Kirigami-inspired technique manipulates light at the nanoscale

Folding and cutting thin metal films could enable microchip-based 3-D optical devices.

At left, different patterns of slices through a thin metal foil, are made by a focused ion beam. These patterns cause the metal to fold up into predetermined shapes, which can be used for such purposes as modifying a beam of light. Courtesy of the researchers
At left, different patterns of slices through a thin metal foil, are made by a focused ion beam. These patterns cause the metal to fold up into predetermined shapes, which can be used for such purposes as modifying a beam of light. Courtesy of the researchers

Nanokirigami is based on the ancient arts of origami (making 3-D shapes by folding paper) and kirigami (which allows cutting as well as folding) but applied to flat materials at the nanoscale, measured in billionths of a meter.

Using this technique, MIT and China scientists have developed nanodevices to manipulate light, potentially opening up new possibilities for research and, ultimately, the creation of new light-based communications, detection, or computational devices.

Scientists used methods based on standard microchip manufacturing technology and focused ion beam in order to create a precise pattern of slits in a metal foil just a few tens of nanometers thick. The procedure makes the thwart twist and curves itself into a mind-boggling three-dimensional shape able to do specifically sifting through light with a specific polarization.

For these initial proof-of-concept devices, the team produced a nanomechanical equivalent of specialized dichroic filters that can filter out circularly polarized light that is either “right-handed” or “left-handed.” To do so, they created a pattern just a few hundred nanometers across in the thin metal foil; the result resembles pinwheel blades, with a twist in one direction that selects the corresponding twist of light.

MIT professor of mechanical engineering Nicholas X Fang said, “Previous attempts to create functional kirigami devices have used more complicated fabrication methods that require a series of folding steps and have been primarily aimed at mechanical rather than optical functions. The new nanodevices, by contrast, can be formed in a single folding step and could be used to perform a number of different optical functions.”

Fanf explained, “The twisting and bending of the foil happens because of stresses introduced by the same ion beam that slices through the metal. When using ion beams with low dosages, many vacancies are created, and some of the ions end up lodged in the crystal lattice of the metal, pushing the lattice out of shape and creating strong stresses that induce the bending.”

“It’s a very nice connection of the two fields, mechanics and optics. The team used helical patterns to separate out the clockwise and counterclockwise polarized portions of a light beam, which may represent “a brand new direction” for nanokirigami research.”

The research is still at an early stage, so more research will be needed on possible applications. But these devices are orders of magnitude smaller than conventional counterparts that perform the same optical functions, so these advances could lead to more complex optical chips for sensing, computation, or communications systems or biomedical devices.

The findings are described today in the journal Science Advances, in a paper by MIT professor of mechanical engineering Nicholas X Fang and five others. The team also included MIT graduate student Huifeng Du; Zhiguang Liu, Jiafang Li (project supervisor), and Ling Lu at the Chinese Academy of Sciences in Beijing; and Zhi-Yuan Li at the South China University of Technology. The work was supported by the National Key R&D Program of China, the National Natural Science Foundation of China, and the U.S Air Force Office of Scientific Research.