  Tunable focusing is a desired property in a wide range of optical imaging and
sensing technologies but has tended to require bulky components which cannot be
integrated on-chip and have slow actuation speeds. Recently, integration of
metasurfaces into electrostatic MEMS architectures has shown potential to
overcome these challenges, but has offered limited out of plane displacement
range while requiring large voltages. We demonstrate for the first time a
movable metasurface lens actuated by integrated thin-film PZT MEMS, which has
the advantage of offering large displacements at low voltages. An out of plane
displacement of a metasurface in the range of 7.2 um is demonstrated under a
voltage application of 23V. This is roughly twice the displacement at a quarter
of the voltage of state of the art electrostatic out of plane actuation of
metasurfaces. Utilizing this tunability we demonstrate a varifocal lens doublet
with a focal shift on the order of 250um at the wavelength 1.55um. Thin-film
PZT MEMS-metasurfaces is a promising platform for miniaturized varifocal
components.
