  Optoelectronic components with adjustable parameters, from
variable-focal-length lenses to spectral filters that can change functionality
upon stimulation, have enormous technological importance. Tuning of such
components is conventionally achieved by either micro- or nano-mechanical
actuation of their consitutive parts, stretching or application of thermal
stimuli. Here we report a new dielectric metasurface platform for
reconfigurable optical components that are created with light in a non-volatile
and reversible fashion. Such components are written, erased and re-written as
two-dimensional binary or grey-scale patterns into a nanoscale film of phase
change material by inducing a refractive-index-changing phase-transition with
tailored trains of femtosecond pulses. We combine
germanium-antimony-tellurium-based films optimized for high-optical-contrast
ovonic switching with a sub-wavelength-resolution optical writing process to
demonstrate technologically relevant devices: visible-range reconfigurable
bi-chromatic and multi-focus Fresnel zone-plates, a super-oscillatory lens with
sub-wavelength focus, a grey-scale hologram and a dielectric metamaterial with
on-demand reflcetion and transmission resonances.
