Tuesday, November 24, 2015
Abstract-Terahertz-bandwidth photonic temporal differentiator based on a silicon-on-isolator directional coupler
Tian Li Huang, Ao Ling Zheng, Jian Ji Dong, Ding Shan Gao, and Xin Liang Zhang
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Monday, November 23, 2015
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
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The transmission properties of a substrate integrated waveguide (SIW) based on periodic stacks have been theoretically investigated in the terahertz (THz) region. The effects of the dielectric-graphene-dielectric structure of the stack on the propagation properties are shown to be significant and different from the conventional active SIW based on active components. By varying the the cut-off frequency of the proposed waveguide can be dynamically tuned from 3 to 3.7 THz. Moreover, the tunable waveguide displays low leakage loss and single-mode propagation with −120 dB stop-band These primary results are very promising for THz integration and SIW-based systems.
We investigate the terahertz electromagnetic responses of meta-atoms (MAs) induced by different mode coupling mechanisms. Two types of MAs based on concentric rectangular square (CRS) are presented: independent CRS (I-CRS) and junctional-CRS (J-CRS). In I-CRS, each works as an independent dipole so as to result in the multiple resonance modes when the level is above 1. In J-CRS, however, the generated layer is rotated by π/2 radius to the adjacent CRS in one MA. The multiple resonance modes are coupled into a single mode resonance. The level increasing induces resonance modes in I-CRS while in J-CRS. When the level is below 4, the mode Q factor of J-CRS is in between the two modes of I-CRS; when the level is 4 or above, the mode Q factor of J-CRS exceeds the two modes of I-CRS. Furthermore, the modulation depth (MD) decreases in I-CRS while it increases in J-CRS with the increase in levels. The surface analysis reveals that the capacitive coupling of modes in I-CRS results in the modes while the conductive coupling of modes in J-CRS induces the mode A high Q mode with large MD can be achieved via conductive coupling between the of different scales in a MA.
An interdisciplinary team at the Ruhr-Universität Bochum has found a way of accessing the interior of transistors. The researchers have manipulated the electron gas contained within by applying resonators to generate rhythmic oscillation in the terahertz range inside. They shared their findings in the magazine Scientific Reports.
Transistors can be manipulated not only with voltages
Used for switching and amplifying, transistors are fundamental elements of modern electronics. By applying a specific voltage externally to a transistor, an electric current is controlled inside, which, in turn, generates a new voltage. Compared with the externally applied voltage, the new voltage may be amplified, may oscillate or be logically connected to it. In order to interact with their surroundings via electric current and voltage, transistors contain ultra-thin electron layers, so-called 2D electron gases. The RUB team demonstrated that these gases can be controlled not only via DC and radio-frequency voltages.
Electron gas can be oscillated like jelly
"A 2D electron gas is like jelly," explains Prof Dr Andreas Wieck from the Chair for Applied Solid State Physics. "If pressure is electrically applied to the gas from above with a characteristic frequency, thickness and density oscillations are generated." Accordingly, the gas can be manipulated via electric forces, which oscillates much more rapidly than any radio or microwave frequency. As it has a thickness of just about ten nanometres, the oscillations follow the laws of quantum mechanics. This means: all occurring oscillations have a specific frequency, namely in the terahertz range, i.e. in the range of 1012 Hertz. "Pressure to the electron gas must be applied in that rapid change," elaborates Wieck. Andreas Wieck, Dr Shovon Pal, Dr Nathan Jukam and other colleagues from the workgroup Terahertz Spectroscopy and Technology as well as from the Chair of Electronic Materials and Nanoelectronics have found a way to trigger the required oscillations. Thus, a new method of accessing the interior of a transistor has been created.
Resonators generate thickness oscillations
One hundred nanometres above the electron gas, the RUB researchers evaporated an array of identical metallic resonators which can oscillate with the required fixed frequency. The electron gas was embedded in a semiconductor and could be modified via external DC voltage, namely it could be made a bit thicker or thinner. The thickness determines the frequency which makes the gas oscillate optimally. Deploying external voltage, the researchers were able to fine-tune the electron gas to the resonators, i.e. adjust the gas so that the alternating electric pressure of the resonators excites it optimally to oscillate in the terahertz range.
Sensors for chemical and environmental technology
This method could be of interest for sensors in chemical and environmental applications, as the researchers suggest. This is because molecule oscillations typically happen in the terahertz range. With modified transistors, such oscillations can be recorded and sensors can be developed that react to the frequencies of certain gases or liquids.
Explore further: Technique makes it possible to measure the intrinsic properties of quantum dot transistors
More information: Shovon Pal et al. Ultrawide electrical tuning of light matter interaction in a high electron mobility transistor structure, Scientific Reports (2015). DOI: 10.1038/srep16812