Recent advancements in cavity optomechanics have demonstrated the potential to manipulate gigahertz acoustic phonons (1using innovative approaches to light confinement and multimodal coupling. In collaboration with a team from the Technical University of Denmark (DTU), an “optomechanical laser” was designed and characterized, enabling the coherent emission of gigahertz phonons within a Fabry-Pérot-type acoustic cavity (see top schematic). Unlike conventional optomechanical systems that rely on deterministic cavities—such as those created through photonic crystal apodization—this approach harnessed Anderson localization of light, induced by scattering on rough sidewalls of an ultra-thin slit (~40 nm). The confinement of optical fields in extremely small modal volumes, combined with high optical quality factors, enhanced optomechanical interactions, enabling the parametric amplification of gigahertz acoustic modes (1), as shown on the opposite plot.

Further developments explored multimodal dynamics involving multiple mechanical modes coupled to a single optical mode (see bottom schematic). A collaborative project at the University of Barcelona demonstrated a novel mechanism for generating optomechanical frequency combs through interactions between distinct mechanical modes, representing a key advance in leveraging multimode coupling to enrich nonlinear dynamical regimes (2).

Building on this approach, subsequent research at ICN2 established a platform capable of coupling two nearly degenerate gigahertz mechanical modes to a single deterministic optical cavity. This system achieved optomechanical coupling rates exceeding 1 MHz, surpassing the state of the art for such platforms. Below the threshold for optomechanical lasing, this configuration offers a promising avenue for investigating parity-time (PT) symmetry breaking through exceptional points. Above the lasing threshold, it enables the study of synchronization phenomena between two optically coupled gigahertz mechanical oscillators. To explore these regimes, a new cavity design was developed, facilitating the coupling of two weakly degenerate mechanical modes to the same optical cavity. Characterization of the fabricated structures, provided by our collaborators at DTU, revealed optomechanical coupling rates beyond the state of the art, along with unique multimodal interactions intrinsic to this configuration.

Finally, an experimental demonstration stimulated the self-oscillation regime of two nearly degenerate mechanical modes by modulating the injection laser at their frequency difference, as reported in Mercadé et al., PRL, 2021. These results (3) underscore the potential of multimodal optomechanical platforms to advance the study of nonlinear dynamics, synchronization, and non-Hermitian physics.