International Journal of Terahertz Science and Technology
Vol.9, No.2, June 2016. PP.45-81 (3)
date2016-06-30 19:48:53 Click No.940

TST, Vol. 9, No. 2, PP. 45-59

(Invited paper) On the dielectric properties of substrates with different surface conditions for submillimeter-wave and terahertz applications

Kung Bo Ng 1 and Chi Hou Chan 1*, 2
1
State Key Laboratory of Millimeter Waves, Partner Laboratory in City University of Hong Kong, Hong Kong SAR, China
2 Department of Electronic Engineering, City University of Hong Kong, Hong Kong SAR, China
*1 Email:
eechic@cityu.edu.hk

(Received August 18, 2015)

Abstract: Dielectric constant and loss tangent are essential material parameters in designing and predicting the performance of submillimeter-wave and terahertz devices. In this paper we investigate dielectric properties of substrate materials using pulsed time-domain spectroscopy. It is found that these dielectric properties depend on the preparation process of the sample under test as different process results in different surface condition. Two different substrates, namely, printed-circuit board laminate and 3D printing polymer, with different preparation methods are used to illustrate the impact of surface condition of the sample to the extracted dielectric properties. A Fresnel zone-plate lens with a circular grating reflecting plane operating at 0.3 THz is designed and measured. Good agreement between simulation and measurement results is achieved when proper dielectric properties and surface model are employed.

Keywords: Terahertz time-domain spectroscopy (THz-TDS), Polymers, Refractive index, Absorption coefficient, Dielectric constants

doi: 10.11906/TST.045-059.2016.06.05

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TST, Vol. 9, No. 2, PP. 60-70

(Invited paper) Modulating the emission properties of superconducting terahertz emitters

X. J. Zhou 1, 2, M. Ji 1, 2, D. Y. An 1, 2, F. Rudau 4, R. Wieland 4, Q. Zhu 1, H. C. Sun 1, 2, L. Y. Hao 1, 2, D. Koelle 4, R. Kleiner 4, H. B. Wang 1, 2, 3* and P. H. Wu 1
1
Research Institute of Superconductor Electronics, Nanjing University, Nanjing 210093, China
2 National Institute for Materials Science, Tsukuba 3050047, Japan
3 Cooperative Innovation Centre of Terahertz Science, Chengdu 610054, China
4 Physikalisches Institut and Center for Quantum Science in LISA+, Universität T┨bingen, T┨bingen D-72076, Germany
* Email:
hbwang1000@gmail.com

(Received May 23, 2016 )

Abstract: Developing compact, tunable sources for terahertz (THz) generation is a highly active field of research. It was found that intrinsic Josephson junction (IJJ) stacks, naturally formed in single crystals of the cuprate superconductor Bi2Sr2CaCu2O8 (BSCCO), can emit coherent radiation in the THz range. With appropriate design, superconducting THz emitters with strong emission power have been fabricated over the last years. To make these emitters versatile for practical applications, e.g. in radio astronomy or for high-speed tele-communication, it is necessary to modulate and tune the THz emission power. We demonstrate two modulation methods. The first method is to use a three-terminal configuration. At high bias currents a hot spot, having a local temperature higher than the superconducting transition temperature, forms in the stack due to Joule-heating. The appearance and the position of the hot spot can be controlled by varying the ratios of the injected currents from two bottom electrodes. The second modulation method is to shine a focused laser beam onto the sample. Also with this method the emission power can be modulated in the high bias regime  by moving the laser beam on the surface of the stack.

Keywords: Intrinsic Josephson junctions, Superconducting terahertz emitter, Manipulation of emission

doi: 10.11906/TST.060-070.2016.06.06

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TST, Vol. 9, No. 2, PP. 71-81

(Invited paper) Excitation of terahertz plasmon in two-dimensional electron gas

Hua Qin 1*, Yao Yu 1, 2, Xiang Li 1, 2, Jiandong Sun 1, and Yongdan Huang 1
1
Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-tech and Nano-bionics (SINANO), Chinese Academy of Sciences, 398 Ruoshui Road, Suzhou 215123, P. R. China
2 Graduate University of Chinese Academy of Sciences, Beijing 100049, P. R. China
*1 Email:
hqin2007@sinano.ac.cn

(Received June 232016 )

Abstract: High-speed electronics is marching towards terahertz frequency regime in which electronics and optoelectronics are merging into a new realm. Efficient solid-state terahertz emitters/oscillators and high-speed high-sensitivity detectors are the most important active devices for terahertz applications. In the frequencies ranging from 1 THz to 3 THz, both electronic and photonic devices become less efficient. As coherent collective charge oscillations in the terahertz frequency range, plasmon in two-dimensional electron gas (2DEG) has long been pursued for active solid-state terahertz devices, especially emitters. However, such emitters are not yet practical since the conversion efficiency is yet lower than 10-3. In this review, we present excitation and probing of localized plasmon modes in grating-coupled and antenna-coupled field-effect transistors based on AlGaN/GaN heterostructures. It is shown that the damping of plasmons remains the critical problem in developing practical terahertz plasmon emitters. Nevertheless, non-resonant excitation of terahertz plasmons in antenna-coupled 2DEG is enabling a technology for high sensitivity detection of terahertz electromagnetic wave at room temperature.

Keywords: Plasmon, Two-dimensional electron gas, Terahertz detector, Terahertz emitter, Terahertz modulator

doi: 10.11906/TST.071-081.2016.06.07

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