Babinet-Inverted GaP Suspended Fishnet Membrane Enables Long-Lasting Unshifted Gigahertz Hypersonic Waves Generation

Nanostructured dielectric optomechanical platforms have facilitated the efficient generation and precise control of hypersonic waves. However, substantial energy losses have thus far prevented the realization of nanoresonators with long-lasting signals and high quality factors. In this study, we propose suspended all-dielectric fishnet structures made of gallium phosphide, which exhibit up to five odd-order resonant modes with an exceptionally low isotropic loss factor (η = 0.01), which is 1 order of magnitude lower than conventional nanosystems. For a representative device, the quality factors reach as high as 65.48 and 90.38 for the fundamental and n = 3 resonant modes, respectively. The resonant frequencies remain unsensitive to changes in lateral geometry (e.g., hole diameters), which is attributed to the dominance of out-of-plane vibrational modes in the fishnet membrane. These results establish a foundation for integrating all-dielectric nanostructures into launching and manipulating gigahertz hypersonic waves at the nanoscale while also addressing responses of complementary structures.