A UNIST research team has succeeded in developing an active conversion nonlinear optical metasurface technology consisting of structures smaller than the wavelength of light. It is expected to bring significant advancements to future communication technology fields such as quantum light sources and medical diagnostic devices.

A research team led by Professor Jong-Won Lee of the Department of Electrical and Electronic Engineering at UNIST (President Jong-Rae Park) has developed a ‘nonlinear optical metasurface’ that can control the third harmonic with electricity. This is a technology that controls complex optical signals by changing the characteristics of light according to signals or stimuli applied from the outside.

Nonlinear optics is the interaction between light and matter, changing the frequency of the light. It produces a variety of wavelengths, which can convey more information than a single wavelength laser. A green laser pointer is a representative application of nonlinear optics technology.

A metasurface is a metal structure bonded to a small semiconductor layer, smaller than the wavelength of light. Since multiple units of the structure are aligned on a substrate, the metasurface can effectively manipulate light.

Nonlinear optical metasurfaces can make optical devices smaller and lighter. Laser devices can be made as thin as paper using artificial materials thinner than a hair. Existing manual methods were difficult to control electrically, but the nonlinear optical metasurface developed by the research team can be controlled electrically.

The research team was the first in the world to demonstrate a technology that can control the second harmonic by voltage, and also implemented a technology that can independently control the intensity and phase of the third harmonic for the first time. The metasurface can now control not only the wavelength of light, but also the intensity and phase.

“The properties of the optical metasurface are determined by the semiconductor layer and metal structure,” said researcher Park Sung-jin. “The metasurface can control not only the frequency of light but also its phase and amplitude, overcoming the limitations of existing optical devices.”

Professor Lee Jong-won said, “This is the first time that the intensity and phase of a nonlinear third harmonic have been electrically controlled,” and “It can also be used in optical modulation cryptography, moving holograms, next-generation quantum sensors, and quantum communication light sources.”

The research results were published as a paper on July 17 in the most prestigious academic journal in the field of optics, 'Light: Science and Applications.' The research was conducted with support from the National Research Foundation of Korea's Mid-career Researcher Support Program.