Dielectric

Scattering

Optoelectronics

Physics

Resonator

Optics

Quantum mechanics

Nanophotonics

Laser

Quality (philosophy)

Lasing threshold

Phase (matter)

Q factor

Nature Nanotechnology

Dielectric microcavities with quality factors (Q-factors) in the thousands to billions markedly enhance light–matter interactions, with applications spanning high-efficiency on-chip lasing, frequency comb generation and modulation and sensitive molecular detection. However, as the dimensions of dielectric cavities are reduced to subwavelength scales, their resonant modes begin to scatter light into many spatial channels. Such enhanced scattering is a powerful tool for light manipulation, but also leads to high radiative loss rates and commensurately low Q-factors, generally of order ten. Here, we describe and experimentally demonstrate a strategy for the generation of high Q-factor resonances in subwavelength-thick phase gradient metasurfaces. By including subtle structural perturbations in individual metasurface elements, resonances are created that weakly couple free-space light into otherwise bound and spatially localized modes. Our metasurface can achieve Q-factors &gt;2,500 while beam steering light to p...

High quality factor phase gradient metasurfaces