- Researchers have come up with next-generation metalenses made of metal nanoparticles and a polymer.
- It has the potential to replace conventional refractive lenses to realize optoelectronic devices and portable imaging systems.
Tiny optical elements are used in a variety of imaging instruments, ranging from wide-angle cameras to multifunctional endoscopes. Metalenses are one of the emerging platforms for such compact optical elements.
However, metalenses are limited by their properties and their intricate and expensive fabrication. They cannot easily image three-dimensional objects or adjust their focal points without physical motion.
Since building blocks of metalenses are made of hard materials, they can’t alter shape once fabricated. In any materials systems, it’s very tough to configure nanoscale-sized features on demand to achieve adjustable focusing in metalenses.
And that’s why researchers at Northwestern University have come up with next-generation metalenses made of metal nanoparticles and a polymer that has the potential to replace conventional refractive lenses to realize optoelectronic devices and portable imaging systems.
What Is Metalens Made Of?
The versatile imaging platform developed in this study is based on completely reconfigurable metalenses made of silver nanoparticles. It can progress from a single focus-lens to a multi-focal lens during each imaging session, forming two or more images at a given programmable 3D location.
Reference: ACS Nano | doi:10.1021/acsnano.9b00651 | Northwestern University
To make these lenses, researchers used an array of cylindrical silver nanoparticles and a sheet of polymer arranged into blocks on top of the metal array. One can easily control the arrangement of these blocks, making the array of nanoparticles direct light at any target focal point(s) without altering the structure of the nanoparticle.
Lattice resonances enabled reconfigurable metalenses for imaging | Courtesy of researchers
The above figure shows metalens architecture based on two kinds of phase elements patterned into a square lattice: silver nanoparticles exposed to air and identical nanoparticles covered by a thin dielectric block.
Researchers used a lattice evolution algorithm to develop surface lattice resonance metalenses for targeted foci by tuning the arrangement of the two building blocks through electric-field data measured by finite difference time-domain simulations. Figure b shows that metalens can be rearranged by solvent-assisted nanoscale embossing (SANE).
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This flexible technique allows manufacturers to produce numerous lens structures in a single step of erasing and writing, without degrading its features after several erase-write cycles. It can also restructure previously formed polymer into another target pattern via soft elastomer masks.
