Friday, September 10, 2021

Abstract-Interdigitated photoconductive terahertz antenna for future wireless communications


Vaisshale Rathinasamy, Rama Rao Thipparaju, Nisha Flora Boby Edwin, Shyamal Mondal,

Recently, the technology buzz on utilization of terahertz (THz) technology in beyond 5G and 6G communication is growing due to the demands for large network capacity, bandwidth, and ultrahigh data rates. The THz frequencies are prudent for short-range future wireless communication systems as they provide extraordinary channel capacity with data rates from few Gb/s to Tb/s due to its ultra-wide spectrum bandwidth. However, there exists many challenges in designing devices that operate under THz frequencies. The photo-conductive antenna (PCA) is one of the crucial components that support realization of ultrafast wireless THz communications. In this paper, investigations on photoconductive antennas with interdigitated electrodes (IDEs) have been presented for THz communications with an equivalent circuit model for IPCA with corresponding solved expressions. The results show that the maximum THz field strength of 4.41 × 105 V/m is achievable by a 10 μm interdigitated teeth length IPCA with larger spectrum bandwidth of about ~8 THz. The antenna module makes the possibility of miniaturization of the THz sources and detectors for the emerging variety of wireless THz applications.

Thursday, September 9, 2021

Abstract-Characterizing the Layer Structures of the Lacquerware From the Palace Museum by Terahertz Imaging in Reflection Geometry


Hongfei Zhang, Yuanmeng Zhao, Chenyu Li, Cunlin Zhang

Chinese lacquerware is an important invention of arts and crafts in China. In this study, Chinese lacquerware is characterized using terahertz reflectometric imaging. The lacquerware studied herein comprises an ornamental wood panel covered by multiple layers of lacquers to portray motifs. For characterizing lacquerware, a terahertz time-domain spectroscopic reflectometric imaging system is proposed. The role of the proposed terahertz imaging system in highlighting the interface between layers during stratigraphic buildup in reflection geometry is proved. The proposed system provides a universal method for assessing the structural information of lacquered objects in a contactless and non-invasive manner; moreover, it provides two-dimensional images, subsurface three-dimensional images, and stratigraphic images (b-scans) in a contactless and non-invasive manner. Using the proposed system, we examine the buried layers of the lacquerware, including faults in the wooden layer and damages in the lacquerware. Research shows the promising prospects of terahertz time-domain spectroscopic reflectometric imaging as a non-destructive detection technique suited to lacquerware.

Wednesday, September 8, 2021

Abstract-Multiple interference theoretical model for graphene metamaterial-based tunable broadband terahertz linear polarization converter design and optimization


Rong Lin, Fake Lu, Xiaoliang He, Zhilong Jiang, Cheng Liu, Shouyu Wang, and Yan Kong

(a) Design of the graphene metamaterial-based tunable broadband THz linear polarization converter: (a1) Structure, and (a2) Period details; (b), (c) and (d) Period structures of different graphene metamaterial-based tunable broadband THz linear polarization converter designs and their polarization conversion performances: (1) Period structures, (2) Amplitude and (3) PCR.

Terahertz (THz) polarization converters often working as modulators and switches have many applications in THz sensing, imaging and communication, but many of them still suffer from low polarization conversion efficiency, fixed and narrow polarization conversion band, and low output polarization purity, which are mainly due to the lack of theoretical model for THz polarization converter design and optimization. In order to solve the problem, we adopt multiple interference theory to successfully design and optimize a graphene metamaterial-based tunable broadband THz linear polarization converter: it achieves polarization conversion ratio (PCR) over 0.97, polarization azimuth angle of almost ±90° and rather low ellipticity within a broad polarization conversion band of 1.25 THz; and additionally, its polarization conversion band can be actively tuned by adjusting the graphene chemical potential and almost insensitive to the incident THz radiation angle below 50°. Considering the high performance of the optimal graphene metamaterial-based tunable broadband THz linear polarization converter, this work provides an optimal design offering a way in high-quality manipulation of THz radiation polarization; but more importantly, delivers a theoretical model for tunable THz polarization converter design and optimization.

© 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Tuesday, September 7, 2021

Abstract-Terahertz photoconductive antenna based on antireflection dielectric metasurfaces with embedded plasmonic nanodisks


Xiao-Qiang Jiang, Wen-Hui Fan, Chao Song, Xu Chen, and Qi Wu

By taking advantage of dielectric metasurfaces and plasmonic nanostructures, a terahertz photoconductive antenna (THz-PCA) is proposed and investigated in detail. The designed dielectric metasurfaces can reduce the optical reflection down to 1.4% and accelerate the switching process (electric conductive to resistive) that broadens the THz spectrum emitted from THz-PCA. Simultaneously, the embedded plasmonic nanostructures can realize 11.2 times enhancement in local electric field without affecting the switching process and the damage threshold of the THz-PCA. Simulated results indicate that the proposed THz-PCA is 70.56 times stronger in THz radiation power than that of the traditional THz-PCA. The significant enhancement ensures the proposed THz-PCA has great prospects in promoting THz technology based on the THz-PCA.

© 2021 Optical Society of America

Monday, September 6, 2021

Abstract-A study of plant growth regulators detection based on terahertz time-domain spectroscopy and density functional theory


Xiaoxue Du, Yafei Wang, Xiaodong Zhang, Guoxin Ma, Yong Liu, Bin Wang,  Hanping Mao

Terahertz technology is receiving increasing attention for its use as an efficient non-destructive, non-contact and label-free optical method for qualitative and quantitative detection. The aim of this study was to develop a chemical analysis methodology based on terahertz time-domain spectra that could be used to detect plant growth regulators, such as glyphosine, naphthaleneacetic acid, daminozide and gibberellic acid. The THz fingerprint spectra of these four PGRs were located in the 0.3–1.8 THz, with the peaks of glyphosine at 0.32, 0.49, 0.74, 0.87, 0.96, and 1.49 THz; daminozide at 0.33, 0.39, 0.55, 0.67, and 1.17 THz; gibberellic acid at 0.46, 0.58, 0.92, and 1.38 THz and naphthaleneacetic acid at 0.43, 0.57, 0.73, and 0.90 THz. The results showed that these four plant growth regulators exhibited numerous distinct spectral features in frequency-dependent absorption spectra, which demonstrated the qualitative capacity of terahertz time-domain. The origin of the observed terahertz absorption peaks of these four plant growth regulators was determined through density functional theory calculations and analysis of absorption spectra. Discriminant analysis method was used to evaluate the classification trends of the four plant growth regulators based on their THz absorbance spectra. Generally, this study provides a reference for the rapid detection of plant growth regulators in fruits and vegetables by using terahertz spectroscopy technology.

Sunday, September 5, 2021

Abstract-Sub-terahertz photonic frequency divider with a large division ratio based on phase locking


Daming Han, Wei Wei, Zhangweiyi Liu, Weilin Xie, and Yi Dong

We present a photonic frequency divider with a large division ratio for microwave signals up to sub-terahertz. A high-operating frequency and a large frequency division ratio have both been achieved by phase-locking a Fabry–Perot frequency comb to the input signal that is to be divided. The input signals ranging from 50.10 GHz to 200.10 GHz are all divided to 2.5 GHz signals, which can be further divided into lower- frequency signals easily. The proposed divider is free of high-speed electrical devices, thanks to the intermediate-frequency detection and feedback control in the phase locking process. Moreover, the phase noise caused by the photonic frequency division is negligible at low offset frequencies, proving that the divider has superior long-term stability. This flexible, cost-efficient, and stable photonic frequency divider is an ideal candidate for frequency division at the remote end of a high-precision frequency transfer system.

© 2021 Optical Society of America