanical motion. The resulting tightly confined Anderson-localized modes can be driven to enable mechanical amplification and self-sustained phonon lasing via optomechanical back-action. We design the photonic and phononic band structures [2,3] to realize mechanical lasing up to 6.8 GHz that results from confinement of the mechanical mode. We confirm the existence of this mode through a combination of cavity optomechanical techniques and Brillouin light scattering spectroscopy. The role of disorder in cavity optomechanics has thus far been largely overlooked but our results show that disorder plays a crucial role, which in part can have a decisive impact on device functionality and in part opens perspectives for studies of multiple scattering and Anderson localization of bosonic excitations with parametric coupling to mechanical degrees of freedom.<br/><br/><b>References</b><br/>Guillermo Arregui, Ryan Cecil Ng, Marcus Albrechtsen, Søren Stobbe, Clivia M. Sotomayor Torres, Pedro David García. Cavity optomechanics with Anderson-localized optical modes. Preprint at https://arxiv.org/abs/2110.11005<br/>Omar Florez, Guillermo Arregui, Marcus Albrechtsen, Ryan C. Ng, Jordi Gomis-Bresco, Søren Stobbe, Clivia. M. Sotomayor-Torres, Pedro David García. Engineering nanoscale hypersonic phonon transport. Nature Nanotechnology 17, 947 (2022)<br/>Guilhem Madiot, Ryan C Ng, Guillermo Arregui, Omar Florez, Marcus Albrechtsen, Søren Stobbe, Pedro D Garcia, Clivia M Sotomayor-Torres. Optomechanical generation of coherent GHz vibrations in a phononic waveguide. Preprint at https://arxiv.org/abs/2206.06913