Gbps Terahertz External Modulator Based on a Composite Metamaterial with a Double-Channel Heterostructure

Abstract

The past few decades have witnessed a substantial increase in terahertz (THz) research. Utilizing THz waves to transmit communication and imaging data has created a high demand for phase and amplitude modulation. However, current active THz devices, including modulators and switches, still cannot meet THz system demands. Double-channel heterostructures, an alternative semiconductor system, can support nanoscale two-dimensional electron gases (2DEGs) with high carrier concentration and mobility and provide a new way to develop active THz devices. In this Letter, we present a composite metamaterial structure that combines an equivalent collective dipolar array with a double-channel heterostructure to obtain an effective, ultrafast, and all-electronic grid-controlled THz modulator. Electrical control allows for resonant mode conversion between two different dipolar resonances in the active device, which significantly improves the modulation speed and depth. This THz modulator is the first to achieve a 1 GHz modulation speed and 85% modulation depth during real-time dynamic tests. Moreover, a 1.19 rad phase shift was realized. A wireless free-space-modulation THz communication system based on this external THz modulator was tested using 0.2 Gbps eye patterns. Therefore, this active composite metamaterial modulator provides a basis for the development of effective and ultrafast dynamic devices for THz wireless communication and imaging systems.

A review of metasurfaces: physics and applications

“…(a) and (b) used with permission from [179], (c) and (d) used with permission from [180], (e) and (f) used with permission from [178].…”

“…Together with the causally connected phase modulation (up to 0.55 rad), this device allows broadband THz modulation [174] that can be used to replace a mechanical optical chopper in a lock-in THz detection scheme with modulation speed in the MHz range [176][177][178], limited either by the large device area accompanied with high stray capacitance or parasitic capacitance from the bonding electrodes and wires. Very recently, GHz electronic modulation speed has been demonstrated by using double-channel heterostructures supporting nanoscale 2DEGs with high carrier concentration and mobility [179], shown in figure 27(a). Through designing a composite hybrid metasurface structure to reduce the stray capacitance, 1 GHz modulation speed, 85% modulation depth (figure 27(b)), and a phase shift of 1.19 rad were experimentally realized during real-time dynamic tests.…”

All-integrated terahertz modulators

“…In Ref. [70], the authors demonstrated more than 1-GHz modulation speed (even though significant degradation was observed already above 200 MHz) and 86% modulation depth. In this work, InAlN/AlN/GaN/AlN/GaN double-channel heterostructures supported a 2DEG channel [68] and as a detector [13].…”

“…Electronically tuneable 2DEG-based devices represent a parallel and viable route to achieving integrated amplitude modulators which yield excellent performances in high-speed modulation and modulation depths. Recent works targeted mostly the sub-THz frequency range [69,70], aiming at a direct monolithic integration of the modulators onto a chip with a view to a THz circuitry platform for communications. In Ref.…”

Advances in terahertz communications accelerated by photonics

“…Further development in plasmonic-based waveguides 88 could offer both low enough loss, field enhancement for interaction with a modulator or detection system and size reduction that are all desirable features in a future THz system. Further to such structures, the development in metamaterials can enable enhanced THz manipulation in devices 89 , in particular interesting work has been done on THz modulators using metamaterials 90,91 .…”