Dynamic focusing with high-quality-factor metalenses.

Metasurface lenses provide an ultrathin platform in which to focus light, but weak light-matter interactions limit their dynamic tunability. Here we design sub-micron-thick, ultrahigh quality factor (high-Q) metalenses that enable dynamic modulation of the focal length and intensity. Using full-field simulations, we show that quality factors exceeding 5000 can be generated by including subtle, periodic perturbations within the constituent Si nanoantennas. Such high-Q resonances enable lens modulation based on the nonlinear Kerr effect, with focal lengths varying from 4 μm to 6.5 μm and focal intensities decreasing by half as input intensity increases from 0.1 mW/μm2 to 1 mW/μm2. We also show how multiple high-Q resonances can be embedded in the lens response through judicious placement of the perturbations. Our high-Q lens design, with quality factors two order of magnitude higher than existing lens designs, provides a foundation for reconfigurable, multiplexed and hyperspectral metasurface imaging platforms.