Preface to Special Issue on Conference Papers
------ 4th EUCWMT and MTSA 2011
This special issue comes out of two successful conferences¡ªthe 4th Europe/UK-China Workshop on Millimetre Waves and Terahertz Technologies (4th EUCWMT), held in Glasgow, UK, 1st-3rd, September 2011 and 2011 International Symposium on Microwave/Terahertz Science and Applications (MTSA 2011), held in Nanjing, China, 19th-22nd, June 2011. Totally, there were over 100 high quality papers presented at these two conferences and authored by a large number of experts from all over the world. It is quite a difficult task to select only very small part of these papers for the special issue due to the limitation of page layout. With the help of the Chairs of 4th EUCWMT, Professor Alan Phelps (University of Strathclyde) and Professor Xiaodong Chen (Queen Mary, University of London), and the Chairs of MTSA 2011, Professor Peiheng Wu (Nanjing University) and Professor Masayoshi Tonouchi (Osaka University), who are also guest editors of our journal, 13 papers representing research progress in THz sources, THz detection, THz devices (systems) and THz technology applications are selected. We hope this special issue can show the readers the most recent progress in THz science and technology as well as benefit their research in the future.
Paper from 4th Europe/UK-China Workshop on Millimetre Waves and Terahertz Technologies
TST, Vol. 4, No. 3, PP. 71-75
Pseudospark-sourced Micro-sized Electron Beams for High Frequency klystron Applications
H. Yin(1)*, D. Bowes(1), A.W. Cross(1), W. He(1), K. Ronald(1), A. D. R. Phelps(1), D. Li(2) and X. Chen(2)
(1) SUPA, Department of Physics, University of Strathclyde, Glasgow, G4 0NG, UK.
(2) Department of Electronic Engineering, Queen Mary University of London, London, E1 4NS, UK.
* Email: h.yin@strath.ac.uk
Abstract: Electron beams of micro sizes have been recently extracted from a pseudospark discharge. A three cavity pseudospark-driven 94 GHz klystron has been designed and simulated using the particle-in-cell (PiC) code MAGIC-2D and modeled with CST Microwave Studio. The simulation results to date look promising.
Keywords: Klystron, Pseudospark discharge
doi: 10.11906/TST.071-075.2011.09.09
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Paper from 4th Europe/UK-China Workshop on Millimetre Waves and Terahertz Technologies
TST, Vol. 4, No. 3, PP. 76-84
W-band Gyro-BWO with a Four-stage Depressed Collector
Liang Zhang*, Wenlong He, Craig R. Donaldson, Adrian W. Cross, Alan D. R. Phelps, Paul McElhinney and Kevin Ronald
SUPA, Department of Physics, University of Strathclyde, Glasgow, G4 0NG, Scotland, UK
* Email: liang.zhang@strath.ac.uk
Abstract: An energy recovery system using a four-stage depressed collector was simulated and designed to improve the overall efficiency of the W-band gyrotron backward wave oscillator (gyro-BWO) at the University of Strathclyde. The spent beam information was exported from the simulation of the gyro-BWO using the 3D PIC code MAGIC. The geometry of the depressed collector was optimized using a genetic algorithm to achieve the optimum overall recovery efficiency for specific parameters of the spent beam. Secondary electron emissions and their effects on the recovery efficiency and the backstreaming of the electrons from the collector region were simulated. The heat power distribution on the electrodes was also simulated to avoid the ¡°hot spot¡±.
Keywords: Gyro-BWO, Depressed collector, Energy recovery, Secondary electron emission.
doi: 10.11906/TST.076-084.2011.09.10
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Paper from 4th Europe/UK-China Workshop on Millimetre Waves and Terahertz Technologies
TST, Vol. 4, No. 3, PP. 85-89
Terahertz Acoustic Optical Modulator and its Application on Free Space Communication
Y. Ma*, S.C. Saha, A. L. Bernassau and D.R.S. Cumming
University of Glasgow, Rankine Building, Oakfield Avenue, Glasgow, UK, G12 8LT
* Email: ma_yong@live.com
Abstract: We demonstrate in this paper a terahertz free space communication system based on acoustic optical modulation and heterodyne detection. A high resistivity silicon acoustic optical modulator (AOM) was used to modulate a continuous terahertz wave at 2.52 THz. A pyroelectric detector was used to detect the modulated terahertz signal via heterodyne detection mode. A modulation frequency of 937 kHz and sampling rate of 1kbit/s was achieved.
Keywords: Terahertz, Free space communication, Acoustic optical modulation
doi: 10.11906/TST.085-089.2011.09.11
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Paper from 4th Europe/UK-China Workshop on Millimetre Waves and Terahertz Technologies
TST, Vol. 4, No. 3, PP. 90-94
The Design of a 200-240-GHz Sub-Harmonic Mixer Based on RAL¡¯s Planar Schottky Diodes
Bo Zhang (1) *, Byron Alderman(2), Zhe Chen(1), Yong Fan(1), Xiaofan Yang(1) and Xiaobo Yang(1)
(1) EHF Key Laboratory of Fundamental Science Universtity of Electronic Science and Technology of China, Chengdu, Sichuan, 610054, P.R.China
(2) Millimetre-Wave Technology Space Science and Technology Department STFC Rutherford Appleton Laboratory Harwell Science and Innovation Campus Didcot, OX11 0QX
* Email: zhangbo.uestc@163.com
Abstract: This paper presents the design of a fixed-tuned 200-240-GHz wide-band sub-harmonic mixer. The mixer is based on an anti-parallel pair of GaAs Schottky diodes fabricated at Rutherford Appleton Laboratory (RAL). The circuits are fully integrated with the RF/IF filter and flip-chipped onto a suspended quartz-based substrate. A best conversion loss of 5.9dB was achieved with 5mW of LO power at 207GHz. Over an RF band of 200-240GHz, the conversion loss is below10dB. This state-of-the-art optimization is attributed to lower parasitic devices and a low-loss waveguide circuit.
Keywords: Sub-harmonic mixer, Planar Schottky diodes, Terahertz-wave, Wide-band
doi: 10.11906/TST.090-094.2011.09.12
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Paper from 4th Europe/UK-China Workshop on Millimetre Waves and Terahertz Technologies
TST, Vol. 4, No. 3, PP. 95-98
The design of a 230GHz unilateral finline SIS mixer
Yangjun Zhou (1) *, Paul Grimes (1), Ghassan Yassin(1)and Jamie Leech(1)
(1) Department of Physics, University of Oxford
* Email: Yangjun.zhou@physics.ox.ac.uk
Abstract: We present the design and the testing results of a broadband Superconducting-Insulating-Superconducting (SIS) unilateral finline mixer operating across 185GHz~275GHz. The mixer will be employed by a single baseline interferometer [1](Gubbins -200GHz Ultra-BroadBand Interferometer for Sunyaev-Zel¡¯dovich), aiming to detect the Sunyaev-Zel'dovich effect [2][3] in bright galaxy clusters. A key feature of the design is the ultra-wide instantaneous bandwidth of 3-13 GHz. It provides heterodyne interferometeric operation with high brightness sensitivity, which enables the instrument to observe the continuous source precisely. The mixer chip has been carefully designed to present low parasitic reactance, in order to realize the wide IF bandwidth. A unilateral finline [4] has been used as the efficient transition between the waveguide mode and the slotline quasi-TEM mode over wide RF bandwidth. A direct coupling slotline-to-microstrip transformer is then used to couple the RF signal from the narrow slotline to the microstrip line, where the Nb-AlOx-Nb SIS junction is fabricated. A silicon substrate was chosen to decrease the impedance of the slotline. The material of silicon enables easier extraction of devices from the substrate, by creating trenches around the individual devices using RIE etching. The hot/cold measurement of the mixer gave a DSB noise temperature of 90K over the bandwidth 200K-250K. In this paper we shall describe the design of the mixer and report the experimental results.
Keywords: Heterodyne Detector, Unilateral finline, SIS junction
doi: 10.11906/TST.095-098.2011.09.13
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Paper from 4th Europe/UK-China Workshop on Millimetre Waves and Terahertz Technologies
TST, Vol. 4, No. 3, PP. 99-103
Characterisation of Terahertz Beam Profile and Propagation through Complex Quasi-Optic Systems
J.F. Molloy*, M. Naftaly, and R.A. Dudley
National Physical Laboratory, Hampton Road, Teddington, Middlesex. TW11 0LT
* Email: John.Molloy@npl.co.uk
Abstract: We report on a simple technique, readily applicable to existing Terahertz Time Domain Spectroscopy (THz-TDS) systems, that allows the spatial distribution of the terahertz beam to be resolved in both the temporal and frequency domains. It requires minimal equipment and no adjustment of the pump/probe path lengths of the electro-optic detection system. While THz TDS has become widely used, in many cases a considerable amount of unknowns exist regarding the THz beam profile and its evolution as it propagates through the system. Misalignment and poor beam shape can lead to results with reduced amplitude of detected frequency components, frequency shifted components, and narrowed spectra. [1] Characterization of the beam profile allows for better alignment of the optics, increased efficiency and improved measurement accuracy. We present the results of this technique and compare them with a model of Gaussian beam optics.
Keywords: Terahertz, Quasi-optical, Beam profile, Coherent, Time-domain Spectroscopy
doi: 10.11906/TST.099-103.2011.09.14
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Paper from 4th Europe/UK-China Workshop on Millimetre Waves and Terahertz Technologies
TST, Vol. 4, No. 3, PP. 104-108
Measurements of Schottky-Diode Based THz Video Detectors
Hairui Liu1, 2*, Junsheng Yu1, Peter Huggard 2* and Byron Alderman2
1 Beijing University of Posts and Telecommunications, Beijing, 100876, P.R. China
*1 Email: liuhairui1983@126.com
2 MMT Group, RAL Space, STFC Rutherford Appleton Laboratory, Didcot, OX11 0QX, UK
*2 Email: Peter.Huggard@stfc.ac.uk
Abstract: Schottky barrier diodes have several advantages when used as millimetre wave and terahertz video, or power detectors. These include their inherent small physical size, a broadband spectral response, a sub-nanosecond response time and room temperature operation. This paper describes the use of air-bridged GaAs Schottky diodes, fabricated at the STFC Rutherford Appleton Laboratory, as such rectifying detectors. Incoming radiation is coupled to the forward biased diodes via a hemispherical silicon lens and a broadband planar bow-tie antenna: the rectified signal then passes to a low noise amplifier. A compact, high speed, photonic system, based on 1.55 µm wavelength fibre-optic telecoms components and a waveguide photomixer, provides the test signal. The spectral dependence of responsivity and noise performance of the detectors will be reported.
Keywords: Schottky diodes, THz, Detector
doi: 10.11906/TST.104-108.2011.09.15
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Paper from 4th Europe/UK-China Workshop on Millimetre Waves and Terahertz Technologies
TST, Vol. 4, No. 3, PP. 109-115
Advances on Polarization Modulator Technology and Methodology for Future Improvements
G. Savini (1) *, J.Zhang(2), P.Ade(2), P.D.Mauskopf(2)
(1) Optical Science Laboratory, University College London, Gower
Street, London, WC1E 6BT, U.K.
(2) School of Physics and Astronomy, Cardiff University, Queens
Buildings, the Parade, Cardiff, CF24 3AA, U.K
* Email: gs@star.ucl.ac.uk
Abstract: In this work we present the latest improvements on the fabrication of a non-crystal achromatic half-wave plate working in the sub-THz frequency range [1]. This is achieved by hot-pressing polypropylene layers with photo-lithographed copper structures. We will discuss the performance of the first prototypes and a few techniques for the improvement of future designs. General considerations at the root of achromatic designs will also be touched upon which are valid for both optical and waveguide phase modulators.
Keywords: Polarization modulator technology, Non-crystal achromatic half-wave plate, Sub-THz
doi: 10.11906/TST.109-115.2011.09.16
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Paper from 4th Europe/UK-China Workshop on Millimetre Waves and Terahertz Technologies
TST, Vol. 4, No. 3, PP. 116-122
Time Varying Conductance in THz Photoconductive Antennas
Neda Khiabani, Yi Huang*, Yao-chun Shen and Stephen Boyes
Department of Electrical Engineering and Electronics, The University of Liverpool, L69 3GJ, UK
* Email: Yi.Huang@liv.ac.uk
Abstract: Terahertz (THz) photoconductive antennas are the most common devices for the generation and detection of THz waves. One of the main problems of the current photoconductive antennas as the emitter is that the optical-THz conversion efficiency is very low, thus it is difficult to obtain high power THz radiation. Source conductance of the photoconductive antenna is one of the primary factors which have significant effects on emitted THz power and optical-to- THz conversion efficiency. Thus, in order to assess the performance of the photoconductive antenna, proper evaluation of the photoconductive material conductance is required. In this paper, the time dependant conductivity of the photoconductive material based on a pulsed system is first derived. Then, through this conductivity, the source conductance (=1/resistance) in THz photoconductive antennas is determined which illustrates the influence of different parameters of the laser pulse, photoconductive material, and THz antenna. This new formula can aid in a better theoretical assessment of the total optical-THz conversion efficiency calculation as the source conductance can be more accurately obtained.
Keywords: Terahertz antennas, Photoconductive antennas, Source conductance, Photoconductive material, Pulsed THz system
doi: 10.11906/TST.116-122.2011.09.17
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Paper from 4th Europe/UK-China Workshop on Millimetre Waves and Terahertz Technologies
TST, Vol. 4, No. 3, PP. 123-127
Josephson Pair Tunnelling Influence on the Performance of an SIS Mixer near its Superconducting Gap
Boon-Kok Tan* and Ghassan Yassin
Department of Physics (Astrophysics), Denys Wilkinson Building,
Keble Road, OX1 3RH, Oxford, United Kingdom.
* E-mail: tanbk@astro.ox.ac.uk
Abstract: We report the investigation of the influence of Josephson pair tunnelling on the sensitivity of an SIS mixer near the superconducting gap of niobium. Hot and cold load measurements were carried out from 600 GHz to 700 GHz, without completely supressing the Josephson effect. We have noticed that when measurements were made at bias points near the first Shapiro step, significantly higher values of Y-factor could be obtained with magnetic field strengths that made the Shapiro step sharper, rather then those that supressed the step. This resulted in a significant improvement in noise temperature of the mixer at those bias points. This observation is important for SIS mixers operating at frequencies near or above gap frequency (¦Øgap) because the warping of the second negative photon step to the positive display side, narrowing down the bias voltage interval in which measurement of the Y-factor at the first photon step could be done.
Keywords: Superconductor-Insulator-Superconductor (SIS) mixers, Josephson mixers, Sub-millimetre astronomy, Shapiro steps, Sub-millimetre receiver
doi: 10.11906/TST.123-127.2011.09.18
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Paper from 2011 International Symposium on Microwave/Terahertz Science and Applications
TST, Vol. 4, No. 3, PP. 128-131
THz techniques using metal mesh sensor for human skin measurement
Yu Guana,*, Koji Mizukoshib, Kazuki Yonekurab, Kei Takeyaa, Kodo Kawasea,c
a Nagoya University, Ecotopia, Furo-cho, Chikusa-ku, Nagoya, Japan 464-8603
b POLA Chemical Industries, INC. 27-1 Takashimadai, Kanagawa-ku, Yokohama, Japan 221-0833
c RIKEN, 519-1399 Aramaki-Aoba, Sendai, Japan 980-0845
* E-mail: guan.yu@j.mbox.nagoya-u.ac.jp
Abstract: Metal meshes work as band-pass filters in the terahertz (THz) region with their transmission spectra acutely being affected by the refractive index of the material inside and above the metal mesh openings. We used a metal mesh for high-sensitivity observations by focusing on the ¡°dip¡±, i. e. a sudden change in transmittance that only appeared when the THz wave was obliquely incident onto the metal mesh. Here we report a measurement of stratum corneum to inspect the feasibility of applying the metal mesh sensor to observations of human skin.
Keywords: Terahertz wave, Metal mesh sensor, Stratum corneum, Transmission spectra
doi: 10.11906/TST.128-131.2011.09.19
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Paper from 2011 International Symposium on Microwave/Terahertz Science and Applications
TST, Vol. 4, No. 3, PP. 132-136
Generation of Widely Tunable Terahertz Waves by Difference-Frequency Generation Using a Configurationally Locked Polyene 2-[3-(4-Hydroxystyryl)-5, 5-Dimethylcyclohex-2-Enylidene] Malononitrile Crystal
Hirohisa Uchida1,2, * , Takashi Sugiyama1 , Koji Suizu1 , Takashi Osumi2 , and Kodo Kawase1,3
1 Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
2 ARKRAY Inc. Yousuien-nai, Gansuin-cho 59, Kamigyo-ku, Kyoto, 6020008, Japan
3 RIKEN, 519-1399 Aramaki-Aoba, Aoba, Sendai 980-0845, Japan
* Email: uchidah@arkray.co.jp
Abstract: We generated widely tunable terahertz (THz) waves using difference-frequency generation (DFG) in a configurationally locked polyene (CLP) 2-[3-(4-hydroxystyryl)- 5, 5-dimethylcyclohex-2-enylidene]malononitrile (OH1) crystal. The two waves generated by a KTiOPO4 (KTP) optical parametric oscillator (OPO) were used to pump the OH1 crystal. The maximum output energy of the THz wave was 604 pJ/pulse. Widely tunable THz waves were successfully generated from 0.5 to 10 THz by using difference-frequency generation source.
Keywords: Nonlinear optical materials, Difference-frequency generation, OH1 crystal
doi: 10.11906/TST.132-136.2011.09.20
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Paper from 2011 International Symposium on Microwave/Terahertz Science and Applications
TST, Vol. 4, No. 3, PP. 137-148
Cross-polarization Response of a Two-contact Photoconductive Terahertz Detector
Yandong Gong*, Hui Dong and Zhining Chen
Institute for Infocomm Research, 1 Fusionopolis Way, # 21-01 Connexis South, Singapore 138632
* Email: gongyd@i2r.a-star.edu.sg
Abstract: The cross-polarization response of a two-contact photoconductive terahertz (THz) detector, is experimentally found in the polarization state measurement of THz radiation in THz time-domain spectroscopy (THz-TDS). It means that this detector responded to a mixture of the two polarization components of THz radiation and such a response is frequency dependent. To evaluate this response quantitatively, three parameters are presented and measured. In the measurement of THz-TDS, such a detector response will result in the distortion of the measured THz spectrum. As a consequence, it will reduce the dynamic range of the system in some frequency bands. In some special cases, it may even lead to a fake ¡°absorption peak¡± in the THz spectrum. Furthermore, when such a detector is used to measure the polarization state of THz radiation with the assistance of THz polarizers, it will be impossible to decide the optimum orientations of the polarizers as its cross-polarized response is frequency dependent. Finally, we experimentally demonstrated that this effect could be partially eliminated by adjusting the focusing condition of the probe laser beam on the antenna.
Keywords: Terahertz time-domain spectroscopy, Photoconductivity, Polarization
doi: 10.11906/TST.137-148.2011.09.21
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