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Terahertz Emitters and Detectors
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Terahertz Emitters and Detectors

A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Physical Sensors".

Deadline for manuscript submissions: closed (30 April 2022) | Viewed by 14877

Special Issue Editor

Prof. Richard Klemm

E-Mail Website
Guest Editor
University of Central Florida, Orlando, United States
Interests: layered superconductors; low-dimensional metals and superconductors; superconducting intrinsic Josephson junction THz emitters; theoretical design of efficient microstrip antenna shapes for IJJ THz emission antennas; Zeeman interaction; quantum spin Hall effect in two-dimensional metals; the Knight shift in unconventional superconductors; single molecule magnets

Special Issue Information

Dear Colleagues,

Terahertz (THz) electromagnetic waves in the frequency f range between 0.1 and 10 THz have recently attracted much attention because of their enormous potential applications in various fields such as non-destructive imaging, spectroscopy, astronomy, medical sciences, food industries, high-speed communications, etc. The detection of several types of cancers is facilitated with circularly polarized THz waves. For such versatile applications, compact, high-performance, all-solid-state, and continuous wave (CW) monochromatic THz sources are in great demand. To be useful as a hand-held device, the emitters should have an output power of at least 1 mW. Resonant tunneling diodes (RTDs) operating at room temperature and quantum cascade lasers (QCLs) may be good candidates. The emission power of RTDs above the central frequency of the THz gap around 1.5 THz at present, however, has severely been limited to about 1 μW and is much lower at higher f values. The emission power of QCLs can be well above 1 mW, but not below 1.5 THz. Difference frequency generation QCLs can operate at about 1 THz. For frequencies near to 1~THz, but only at powers in the μW range. By using the intrinsic Josephson junctions (IJJs) in the layered high temperature superconductor, Bi2Sr2CaCu2O8+d (Bi2212), the range from 1 to 11 THz has been achieved for both single device emitters and detectors. Although the emission power is less than 1 μW, the power can in principle be increased substantially by forming emission arrays and making efficient use of internal and external electromagnetic cavities. One array was reported to emit at 0.6 mW below 1 THz. Although such devices require cryo-cooling, overall, devices including the cooler can now be made of hand-held size.  

Sensors authorizes both original and review articles on any of these topics in this special issue. Review articles on the state-of-the-art of RTDs, QCLs, Difference generation QCLs, and superconducting IJJs are especially welcome. Original articles that demonstrate or predict improvement upon the existing performance features of any of these or possibly other techniques are also most welcome. Also welcome are original and review articles on uses of such devices in applications.

Prof. Richard Klemm
Guest Editor

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. Sensors is an international peer-reviewed open access semimonthly 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 2600 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

  • Quantum cascade lasers (QCLs)
  • Difference frequency generation QCLS
  • resonant tunneling diodes (RTDs)
  • high-temperature superconducting intrinsic Josephson junction (IJJ) emitters and detectors
  • THz emitters and detectors
  • emission power enhancement
  • control of Joule heating
  • circularly polarized THz waves

Published Papers (5 papers)

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Research

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16 pages, 1911 KiB  
Article
A Novel System for Quasi-Continuous THz Signal Transmission and Reception
by Andrej Sarjaš, Blaž Pongrac and Dušan Gleich
Sensors 2022, 22(12), 4448; https://0-doi-org.brum.beds.ac.uk/10.3390/s22124448 - 12 Jun 2022
Viewed by 1115
Abstract
This paper presents a novel system for generating and receiving quasi-continuous (QC) TeraHertz (THz) waves. A system design and theoretical foundation for QC-THz signal generation are presented. The proposed QC-THz system consists of commercially available photo-conductive antennas used for transmission and reception of [...] Read more.
This paper presents a novel system for generating and receiving quasi-continuous (QC) TeraHertz (THz) waves. A system design and theoretical foundation for QC-THz signal generation are presented. The proposed QC-THz system consists of commercially available photo-conductive antennas used for transmission and reception of THz waves and a custom-designed QC optical signal generator, which is based on a fast optical frequency sweep of a single telecom distributed-feedback laser diode and unbalanced optical fiber Michelson interferometer used for a high-frequency modulation. The theoretical model for the proposed system is presented and experimentally evaluated. The experimental results were compared to the state-of-the-art continuous-wave THz system. The comparison between the continuous-wave THz system and the proposed QC-THz system showed the ability to transmit and receive QC-THz waves up to 300 GHz. The upper-frequency limit is bounded by the length of the used Michelson interferometer. The presented design of THz signal generation has a potential for industrial application because it is cost-efficient and can be built using commercially available components. Full article
(This article belongs to the Special Issue Terahertz Emitters and Detectors)
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11 pages, 2742 KiB  
Article
Characteristics of Bow-Tie Antenna Structures for Semi-Insulating GaAs and InP Photoconductive Terahertz Emitters
by Salman Alfihed, Ian G. Foulds and Jonathan F. Holzman
Sensors 2021, 21(9), 3131; https://0-doi-org.brum.beds.ac.uk/10.3390/s21093131 - 30 Apr 2021
Cited by 3 | Viewed by 2156
Abstract
This work presents a study of photoconductive (PC) terahertz (THz) emitters based upon varied bow-tie (BT) antenna structures on the semi-insulating (SI) forms of GaAs and InP. The BT antennas have electrodes in the form of a Sharp BT, a Broad BT, an [...] Read more.
This work presents a study of photoconductive (PC) terahertz (THz) emitters based upon varied bow-tie (BT) antenna structures on the semi-insulating (SI) forms of GaAs and InP. The BT antennas have electrodes in the form of a Sharp BT, a Broad BT, an Asymmetric BT, a Blunted BT, and a Doubled BT. The study explores the main features of PC THz emitters for spectroscopic studies and sensors application in terms of THz field amplitude and spectral bandwidth. The emitters’ performance levels are found to depend strongly upon the PC material and antenna structure. The SI-InP emitters display lower THz field amplitude and narrower bandwidth compared to the SI-GaAs emitters with the same structure (and dimensions). The characterized Doubled BT structure yields a higher THz field amplitude, while the characterized Asymmetric BT structure with flat edges yields a higher bandwidth in comparison to the sharp-edged structures. This knowledge on the PC THz emitter characteristics, in terms of material and structure, can play a key role in future implementations and applications of THz sensor technology. Full article
(This article belongs to the Special Issue Terahertz Emitters and Detectors)
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12 pages, 1435 KiB  
Communication
A Highly Birefringent Photonic Crystal Fiber for Terahertz Spectroscopic Chemical Sensing
by Tianyu Yang, Liang Zhang, Yunjie Shi, Shidi Liu and Yuming Dong
Sensors 2021, 21(5), 1799; https://0-doi-org.brum.beds.ac.uk/10.3390/s21051799 - 05 Mar 2021
Cited by 27 | Viewed by 2487
Abstract
A photonic crystal fiber (PCF) with high relative sensitivity was designed and investigated for the detection of chemical analytes in the terahertz (THz) regime. To ease the complexity, an extremely simple cladding employing four struts is adopted, which forms a rectangular shaped core [...] Read more.
A photonic crystal fiber (PCF) with high relative sensitivity was designed and investigated for the detection of chemical analytes in the terahertz (THz) regime. To ease the complexity, an extremely simple cladding employing four struts is adopted, which forms a rectangular shaped core area for filling with analytes. Results of enormous simulations indicate that a minimum 87.8% relative chemical sensitivity with low confinement and effective material absorption losses can be obtained for any kind of analyte, e.g., HCN (1.26), water (1.33), ethanol (1.35), KCN (1.41), or cocaine (1.50), whose refractive index falls in the range of 1.2 to 1.5. Besides, the PCF can also achieve high birefringence (∼0.01), low and flat dispersion, a large effective modal area, and a large numerical aperture within the investigated frequency range from 0.5 to 1.5 THz. We believe that the proposed PCF can be applied to chemical sensing of liquid and THz systems requiring wide-band polarization-maintaining transmission and low attenuation. Full article
(This article belongs to the Special Issue Terahertz Emitters and Detectors)
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11 pages, 4601 KiB  
Communication
Numerical Study of the Coupling of Sub-Terahertz Radiation to n-Channel Strained-Silicon MODFETs
by Jaime Calvo-Gallego, Juan A. Delgado-Notario, Jesús E. Velázquez-Pérez, Miguel Ferrando-Bataller, Kristel Fobelets, Abdelaziz El Moussaouy and Yahya M. Meziani
Sensors 2021, 21(3), 688; https://0-doi-org.brum.beds.ac.uk/10.3390/s21030688 - 20 Jan 2021
Cited by 1 | Viewed by 1716
Abstract
This paper reports on a study of the response of a T-gate strained-Si MODFETs (modulation-doped field-effect transistor) under continuous-wave sub-THz excitation. The sub-THz response was measured using a two-tones solid-state source at 0.15 and 0.30 THz. The device response in the photovoltaic mode [...] Read more.
This paper reports on a study of the response of a T-gate strained-Si MODFETs (modulation-doped field-effect transistor) under continuous-wave sub-THz excitation. The sub-THz response was measured using a two-tones solid-state source at 0.15 and 0.30 THz. The device response in the photovoltaic mode was non-resonant, in agreement with the Dyakonov and Shur model for plasma waves detectors. The maximum of the photoresponse was clearly higher under THz illumination at 0.15 THz than at 0.3 THz. A numerical study was conducted using three-dimensional (3D) electromagnetic simulations to delve into the coupling of THz radiation to the channel of the transistor. 3D simulations solving the Maxwell equations using a time-domain solver were performed. Simulations considering the full transistor structure, but without taking into account the bonding wires used to contact the transistor pads in experiments, showed an irrelevant role of the gate length in the coupling of the radiation to the device channel. Simulations, in contradiction with measurements, pointed to a better response at 0.3 THz than under 0.15 THz excitation in terms of the normalized electric field inside the channel. When including four 0.25 mm long bonding wires connected to the contact pads on the transistor, the normalized internal electric field induced along the transistor channel by the 0.15 THz beam was increased in 25 dB, revealing, therefore, the important role played by the bonding wires at this frequency. As a result, the more intense response of the transistor at 0.15 THz than at 0.3 THz experimentally found, must be attributed to the bonding wires. Full article
(This article belongs to the Special Issue Terahertz Emitters and Detectors)
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Review

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19 pages, 6764 KiB  
Review
Terahertz Emitter Using Resonant-Tunneling Diode and Applications
by Masahiro Asada and Safumi Suzuki
Sensors 2021, 21(4), 1384; https://0-doi-org.brum.beds.ac.uk/10.3390/s21041384 - 16 Feb 2021
Cited by 66 | Viewed by 6318
Abstract
A compact source is important for various applications utilizing terahertz (THz) waves. In this paper, the recent progress in resonant-tunneling diode (RTD) THz oscillators, which are compact semiconductor THz sources, is reviewed, including principles and characteristics of oscillation, studies addressing high-frequency and high [...] Read more.
A compact source is important for various applications utilizing terahertz (THz) waves. In this paper, the recent progress in resonant-tunneling diode (RTD) THz oscillators, which are compact semiconductor THz sources, is reviewed, including principles and characteristics of oscillation, studies addressing high-frequency and high output power, a structure which can easily be fabricated, frequency tuning, spectral narrowing, different polarizations, and select applications. At present, fundamental oscillation up to 1.98 THz and output power of 0.7 mW at 1 THz by a large-scale array have been reported. For high-frequency and high output power, structures integrated with cylindrical and rectangular cavities have been proposed. Using oscillators integrated with varactor diodes and their arrays, wide electrical tuning of 400–900 GHz has been demonstrated. For spectral narrowing, a line width as narrow as 1 Hz has been obtained, through use of a phase-locked loop system with a frequency-tunable oscillator. Basic research for various applications—including imaging, spectroscopy, high-capacity wireless communication, and radar systems—of RTD oscillators has been carried out. Some recent results relating to these applications are discussed. Full article
(This article belongs to the Special Issue Terahertz Emitters and Detectors)
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