Tunable focusing is a desirable property in many optical imaging and sensing technologies. Still, it traditionally requires bulky components that cannot be integrated on-chip and have slow actuation speeds. Integration of metasurfaces into electrostatic micro-electromechanical system (MEMS) architectures have recently shown promise in overcoming these challenges but has limited out-of-plane displacement range while requiring high voltages. Researchers present a movable metasurface lens actuated by integrated thin-film piezoelectric MEMS for the first time, which offers large displacements at low voltages.
Under a voltage of 23 V, an out-of-plane displacement of a metasurface in the range of 7.2 microns was demonstrated. It is roughly twice the displacement at a quarter of the current electrostatic out-of-plane metasurface actuation voltage. Using this tunability, they have demonstrated a varifocal lens doublet with a focal shift of 250 microns at 1.55 microns. The thin-films Piezoelectric MEMS-metasurface holds promise for miniaturized varifocal components.
The ability to change the focal length of a lens enables optical probing or imaging at various spatial depths. As a result, varifocal lenses are critical components in a wide range of optical sensors and imaging technologies. Varifocal lenses, on the other hand, have a reputation for being bulky, slow, and power-hungry due to the use of bulky refractive (curved) lenses and stepper motors in their fabrication.
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