Journal Article

Achieving 100% amplitude modulation depth in the terahertz range with graphene-based tuneable capacitance metamaterials

Ritchie, David A., Almond, Nikita W., Degl’Innocenti, Riccardo, Tadbier, Wadood, Mikhailov, Sergey A., Lowe, Abbie, Michailow, Wladislaw, Kindness, Stephen J., Xia, Ruqiao, Dann, James, Jakob, Lukas A., Hofmann, Stephan, Lu, Yuezhen, Ramsay, Ben, Beere, Harvey E.

2025

Overview

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. By switching from a variable resistance to a tunable capacitance modulation principle using nanoscale lateral capacitors and leveraging substrate-side reflection, we achieve 100% amplitude modulation in graphene-based metamaterial terahertz modulators.

• Publisher: Nature Publishing Group UK,Springer Nature B.V,Nature Publishing Group
• Subject: 639/624/399/1015 / 639/624/399/918/1054 / 639/766/1130/2799 / 639/766/400/561 / Capacitance / Electric fields / Electrons / Graphene / Lasers / Microwaves / Optical and Electronic Materials / Optical Devices / Optics / Photonics / Physics / Physics and Astronomy / Radiation / RF and Optical Engineering