Janus-like metasurface technology shows different optical responses depending on light direction

Metasurface technology is an advanced optical technology that is thinner, lighter and more capable of precisely controlling light through nano-sized artificial structures than conventional technologies. KAIST researchers overcame the limitations of existing metasurface technologies and successfully designed a Janus metasurface capable of perfectly controlling asymmetric light transmission. By applying this technology, they also proposed an innovative method to significantly improve security by only decoding information under specific conditions.

The team’s research is published in the journal Advanced materials. The research team was led by Professor Jonghwa Shin from the Department of Materials Science and Engineering.

Asymmetric properties, which react differently depending on direction, play a crucial role in various scientific and engineering fields. The Janus metasurface developed by the research team implements an optical system capable of performing different functions in both directions.

Like the two-faced Roman god Janus, this metasurface exhibits entirely different optical responses depending on the direction of incoming light, effectively operating two independent optical systems with a single device (e.g., a metasurface that acts as a magnifying glass in one direction and like a polarized camera in the other). In other words, thanks to this technology it is possible to operate two different optical systems (for example, a lens and a hologram) depending on the direction of the light.

This achievement addresses a challenge that existing metasurface technologies had not resolved. Conventional metasurface technology had limitations in selectively controlling the three properties of light (intensity, phase, and polarization) based on the direction of incidence.

The research team proposed a solution based on mathematical and physical principles and succeeded in experimentally implementing different vector holograms in both directions. With this achievement, they presented a comprehensive technology for controlling asymmetric light transmission.

Additionally, the research team developed a new optical encryption technology based on this metasurface technology. Using the Janus metasurface, they implemented a vector hologram that generates different images depending on the direction and polarization state of the incoming light, presenting an optical encryption system that significantly improves security by allowing decoding information only under specific conditions.

This technology is expected to constitute a next-generation security solution, applicable in various fields such as quantum communication and secure data transmission.

Furthermore, the ultra-thin structure of the metasurface is expected to significantly reduce the volume and weight of traditional optical devices, thereby greatly contributing to the miniaturization and lightweight design of next-generation devices.

Professor Jonghwa Shin from the Department of Materials Science and Engineering at KAIST said: “This research has achieved the complete control of the asymmetric transmission of light intensity, phase and polarization, which constitutes a long-standing challenge in optics. possibility of developing various applied optical devices.

“We plan to continue developing optical devices that can be applied to various fields such as augmented reality (AR), holographic displays and LiDAR systems for autonomous vehicles, using the full potential of metasurface technology.”