Abstract-Optimization of tunable symmetric SPR sensor based on Ag-Graphene

Xiang Sheng, Jin Liu,  Haima Yang, Linlin Chen, Jun Li, Haishan Liu


https://www.sciencedirect.com/science/article/pii/S0030402619305455

To overcome the limitations of low sensitivity and instability of metal-medium-metal tunable surface plasmon resonance (SPR) sensors excited by planar waveguides, a silver-graphene-medium-graphene-silver film symmetrical SPR sensing structure excited by planar waveguides is proposed. And optimize sensor performance through modeling. The principle of symmetry structure for sensing tunability is analysed, finding that sensing with a silver film has a higher sensitivity than a gold film. However, since the silver film is easily oxidized, it affects the stability and repeatability of the sensor. To solve this problem, the graphene layer is added to the silver film to improve the disadvantage of easy oxidation of the silver film. A plane waveguide with a refractive index distribution of the residual error function of the excitation is prepared by ion exchange. The sensor structure was modeled and analyzed, and the influence of metal material, metal thickness, graphene layer number and thickness of the detection medium on the performance of the sensor was studied, and the sensing structure was better optimized. The results show that the silver film has a better sensing performance and higher sensitivity than the gold film. By adjusting the thickness of the detection medium, the refractive index range of the detection medium has a certain tunability: the choice of graphene thickness optimises sensor stability and detection sensitivity.

Abstract-Scattering Mechanisms and Modeling for Terahertz Wireless Communications

Shihao Ju, Syed Hashim Ali Shah, Muhammad Affan Javed, Jun Li, Girish Palteru, Jyotish Robin, Yunchou Xing, Ojas Kanhere, Theodore S. Rappaport

https://arxiv.org/abs/1903.02657

This paper provides an analysis of radio wave scattering for frequencies ranging from the microwave to the Terahertz band (e.g., 1 GHz - 1 THz), by studying the scattering power reradiated from various types of materials with different surface roughnesses. First, fundamentals of scattering and reflection are developed and explained for use in wireless mobile radio, and the effect of scattering on the reflection coefficient for rough surfaces is investigated. Received power is derived using two popular scattering models - the directive scattering (DS) model and the radar cross section (RCS) model through simulations over a wide range of frequencies, materials, and orientations for the two models, and measurements confirm the accuracy of the DS model at 140 GHz. This paper shows that scattering can become a prominent propagation mechanism as frequencies extend to millimeter-wave (mmWave) and beyond, but at other times can be treated like simple reflection. Knowledge of scattering effects is critical for appropriate and realistic channel models, which further support the development of massive multiple input-multiple output (MIMO) techniques, localization, ray tracing tool design, and imaging for future 5G and 6G wireless systems. 
https://arxiv.org/abs/1903.02657

Abstract-Compact high- T c superconducting terahertz emitter operating up to 86 Kelvin

Hancong Sun, Raphael Wieland, Zuyu Xu, Zaidong Qi, Yangyang Lv, Ya Huang, Huili Zhang, Xianjing Zhou, Jun Li, Yonglei Wang, Fabian Rudau, Johannes S. Hampp, Dieter Koelle, Shigeyuki Ishida, Hiroshi Eisaki, Yoshiyuki Yoshida, Biaobing Jin, Valery P. Koshelets, Reinhold Kleiner, Huabing Wang, Peiheng Wu,

https://journals.aps.org/prapplied/accepted/c4071A2fE601520eb1472e406dee8430aae0a3f93

We report on a Stirling-cooled compact Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8+\delta }$ intrinsic Josephson-junction stack with very high critical current density and improved cooling, operating at bath temperatures $T_b$ up to 86\,K. The square stand-alone stack is embedded between two sapphire substrates. For bath temperatures between 27.8\,K and 86\,K emission was observed at frequencies from 0.356\,THz to 2.09\,THz. The emission power exceeded 1\,$\mu$W at bath temperatures between 60\,K and 80\,K for emission frequencies between 0.5\,THz and 0.88\,THz. A record high value of 0.577\,THz was obtained for the emission frequency at $T_b$ = 80\,K, which is important for potential applications using liquid nitrogen as coolant. We also compare our experimental results to numerical simulations based on 3D coupled sine-Gordon equations combined with heat diffusion equations.

Abstract-Self-Mixing Spectra of Terahertz Emitters Based on Bi 2 Sr 2 CaCu 2 O 8 + δ Intrinsic Josephson-Junction Stacks

Ya Huang, Hancong Sun, Deyue An, Xianjing Zhou, Min Ji, Fabian Rudau, Raphael Wieland, Johannes S. Hampp, Olcay Kizilaslan, Jie Yuan, Nickolay Kinev, Oleg Kiselev, Valery P. Koshelets, Jun Li, Dieter Koelle, Reinhold Kleiner, Biaobing Jin, Jian Chen, Lin Kang, Weiwei Xu, Huabing Wang, and Peiheng Wu

https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.8.054023

Josephson junctions can serve as mixers for electromagnetic radiation, producing difference frequencies $\left|m{f}_s–n{f}_{\mathrm{LO}}\right|$ of the signal frequency $f_s$ and the local oscillator frequency $f_{\mathrm{LO}}$, where the latter can be provided by ac Josephson currents, and $m$ and $n$ are natural numbers. In order to obtain a better understanding of the purity of the terahertz radiation generated by stacks of intrinsic Josephson junctions (IJJs), we study self-mixing—i.e., $f_s$ is also produced by Josephson currents inside the stacks—in the difference-frequency range between 0.1 and 3.0 GHz. Simultaneously, we perform off-chip terahertz emission detection and transport measurements. We find that at high-bias currents, when a hot spot has formed in the stack, the power level of self-mixing can be low and sometimes is even absent at the terahertz emission peak, pointing to a good phase locking among all IJJs. By contrast, at low-bias currents where no hot spot exists, the self-mixing products are pronounced even if the terahertz emission peaks are strong. The mixing products at high operation temperature, at which the temperature variation within the stack is moderate, are minor, indicating that the low junction resistance, perhaps in combination with the lowered Josephson critical current density, may play a similar role for synchronization as the hot spot does at low temperature. While these observations are helpful for the task to synchronize thousands of IJJs, the observation of self-mixing in general may offer a simple method in evaluating the coherence of terahertz radiation produced by the IJJ stacks.

Abstract-Optimization of terahertz generation from LiNbO3 under intense laser excitation with the effect of three-photon absorption

Sen-Cheng Zhong, Zhao-Hui Zhai, Jiang Li, Li-Guo Zhu, Jun Li, Kun Meng, Qiao Liu, Liang-Hui Du, Jian-Heng Zhao, and Ze-Ren Li
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-23-24-31313

We proposed a three-dimensional model to simulate terahertz generation from LiNbO3crystal under intense laser excition (up to ~50 mJ/cm2). The impact of three-photon absorption, which leads to free carrier generation and free carrier saturation (when pump fluence above ~10 mJ/cm2) on terahertz generation was investigated. And further with this model, we stated the optimized experimental conditions (incident postion, beam diameter, and pulse duration, etc) for maximum generation efficiency in commonly-used tilted-pulse-front scheme. Red shift of spectrum, spatial distribution “splitting” effects of emitted THz beam, and primilary experimental verification under intense laser excitation are given.

© 2015 Optical Society of America

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Abstract-Linewidth dependence of coherent terahertz emission from Bi2Sr2CaCu2O8 intrinsic Josephson junction stacks in the hot-spot regime

http://prb.aps.org/abstract/PRB/v86/i6/e060505
Mengyue Li^1,2, Jie Yuan^2,3,*, Nickolay Kinev⁴, Jun Li^2,5, Boris Gross⁶, Stefan Guénon⁶, Akira Ishii², Kazuto Hirata², Takeshi Hatano², Dieter Koelle⁶, Reinhold Kleiner⁶, Valery P. Koshelets⁴, Huabing Wang^1,2,†, and Peiheng Wu^1 
1Research Institute of Superconductor Electronics, Nanjing University, Nanjing 210093, China
²National Institute for Materials Science, Tsukuba 3050047, Japan
³Department of Applied Physics, Wuhan University of Science and Technology, Wuhan 430081, China
⁴Kotel'nikov Institute of Radio Engineering and Electronics, Moscow 125009, Russia
⁵Hokkaido University, Hokkaido 0600810, Japan
⁶Physikalisches Institut and Center for Collective Quantum Phenomena in LISA⁺, Universität Tübingen, D-72076 Tübingen, Germany

 Received 3 April 2012; revised 20 July 2012; published 8 August 2012

We report on measurements of the linewidth Δf of terahertz radiation emitted from intrinsic Josephson junction stacks, using a Nb/AlN/NbN integrated receiver for detection. Previous resolution-limited measurements indicated that Δf may be below 1 GHz—much smaller than expected from a purely cavity-induced synchronization. While at low bias we found Δf to be not smaller than ∼500 MHz, at high bias, where a hot spot coexists with regions which are still superconducting, Δfturned out to be as narrow as 23 MHz. We attribute this to the hot spot acting as a synchronizing element. Δf decreases with increasing bath temperature, a behavior reminiscent of motional narrowing in NMR or electron spin resonance (ESR), but hard to explain in standard electrodynamic models of Josephson junctions.

©2012 American Physical Society

URL:

http://link.aps.org/doi/10.1103/PhysRevB.86.060505

DOI:

10.1103/PhysRevB.86.060505

PACS:

74.50.+r, 74.72.-h, 85.25.Cp

^*phy.wust@gmail.com

^†hbwang1000@gmail.com