  Tunable optical devices, in particular, varifocal lenses, have important
applications in various fields, including imaging and adaptive vision. Recent
advances in metasurfaces, which control the wavefront of light using
subwavelength-spaced nanostructures, open up new opportunities to replace bulk
optical devices, with thin, flat, lightweight devices. We have demonstrated for
the first time an electrically tunable flat lens, based on large area
metasurfaces combined with a dielectric elastomer actuator having inline
transparent electrodes, that is capable of simultaneously performing focal
length tuning (>100%) as well as dynamic corrections, including astigmatism and
image shift. This offers control versatility to flat optics hitherto only
possible in electron microscopes. The water-based transfer process, which we
describe, also enables wide compatibility across materials. The combination of
metasurface optics and dielectric elastomer actuators enables a new, versatile
platform for creating all kinds of tunable optical devices, through the design
of tunable phase, amplitude, and polarization profiles.
