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Micromachines
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Broadband Terahertz Devices and Communication Technologies, 2nd Edition
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Broadband Terahertz Devices and Communication Technologies, 2nd Edition

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "A：Physics".

Deadline for manuscript submissions: closed (25 February 2026) | Viewed by 18791

Special Issue Editors

Dr. Jiao Zhang

E-Mail Website
Guest Editor
Purple Mountain Laboratories, Southeast University, Nanjing 210096, China
Interests: broadband fiber-wireless integration; photonics-aided millimeter-wave/THz-wave communication; next-generation optical access networks
Special Issues, Collections and Topics in MDPI journals
Dr. Lu Zhang

E-Mail Website
Guest Editor
College of Information Science and Electronic Engineering, Zhejiang University, Hangzhou 310027, China
Interests: broadband THz communications; ultra-fast fiber-optical communications; advanced signal processing; THz sensing
Special Issues, Collections and Topics in MDPI journals
Dr. Kaihui Wang

E-Mail Website
Guest Editor
School of Information Science and Technology, Fudan University, Shanghai 200433, China
Interests: 6G terahertz technology; p-bit/s optical fiber transmission technology; low-complexity integrated circuit design
Dr. Xiongbin Yu

E-Mail Website
Guest Editor
Pengcheng Laboratory, Shenzhen 518000, China
Interests: THz semiconductor devices; THz photonics; THz communications and sensing

Special Issue Information

Dear Colleagues,

The Recommendation Framework for IMT-2030 (Global 6G Vision) was completed by the International Telecommunication Union (ITU-R) radio communication division in 2023. Multiple frequency ranges will be needed to meet the capacity and coverage requirements and to serve emerging services and bandwidth-consuming Internet applications. The wireless traffic volume is foreseen to be sufficient to match or even surpass wired services by 2030, and the high-precision wireless services will need to be guaranteed with a peak data rate of well beyond 100 Gbit/s, eventually 1 Tbit/s. There has been ongoing academic and industry research and development related to the suitability of mobile broadband systems in frequency bands above 100 GHz. The terahertz band (0.1 THz-10 THz), sandwiched between microwave and optical frequencies, is considered the next breakthrough point to revolutionize communication technology due to its rich spectrum resources. It is recognized as a promising candidate for future rate-greedy applications, such as 6G communications. In the World Radio Communication Conferences 2019, identifying frequency bands in the frequency range 275 GHz–450 GHz was permitted for land-mobile and fixed services applications, with a total spectrum bandwidth of 137 GHz. In May 2024, the ITU-R approved a new Report about the “Technical feasibility of IMT in bands above 100 GHz”, which provides information in bands between 100 GHz and 400 GHz.

Motivated by the potential of terahertz wireless communications, this Special Issue seeks critical technology breakthroughs in terahertz communications. The Special Issue topics include but are not limited to, broadband terahertz devices, terahertz frontend and antenna design, baseband processing for THz links, terahertz propagation and channel modeling, system-level demonstration of terahertz communications, integrated sensing, and communication.

Dr. Jiao Zhang
Dr. Lu Zhang
Dr. Kaihui Wang
Dr. Xiongbin Yu
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 250 words) can be sent to the Editorial Office for assessment.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2100 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • THz source (electrical, photonic)
  • THz mixer (electrical, photonic)
  • THz modulator (electrical, photonic)
  • THz beam steering (electrical, photonic)
  • THz topological photonics
  • THz amplifier (low-noise, power, traveling wave tube, etc.)
  • passive THz devices (filter, polarizer, antenna, etc.)
  • baseband processing for THz links (transmitter, receiver)
  • THz propagation and channel modeling
  • system-level demonstration of electrical THz communications
  • system-level demonstration of photonic THz communications
  • THz-orbital angular momentum (OAM) communications
  • THz integrated sensing and communication (ISAC)

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Published Papers (15 papers)

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Research

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18 pages, 1555 KB  
Article
Intrinsic Relations Between Transmission and Reflection in Metamaterials
by Boli Xu and Renbin Zhong
Micromachines 2026, 17(4), 493; https://doi.org/10.3390/mi17040493 - 17 Apr 2026
Viewed by 286
Abstract
Metamaterials possess high freedom on structural design, yet their ability to modulate electromagnetic waves is subject to intrinsic constraints that are independent of specific meta-atom geometries. The constraints are revealed by analyzing the statistical amplitudes and phases of transmission and reflection wave in [...] Read more.
Metamaterials possess high freedom on structural design, yet their ability to modulate electromagnetic waves is subject to intrinsic constraints that are independent of specific meta-atom geometries. The constraints are revealed by analyzing the statistical amplitudes and phases of transmission and reflection wave in some representative metamaterials. Based on scattering theory, a reconstructed and more general description of the electromagnetic modulation process in metamaterials is established. Two explicit and geometry-independent corollaries concerning the coupling between transmission and reflection waves are further obtained and verified. The results provide a new perspective on the fundamental modulation mechanism of metamaterials on electromagnetic waves. Full article
(This article belongs to the Special Issue Broadband Terahertz Devices and Communication Technologies, 2nd Edition)
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13 pages, 7762 KB  
Article
Dual-Side Hybrid Embedding Network for Gain Enhancement of Terahertz Amplifiers at Frequencies Near fmax
by Xiaorui Liu, Jianguo Yu, Yun Wang, Yibo Huang, Feixiang Zhang, Zhanjiang Wang and Yaqi Cheng
Micromachines 2026, 17(4), 432; https://doi.org/10.3390/mi17040432 - 31 Mar 2026
Viewed by 402
Abstract
This paper proposes a dual-side hybrid embedding network (DHEN) to mitigate gain degradation in terahertz amplifiers at frequencies near fmax. The proposed approach employs a pre-embedding network for parasitic absorption, followed by Y-embedding for gain enhancement. A theoretical analysis is conducted [...] Read more.
This paper proposes a dual-side hybrid embedding network (DHEN) to mitigate gain degradation in terahertz amplifiers at frequencies near fmax. The proposed approach employs a pre-embedding network for parasitic absorption, followed by Y-embedding for gain enhancement. A theoretical analysis is conducted to derive the embedding conditions for process-constrained circuit synthesis. In this architecture, a capacitive base-side pre-embedding provides intrinsic DC isolation, while a defected-ground-structure (DGS) inductor realizes the Y-embedding inductive element with reduced layout area. Based on the DHEN, a four-stage amplifier is designed in a 130 nm SiGe BiCMOS process. Electromagnetic co-simulation results demonstrate a power gain of 19.3 dB at 280 GHz, corresponding to an 11.5 dB improvement over a conventional unboosted amplifier. The proposed approach provides a unified synthesis methodology that simultaneously addresses parasitic absorption, DC isolation, and gain enhancement for near-fmax THz amplifier design. Full article
(This article belongs to the Special Issue Broadband Terahertz Devices and Communication Technologies, 2nd Edition)
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11 pages, 2777 KB  
Article
A Compact 380 GHz Zero-Bias Schottky Diode Detector for High-Sensitivity Radiometer Applications
by Huilin Tang, Yongsheng Deng and Dehai Zhang
Micromachines 2026, 17(3), 352; https://doi.org/10.3390/mi17030352 - 13 Mar 2026
Viewed by 491
Abstract
Reliable terahertz radiometer receiver systems demand detectors that combine high sensitivity with structural robustness. This paper presents the design, fabrication, and characterization of a 380 GHz zero-bias detector based on an ACST Schottky diode. The detector uses a high-impedance grounding topology to reduce [...] Read more.
Reliable terahertz radiometer receiver systems demand detectors that combine high sensitivity with structural robustness. This paper presents the design, fabrication, and characterization of a 380 GHz zero-bias detector based on an ACST Schottky diode. The detector uses a high-impedance grounding topology to reduce parasitic resonances and enhance output stability. A compact U-shaped waveguide transition is adopted to realize an inline port configuration. This configuration simplifies system integration. Measurements demonstrate a peak voltage responsivity of 2318 V/W and a linearity of 0.9996 at 380 GHz, validating the effectiveness of the proposed design. This work establishes a practical design approach for zero-bias terahertz detectors and supports future high-frequency radiometer and sensing applications. Full article
(This article belongs to the Special Issue Broadband Terahertz Devices and Communication Technologies, 2nd Edition)
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17 pages, 7117 KB  
Article
MUTC-PD-Based High-Efficiency Photonic Terahertz Generation and Radiation in the 275–296 GHz Band
by Yun Wang, Xiaorui Liu and Jianguo Yu
Micromachines 2026, 17(2), 196; https://doi.org/10.3390/mi17020196 - 31 Jan 2026
Viewed by 825
Abstract
We design a photonic terahertz (THz) antenna operating in the 275–296 GHz band, integrating two identical modified uni-traveling-carrier photodiodes (MUTC-PDs), two impedance matching networks, a Wilkinson power combiner and a Vivaldi antenna. Simulation results show a saturated output power of 1.58 dBm at [...] Read more.
We design a photonic terahertz (THz) antenna operating in the 275–296 GHz band, integrating two identical modified uni-traveling-carrier photodiodes (MUTC-PDs), two impedance matching networks, a Wilkinson power combiner and a Vivaldi antenna. Simulation results show a saturated output power of 1.58 dBm at 280 GHz, achieving a 4.13× power enhancement through optimized impedance and power combining compared to a standalone device. The integrated antenna achieves a peak gain of 7.93 dBi, with reflection coefficients below −10 dB. The system demonstrates a power combining efficiency exceeding 95% for phase imbalances up to 20°, and the Wilkinson combiner exhibits only 0.76 dB insertion loss at 285 GHz, demonstrating high radiation and combining efficiency in the 275–296 GHz band. Full article
(This article belongs to the Special Issue Broadband Terahertz Devices and Communication Technologies, 2nd Edition)
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11 pages, 538 KB  
Article
Metamaterial Incident Photon Reconstruction Theory Based on Resonant Dipole Phase
by Boli Xu and Renbin Zhong
Micromachines 2026, 17(1), 130; https://doi.org/10.3390/mi17010130 - 20 Jan 2026
Viewed by 385
Abstract
In this study, a Metamaterial Incident Photon Reconstruction Theory (MIPRT) is developed to describe the modulation process of metamaterials on incident photons. The theory includes the Invariant Incident Photon Hypothesis and Resonant Phase Deconstruction and Quantification; it reveals the modulation characteristics of metamaterials [...] Read more.
In this study, a Metamaterial Incident Photon Reconstruction Theory (MIPRT) is developed to describe the modulation process of metamaterials on incident photons. The theory includes the Invariant Incident Photon Hypothesis and Resonant Phase Deconstruction and Quantification; it reveals the modulation characteristics of metamaterials on incident photons, not by first absorption and then re-emission but by inducing coherent destructive interference, which brings about redistribution of the spatial probability of photon occurrence. This theory is validated in a single-layer metamaterial, and a unique relationship between the resonant phase and amplitude is derived and confirmed by simulation. The proposed MIPRT brings a comprehensive understanding of the electromagnetic (EM) response characteristics of metamaterials and provides a new idea for metamaterial theory from another perspective. Full article
(This article belongs to the Special Issue Broadband Terahertz Devices and Communication Technologies, 2nd Edition)
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10 pages, 1503 KB  
Article
High Spectrum Efficiency and High Security Radio-Over-Fiber Systems with Compressive-Sensing-Based Chaotic Encryption
by Zhanhong Wang, Lu Zhang, Jiahao Zhang, Oskars Ozolins, Xiaodan Pang and Xianbin Yu
Micromachines 2026, 17(1), 80; https://doi.org/10.3390/mi17010080 - 7 Jan 2026
Viewed by 552
Abstract
With the increasing demand for high throughput and ultra-dense small cell deployment in the next-generation communication networks, spectrum resources are becoming increasingly strained. At the same time, the security risks posed by eavesdropping remain a significant concern, particularly due to the broadcast-access property [...] Read more.
With the increasing demand for high throughput and ultra-dense small cell deployment in the next-generation communication networks, spectrum resources are becoming increasingly strained. At the same time, the security risks posed by eavesdropping remain a significant concern, particularly due to the broadcast-access property of optical fronthaul networks. To address these challenges, we propose a high-security, high-spectrum efficiency radio-over-fiber (RoF) system in this paper, which leverages compressive sensing (CS)-based algorithms and chaotic encryption. An 8 Gbit/s RoF system is experimentally demonstrated, with 10 km optical fiber transmission and 20 GHz radio frequency (RF) transmission. In our experiment, spectrum efficiency is enhanced by compressing transmission data and reducing the quantization bit requirements, while security is maintained with minimal degradation in signal quality. The system could recover the signal correctly after dequantization with 6-bit fronthaul quantization, achieving a structural similarity index (SSIM) of 0.952 for the legitimate receiver (Bob) at a compression ratio of 0.75. In contrast, the SSIM for the unauthorized receiver (Eve) is only 0.073, highlighting the effectiveness of the proposed security approach. Full article
(This article belongs to the Special Issue Broadband Terahertz Devices and Communication Technologies, 2nd Edition)
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11 pages, 2418 KB  
Article
A Dual-Band Bandpass Filter with Wide Upper Stopband Using Stepped-Impedance Resonators and an Integrated Low-Pass Filter
by Liqin Liu, Yuanmo Lin, Qun Chen, Li Zhang and Minhang Weng
Micromachines 2026, 17(1), 75; https://doi.org/10.3390/mi17010075 - 6 Jan 2026
Viewed by 618
Abstract
In this paper, a dual-band bandpass filter with a wide upper stopband is proposed and designed by integrating stepped-impedance resonators (SIRs) and a low-pass filter. The operating center frequencies of the designed dual-band filter are targeted at 2.5 GHz and 5.35 GHz, respectively, [...] Read more.
In this paper, a dual-band bandpass filter with a wide upper stopband is proposed and designed by integrating stepped-impedance resonators (SIRs) and a low-pass filter. The operating center frequencies of the designed dual-band filter are targeted at 2.5 GHz and 5.35 GHz, respectively, to meet the frequency requirements of typical wireless communication scenarios. Notably, the filter achieves a wide upper stopband ranging from 6.1 GHz to 25 GHz, which can effectively suppress unwanted high-frequency interference signals within this frequency range and avoid mutual interference with other high-frequency communication systems. And it exhibits insertion losses of 0.12 dB (2.5 GHz) and 0.6 dB (5.35 GHz) in its two passbands to ensure minimal useful signal attenuation. The simulation results agree well with the measured results. Full article
(This article belongs to the Special Issue Broadband Terahertz Devices and Communication Technologies, 2nd Edition)
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10 pages, 2350 KB  
Article
Design of Dual Continuous-Mode Class-J Power Amplifiers with Harmonic Matching Networks for X and Ku Bands
by Yang Yuan, Xuesong Zhao, Jingxin Fan and Zhongjun Yu
Micromachines 2025, 16(12), 1362; https://doi.org/10.3390/mi16121362 - 29 Nov 2025
Viewed by 693
Abstract
In this article, two wideband high-efficiency Class-J power amplifiers operating in X and Ku bands, respectively, are designed based on continuous mode. The optimal impedance regions of the transistors are determined using harmonic load-pull techniques. An on-chip output matching network with second harmonic [...] Read more.
In this article, two wideband high-efficiency Class-J power amplifiers operating in X and Ku bands, respectively, are designed based on continuous mode. The optimal impedance regions of the transistors are determined using harmonic load-pull techniques. An on-chip output matching network with second harmonic control functionality is designed to achieve Class-J operation. To verify the feasibility of designed circuits, both power amplifiers are designed and fabricated using a 0.25 mm GaAs pseudomorphic high electron mobility transistor (pHEMT) process. The power amplifiers are both biased at 6 V/−1 V. The measured results show the X-band and Ku-band power amplifiers achieve peak saturated output powers of 31.2 dBm and 30.8 dBm, respectively. The power-added efficiencies (PAEs) of the two amplifiers within their operating bands reach up to 48% and 45.3%, respectively. Compact size and high efficiency make them suitable for integration into phased array transmit/receiver (T/R) modules. Full article
(This article belongs to the Special Issue Broadband Terahertz Devices and Communication Technologies, 2nd Edition)
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10 pages, 2984 KB  
Article
A Wideband D-Band Frequency Sextupler Chain with High Harmonic Rejection in 100 nm GaAs pHEMT Technology
by Pinqing Wang, Zhe Chen, Yubin Guo, Yue Qi and Peng Yang
Micromachines 2025, 16(9), 984; https://doi.org/10.3390/mi16090984 - 27 Aug 2025
Viewed by 920
Abstract
This paper presents a wideband D-band frequency sextupler chain implemented in a 100 nm GaAs pHEMT process. The proposed circuit comprises an input-stage frequency tripler, an inter-stage harmonic-rejection power amplifier, and an output-stage frequency doubler. The tripler adopts a balanced topology, which effectively [...] Read more.
This paper presents a wideband D-band frequency sextupler chain implemented in a 100 nm GaAs pHEMT process. The proposed circuit comprises an input-stage frequency tripler, an inter-stage harmonic-rejection power amplifier, and an output-stage frequency doubler. The tripler adopts a balanced topology, which effectively suppresses the fundamental frequency component. The inter-stage power amplifier not only delivers sufficient drive power to the doubler but also enhances suppression of undesired harmonics. The output doubler employs a single-balanced configuration to suppress odd-order harmonics while extracting the second harmonic. The measured peak output power of the sextupler chain is 2.33 dBm, corresponding to an input power of 2 dBm, resulting in a conversion gain of 0.33 dB. The 3 dB output bandwidth spans from 126.3 to 152.7 GHz, corresponding to a relative bandwidth of 18.9%. Owing to the balanced multiplier topology and harmonic-rejection PA, the 5th and 7th harmonics are suppressed by more than 20 dBc. The combination of high output power, wide operating bandwidth, and excellent harmonic suppression makes the design well suited for wideband D-band signal generation in diverse applications. Full article
(This article belongs to the Special Issue Broadband Terahertz Devices and Communication Technologies, 2nd Edition)
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9 pages, 2467 KB  
Article
Design and Simulation of an Electron Optical System for Terahertz Vacuum Devices
by Muhammad Haris Jamil, Zhiwei Lin, Hamid Sharif, Nazish Saleem Abbas and Wenlong He
Micromachines 2025, 16(8), 928; https://doi.org/10.3390/mi16080928 - 13 Aug 2025
Cited by 1 | Viewed by 1140
Abstract
An electron optic system (EOS) consisting of a sheet electron beam gun (SEB) and a pole offset periodic cusped magnet (PO-PCM) is reported for 340-GHz frequency. A sheet electron beam with a voltage of 29 kV, beam compression ratio of 16, and a [...] Read more.
An electron optic system (EOS) consisting of a sheet electron beam gun (SEB) and a pole offset periodic cusped magnet (PO-PCM) is reported for 340-GHz frequency. A sheet electron beam with a voltage of 29 kV, beam compression ratio of 16, and a beam waist of size 0.17 mm × 0.044 mm was designed and optimized using computer simulation technology (CST). The EOS was capable of transmitting the beam with a current of 6.9 mA through a beam tunnel of size 0.516 mm × 0.091 mm, having a length of 60 mm with the help of a pole offset periodic cusped magnet. The axial magnetic field generated by the PCM was 0.32 T. The EOS was efficient enough to transmit the beam stably through the beam tunnel with a transmission rate of 100%. Full article
(This article belongs to the Special Issue Broadband Terahertz Devices and Communication Technologies, 2nd Edition)
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13 pages, 10213 KB  
Article
2 km Uncompressed HD Video Wireless Transmission at 100 GHz Based on All-Optical Frequency Up- and Down-Conversion
by Shuang Gao, Yutong Jiang, Zhuoxin Li, Qing Zhong, Min Zhu and Jiao Zhang
Micromachines 2024, 15(12), 1488; https://doi.org/10.3390/mi15121488 - 11 Dec 2024
Cited by 2 | Viewed by 1753
Abstract
The millimeter-wave wireless transmission system is widely regarded as a promising solution for applications of future 6G communication. This paper presents an experimental comparison between all-optical and all-electric receivers for millimeter-wave communication systems over a 15 m wireless link and demonstrates 200 m [...] Read more.
The millimeter-wave wireless transmission system is widely regarded as a promising solution for applications of future 6G communication. This paper presents an experimental comparison between all-optical and all-electric receivers for millimeter-wave communication systems over a 15 m wireless link and demonstrates 200 m and 2 km real-time uncompressed HD video transmission using an all-optical transceiver at 100 GHz. The systems leverage photonics-assisted heterodyne beating techniques at the transmitter, while the receivers employ either an avalanche photodiode (APD)-based all-optical approach or an envelope detection-based all-electric approach. Experimental results show that the all-optical transceiver supports significantly higher transmission rates, achieving error-free transmission at up to 11.318 Gbps over a 200 m wireless link without clock recovery, compared to the all-electric receiver, which is limited to only 3.125 Gbps error-free 15 m transmission. This work proves that the proposed system based on the all-optical receiver is more promising for supporting future 6G scenarios requiring ultra-wideband, high capacity, and wide coverage high-speed wireless communications. Full article
(This article belongs to the Special Issue Broadband Terahertz Devices and Communication Technologies, 2nd Edition)
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12 pages, 5641 KB  
Article
A Compact V-Band Temperature Compensation Low-Noise Amplifier in a 130 nm SiGe BiCMOS Process
by Yi Shen, Jiang Luo, Wei Zhao, Jun-Yan Dai and Qiang Cheng
Micromachines 2024, 15(10), 1248; https://doi.org/10.3390/mi15101248 - 11 Oct 2024
Viewed by 2281
Abstract
This paper presents a compact V-band low-noise amplifier (LNA) featuring temperature compensation, implemented in a 130 nm SiGe BiCMOS process. A negative temperature coefficient bias circuit generates an adaptive current for temperature compensation, enhancing the LNA’s temperature robustness. A T-type inductive network is [...] Read more.
This paper presents a compact V-band low-noise amplifier (LNA) featuring temperature compensation, implemented in a 130 nm SiGe BiCMOS process. A negative temperature coefficient bias circuit generates an adaptive current for temperature compensation, enhancing the LNA’s temperature robustness. A T-type inductive network is employed to establish two dominant poles at different frequencies, significantly broadening the amplifier’s bandwidth. Over the wide temperature range of −55 °C to 85 °C, the LNA prototype exhibits a gain variation of less than 1.5 dB at test frequencies from 40 GHz to 65 GHz, corresponding to a temperature coefficient of 0.01 dB/°C. At −55 °C, 25 °C, and 85 °C, the measured peak gains are 25.5 dB, 25 dB, and 24.4 dB, respectively, with minimum noise figures (NF) of 3.0 dB, 3.5 dB, and 4.2 dB, and DC power consumptions of 22.3 mW, 27.6 mW, and 34.4 mW. Moreover, the total silicon area of the LNA chip is 0.37 mm2, including all test pads, while the core area is only 0.09 mm2. Full article
(This article belongs to the Special Issue Broadband Terahertz Devices and Communication Technologies, 2nd Edition)
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11 pages, 3608 KB  
Article
A V-Band Wideband Power Amplifier with High Gain in a 130 nm SiGe BiCMOS Process
by Jianing Hu, Jialong Wan, Yi Shen, Wei Zhao and Jiang Luo
Micromachines 2024, 15(9), 1077; https://doi.org/10.3390/mi15091077 - 26 Aug 2024
Viewed by 1972
Abstract
This paper introduces a high-gain wideband power amplifier (PA) designed for V-band applications, operating across 52 to 65 GHz. The proposed PA design employs a combination of techniques, including pole-gain distribution, base-capacitive peaking, and the parallel configuration of multiple small-sized transistors. These strategies [...] Read more.
This paper introduces a high-gain wideband power amplifier (PA) designed for V-band applications, operating across 52 to 65 GHz. The proposed PA design employs a combination of techniques, including pole-gain distribution, base-capacitive peaking, and the parallel configuration of multiple small-sized transistors. These strategies enable significant bandwidth extension while maintaining high gain, substantial output power, and a compact footprint. A two-stage PA using the combination technique was developed and fabricated in a 130 nm SiGe BiCMOS process. The PA prototype achieved a peak gain of 27.3 dB at 64 GHz, with a 3 dB bandwidth exceeding 13 GHz and a fractional bandwidth greater than 22.2%. It delivered a maximum saturated output power of 19.7 dBm and an output 1 dB compression point of 18 dBm. Moreover, the PA chip occupied a total silicon area of 0.57 mm2, including all testing pads with a compact core size of 0.198 mm2. Full article
(This article belongs to the Special Issue Broadband Terahertz Devices and Communication Technologies, 2nd Edition)
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Review

Jump to: Research

28 pages, 1299 KB  
Review
Integrated THz/FSO Communications: A Review of Practical Constraints, Applications and Challenges
by Jingtian Liu, Xiongwei Yang, Yi Wei and Feng Zhao
Micromachines 2025, 16(11), 1297; https://doi.org/10.3390/mi16111297 - 19 Nov 2025
Cited by 1 | Viewed by 1765
Abstract
This paper presents a comprehensive review of integrated terahertz (THz) and free-space optical (FSO) communication systems, focusing on their potential to address the escalating demands for high-capacity, long-distance, and ultra-reliable transmission in future six-generation (6G) and space–air–ground integrated networks (SAGIN). The study systematically [...] Read more.
This paper presents a comprehensive review of integrated terahertz (THz) and free-space optical (FSO) communication systems, focusing on their potential to address the escalating demands for high-capacity, long-distance, and ultra-reliable transmission in future six-generation (6G) and space–air–ground integrated networks (SAGIN). The study systematically examines recent advancements in three critical areas: channel modeling, transmission performance, and integrated system architectures. Specifically, it analyzes THz and FSO channel characteristics, including attenuation mechanisms, turbulence effects, pointing errors, and noise sources, and compares their complementary strengths under diverse atmospheric conditions. Key findings reveal that THz communication achieves transmission rates up to several Tbps over distances of several kilometers but is constrained by molecular absorption and weather-induced attenuation, while FSO offers superior bandwidth-distance products yet suffers from turbulence-induced fading, posing significant reliability challenges. The integration of THz and FSO through adaptive switching strategies (e.g., hard and soft switching) demonstrates enhanced reliability and spectral efficiency, with experimental results showing seamless data rates exceeding Tbps in hybrid systems. However, challenges persist in transceiver hardware integration, algorithmic optimization, and dynamic resource allocation. The review concludes by identifying future research directions, including the development of unified channel models, shared architectures, and intelligent switching algorithms to achieve robust integrated communication infrastructures. Full article
(This article belongs to the Special Issue Broadband Terahertz Devices and Communication Technologies, 2nd Edition)
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24 pages, 4549 KB  
Review
Research on Tbps and Kilometer-Range Transmission of Terahertz Signals
by Jianjun Yu and Jiali Chen
Micromachines 2025, 16(7), 828; https://doi.org/10.3390/mi16070828 - 20 Jul 2025
Cited by 1 | Viewed by 3051
Abstract
THz communication stands as a pivotal technology for 6G networks, designed to address the critical challenge of data demands surpassing current microwave and millimeter-wave (mmWave) capabilities. However, realizing Tbps and kilometer-range transmission confronts the “dual attenuation dilemma” comprising severe free-space path loss (FSPL) [...] Read more.
THz communication stands as a pivotal technology for 6G networks, designed to address the critical challenge of data demands surpassing current microwave and millimeter-wave (mmWave) capabilities. However, realizing Tbps and kilometer-range transmission confronts the “dual attenuation dilemma” comprising severe free-space path loss (FSPL) (>120 dB/km) and atmospheric absorption. This review comprehensively summarizes our group′s advancements in overcoming fundamental challenges of long-distance THz communication. Through systematic photonic–electronic co-optimization, we report key enabling technologies including photonically assisted THz signal generation, polarization-multiplexed multiple-input multiple-output (MIMO) systems with maximal ratio combining (MRC), high-gain antenna–lens configurations, and InP amplifier systems for complex weather resilience. Critical experimental milestones encompass record-breaking 1.0488 Tbps throughput using probabilistically shaped 64QAM (PS-64QAM) in the 330–500 GHz band; 30.2 km D-band transmission (18 Gbps with 543.6 Gbps·km capacity–distance product); a 3 km fog-penetrating link at 312 GHz; and high-sensitivity SIMO-validated 100 Gbps satellite-terrestrial communication beyond 36,000 km. These findings demonstrate THz communication′s viability for 6G networks requiring extreme-capacity backhaul and ultra-long-haul connectivity. Full article
(This article belongs to the Special Issue Broadband Terahertz Devices and Communication Technologies, 2nd Edition)
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