A sand-grain-sized chip capable of independently controlling light's wavelength and intensity has been developed, opening possibilities for quantum entanglement light sources and miniaturized optical signal processors.
A research team led by Professor Lee Jong-won at the Department of Electrical and Electronic Engineering at Ulsan National Institute of Science and Technology (UNIST) announced Wednesday that they have developed the world's first metasurface device that can independently control light's intensity and wavelength.
A metasurface is a micro-artificial device that arranges nano-structures much smaller than light wavelengths on a surface to manipulate light's optical properties in ways not found in nature. It can replace bulky media used in commercial light modulation technology, enabling lighter devices and creating optical phenomena impossible with existing light modulation techniques.
The metasurface developed by the team controls a special optical phenomenon called second harmonic generation (SHG). This technology amplifies the energy of input light (fundamental wavelength) by twofold, converting it into new light (second harmonic) with half the wavelength. For example, when infrared light is input, it transforms into light with a different wavelength, which can be used for sensors detecting trace biomolecules or developing eavesdrop-proof quantum communication technology.
However, the technology has been limited by the complex interdependence between light's wavelength and intensity. Increasing conversion efficiency to strengthen light intensity narrowed the wavelength control range, while expanding wavelength control range caused efficiency to drop sharply—a persistent trade-off.
The research team solved this by designing a device that separates light processing inside the metasurface into "entry" and "exit" pathways. The process of light entering the chip and energy accumulating (generation) and the process of transformed light exiting (emission) are handled by different control mechanisms. The team named this the "local-to-nonlocal" approach.
The metasurface chip designed this way has two independent control methods. Adjusting the voltage flowing through the chip changes only the intensity while wavelength remains constant. Conversely, slightly altering the angle at which light enters the chip changes only the wavelength while intensity stays the same. Light's properties can be perfectly separated and controlled without mutual interference.
In experiments, when researchers adjusted the light's incident angle, the output wavelength changed continuously. When only electrical signals were changed while fixing a specific wavelength, intensity varied while wavelength remained constant.
"While previous research relied on only one method—either confining light (local mode) or letting it flow (nonlocal mode)—this technology combines both approaches, enabling much freer device design and resolving the long-standing dilemma between efficiency and controllability," Professor Lee explained.
"This will contribute to completing next-generation active quantum light source technology, including real-time quantum information control and freely adjusting the wavelength spectrum of entangled photons, which are central to quantum communication," he added.
The research was published in Advanced Science on November 29 and was supported by the Institute for Information & Communications Technology Planning & Evaluation (IITP) and the National Research Foundation of Korea.
