Xia Ruqiao, Almond Nikita W, Tadbier Wadood, Kindness Stephen J, Degl'Innocenti Riccardo, Lu Yuezhen, Lowe Abbie, Ramsay Ben, Jakob Lukas A, Dann James, Hofmann Stephan, Beere Harvey E, Mikhailov Sergey A, Ritchie David A, Michailow Wladislaw
Cavendish Laboratory, University of Cambridge, Cambridge, UK.
Department of Engineering, University of Cambridge, Cambridge, UK.
Light Sci Appl. 2025 Aug 4;14(1):256. doi: 10.1038/s41377-025-01945-4.
Effective control of terahertz radiation requires fast and efficient modulators with a large modulation depth-a challenge that is often tackled by using metamaterials. Metamaterial-based active modulators can be created by placing graphene as a tuneable element shunting regions of high electric field confinement in metamaterials. However, in this common approach, the graphene is used as a variable resistor, and the modulation is achieved by resistive damping of the resonance. In combination with the finite conductivity of graphene due to its gapless nature, achieving 100% modulation depth using this approach remains challenging. Here, we embed nanoscale graphene capacitors within the gaps of the metamaterial resonators, and thus switch from a resistive damping to a capacitive tuning of the resonance. We further expand the optical modulation range by device excitation from its substrate side. As a result, we demonstrate terahertz modulators with over four orders of magnitude modulation depth (45.7 dB at 1.68 THz and 40.1 dB at 2.15 THz), and a reconfiguration speed of 30 MHz. These tuneable capacitance modulators are electrically controlled solid-state devices enabling unity modulation with graphene conductivities below 0.7 mS. The demonstrated approach can be applied to enhance modulation performance of any metamaterial-based modulator with a 2D electron gas. Our results open up new frontiers in the area of terahertz communications, real-time imaging, and wave-optical analogue computing.
有效控制太赫兹辐射需要具有大调制深度的快速高效调制器，这一挑战通常通过使用超材料来解决。基于超材料的有源调制器可以通过将石墨烯作为可调谐元件放置在超材料中高电场限制区域来创建。然而，在这种常见方法中，石墨烯被用作可变电阻器，调制是通过共振的电阻阻尼来实现的。由于石墨烯的无隙性质导致其具有有限的电导率，使用这种方法实现100%的调制深度仍然具有挑战性。在这里，我们将纳米级石墨烯电容器嵌入超材料谐振器的间隙中，从而从电阻阻尼切换到共振的电容调谐。我们通过从衬底侧对器件进行激发来进一步扩大光调制范围。结果，我们展示了具有超过四个数量级调制深度（在1.68太赫兹时为45.7分贝，在2.15太赫兹时为40.1分贝）和30兆赫兹重构速度的太赫兹调制器。这些可调谐电容调制器是电控固态器件，在石墨烯电导率低于0.7毫西门子时能够实现单位调制。所展示的方法可应用于增强任何基于二维电子气的超材料调制器的调制性能。我们的结果在太赫兹通信、实时成像和波光学模拟计算领域开辟了新的前沿。
