image: Figure | Single-gate electro-optic beam switching metasurfaces. a, (left) Schematic of an active beam switching graphene metasurface. (top right) Optical microscope top-view image of the fabricated device. (bottom right) Scanning electron microscope (SEM) top-view image of the grating for one period (false colored). b, Angle-resolved far-field pattern measured at the gate bias 10 V and -80 V at the operation frequency 41.17 THz. c, Experimentally measured absolute efficiencies and relative efficiencies for the 0th and the -1st order diffractions when the gate bias is swept from -80 V to 70 V.
Credit: Sangjun Han et al.
For contemporary applications like LiDAR, free-space optical communication, augmented reality, and on-chip photonics, dynamic light steering is essential. Traditionally, this has been accomplished through the use of micro-electromechanical systems (MEMS) or mechanically movable mirrors, both of which have large sizes, poor durability, and slow response times. Electro-optic active metasurfaces have recently become a viable substitute. These surfaces can use electrical signals to change the polarization, amplitude, or phase of light. To control each unit-cell (also known as a meta-atom), the majority of electro-optic active metasurfaces still employ dense arrays of independently controlled electrodes. Device complexity, power consumption, and failure risk are all increased by this design. Furthermore, unit-cell-based local gating schemes are challenging to scale for high-resolution or large-area applications and frequently produce uneven optical performance.
A group of researchers from the Korea Advanced Institute of Science and Technology (KAIST), led by Professor Min Seok Jang, reports a major innovation in a new paper published in Light: Science & Applications: a graphene-based electro-optic metasurface that enables wide-angle beam steering using only a single-gate electrode. This technique opens the door for scalable, useful applications of dynamic beam control by significantly simplifying the device structure while maintaining high optical efficiency and deflection angle. They created a reflective metasurface made of periodic gold gratings on a monolayer of graphene on a substrate. They were able to control the direction of scattered light between the 0th and -1st diffraction orders by modulating the graphene's Fermi level with a single-gate bias.
They achieved a beam switching angle of 57°, which is a remarkably large angle for such a simple gating configuration. The group employed a genetic algorithm to optimize performance. The metasurface attained relative efficiencies exceeding 75% and absolute efficiencies of approximately 8% in both beam directions. Instead of relying on localized surface plasmons, theoretical analysis using quasinormal mode expansion demonstrated that the beam switching originates from the interference between a gate-tunable resonant mode and a non-resonant background response. By choosing multiple Fermi levels, the authors further demonstrated that this design approach could be extended to multi-level beam switching, enabling more than two output directions. Their metasurface may play a significant role in next-generation programmable photonic systems due to its scalability and simplified single-gate design.
Professor Min Seok Jang stated, "This study demonstrates that precise and efficient beam control can be achieved without the need for complex driving circuits or high power consumption." He added, " Our single-gate structure not only simplifies the system but also shows excellent performance, making it suitable for practical optical devices for sensing, communication, and computing."
Journal
Light Science & Applications