Abstract-Substrate integrated frequency selective surface in microwave and terahertz bands

H. B. Wang, Y. J. Cheng,

http://ieeexplore.ieee.org/document/8068481/

Frequency selective surface (FSS) based on substrate integrated waveguide (SIW) technology is a passband spatial filter with periodic arrays of slots, which has wide applications, such as the sub-reflecting surface of the reflector antenna, and the antenna radome. Compared with the conventional FSS, the SIW FSS is a better candidate with high rectangular coefficient, good incident angle stability, low loss and easy fabrication using the PCB process. The existing SIW FSS unit has a relatively large area which leads to poor grating lobe suppression. In this presentation, an X-band FSS based on a quarter-mode SIW (QMSIW) cavity will be presented, which pushes the grating lobe up to high frequency band. Based on the QMSIW cavity, a two-band FSS and a four-band FSS are investigated subsequently. After that, the design of a THz SIW FSS is introduced. A FSS using the hexagon SIW cavity is designed in THz band. The FSS with the hexagon element has a wide band and good incident angle stability. Besides, it has a good out-of-band suppression and polarization stability.

Abstract-Fabrication of Bi2212 Single Crystal Bolometer for Detection of Terahertz Waves

T. Semerci, Y. Demirhan, N. Miyakawa, H. B. Wang, L. Ozyuzer,

https://link.springer.com/chapter/10.1007/978-94-024-1093-8_11

Terahertz (THz) radiation is in powerful region of electromagnetic spectrum because of prosperous application areas yet deficiency still exists about sources and detectors in despite of improvements of the research field in this range. This gap can be filled by focusing on development of THz detectors. Therefore, bolometers were preferred through many detectors due to detection sensitivity above 1 THz. In this study, Bi2Sr2CaCu2O8+δ (Bi2212) single crystals were used to fabricate THz bolometric detector. Bi2212 single crystals were transferred on sapphire substrate by cleavage process and e-beam lithography and ion beam etching were used to fabricate the microchip clean room facilities. Custom-designed cryogenic cryostat was used for a-b axis electrical and THz response measurements with liquid nitrogen cooled system. After electrical measurements, Bi2212 microchips detected the signals using Stefan-Boltzmann Lamp and response time were calculated. This study have shown with our experimental results that Bi2212 single crystals are potential candidates for THz bolometric detectors.

Abstract-A power-adjustable superconducting terahertz source utilizing electrical triggering phase transitions in vanadium dioxide

L. Y. Hao1,2, X. J. Zhou1,2, Z. B. Yang1, H. L. Zhang1, H. C. Sun1,2, H. X. Cao3, P. H. Dai3, J. Li1, T. Hatano2, H. B. Wang1,2,a), Q. Y. Wen3,b) and P. H. Wu1
http://scitation.aip.org/content/aip/journal/apl/109/23/10.1063/1.4971408
1 Research Institute of Superconductor Electronics, Nanjing University, Nanjing 210023, China
2 National Institute for Materials Science, Tsukuba 3050047, Japan
3 State Key Laboratory of Electronic Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China
a) Electronic mail: hbwang1000@gmail.com
b) Electronic mail: qywen@163.com
Appl. Phys. Lett. 109, 233503 (2016); http://dx.doi.org/10.1063/1.4971408

We report a practical superconducting terahertz (THz) source, comprising a stack of Bi2Sr2CaCu2O8intrinsic Josephson junctions (IJJs) and a vanadium dioxide (VO2) tunable attenuator with coplanar interdigital contacts. The electrical triggering phase transitions are observed not only at room temperature, but also at low temperatures, which provides a proof of the electrical triggering. Applying this, the VO2 attenuator is implemented for the independent regulations on the emission powers from the IJJ THz emitter, remaining frequencies and temperatures unchanged. The attenuation can be tuned smoothly and continuously within a couple of volts among which the maximum is, respectively, −5.6 dB at 20 K or −4.3 dB at 25 K. Such a power-adjustable radiation source, including the VO2 attenuator, can further expand its practicability in cryogenic THz systems, like superconducting THz spectrometers.

Abstract-Three-Dimensional Simulations of the Electrothermal and Terahertz Emission Properties of Bi2Sr2CaCu2O8 Intrinsic Josephson Junction Stacks

F. Rudau, R. Wieland, J. Langer, X. J. Zhou, M. Ji, N. Kinev, L. Y. Hao, Y. Huang, J. Li, P. H. Wu, T. Hatano, V. P. Koshelets, H. B. Wang, D. Koelle, and R. Kleiner

Phys. Rev. Applied 5, 044017 – Published 27 April 2016

https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.5.044017

We use 2D coupled sine-Gordon equations combined with 3D heat diffusion equations to numerically investigate the thermal and electromagnetic properties of a 250×70  μm2intrinsic Josephson junction stack. The 700 junctions are grouped to 20 segments; we assume that in a segment all junctions behave identically. At large input power, a hot spot forms in the stack. Resonant electromagnetic modes oscillating either along the length [(0, n) modes] or the width [(m, 0) modes] of the stack or having a more complex structure can be excited both with and without a hot spot. At fixed bath temperature and bias current, several cavity modes can coexist in the absence of a magnetic field. The (1, 0) mode considered to be the most favorable mode for terahertz emission can be stabilized by applying a small magnetic field along the length of the stack. A strong field-induced enhancement of the emission power is also found in experiment for an applied field around 5.9 mT.

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Abstract-The dynamic process and microscopic mechanism of extraordinary terahertz transmission through perforated superconducting films

• J. B. Wu
• , X. Zhang
• , B. B. Jin
• , H. T. Liu
• , Y. H. Chen
• , Z. Y. Li
• , C. H. Zhang
• , L. Kang
• , W. W. Xu
• , J. Chen
• ,H. B. Wang
• , M. Tonouchi
•  & P. H. Wu

http://www.nature.com/articles/srep15588

Superconductor is a compelling plasmonic medium at terahertz frequencies owing to its intrinsic low Ohmic loss and good tuning property. However, the microscopic physics of the interaction between terahertz wave and superconducting plasmonic structures is still unknown. In this paper, we conducted experiments of the enhanced terahertz transmission through a series of superconducting NbN subwavelength hole arrays, and employed microscopic hybrid wave model in theoretical analysis of the role of hybrid waves in the enhanced transmission. The theoretical calculation provided a good match of experimental data. In particular, we obtained the following results. When the width of the holes is far below wavelength, the enhanced transmission is mainly caused by localized resonance around individual holes. On the contrary, when the holes are large, hybrid waves scattered by the array of holes dominate the extraordinary transmission. The surface plasmon polaritions are proved to be launched on the surface of superconducting film and the excitation efficiency increases when the temperature approaches critical temperature and the working frequency goes near energy gap frequency. This work will enrich our knowledge on the microscopic physics of extraordinary optical transmission at terahertz frequencies and contribute to developing terahertz plasmonic devices.

Abstract-Tuning the Terahertz Emission Power of an Intrinsic Josephson-Junction Stack with a Focused Laser Beam

X. J. Zhou, J. Yuan, H. Wu, Z. S. Gao, M. Ji, D. Y. An, Y. Huang, F. Rudau, R. Wieland, B. Gross, N. Kinev, J. Li, A. Ishii, T. Hatano, V. P. Koshelets, D. Koelle, R. Kleiner, H. B. Wang, and P. H. Wu

Phys. Rev. Applied 3, 044012 – Published 21 April 2015

http://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.3.044012

We report on tuning the THz emission of a Bi2Sr2CaCu2O8 (BSCCO) intrinsic Josephson-junction stack by a focused laser beam which is scanned across the stack. The emission power Pe increases by up to 75% upon laser irradiation for a bath temperature near 22 K. The laser-induced changes in the voltage Vdc across the stack and in the emission power are measured simultaneously. The maximum of the laser-induced changes in emission power ΔPe is achieved by irradiating the stack on the location where the local temperature is about the critical temperature Tc. However, ΔPe is found to be proportional to the laser-induced global voltage change ΔVdc, irrespective of the laser position. This unexpected global response is likely to be related to a change in the average stack temperature and is consistent with the change in Pe when increasing the bath temperature by about 0.2 K. This tuning method can be employed in the application of BSCCO THz sources.

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