  We present a new approach to dielectric metasurface design that relies on a
single resonator per unit cell and produces robust, high quality-factor Fano
resonances. Our approach utilizes symmetry breaking of highly symmetric
resonator geoemetries, such as cubes, to induce couplings between the otherwise
orthogonal resonator modes. In particular, we design perturbations that couple
"bright" dipole modes to "dark" dipole modes whose radiative decay is
suppressed by local field effects in the array. Our approach is widely scalable
from the near-infrared to radio frequencies. We first unravel the Fano
resonance behavior through numerical simulations of a germanium resonator-based
metasurface that achieved a quality-factor of ~1300 at ~10.8 um. Then, we
present two experimental demonstrations operating in the near-infrared (~1 um):
a silicon-based implementation that achieved a quality-factor of ~350; and a
gallium arsenide-based structure that achieves a quality-factor of ~600 - the
highest near-infrared quality-factor experimentally demonstrated to date with
this kind of metasurfaces. Importantly, large electromagnetic field
enhancements appear within the resonators at the Fano resonant frequencies. We
envision that combining high-quality factor, high field enhancement resonances
with nonlinear and active/gain materials such as gallium arsenide will lead to
new classes of active optical devices.
