Terahertz (THz) radiation has received much attention during the past few decades for its potential applications in various fields, such as spectroscopy, imaging, and wireless communications. To use terahertz waves for data transmission in different application systems, the efficient and rapid modulation of terahertz waves is required and has become an in-depth research topic. Since the turn of the century, research on metasurfaces has rapidly developed, and the scope of novel functions and operating frequency ranges has been substantially expanded, especially in the terahertz range. The combination of metasurfaces and semiconductors has facilitated both new opportunities for the development of dynamic THz functional devices and significant achievements in THz modulators. This paper provides an overview of THz modulators based on different kinds of dynamic tunable metasurfaces combined with semiconductors, two-dimensional electron gas heterostructures, superconductors, phase-transition materials, graphene, and other 2D material. Based on the overview, a brief discussion with perspectives will be presented. We hope that this review will help more researchers learn about the recent developments and challenges of THz modulators and contribute to this field.

High-speed logic modulation of terahertz (THz) waves is crucial for future communications, yet a technology gap persists. Here, we report a dual gate–controlled two-dimensional electronic gas logic modulation metasurface that enables symmetric and asymmetric electron distribution states through independent control of the two electron transport channels. The transition between these two states leads to various response modes in the metasurface and notably increases the diversity of the spectrum transformation, resulting in a multivalued relationship in which each output corresponds to more than one input signal, thus establishing the logical modulation. Our results demonstrate the common logical functions of AND, OR, XOR, XNOR, NOR, and NAND at different frequencies with a modulation speed faster than 250 picoseconds. This work offers a unique avenue for the high-speed, free-space logical operation of THz waves and increases the security of secure communication.

Terahertz communication technology based on on-off keying (OOK) direct modulation is vital for sixth-generation communication systems, especially in short-distance and high-rate applications. However, low-order OOK modulation often leads to suboptimal anti-interference capabilities and a heightened demodulation threshold. Here, we propose a high-order direct modulation terahertz communication framework using a wideband time-coding metachip modulator. The modulator leverages the electromagnetic resonance properties within the metaunit structure, with control enabled by gallium arsenide Schottky diodes. By manipulating the timing of voltage pulses applied to these diodes, the equivalent electromagnetic resonance distributions can be precisely regulated in the time domain. This enables independent and accurate control over the amplitude and phase of terahertz harmonics. Leveraging this technique, three high-order modulation schemes—quadrature phase-shift keying, 16-phase-shift keying, and 16-quadrature amplitude modulation— are achieved in a direct modulation and direct detection system, demonstrating the real-time image transmission. The proposed method offers an important way to develop integrated and low-complexity terahertz wireless communication systems.

In recent years, terahertz waves have attracted significant attention for their promising applications. Due to a broadband optical response, an ultra-fast relaxation time, a high nonlinear coefficient of graphene, and the flexible and controllable physical characteristics of its meta-structure, graphene metamaterial has been widely explored in interdisciplinary frontier research, especially in the technologically important terahertz (THz) frequency range. Here, graphene’s linear and nonlinear properties and typical applications of graphene metamaterial are reviewed. Specifically, the discussion focuses on applications in optically and electrically actuated terahertz amplitude, phase, and harmonic generation. The review concludes with a brief examination of potential prospects and trends in graphene metamaterial.

The developing terahertz wireless communication demands higher performance modulators. In this Letter, a mechanism of resonance mode transformation for a high-speed terahertz direct amplitude modulator with rather low insertion loss and high modulation depth is presented. By embedding an H-shaped resonance structure, which consists of a fin-line and two flip-flopped GaAs Schottky diodes, into the E-wall of a waveguide, the fed terahertz waves are modulated by the inductive-capacitive (LC) resonance transformation of the structure. Based on this mechanism, a modulator working in the frequency band around 140 GHz is fabricated and packaged. Thanks to the LC resonance transformation, the presented modulator exhibits a low insertion loss of 1.8 dB at 138 GHz, a large modulation depth higher than 99% at 148 GHz, and high modulation speeds up to 30 Gbps at 146 GHz. Accordingly, the presented mechanism paves a promising route to develop high performance terahertz direct modulators, which is of great significance for terahertz high-speed wireless communication.

As an exceptional nonlinear material, graphene offers versatile appealing properties, such as electro‐optic tunability and high electromagnetic field confinement in the terahertz regime, spurring advance in ultrashort pulse formation, photodetectors and plasmonic emission. However, limited by atomic thickness, weak light–matter interaction still limits the development of integrated optical devices based on graphene. Here, an exquisitely designed meta‐cavities combined with patterned graphene is used to overcome this challenge and promote THz‐graphene interaction via terahertz location oscillation. By using an 800 nm pump laser, the local field‐induced strong interaction allows sensitive responses to the ultrafast energy transfer from the ultrafast optical pump to graphene electron heat, enabling 46.2% enhancement of terahertz transparency. Such optical modulation of terahertz waves shows ultrafast response in delay less than 10 ps. Moreover, thanks to the nature of graphene, the device shows unique potential for electrically dynamic tuning and further bandwidth broadening.