University of Cambridge > > Isaac Newton Institute Seminar Series > Dirty and Messy Cavity-Optomechanics: a cavity optomechanical platform for GHz phonon amplification via Anderson-localized optical modes

Dirty and Messy Cavity-Optomechanics: a cavity optomechanical platform for GHz phonon amplification via Anderson-localized optical modes

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MWSW04 - Multiple scattering in engineering and applied sciences

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.   Figure 1. (a) Micrograph (top view) of an optomechanical nanostructure. Detail of the roughness due to the fabrication process which leads to the localization of the electromagnetic field within the air gap. (b) Coherent amplification of a vibrational mode of the structure by dynamical backaction: the linewidth of a mechanical mode with a frequency around 240 MHz (top panel) is narrowed down by red-detuning an external driving laser to an Anderson-localized optical mode. This dynamical backaction leads to a coherent amplification of the vibrational mode or phonon lasing (lower panel).    References [1] G. Arregui, R. Cecil Ng, M. Albrechtsen, S. Stobbe, C. M. Sotomayor Torres, P. David García. Cavity optomechanics with Anderson-localized optical modes. Preprint at (accepted in Physical Review Letters) 2023. [2] O. Florez, G. Arregui, M. Albrechtsen, R. C. Ng, J. Gomis-Bresco, S. Stobbe, C. M. Sotomayor-Torres, P. David García. Engineering nanoscale hypersonic phonon transport. Nature Nanotechnology, 2022, 17, 947. [3] G. Madiot, R. C Ng, G. Arregui, O. Florez, M. Albrechtsen, S. Stobbe, P. D Garcia, C. M Sotomayor-Torres. Optomechanical generation of coherent GHz vibrations in a phononic waveguide. Preprint at, 2022.

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