Abstract-Flexible terahertz modulators based on graphene FET with organic high-k dielectric layer

Yu-Lian He, Jing-Bo Liu, Tian-Long Wen, Qing-Hui Yang, Zheng Feng, Wei Tan, Xue-Song Li, Qi-Ye Wen, Huai-Wu Zhang

https://iopscience.iop.org/article/10.1088/2053-1591/aadeca

Graphene field-effect-transistor (GFET) based terahertz (THz) modulators usually possess an unfulfilling modulation depth (MD) of 15% ~ 20%. In this work we developed a flexible GFET based THz modulator, where the graphene monolayer is coated with an organic high-K dielectric as the screening layer and an ion-gel layer as the gate. With this exquisite composite modulating structure, the new device possesses a significantly enhanced modulation depth (MD) up to 70% over a broad frequency band, an extremely low insert loss (IL) of 1.3 dB, and unexpected good structural and properties stability. The large intrinsic MD, low IL, as well as its flexibility, render this performance enhanced modulator versatile in fabrication of novel THz devices, such as multi-level modulator, for nonplanar or wearable applications.

Abstract-Semiconductor terahertz spatial modulators with high modulation depth and resolution for imaging applications

Tianlong Wen, Jing Tong, Dai-nan Zhang, Yunqiao Zhu, Qi-Ye Wen, Yuanpeng Li, Huai-Wu Zhang, Yu-Lan Jing,  Zhi-Yong Zhong

https://iopscience.iop.org/article/10.1088/1361-6463/ab146d/pdf

Spatial modulation of terahertz wave enabled by the charge carrier generation-recombination dynamics in semiconductor is promising for terahertz compressive sensing imaging since the modulation is broadband, low-loss and of enough speed (tens of thousands of Hertz). However their performance in terahertz compressive sensing imaging is significantly limited by their inferior modulation depth and resolution. Here silicon was cut into small pieces and packed closely in arrays to shut off the charge carrier diffusion between them and increase the resolution of the terahertz spatial modulator. A monolayer of gold nanoparticles was coated on the silicon surface to enhance the terahertz modulation depth through the enhanced generation of charge carriers by surface plasma. By comparison test, it is found that the gold nanoparticle coated small silicon arrays have improved contrast and resolution for terahertz imaging over the uncoated and coated large pieces of silicon respectively.

Abstract-Terahertz Modulators Based on Silicon Nanotip Array

Zhong-Wei Shi,Xing-Xing Cao,Qi-Ye Wen, Tian-Long Wen, Qing-Hui Yang, Zhi Chen, Wen-Sheng Shi, Huai-Wu Zhang.

http://onlinelibrary.wiley.com/doi/10.1002/adom.201700620/full

As an attractive applications of terahertz (THz) radiation, imaging with THz technique stands at the focus of current interest. THz spatial modulators are key issue for fast imaging with a single detector. Here, for the first time, the silicon nanotip (SiNT) arrays are reported that can be utilized as antireflection layers for the THz wave to achieve a low-loss and spectrally broadband optical-driven THz modulator. Compared with the modulator fabricated with bare silicon, a 2–3-time larger modulation depth is achieved in SiNT modulator. Moreover, it is found that the intrinsic THz transmission of SiNT is as high as 90%, which is much higher than that of bare silicon. The theoretical simulation results reveal that a strong antireflection effect induced from SiNT layer plays a crucial role in enhancing the properties of modulator. The SiNT-based optical-driven THz modulator with low loss and high modulation depth is promising for potential application to THz imaging.

Abstract-A novel method to measure dielectric properties of materials in terahertz spectroscopy

• Wei-en Lai^, , 
• Huai-wu Zhang, 
• Yao-hua Zhu, 
• Qi-ye Wen

• State Key Laboratory of Electronic Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China
• 
  
• http://www.sciencedirect.com/science/article/pii/S0030402613000922

We present a simple method to obtain the optical and dielectric properties of samples without reference measurement in the reflection-type terahertz time-domain spectroscopy. The dielectric properties of the samples of silicon and gallium arsenide were examined. The optical and dielectric properties of the samples were measured through only simple configuration, without the misplacement error. The obtained dielectric functions of the samples in reflection geometry are in good agreement with that predicated by the theory. The main advantage of this method over other methods is its simplicity and accuracy and ease for application of the reflection systems with different incident angle.

Abstract-Broadband diffusion of terahertz waves by multi-bit coding metasurfaces

Li-Hua Gao¹, Qiang Cheng^1,2, Jing Yang³, Shao-Jie Ma⁴, Jie Zhao¹, Shuo Liu¹, Hai-Bing Chen¹, Qiong He⁴, Wei-Xiang Jiang^1,2, Hui-Feng Ma^1,2, Qi-Ye Wen^2,5, Lan-Ju Liang^6,7, Biao-Bing Jin^2,6, Wei-Wei Liu^2,3, Lei Zhou⁴, Jian-Quan Yao⁷, Pei-Heng Wu⁶ and Tie-Jun Cui^1,2

1. ¹State Key Laboratory of Millimeter Waves, Department of Radio Engineering, Southeast University, Nanjing 210096, China
2. ²Cooperative Innovation Centre of Terahertz Science, No. 4, Section 2, North Jianshe Road, Chengdu 610054, China
3. ³Institute of Modern Optics, Key Laboratory of Optical Information Science and Technology (Ministry of Education), Nankai University, Tianjin 300071, China
4. ⁴State Key Laboratory of Surface Physics, Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Department of Physics, Fudan University, Shanghai 200433, China
5. ⁵State Key Laboratory of Electronic Films and Integrated Devices, University of Electronic Science and Technology, Chengdu 610054, China
6. ⁶Research Institute of Superconductor Electronics (RISE), School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China
7. ⁷Institute of Lasers and Optoelectronics, College of Precision Instrument and Opto-Electronics Engineering, Tianjin University, Tianjin 300072, China

Correspondence: Q Cheng, Email: qiangcheng@seu.edu.cn; TJ Cui, Email: tjcui@seu.edu.cn

Received 16 January 2015; Revised 23 April 2015; Accepted 26 April 2015

http://www.nature.com/lsa/journal/v4/n9/full/lsa201597a.html

The terahertz region is a special region of the electromagnetic spectrum that incorporates the advantages of both microwaves and infrared light waves. In the past decade, metamaterials with effective medium parameters or gradient phases have been studied to control terahertz waves and realize functional devices. Here, we present a new approach to manipulate terahertz waves by using coding metasurfaces that are composed of digital coding elements. We propose a general coding unit based on a Minkowski closed-loop particle that is capable of generating 1-bit coding (with two phase states of 0 and 180°), 2-bit coding (with four phase states of 0, 90°, 180°, and 270°), and multi-bit coding elements in the terahertz frequencies by using different geometric scales. We show that multi-bit coding metasurfaces have strong abilities to control terahertz waves by designing-specific coding sequences. As an application, we demonstrate a new scattering strategy of terahertz waves—broadband and wide-angle diffusion—using a 2-bit coding metasurface with a special coding design and verify it by both numerical simulations and experiments. The presented method opens a new route to reducing the scattering of terahertz waves.

Abstract-High-speed and broadband terahertz wave modulators based on large-area graphene field-effect transistors

Qi Mao, Qi-Ye Wen, Wei Tian, Tian-Long Wen, Zhi Chen, Qing-Hui Yang, and Huai-Wu Zhang  »View Authors http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-39-19-5649 Optics Letters, Vol. 39, Issue 19, pp. 5649-5652 (2014) http://dx.doi.org/10.1364/OL.39.005649

We present a broadband terahertz wave modulator with improved modulation depth and switch speed by cautiously selecting the gate dielectric materials in a large-area graphene-based field-effect transistor (GFET). An ultrathin Al2O3film (∼60  nm) is deposited by an atomic-layer-deposition technique as a high-k gate dielectric layer, which reduces the Coulomb impurity scattering and cavity effect, and thus greatly improves the modulation performance. Our modulator has achieved a modulation depth of 22% and modulation speed of 170 kHz in a frequency range from 0.4 to 1.5 THz, which is a large improvement in comparison to its predecessor of SiO2-based GFET.

© 2014 Optical Society of America

Abstract-High-speed and broadband terahertz wave modulators based on large-area graphene field-effect transistors

Qi Mao, Qi-Ye Wen, Wei Tian, Tian-Long Wen, Zhi Chen, Qing-Hui Yang, and Huai-Wu Zhang  »View Author Affiliations

http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-39-19-5649

Optics Letters, Vol. 39, Issue 19, pp. 5649-5652 (2014)

We present a broadband terahertz wave modulator with improved modulation depth and switch speed by cautiously selecting the gate dielectric materials in a large-area graphene-based field-effect transistor (GFET). An ultrathin Al2O3film (∼60  nm) is deposited by an atomic-layer-deposition technique as a high-k gate dielectric layer, which reduces the Coulomb impurity scattering and cavity effect, and thus greatly improves the modulation performance. Our modulator has achieved a modulation depth of 22% and modulation speed of 170 kHz in a frequency range from 0.4 to 1.5 THz, which is a large improvement in comparison to its predecessor of SiO2-based GFET.

© 2014 Optical Society of America