Metalens Design Enables Reconfigurable Imaging

A Northwestern University research team has developed an imaging platform based on fully reconfigurable metalenses. The lenses focus light by exciting surface lattice resonances that are tuned by patterned polymer blocks on single-particle sites. The system can image at visible wavelengths and is based on arrays of coupled plasmonic nanoparticles.

The lenses are built from an array of cylindrical silver nanoparticles and a layer of polymer patterned into blocks on top of the metal array. By controlling the arrangement of the polymer patterns, the nanoparticle array can direct visible light to any targeted focal points without needing to change its structure.

During a single imaging session, the device can evolve from a single-focus lens to a multifocal lens that can produce more than one image at any programmable 3D position. Courtesy of Northwestern University.

The team performed predictive design of the dielectric nanoblocks to create a range of 3D focusing responses. To show scalability, the researchers demonstrated a technique for erasing and writing the polymer nanostructures on the metal nanoparticle arrays in a single step using solvent-assisted nanoscale embossing. This scalable method enables different lens structures to be made in one step of erasing and writing, with no noticeable degradation in nanoscale features after multiple erase-and-write cycles.

This reconfigurable materials platform enables tunable focusing with diffraction-limited resolution and could offer prospects for highly adaptive, compact imaging. “In this study, we demonstrated a versatile imaging platform based on fully reconfigurable metalenses made from silver nanoparticles,” said professor Teri W. Odom. “During a single imaging session, our metalens device can evolve from a single-focus lens to a multifocal lens that can form more than one image at any programmable 3D position.”

For imaging operations such as zooming and focusing, most existing metalenses cannot adjust their focal spots without physical motion. One major reason, Odom said, is that the building blocks of these lenses are made of hard materials that cannot change shape once fabricated.

The Northwestern team’s reconfigurable metalens system could one day be used in portable imaging systems and optoelectronic devices. “This miniaturization and integration with detectors offers promise for high-resolution imaging in devices from small wide-angle cameras to miniature endoscopes,” Odom said.

The research was published in ACS Nano (https://pubs.acs.org/doi/10.1021/acsnano.9b00651).