Gigahertz All-Optical Modulation Using Reconfigurable Nanophotonic Metamolecules.

We report the design of reconfigurable metamolecules consisting a large array of nanowire featuring U-shaped cross section. These nanoscale metamolecules support colocalized electromagnetic resonance at optical frequencies and mechanical resonance at GHz frequencies with a deep-subdiffraction-limit spatial confinement (∼λ2 /100). The coherent coupling of those two distinct resonances manifests a strong optical force, which is fundamentally different from the commonly studied forms of radiation forces, gradient forces, or photothermal induced deformation. The strong optical force acting upon the built-in compliance further sets the stage for allowing the metamolecules to dynamically change their optical properties upon the incident light. The all-optical modulation at the frequency at 1.8 GHz has thus been demonstrated experimentally using a monolayer of metamolecules. The metamolecules were conveniently fabricated using complementary metal-oxide-semiconductor-compatible metal deposition and nanoimprinting processes and thus offer promising potential in developing integrated all-optical modulator.