Saturday, April 21, 2018

Abstract-Interconnect and packaging technologies for terahertz communication systems

 Goutam Chattopadhyay,Theodore Reck, Cecile Jung-Kubiak, Maria Alonso-delPino, Choonsup Lee,

Using newly developed silicon micromachining technology that enables low-loss and highly integrated packaging 
solutions, we are developing vertically stacked transmitters and receivers at terahertz frequencies that can be used for communication and other terahertz systems. Although there are multiple ways to address the problem of interconnect and packaging solutions at these frequencies, such as system-on-package (SOP), multi-chip modules (MCM), substrate integrated waveguide (SIW), liquid crystal polymer (LCP) based multilayer technologies, and others, we show that deep reactive ion etching (DRIE) based silicon micromachining with vertical integration allows the most effective solutions at terahertz frequencies.

Abstract-Ultralow loss graphene-based hybrid plasmonic waveguide with deep-subwavelength confinement

Xueqing He, Tigang Ning, Shaohua Lu, Jingjing Zheng, Jing Li, Rujiang Li, and Li Pei

In this paper, we theoretically propose a novel graphene-based hybrid plasmonic waveguide (GHPW) consisting of a low-index rectangle waveguide between a high-index cylindrical dielectric waveguide and the substrate with coated graphene on the surface. The geometric dependence of the mode characteristics on the proposed structure is analyzed in detail, showing that the proposed GHPW has a low loss and consequently a relatively long propagation distance. For TM polarization, highly confined modes guided in the low-index gap region between the graphene and the high-index GaAs and the normalized modal area is as small as 0.0018 (λ2/4) at 3 THz. In addition to enabling the building of high-density integration of the proposed structure are examined by analyzing crosstalk in a directional coupler composed of two GHPWs. This structure also exhibits ultra-low crosstalk when a center-to-center separation between adjacent GHPWs is 32μm, which shows great promise for constructing various terahertz integrated devices.
© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Friday, April 20, 2018

Seminar Presentation:Terahertz Spectrum Measurement of Corrosion Products on Coated Steel Sheet Surface

Wednesday, 16 May 2018: 14:40
Room 304 (Washington State Convention Center)
R. Hasegawa, T. Kimura, T. Tanabe (Tohoku Univ.), K. Nishihara, A. Taniyama (Nippon Steel & Sumitomo Metal Co., Ltd.), and Y. Oyama (Tohoku Univ.)
Our research group has developed a terahertz light source with high luminance and broadband, and is developing research on non-destructive inspection technology. As a nondestructive inspection technology for hot-dip galvanized steel sheets, we have built a terahertz spectrum database for corrosion products that may exist there. In this research, we aim to newly obtain spectral data of β-FeOOH. Absorption Spectrum is shown in Figure.1. Optical system is shown in Figure.2. The terahertz wave was generated by difference frequency mixing using a GaP crystal which is a nonlinear optical crystal. The standard powder sample was diluted with polyethylene powder and pelletized, and it was measured at room temperature by a permeation method. As a result of spectroscopic measurement, an absorption peak was obtained around 3.06 THz. On the day of the presentation, in addition to discussions on attribution of peaks, report together with ATR-FTIR results.

Abstract- A Causal Channel Model for the Terahertz Band

Kazuhiro Tsujimura,  Kenta Umebayashi, Joonas Kokkoniemi,  Janne Lehtomäki,  Yasuo Suzuki

Impulse response is vital for wireless communication analysis and modeling. This paper considers the impulse response of the terahertz band (THz band: 0.1-10 THz) for short range (1-100 cm) wireless communication. Earlier works derived the impulse response from transmittance by assuming a linear phase, which corresponds to a line-of-sight (LoS) propagation delay to a receiver. However, the linear phase leads to a symmetric impulse response before and after the LoS propagation delay. Physically, it is impossible for a signal to arrive before the LoS propagation delay since this violates causality. To address this issue, this study derives a phase function leading to an impulse response that satisfies causality. The validity of the derived model is verified with experimental THz band measurements (up to 2 THz), which show excellent agreement with the results predicted by the theory. From the impulse response, coherence bandwidth is found for both the entire THz band and its subbands. The results show significant variations in the coherence bandwidth as a function of the center frequency. Knowledge of these variations supports selection of the proper center frequency for wireless communications in the THz band.

Abstract-Terahertz surface emission from layered semiconductor WSe2

Keyu Si, Yuanyuan Huang, Qiyi Zhao, Lipeng Zhu, Longhui Zhang, Zehan Yao, Xinlong Xu,

Ultrafast laser interaction with the layered semiconductors has attracted wide interest due to not only the fundamental physical understanding of the light-matter interaction in these advanced materials, but also the potential optoelectronic devices from visible region to THz region based on these emergent semiconductors. Herein, we investigated the THz radiation property from the layered WSe2 due to the d-d photo-transition by an ultrafast laser excitation. We observed strong broadband p-polarized THz radiation under different pump polarization and an evident THz radiation saturation with the pump fluence. The THz radiation demonstrated a cosine function with the polarization angle of the pump beam. Angular dependent THz radiation had a polarity reverse with the opposite incident angle and could be fitted well with a dipole approximation model. These results reveal that the dominant mechanism of THz emission is due to the photocarrier surging under the surface field. The azimuthal angle dependence of THz radiation suggested that the dominant contribution is due to the surface depletion field rather than surface field induced optical rectification. In addition, we inferred that the laser damage threshold for the WSe2 crystal is 3.11 mJ/cm2 confirmed by both THz emission spectroscopy and Raman Spectroscopy. Our results could provide the fundamental light-matter interaction data for the layered WSe2 and promise the potential applications of this semiconductor for THz devices.

Abstract-Terahertz generation from reduced graphene oxide

Huan Wang, Yixuan Zhou, , Zehan Yao, Lipeng Zhu, Yuanyuan Huang, Xinlong Xu, Zhaoyu Ren,

We firstly investigate the generation of terahertz (THz) wave from reduced graphene oxide (RGO) illuminated with femtosecond near-infrared laser pulse. Experiment results show that the THz generation from RGO can be enhanced by increasing the reduction degree and reducing the film thickness. The former can be attributed to the increase of sp2 carbon region, which has much smaller band gap and graphene-like photoelectric properties. The latter is due to the suppression of the light-induced lateral currents in the surface RGO layers. The linear dependency of the THz electrical field on the pump power confirms that the THz emission from RGO is governed by second-order nonlinear properties. When exciting laser irradiates from opposite sample sides, π phase shift of the generated THz wave has been observed, suggesting the transient photocurrent related to THz emission is induced by the photon drag effect. The conclusion has been further confirmed by the well fitting of the experiment and theoretical calculation based on the symmetry of RGO. This work makes it clear the THz generation mechanism of RGO and paves a way for developing new THz sources.