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Photonics
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Frontiers in Terahertz Technology and Applications
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Frontiers in Terahertz Technology and Applications

A special issue of Photonics (ISSN 2304-6732). This special issue belongs to the section "New Applications Enabled by Photonics Technologies and Systems".

Deadline for manuscript submissions: closed (30 September 2021) | Viewed by 18922

Special Issue Editors

Dr. Arya Fallahi

E-Mail Website
Guest Editor
1. ETH Zurich, 648093 Zürich, Switzerland
2. IT'IS Foundation, 43 CH-8004 Zurich, Switzerland
Interests: electromagnetic metamaterials; computational nano-optics; plasmonics; compact electron accelerators and injectors; high-power THz generation; THz acceleration; free-electron laser science
Dr. Krishnaswamy Sankaran

E-Mail Website
Guest Editor
Radical Innovations Group Ab, Finland, 65380 Vaasa, Finland
Interests: sensor development; terahertz technology; clean energy; blockchain; IoT; circular materials; energy; economy

Special Issue Information

Dear Colleagues,

THz technology has been one of the most significant research topics in the last decade. It has played a vital role in advancing science and technology, and new inventions in various domains from telecommunication devices to medical health practices. Devices operating in the THz frequency range (0.1 to 10 THz) have been increasingly studied in recent years. Progress in nonlinear optical materials and ultrafast optical and electronic techniques has strengthened research in THz application developments. Due to unique interaction of THz waves with materials, applications with new capabilities can be developed. In theory, these can penetrate somewhat like X-rays, but they are not considered harmful radiation, because the THz energy level is low. They should be able to provide resolution which is as good as or better than that of magnetic resonance imaging (MRI), possibly with simpler equipment. Imaging, very-high bandwidth communication, and energy harvesting are the most widely explored THz application areas.

This Special Issue will provide a solid foundation for understanding the physical principles of THz sources, detectors, and applications. The Special Issue aims at presenting the latest developments in building blocks of THz technology—components dealing with generation, manipulation, and detection of THz electromagnetic radiation. Regarding THz applications, research efforts in the domain of imaging, sensing, communications, non-destructive testing, and evaluations will be covered. Recent application developments in material science—identification, classification, segregation, and recycling—are also of interest.

Topics of interest include but are not limited to the following areas:

  • THz radiation sources;
  • Manipulation of THz pulses;
  • THz integrated optics, waveguides, metamaterials, and photonic crystals;
  • THz detectors;
  • THz imaging;
  • THz sensing;
  • Other THz applications (non-destructive testing, particle beam manipulation and diagnostics).

Dr. Arya Fallahi
Dr. Krishnaswamy Sankaran
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 100 words) can be sent to the Editorial Office for announcement on this website.

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. Photonics 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 2400 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 sources
  • THz detectors
  • THz imaging
  • THz sensing
  • THz applications

Published Papers (7 papers)

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Research

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15 pages, 1992 KiB  
Article
Broadband Terahertz Photonic Integrated Circuit with Integrated Active Photonic Devices
by Amlan Kusum Mukherjee, Mingjun Xiang and Sascha Preu
Photonics 2021, 8(11), 492; https://doi.org/10.3390/photonics8110492 - 03 Nov 2021
Cited by 10 | Viewed by 2637
Abstract
Present-day photonic terahertz (100 GHz–10 THz) systems offer dynamic ranges beyond 100 dB and frequency coverage beyond 4 THz. They yet predominantly employ free-space Terahertz propagation, lacking integration depth and miniaturisation capabilities without sacrificing their extreme frequency coverage. In this work, we present [...] Read more.
Present-day photonic terahertz (100 GHz–10 THz) systems offer dynamic ranges beyond 100 dB and frequency coverage beyond 4 THz. They yet predominantly employ free-space Terahertz propagation, lacking integration depth and miniaturisation capabilities without sacrificing their extreme frequency coverage. In this work, we present a high resistivity silicon-on-insulator-based multimodal waveguide topology including active components (e.g., THz receivers) as well as passive components (couplers/splitters, bends, resonators) investigated over a frequency range of 0.5–1.6 THz. The waveguides have a single mode bandwidth between 0.5–0.75 THz; however, above 1 THz, these waveguides can be operated in the overmoded regime offering lower loss than commonly implemented hollow metal waveguides, operated in the fundamental mode. Supported by quartz and polyethylene substrates, the platform for Terahertz photonic integrated circuits (Tera-PICs) is mechanically stable and easily integrable. Additionally, we demonstrate several key components for Tera-PICs: low loss bends with radii ∼2 mm, a Vivaldi antenna-based efficient near-field coupling to active devices, a 3-dB splitter and a filter based on a whispering gallery mode resonator. Full article
(This article belongs to the Special Issue Frontiers in Terahertz Technology and Applications)
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12 pages, 5406 KiB  
Article
Pulse Length Monitor for Breakdown Diagnostics in THz and Mm-Wave Accelerators
by Sergey V. Kutsaev, Vladimir Goncharik, Alex Murokh, Ilya Rezanov, Dmitry Shchegolkov and Alexander Y. Smirnov
Photonics 2021, 8(10), 442; https://doi.org/10.3390/photonics8100442 - 14 Oct 2021
Viewed by 1793
Abstract
The development of novel high-gradient accelerating structures operating at THz frequencies is critical for future free-electron lasers and TeV scale linear colliders. To reach high energies with reasonable length requires high accelerating gradients of ~100 MV/m. The main limitation to reaching these high-energy [...] Read more.
The development of novel high-gradient accelerating structures operating at THz frequencies is critical for future free-electron lasers and TeV scale linear colliders. To reach high energies with reasonable length requires high accelerating gradients of ~100 MV/m. The main limitation to reaching these high-energy gradients is the vacuum RF breakdown phenomenon, which disrupts normal accelerator operations. For stable operations and to understand the breakdown microscopic dynamics, a new device capable of detecting the breakdown occurrences is required. In this paper, we provide the design of a pulse length monitor based on an analog to digital converter for fast signal digitization without the need to use high-speed digitizers to be used in a commercial mm-wave heterodyne spectrometer. Full article
(This article belongs to the Special Issue Frontiers in Terahertz Technology and Applications)
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10 pages, 1593 KiB  
Article
Comparison of THz-QCL Designs Supporting Clean N-Level Systems
by Nathalie Lander Gower, Silvia Piperno and Asaf Albo
Photonics 2021, 8(7), 248; https://doi.org/10.3390/photonics8070248 - 30 Jun 2021
Cited by 6 | Viewed by 2076
Abstract
Three different Terahertz quantum-cascade-laser designs supporting clean n-level systems were analyzed using nonequilibrium Green’s functions. In clean n-level systems, most of the electrons occupy the active laser levels, with thermally activated leakage channels being suppressed almost entirely up to room temperature. Simulations of [...] Read more.
Three different Terahertz quantum-cascade-laser designs supporting clean n-level systems were analyzed using nonequilibrium Green’s functions. In clean n-level systems, most of the electrons occupy the active laser levels, with thermally activated leakage channels being suppressed almost entirely up to room temperature. Simulations of the three designs, namely a resonant phonon design, a two-well design, and a split-well direct-phonon design were investigated. The results from the simulations indicated that the two-well design would perform best overall, in terms of variations in current density, interface roughness, and ionized impurity scattering. We conclude that future research aiming to improve the temperature performance of such laser designs should be based on a two-well design. Full article
(This article belongs to the Special Issue Frontiers in Terahertz Technology and Applications)
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20 pages, 4933 KiB  
Article
Particle-in-Cell Simulations of High-Power THz Generator Based on the Collision of Strongly Focused Relativistic Electron Beams in Plasma
by Vladimir Annenkov, Evgeny Berendeev, Evgeniia Volchok and Igor Timofeev
Photonics 2021, 8(6), 172; https://doi.org/10.3390/photonics8060172 - 21 May 2021
Cited by 4 | Viewed by 1691
Abstract
Based on particle-in-cell simulations, we propose to generate sub-nanosecond pulses of narrowband terahertz radiation with tens of MW power using unique properties of kiloampere relativistic (2 MeV) electron beams produced by linear induction accelerators. Due to small emittance of such beams, they can [...] Read more.
Based on particle-in-cell simulations, we propose to generate sub-nanosecond pulses of narrowband terahertz radiation with tens of MW power using unique properties of kiloampere relativistic (2 MeV) electron beams produced by linear induction accelerators. Due to small emittance of such beams, they can be focused into millimeter and sub-millimeter spots comparable in sizes with the wavelength of THz radiation. If such a beam is injected into a plasma, it becomes unstable against the two-stream instability and excites plasma oscillations that can be converted to electromagnetic waves at the plasma frequency and its harmonics. It is shown that several radiation mechanisms with high efficiency of power conversion (∼1%) come into play when the radial size of the beam–plasma system becomes comparable with the wavelength of the emitted waves. Full article
(This article belongs to the Special Issue Frontiers in Terahertz Technology and Applications)
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13 pages, 865 KiB  
Article
Novel Broadband Slot-Spiral Antenna for Terahertz Applications
by Zhen Huang, Zhaofeng Li, Hui Dong, Fuhua Yang, Wei Yan and Xiaodong Wang
Photonics 2021, 8(4), 123; https://doi.org/10.3390/photonics8040123 - 14 Apr 2021
Cited by 7 | Viewed by 3060
Abstract
We report a novel broadband slot-spiral antenna that can be integrated with high-electron-mobility transistor (HEMT) terahertz (THz) detectors. The effect of various antenna parameters on the transmission efficiency of the slot-spiral structure at 150–450 GHz is investigated systematically. The performances of the slot-spiral [...] Read more.
We report a novel broadband slot-spiral antenna that can be integrated with high-electron-mobility transistor (HEMT) terahertz (THz) detectors. The effect of various antenna parameters on the transmission efficiency of the slot-spiral structure at 150–450 GHz is investigated systematically. The performances of the slot-spiral antenna and the spiral antenna both integrated with HEMTs are compared. The results show that the slot-spiral structure has a better transmission and miniaturization capability than the spiral structure. A formula for the responsivity is derived based on the transmission line principle and antenna theory, and results show that the detector responsivity is correlated with the antenna absorptivity. Additionally, guidelines for HEMT THz detector design are proposed. The results of this study indicate the excellent application prospects of the slot-spiral antenna in THz detection and imaging. Full article
(This article belongs to the Special Issue Frontiers in Terahertz Technology and Applications)
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11 pages, 14728 KiB  
Article
Photothermal, Photoelectric, and Photothermoelectric Effects in Bi-Sb Thin Films in the Terahertz Frequency Range at Room Temperature
by Mikhail K. Khodzitsky, Petr S. Demchenko, Dmitry V. Zykov, Anton D. Zaitsev, Elena S. Makarova, Anastasiia S. Tukmakova, Ivan L. Tkhorzhevskiy, Aleksei V. Asach, Anna V. Novotelnova and Natallya S. Kablukova
Photonics 2021, 8(3), 76; https://doi.org/10.3390/photonics8030076 - 12 Mar 2021
Cited by 8 | Viewed by 2807
Abstract
The terahertz frequency range is promising for solving various practically important problems. However, for the terahertz technology development, there is still a problem with the lack of affordable and effective terahertz devices. One of the main tasks is to search for new materials [...] Read more.
The terahertz frequency range is promising for solving various practically important problems. However, for the terahertz technology development, there is still a problem with the lack of affordable and effective terahertz devices. One of the main tasks is to search for new materials with high sensitivity to terahertz radiation at room temperature. Bi1−xSbx thin films with various Sb concentrations seem to be suitable for such conditions. In this paper, the terahertz radiation influence onto the properties of thermoelectric Bi1−xSbx 200 nm films was investigated for the first time. The films were obtained by means of thermal evaporation in vacuum. They were affected by terahertz radiation at the frequency of 0.14 terahertz (THz) in the presence of thermal gradient, electric field or without these influences. The temporal dependencies of photoconductivity, temperature difference and voltage drop were measured. The obtained data demonstrate the possibility for practical use of Bi1−xSbx thin films for THz radiation detection. The results of our work promote the usage of these thermoelectric materials, as well as THz radiation detectors based on them, in various areas of modern THz photonics. Full article
(This article belongs to the Special Issue Frontiers in Terahertz Technology and Applications)
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Review

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15 pages, 2465 KiB  
Review
High Field Single- to Few-Cycle THz Generation with Lithium Niobate
by Xing Zhu, David R. Bacon, Julien Madéo and Keshav M. Dani
Photonics 2021, 8(6), 183; https://doi.org/10.3390/photonics8060183 - 24 May 2021
Cited by 7 | Viewed by 3840
Abstract
The transient terahertz (THz) pulse with high peak field has become an important tool for matter manipulation, enabling many applications such as nonlinear spectroscopy, particle acceleration, and high harmonic generation. Among the widely used THz generation techniques, optical rectification in lithium niobate (LN) [...] Read more.
The transient terahertz (THz) pulse with high peak field has become an important tool for matter manipulation, enabling many applications such as nonlinear spectroscopy, particle acceleration, and high harmonic generation. Among the widely used THz generation techniques, optical rectification in lithium niobate (LN) has emerged as a powerful method to achieve high fields at low THz frequencies, suitable to exploring novel nonlinear phenomena in condensed matter systems. In this review, we focus on introducing single- to few-cycle THz generation in LN, including the basic principles, techniques, latest developments, and current limitations. We will first discuss the phase matching requirements of LN, which leads to Cherenkov-like radiation, and the tilted pulse front (TPF) technique. Emphasis will be put on the TPF technique, which has been shown to improve THz generation efficiency, but still has many limitations. Different geometries used to produce continuous and discrete TPF will be systematically discussed. We summarize the advantages and limitations of current techniques and future trends. Full article
(This article belongs to the Special Issue Frontiers in Terahertz Technology and Applications)
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