Although modulated metasurface antennas (MMAs) offer planar terahertz solutions, scaling them to the WR-1.0 band faces fundamental physical and manufacturing bottlenecks. Nanometer-scale skin depths induce significant Ohmic loss, demanding smooth all metallic architectures, yet conventional UV-LIGA fabrication suffers from microstructure delamination. These bottlenecks are simultaneously addressed by an 860 GHz all-metallic MMA developed through a holistic design fabrication co-optimization framework. A developed over electroforming UV-LIGA process leverages mushroom shaped interlocking unit cells to prevent delamination while guaranteeing sub-micron surface smoothness to bound high-frequency insertion loss. Measurements demonstrate a maximum realized gain of 13.8 dBi at 862 GHz. To the best of the authors' knowledge, this is the first experimental demonstration of an all-metallic MMA in the WR-1.0 band.
This editorial recalls the start and early years of the IEEE Transactions on Terahertz Science and Technology from the viewpoint of the founding Editor-in-Chief. It covers some of the startup steps as well as the journal philosophy, scope, goals, and early operational structure. It concludes with the first set of journal metrics and a summary of the journal's accomplishments from its founding in 2010 through just a tad over its fourth year of issues, ending in December 2015.
This letter presents an H-band (220-330 GHz) fully-metallic multilayer waveguide (MLW), that consists of five stacked metallic layers forming an air-filled groove. The waveguide is surrounded by a locally glide-symmetric holey electromagnetic bandgap (EBG) structure that prevents electric field leakage across the interlayer gaps. A diamond-shaped unit cell is selected for the EBG due to its high effectiveness in suppressing leakage. To enable practical characterization, a well matched vertical transition is developed using a discretized stepped corner via a novel design process, crucial to achieve good impedance matching at high frequencies. The prototype exhibits a measured reflection coefficient lower than-10dB in the entire H-band, and an average loss of the waveguide channel of 0.032dB/mm.
Terahertz (THz) space-division multiplexing (SDM) using highly directional beams is a promising approach for high-capacity fixed wireless backhaul and fronthaul, but its spatial isolation can be significantly affected by weather-induced impairments under outdoor conditions. This paper investigates rain-induced crosstalk in space-division-multiplexed THz fixed wireless systems from a design-oriented perspective. Controlled rainfall measurements were performed at 300 GHz using receiver (Rx) angular scanning under both aligned and intentionally beam-offset transmitter (Tx) configurations in the far-field. The measurement results show that rainfall generates off-axis scattered components that couple energy into adjacent spatial channels, in addition to conventional rain attenuation and wind-induced effective gain degradation. This scattering-induced coupling establishes a weather-dependent limitation on achievable spatial isolation that cannot be mitigated simply by increasing transmit power, making it a critical factor for robust link design in SDM systems.
This paper presents a review of CMOS-based integrated circuits operating above 200 GHz for future wireless communication systems. Key building blocks are reviewed, including power amplifiers, low-noise amplifiers, mixers, voltage controlled oscillators, and frequency multipliers, with emphasis on circuit techniques that overcome the fundamental limitations of CMOS technology at terahertz frequencies. Recent system-level transceiver demonstrations for high-speed communication, radar, and imaging are also introduced. This paper provides a comprehensive overview of the circuit techniques and system implementations that enable CMOS technology to operate at terahertz frequencies, highlighting both the progress achieved and the challenges that remain.
The terahertz frequency band offers unprecedented bandwidths for next-generation wireless communications, but suffers from significant free-space path loss that necessitates highly directive antennas. Beam steering antennas are therefore essential to dynamically align high-gain beams and maintain link reliability in practical terahertz wireless systems. In this work, we propose a phased-array antenna based on an all-silicon effective-medium waveguide platform. The proposed architecture integrates a feeding network, terahertz phase shifters, and a dense waveguide array terminated by dielectric rod antennas, with each component realized in a modular hollow waveguide package. Compared with conventional terahertz phased arrays that achieve phase control in either the electronic or photonic domain, the proposed design enables direct phase tuning in the terahertz domain using widely accessible phase shifters, while maintaining low loss, broad bandwidth, and scalability. As a proof of concept, a two-element phased array is demonstrated, achieving continuous beam steering over $\pm 20^{\circ }$ at the 300-GHz band. The impact of inter-waveguide coupling and radiator mutual interaction is systematically investigated. Wireless communications experiments further validate the beam-steering functionality, supporting transmission data rates up to 40 Gbit/s with 16-QAM modulation and real-time high-definition video transmission. The proposed design demonstrates the feasibility of all-dielectric waveguide platforms for dynamic beam-steerable antennas and lays the foundation for efficient fully integrated terahertz phased arrays for 6 G and beyond.
This paper presents the design, simulation, fabrication, and measurement of a wideband, high-efficiency in package Vivaldi antenna for D-band imaging application. The proposed single-layer antenna design avoids vias and polymer dielectric lamination, thereby simplifying the fabrication process. The antenna is fed by a wideband 90° coplanar waveguide–to coplanar slotline (CPW–CPS) transition incorporating a radial stub, which does not require vias for ground connections and enables heterogeneous integration with an integrated circuit (IC) die via flip chip bonding. In fact, it emphasizes the broadband feature of CPW-CPS in D-band and its compatibility for integration with a Vivaldi antenna. The antenna size is 1.42λ0 × 0.95λ0 at 140 GHz. The proposed antenna is developed on a 100 μm-thick one-layer seedless quartz glass substrate with titanium/copper metallization at in-house cleanroom facility. It is measured using a ground-signal-ground (GSG) probe to characterize return loss, peak realized gain, and radiation patterns at D-band. The Vivaldi antenna, excited through a CPW to CPS transition, achieves wideband operation covering the entire D band (110–170 GHz) with a maximum realized gain of 14 dBi corresponding to 88% efficiency. The measured cross-polarization are 15 dB lower than the associated co-polarization levels. This research leverages microfabrication on quartz substrates with via less implementations while achieving high efficiency and wide bandwidth, providing novel antenna-in-package structures for potential D-band imaging applications.
This letter presents an experimental realization of a sub-terahertz (sub-THz) fully metallic sliding-aperture multibeam antenna with a wide beam scanning range based on mixed-waveguide (mixed-WG) phase shifter array for the first time to the best of the authors' knowledge. To meet the requirements of wide scanning range without grating lobes, each mixed-WG phase shifter array is composed of a rectangular waveguide (WG) phase shifter and a double-ridge WG phase shifter, yielding a much smaller element spacing in the radiating aperture. To reduce the effect of the open boundary condition which damages the illuminating property from the edge port and causes worse scan loss, additional mixed-WGs are added symmetrically on both sides. The antenna is fed by nine rectangular WGs, serving nine independent beams. A ridged flare is added as a transition from the mixed-WG phase shifter array to free space, improving the radiation performance. A prototype operating within the band from 175 to 195 GHz is fabricated by high-precision computer numerical control (CNC) machining technique and experimentally verified. The measured results show good reflection coefficients below -15 dB at all ports, a best beam scanning range of ±52°, peak gains above 15.5 dBi, and scan loss better than 2.2 dB, agreeing well with simulation. This work demonstrates a novel feasible and reliable solution of waveguide-based fully metallic sub-THz multibeam antenna for the application demanding wide angle scanning.
Terahertz sources, such as free-electron lasers, quantum-cascade lasers, and other pulsed systems, contain frequency components across multiple terahertz. Grating-based spectrometers are commonly used for identifying their emitted spectrum, providing access only to the envelope with insufficient resolution for their substructure. Established methods for precise analysis of the source's spectral substructure remain limited, particularly in the terahertz domain. We demonstrate MHz-resolved spectral characterization of the free-electron laser FELBE at frequencies beyond 2 THz with a photonic spectrum analyzer. At a resolution bandwidth of 3.6 MHz, we reveal a comb-like substructure of the free-electron laser with 13 MHz spacing, matching its repetition rate, and an envelope width of 42 GHz. The envelope width is consistent with the grating spectrometer recording. The photonic spectrum analyzer offers frequency coverage of several terahertz in a single system, far beyond what is accessible by current commercial spectrum analyzers.
This paper investigates the properties of a new nonlinear crystal, BaHgGeSe$_{4}$ (BHGSe), in the terahertz (THz) frequency range of 0.1 - 4 THz. Narrowband THz generation was achieved for the first time at a frequency of 0.75 THz with a relative FWHM spectral width of $\Delta f/f$ = 8% when the crystal is excited by high-power femtosecond pulses from a Cr:forsterite laser system, as verified by interferometric and electro-optical detection. Combined Raman and terahertz time-domain spectroscopy (THz-TDS) reveal that this frequency coincides with a phonon mode that is simultaneously active in both Raman scattering and IR absorption spectra. Careful dispersion analysis indicates that the observed THz emission originates from optical rectification (OR) of femtosecond pump pulses. The phase-matching condition is satisfied within a narrow frequency interval, where phonon resonance provide pronounced refractive index dispersion. The dependence of generation efficiency on the pump power density was determined, reaching 10$^{-6}$ in the saturation regime, which corresponds to an energy of approximately 3 nJ.
We present a lens-to-lens system for characterizing the transmission through metasurfaces integrated in silicon technology. The system employs two confocal elliptical silicon lenses, with the metasurface positioned at their focal points. This system allows to uniformly illuminate the center of the metasurface with plane wave incidence, while avoiding illumination of the edges. The lens-to-lens characterization system was fabricated and used to measure the transmission magnitude and phase through a metasurface integrated in 130-nm SiGe BiCMOS between 330GHz and 500GHz. The measured magnitude of the transmission was within 1 dB of simulations. Agreement with simulations for the phase measurement was within 10° after compensating for a small air gap in the assembly. The proposed lens-to-lens system provides a practical and reliable platform for over-the-air characterization of silicon-integrated metasurfaces operating at terahertz frequencies.
The terahertz (THz) frequency band, ranging from 0.1 to 10 THz and bridging the microwave bands and infrared regions, has been the focus of intensive R&D since the 1960s. Despite its considerable progress, THz technology continues to face major challenges in signal generation, detection, and transmission. Overcoming these hurdles depends on advances in materials science, design considerations, fabrication techniques, and system integration. Researchers from both the electronics and photonics communities have played instrumental roles in advancing THz technologies and systems. One core of these developments are THz waveguides or guided-wave structures, which serve as fundamental building blocks in the development of antennas, circuits, and systems. They are set to directly influence the performance of both passive components and active devices, affecting key parameters of performance. Although THz waveguides present structural similarities with respect to those used in microwave and optical domains, they are usually different technically, often suffering from transmission inefficiencies due to geometric, material, and fabrication constraints. However, recent breakthroughs have significantly enhanced their performance. In this article, we present a comprehensive review of THz waveguide technologies from the perspective of guided-wave structures and electrical performances, classifying them into four principal types: transitional planar transmission lines, metallic waveguides, dielectric waveguides, and substrate-integrated structures. We also explore emerging hybrid architectures such as metallo dielectric technologies and assess their potential in enabling practical and scalable THz system developments and applications.
Traditional perfect vortex beams possess inherently fixed shapes and carry only a single topological charge, limiting their flexibility. Here, we propose a segmented beam shaping technique to generate terahertz grafted generalized perfect vortex beams with intensity and phase distributed along arbitrary two-dimensional and three-dimensional curves. Phase holograms are theoretically designed and fabricated via 3Dprinting for experimental validation. Results demonstrate that the beam shape, as well as the values, proportions, and segment numbers of grafted topological charges, can be independently and flexibly controlled. This method enhances orbital angular momentum diversity and provides additional degrees of freedom for structured light design.
In recent years, the photonics-assisted terahertz (THz) communication system has garnered extensive research interest due to its ultra-broad bandwidth and large capacity, making it highly beneficial for next-generation ultra-high-speed wireless transmission scenarios. However, this system often suffers from the issue of polarization sensitivity between the two lightwaves which are used to generate THz signal through heterodyne photomixing, significantly compromising its robustness and practicality. In this paper, we propose a coherent polarization-insensitive photonics-assisted THz communication system based on a blockwise Alamouti coding scheme, which can maintain stable performance over extended periods. Firstly, the principle of the polarization-insensitive scheme is thoroughly derived, and then a simulation link is established to verify its feasibility and meanwhile to evaluate the influences of factors such as laser linewidth and fiber chromatic dispersion on the system performance. Subsequently, a 50-Gbps polarization-insensitive photonics-assisted THz wireless transmission experiment over the hybrid 20-km optical fiber and 200-m outdoor long-distance 300 GHz THz wireless links is successfully demonstrated. Under artificially controlled polarization states, the proposed scheme reduces the bit error rate fluctuations by two orders of magnitude, as compared to conventional polarization-sensitive approaches. After continuous seven hours of stability testing, the maximum fluctuation range of Q-factor in this system is less than 0.5 dB.
Fiber-coupled terahertz (THz) time-domain spectroscopy (TDS) systems often employ photoconductive antennas (PCAs) as THz emitters due to their high IR-to-THz conversion efficiency. However, their THz power has been constrained to about 1 mW, as fiber-based pulse delivery limits the excitation power to under 60 mW at typical fiber laser repetition rates around 100 MHz. Here, we report the first THz TDS setup that overcomes this limitation by operating at an elevated repetition rate of 1 GHz. We show that the conversion efficiency of InGaAs:Rh-based PCAs is preserved at this one-order-of-magnitude higher repetition rate, resulting in a record emitted THz power of 1.58 ± 0.08 mW for fiber-coupled THz emitters. This significant improvement is enabled by an ultrafast dual-comb optical parametric oscillator operating at 1 GHz repetition rate, delivering two trains of 200 fs pulses centered at 1.55 μm wavelength with up to 650 mW average power. Further pulse compression to 86 fs is achieved using a 2.6 m long fiber delivery to the PCAs, combining dispersion-compensating and standard polarization-maintaining fibers. Using this setup, we demonstrate THz TDS utilizing asynchronous optical sampling at a scan rate of 414 Hz with a peak dynamic range of up to 92 dB at 20 GHz frequency resolution, and 79 dB at 1.1 GHz frequency resolution in 113 seconds integration time.
Terahertz time-domain spectroscopy is a powerful tool for materials science. It can be used to extract the complex optical properties of a material by measuring the electric field of a terahertz probe pulse in the time domain after interaction with a sample. The spatial resolution of terahertz time-domain spectroscopy has recently advanced to the atomic scale through the introduction of a method in which the time trace of the local electric field is read out directly via the tunneling current in a terahertz scanning tunneling microscope junction. This detection mechanism fundamentally differs from those employed in more conventional approaches, which collect and measure scattered light. Consequently, the parameter space and data analysis for this new method deviates from that of free-space measurements. Here, we demonstrate the optimization of atomic-scale terahertz time-domain spectroscopy measurement parameters by using data-informed quantitative and qualitative validation techniques to ensure accurate sampling of the terahertz electric near-field. By combining experiments on Au(111) with data-driven simulations, we show the influence of various parameters on the waveform sampling technique and present a comprehensive description of the terahertz-field-induced tunneling mechanism in a scanning tunneling microscope tip–sample junction.
