Sen Gong

Direct amplitude modulation above 300GHz is challenged by strong device parasitics, high structural sensitivity, and limited separation between high- and low-transmission states. This letter presents a waveguide-compatible terahertz (THz) direct amplitude modulator using a Schottky barrier diode (SBD) reconfigurable square-ring unit. Two Schottky diodes are mounted across the gaps between metal patches and form a reconfigurable square-ring unit with the metal structure. With bias control, the unit changes between an open-ring, weak-loading state and a closed-ring, resonant-loading state. When the SBDs are cutoff, the unit weakly loads the incident THz field and maintains a high transmission. When the SBDs conduct, the metal patches and diodes form a closed square ring, which enhances the local resonance and suppresses the transmitted signal. Measurements show clear static transmission modulation above 300GHz and OOK-NRZ direct amplitude modulation up to 25Gb/s. The proposed structure provides a practical route for waveguide-compatible, THz direct amplitude modulation above 300GHz.

High-speed terahertz (THz) binary phase shift keying (BPSK) phase modulation is often limited by state switching that perturbs the effective port impedance and boundary conditions, where the resulting reflections and parasitic round-trip multipath convert amplitude ripple into phase error. This article presents a THz BPSK phase modulator based on a differential absorption control network (DACN). By swapping and reconstructing the transmissions of two complementary differential paths, the DACN produces an end-to-end sign reversal and enables a phase-state transition close to 180°. An impedance-stable THz absorptive modulator (TAM) is further introduced to keep the input boundary nearly unchanged between switching states, thereby suppressing reflection-enhancement effects and improving amplitude–phase consistency. Experimental results show that the phase error stays below 5° over an approximately 25 GHz bandwidth, while the amplitude imbalance remains below 1 dB over an approximately 15 GHz bandwidth. High-speed coherent demodulation demonstrates BPSK modulation up to 30 Gb/s with an EVM of −12.06 dB (24.94%). The proposed structure provides a practical solution for next-generation THz high-speed phase-modulation systems.

Efficient amplitude modulation of terahertz (THz) waves is essential for high-speed communication systems. However, the long-standing trade-off between low insertion loss (IL) and high-modulation depth (MD) in THz modulators is fundamentally constrained by parasitic energy leakage and inefficient field–carrier interaction. Here, we propose a THz amplitude modulator based on a longitudinal–transverse coupled-resonance mechanism. By introducing a transverse open-ended T-shaped stub, the resonant current distribution is effectively tailored, and parasitic leakage along the device edges and feeding paths is strongly suppressed, enabling large MD under low-loss operation. The proposed modulator exhibits an IL of only 0.9 dB and a MD of 31 dB at 140 GHz, while supporting high-speed modulation of up to 30 Gbps. This work provides a compact and scalable structural approach for realizing low-loss, high-modulation depth, and high-speed THz amplitude modulation.

The terahertz band is essential for high-capacity single-carrier communications due to its large bandwidth and wireless transmission capability. However, its performance is constrained by the limitations of solid-state device technology, especially on conventional metal waveguide transmission lines. This article analyzes the dispersion characteristics of transmission modes to identify the physical mechanism behind bandwidth constraints in terahertz devices. Through targeted phase response optimization, we develop a highly balanced broadband hybrid coupler and a low-insertion-loss mixer, resulting in a solid-state in-phase-quadrature (I/Q) mixer operating in the 0.215-THz band, achieving an image rejection ratio (IRR) exceeding 20dB across a 64-GHz bandwidth. This design supports 300-Gbit/s transmission using 64-quadrature amplitude modulation (QAM) at 50 Gbaud, with a bit error rate (BER) of $\boldsymbol {5.68{\,}\times {\,}10^{-3}}$ , representing the highest reported communication rate for an all-solid-state single-channel link in this band.

Current terahertz direct modulators suffer from significant reflections during modulation. This paper proposes an absorptive terahertz amplitude modulator based on dual-path coherent interference by integrating a ring circuit structure with Schottky diodes. Through dynamic regulation of interference effects between dual paths by controlling diode states, coherent modulation at the output port is achieved while effectively suppressing reflections under modulated conditions. The designed 220 GHz central frequency modulator demonstrates return loss below 16 dB in both “ON/OFF” states, successfully overcoming the high-reflection issue inherent to traditional impedance-mismatch-based modulators. This approach breaks through the reflection bottleneck of conventional impedance modulation methods and provides a novel pathway for high-performance terahertz communication devices.

Current terahertz amplitude modulators predominantly employ reflective modulation principles, which often lead to impedance mismatch with terahertz sources during modulation process, resulting in degraded signal-to-noise ratio (SNR) and increased timing jitter in demodulated signals. This article proposes a terahertz absorption-type modulator designbased on quasi- $\pi $ reconfigurable networks. When absorption conditions are met, the modulator maintains constant input port impedance during the “on” to “off”-state transitions, achieving unidirectional reflectionless absorption modulation. Based on this design, we developed a 140-GHz band quasi- $\pi $ network unidirectional absorption-type amplitude modulator with an optimal voltage standing wave ratio (VSWR) of 1.1. Dynamic testing demonstrates that the absorption state exhibits superior eye diagram performance compared to the high-reflection state. The proposed absorption-type amplitude modulation technique thus provides robust support for high-speed and high-precision terahertz amplitude control while pioneering new pathways for integrated on-chip terahertz system design.

Terahertz (THz) wireless links have attracted significant attention due to their pivotal role in next-generation communication systems. Multiplexing is one of the key techniques used to expand channel capacity for high-speed data transmission in point-to-point wireless communication. Using a pair of multifunction metasurfaces, we construct mode division multiplexing (MDM) in THz wireless link with cylindrical vector beams (CVBs) as orthogonal channels. The proposed metasurfaces integrate the functions of CVB generation and vector mode multiplexing, greatly simplifying MDM links. The simulated and measured results show that the multiplexer/demultiplexers are broadband in the frequency range of concern (from 0.36 to 0.44 THz) and compatible with frequency-division-multiplexing and polarization-division-multiplexing. Importantly, we experimentally accomplished a two-channel MDM in a direct modulation THz communication system at 0.36 THz in which the maximum modulation speed is 5 GHz (isolation>20dB). This study will lay the groundwork for CVB-based multidimensional multiplexing in the THz spectrum, potentially enhancing high-capacity THz communication.

Electromagnetic (EM) metamaterials represent a cutting-edge field that achieves anomalously macroscopic properties through artificial design and arrangement of microstructure arrays to freely manipulate EM fields and waves in desired ways. The unit cell of a microstructure array is also called a meta-atom, which can construct effective medium parameters that do not exist in traditional materials or are difficult to realize with traditional technologies. By deep integration with digital information, the meta-atom is evolved to a digital meta-atom, leading to the emergence of information metamaterials. Information metamaterials break the inherent barriers between the EM and digital domains, providing a physical platform for controlling EM waves and modulating digital information simultaneously. The concepts of meta-atoms and metamaterials are also introduced to high-frequency integrated circuit designs to address issues that cannot be solved by traditional methods, since lumped-parameter models become unsustainable at microscopic scales. By incorporating several meta-atoms to form a metachip, precise manipulation of the EM field distribution can be achieved at microscopic scales. In this perspective, we summarize the physical connotations and main classifications of meta-atoms and briefly discuss their future development trends. Through this article, we hope to draw more research attention to explore the potential values of meta-atoms, thereby opening up a broader stage for the in-depth development of metamaterials.

With the rapid development of modern communication technology, spectrum resources have become non-renewable and precious resources, and the terahertz frequency band has entered people's vision. Nowadays, terahertz communication technology has become one of the core technologies for future high-capacity and high-rate communication. This paper discusses and analyzes the core technologies related to the field of terahertz communication. We introduce the characteristics, domestic and international comparisons and development trends of the core devices for terahertz communication, and also introduce and discuss the terahertz solid-state frequency mixing communication system, terahertz direct modulation communication system, and terahertz optoelectronic communication system. Finally, we summarize the development of terahertz communication technology and the outlook of future applications.

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.