Abstract-A flexible, multifunctional, active terahertz modulator with an ultra-low triggering threshold

He Ma,   Yu Wang,   Rong Lu,   Fangrui Tan,  Yulan Fu,  Guang Wang,  Dayong Wang,  Kai Liu,   Shoushan Fan,  Kaili Jiang  Xinping Zhang 

https://pubs.rsc.org/en/content/articlelanding/2020/tc/d0tc02446e#!divAbstract

Active terahertz (THz) modulators play an essential role in THz technology. Because of the excellent THz modulation properties bestowed by its intrinsic metal-insulator transition (MIT) at 68 °C, vanadium dioxide (VO2) is an appealing active THz modulator material. Current active THz modulator designs based on pure VO2 films or metasurfaces deposited on traditional semiconductor substrates are typically subject to high triggering thresholds and slow responses. Therefore, further development of VO2 active THz modulators for superior performance requires new material and device designs. In this paper, we develop a flexible active THz modulator based on an aligned carbon nanotube thin film coated with VO2. THz wave modulation driven by the MIT of VO2 presents a giant modulation depth up to 91% and broad bandwidth (>2.3 THz). Various stimuli can be utilized to trigger the THz modulator. The response time of the THz modulator is 27 ms, which can be further shortened by decreasing the device size. In addition, the light-triggering threshold is quite low (0.58 mW/mm2). Optical anisotropy enables polarization of the THz modulator. Since they combine superior modulation performance, responsive stimuli diversity, versatility, and flexibility, these active THz modulators find applications in THz communication, THz imaging, etc.

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-Modulators for Terahertz Communication: The Current State of the Art

Z. T. Ma, Z. X. Geng, Z. Y. Fan3, J. Liu, H. D. Chen

https://spj.sciencemag.org/research/2019/6482975/

With the increase of communication frequency, terahertz (THz) communication technology has been an important research field; particularly the terahertz modulator is becoming one of the core devices in THz communication system. The modulation performance of a THz communication system depends on the characterization of THz modulator. THz modulators based on different principles and materials have been studied and developed. However, they are still on the way to practical application due to low modulation speed, narrow bandwidth, and insufficient modulation depth. Therefore, we review the research progress of THz modulator in recent years and evaluate devices critically and comprehensively. We focus on the working principles such as electric, optical, optoelectrical, thermal, magnetic, programmable metamaterials and nonlinear modulation methods for THz wave with semiconductors, metamaterials, and 2D materials (such as graphene, molybdenum disulfide, and tungsten disulfide). Furthermore, we propose a guiding rule to select appropriate materials and modulation methods for specific applications in THz communication.

Abstract-Deep Electrical Modulation of Terahertz Wave Based on Hybrid Metamaterial-Dielectric-Graphene Structure

Liangping Xia, Xin Zhang, Man Zhang, Suihu Dang, Shijian Huang, Yong Tan, Wenjuan Yan, Hong-Liang Cui

https://www.mdpi.com/2076-3417/9/3/507

A terahertz modulation structure based on hybrid metamaterial and graphene is proposed and demonstrated in this work. The metamaterial with a square slit ring array excites terahertz resonance in the slits and enhances the interaction between the terahertz wave and graphene. The graphene layer acting as the active material is tuned by the applied electrical field. With the separation by a dielectric layer between the graphene and the metallic structure, the resonant frequency and transmitted energy are both modulated by the graphene. Experimental result indicates that the modulation depth of the terahertz transmitted amplitude is 65.1% when the applied modulation voltage is tuned 5 V.

Abstract-Ultrafast THz modulators with WSe2 thin films [Invited]

Prashanth Gopalan, Ashish Chanana, Sriram Krishnamoorthy, Ajay Nahata, Michael A. Scarpulla, and Berardi Sensale-Rodriguez

Fig. 1 (a) XRD scans indicating highly crystalline WSe2 films showing only the (002) family of planes. (b) Raman mode at 251.2 cm−1, which agrees with reports in [24] for multilayer films. (c) UV-vis absorption measurements of WSe2 thin films indicating a strong excitonic absorption peak at ~740 nm. Based on this, optical excitation for OPTP and TRTS were chosen at 800 nm and 400 nm. (d) SEM image of WSe2 thin film shows grain size of ~1 µm.

https://www.osapublishing.org/ome/abstract.cfm?uri=ome-9-2-826

Tungsten diselenide (WSe2) thin films exhibit ultrafast carrier recombination lifetimes, which makes them promising candidates for high speed modulators. With pulsed optical excitation, they could be used to realize all-optical, frequency agile, terahertz devices. Looking into the potential of this material for such applications, time-resolved terahertz spectroscopy can provide significant insight into its free carrier and exciton dynamics such as recombination lifetimes, photo-induced conductivity and decay pathways. In this study, we measure transient terahertz conductivity and photo-generated carrier lifetimes in custom-grown large-area WSe2thin-films. We discuss its dependence on grain size and number of layers. By analyzing the tradeoffs between carrier-lifetimes, photo-generated conductivity, grain size, and the number of layers, we show that the response of these films can be tailored by controlling the growth parameters. Customizing the film terahertz response can enable large modulation without the need for integration with bulk semiconductors, as widely reported in the literature, thereby achieve high terahertz photoconductivity and high-speed operation. Across samples, our measurements show carrier decay timescale on the order ~10 to 100 ps and a transient conductivity that shows non-Drude behavior. This deviation from a Drude response is dominant within the first few picoseconds (<10 ps) before changing into a Drude like free-carrier response at longer delays. Based on our grown films, we experimentally demonstrate a metamaterial terahertz modulator with WSe2 as the only active element, attaining ~40% modulation depth.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Active multifunctional terahertz modulator based on plasmonic metasurface

Jie Ji, Siyan Zhou, Weijun Wang, Chunya Luo, Yong Liu, Furi Ling, and Jianquan Yao

Fig. 1 (a) The schematic of an efficient light modulator based on a frequency-selective tunable terahertz metasurface. The sample size was 15 mm*15mm. (b) the OM image of the sample when the photo-resist was lift off. (c) Geometry of the unit-cell of the metasurface with parameters: L1 = 120 um, L2 = 80 um, h1 = 30 um, h2 = 25 um, a = 30 um, g = w = 5um. Metal thickness for the metasurface: d = 100 nm (5 nm Ti + 95 nm Al).

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-27-3-2363&id=404331

An active multifunctional terahertz modulator based on plasmon-induced transparency (PIT) metasurface under the effect of external infrared light was investigated theoretically and experimentally. A distinct transparency window, which resulted from the near-field coupling between two resonators, could be observed in the transmission spectra. Experimental results showed a phenomenon infrared light induced blue shift on the both resonator with increasing optical powers. When the optical power was tuned from 0 mW to 400 mW, the amplitude tunability of transmission at transparency window reached to 34.01%, much larger than that at the two resonance frequencies. Moreover, the phase tunability of the transmission at 0.98 THz reached to 31.35%. Meanwhile, the amplitude variation was limited to 10%. Furthermore, a coupled Lorentz oscillator model was adopted to analyze the near-field interaction of the resonances. Experimental results were in good agreement with the analytical fitting results.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Terahertz modulator a using CsPbBr3 perovskite quantum dots heterostructure

• Li Shao-he, 
• Li Jiu-sheng
• 
  
• https://link.springer.com/article/10.1007/s00340-018-7094-7

A novel terahertz wave modulator based on CsPbBr3 perovskite quantum dots heterostructure is proposed. An external modulated 450 nm pumping laser is utilized to generate photoexcited free carriers at the CsPbBr3 perovskite quantum dots heterostructure medium. We measured an amplitude modulation of the terahertz transmission in the frequency range from 0.23 to 0.35 THz with various laser intensity irradiances. In addition, dynamic amplitude modulation at 0.27 THz carrier wave show that the modulator provides a modulation speed of 2.5 MHz at a external pump laser irradiance of 2.0 W/cm2. Our CsPbBr3 perovskite quantum dots heterostructure can high speed modulation and can be used for terahertz modulation in addition to photovoltaics application

Abstract- Terahertz Modulator Using 4-N,N-Dimethylamino-4′-N′-Methyl-Stilbazolium Tosylate (DAST)/Si Hybrid Structure

Li Jiu-sheng, Li Shao-he, Zhang Le,

(a) The image of the prepared DAST-Si sample, (b) Scanning microscope images of DAST film surface, (c) Raman spectra of the prepared DAST film, and (d) X-ray diffraction spectrum of the DAST film

https://ieeexplore.ieee.org/document/8306983/

Terahertz high-data communication creates numerous demands for terahertz wave amplitude modulation. Here, we experimentally demonstrate a high-speed terahertz wave modulator based on 4-N,N-dimethylamino-4'-N'-methyl-stilbazolium tosylate (DAST)/Si hybrid structure. An externally modulated 808-nm pumping laser is utilized to generate photoexcited free carriers at the DAST medium. With the increase of illumination laser intensity, the modulation depth continues to increase in the frequency range from 0.23 to 0.35 THz. A dynamic amplitude modulation at 0.25-THz carrier wave shows that the our modulator provides a modulation speed of 1.26 MHz with a depth of up to 53% at an external pump laser irradiance of 3.5 W/cm2. Our present DAST/Si hybrid structure provides a practicable route to achieve effective signal modulation for terahertz communication system.

Abstract-Single-walled carbon nanotubes assisted THz silicon grating modulator

Yang Liu, Tianxiang Zhu, Jijun Feng, Shuai Yuan, Xinluo Zhao, Tengfei Wu, and Heping Zeng

https://www.blogger.com/blogger.g?blogID=124073320791841682#editor/target=post;postID=6457046985648642545

Single-walled carbon nanotubes (SWCNTs) are applied to realize an enhanced frequency modulation for a suspended THz silicon grating, which is fabricated by a nanosecond laser direct writing and coated with the synthetic SWCNTs/polyacrylic emulsion composite. With terahertz time domain spectroscopy system, the transmission spectra of the bare and SWCNTs coated silicon grating are measured and compared. The SWCNTs coated silicon grating can realize an improved extinction ratio and quality factor, which is due to the SWCNTs caused local field enhancement and can be explained by the theoretical simulation with finite element method. Besides the effective modulation of the grating transmittance, SWCNTs can also be integrated with other platforms and applied in future THz imaging and communication systems.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-An active optically controlled broadband terahertz modulator based on Fe3O4 nano-particles

Luyao Xiong, Bo Zhang, Hongyu Ji, Wei Wang, Xin Liu, and Jing L. Shen

https://www.osapublishing.org/abstract.cfm?uri=ISUPTW-2018-TuK34

We report an active easily fabricated broadband terahertz modulator based on Fe3O4 nano-particles/Si structure,for which as high as 92% modulation depth was achieved at an external excitation laser of 3.6 W/cm2.

© 2018 OSA

Abstract-Electrical terahertz modulator based on photo-excited ferroelectric superlattice

Jie Ji, Siyan Zhou, Jingcheng Zhang, Furi Ling,  Jianquan Yao,

https://www.nature.com/articles/s41598-018-21095-5

The transmission and dielectric spectra of ferroelectric STO/PT superlattice on Si substrate under simultaneous external optical and electric field were investigated and compared at room temperature. Results found that when with an optical field, the electric field realized an effective modulation on the transmission, which displayed a diode property. In addition, a comprehensive model combined with Debye relaxation and Lorentz model was used to analyze the dielectric spectra, variation of the soft mode with external field was put emphasis on exploring.

Abstract-A Tunable Eight-Wavelength Terahertz Modulator Based on Photonic Crystals

K. Ji, H. Chen, W. Zhou, Y. Zhuang, J. Wang

https://link.springer.com/article/10.1007%2Fs10812-017-0551-y


We propose a tunable eight-wavelength terahertz modulator based on a structure of triple triangular lattice photonic crystals by using photonic crystals in the terahertz regime. The triple triangular lattice was formed by nesting circular, square, and triangular dielectric cylinders. Three square point defects were introduced into the perfect photonic crystal to produce eight defect modes. GaAs was used as the point defects to realize tunability. We used a structure with a reflecting barrier to achieve modulation at high transmission rate. The insertion loss and extinction ratio were 0.122 and 38.54 dB, respectively. The modulation rate was 0.788 dB. The performance of the eightwavelength terahertz modulator showed great potential for use in future terahertz communication systems.

Abstract-Optical Controlled Terahertz Modulator Based on Tungsten Disulfide Nanosheet

• Zhiyuan Fan, 
• Zhaoxin Geng, 
• Xiaoqin Lv, 
• Yue Su, 
• Yuping Yang, 
• Jian Liu & 
• Hongda Chen

https://www.nature.com/articles/s41598-017-13864-5?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+srep%2Frss%2Fcurrent+%28Scientific+Reports%29

The terahertz (THz) modulator, which will be applied in next-generation wireless communication, is a key device in a THz communication system. Current THz modulators based on traditional semiconductors and metamaterials have limited modulation depth or modulation range. Therefore, a THz modulator based on annealed tungsten disulfide (WS2, p-type) and high-resistivity silicon (n-type) is demonstrated. Pumped by a laser, the modulator presents a laser power-dependent modulation effect. Ranging from 0.25 to 2 THz, the modulation depth reaches 99% when the pumping laser is 2.59 W/cm2. The modulator works because the p-n heterojunction can separate and limit carriers to change the conductivity of the device, which results in a modulation of the THz wave. The wide band gap of WS2 can promote the separation and limitation of carriers to obtain a larger modulation depth, which provides a new direction for choosing new materials and new structures to fabricate a better THz modulator.

Abstract-Optically controlled terahertz modulator by liquid-exfoliated multilayer WS2 nanosheets

                                                               

Dong-Sheng Yang, Tian Jiang, and Xiang-Ai Cheng

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-14-16364

Lack of efficient routes to modulate the propagation properties of the terahertz (THz) wave is a major barrier for the further development of THz technology. In recent years, two dimensional transition metal dichalcogenides (2D TMDCs) were applied to the design of effective THz modulator by forming heterostructure with Si. Here, we experimentally demonstrate an optical controlled THz modulator consisting of liquid-exfoliated WS2 nanosheets and a silicon substrate (WS2-Si). By innovatively depositing liquid-exfoliated WS2 nanosheets on the Si instead of growing by chemical vapor deposition (CVD) method, both of the size and the thickness of WS2 film is controlled. The WS2-Si sample presents a flat modulation depth from 0.2 THz to 1.6 THz. The modulation depth reaches 56.7% under a 50 mW pumping power, which is over 5 times enhanced compared with that of the Si substrate. With the increase of illumination power, the modulation depth continues to increase, finally reaching up to 94.8% under 470 mW. Besides, the WS2-Si sample also achieves ~80% modulation depth under 450 nm illumination, indicating its ability to operate under either of wavelength in visible spectra. Moreover, we compare the sample to the reported modulators including CVD growth TMDCs-Si ones and find our sample has comparable modulation effects while is much easy to be prepared. Therefore, we believe our work is meaningful to provide an alternative route to achieve effective modulation of THz waves by adopting liquid-exfoliated 2D materials.

© 2017 Optical Society of Americahttps://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-14-16364

US Patent Application and Abstract-Terahertz modulator based on low-dimension electron plasma wave and manufacturing method thereof

USPTO Applicaton #: #20170108756 
Inventors: Yongdan Huang, Hua Qin, Zhipeng Zhang, Yao Yu

http://www.freshpatents.com/-dt20170420ptan20170108756.php

A terahertz modulator based on low-dimension electron plasma wave, a manufacturing method thereof, and a high speed modulation method are provided. The terahertz modulator includes a plasmon and a cavity. The present disclosure discloses the resonance absorption mechanism caused by collective oscillation of electrons (plasma wave, namely, the plasmon). In order to enhance the coupling strength between the terahertz wave and the plasmon, a GaN/AlGaN high electron mobility transistor structure having a grating gate is integrated in a terahertz Fabry-Pérot cavity, and a plasmon polariton is formed arising from strong coupling of the plasmon and a cavity mode.

Abstract-Terahertz broadband modulation in a biased BiFeO3/Si heterojunction

Xiankuan Liu, Zeyu Zhang, Xian Lin, Kailin Zhang, Zuanming Jin, Zhenxiang Cheng, and Guohong Ma

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-23-26618

A new terahertz (THz) modulator based on bias-driven carrier conductivity change in a heterojunction was proposed. BiFeO3 film and silicon were selected as building blocks for fabricating the THz modulator. THz nonlinear transmission as a function of bias voltage was studied systematically. THz peak transmission as a function of bias shows a similar tendency as the current-voltage response of the heterojunction: the forward bias leads to the exponential enhancement of THz transmission, and in contrast, the reverse bias shows no observable changes in THz transmission. The modulation depth and modulation bandwidth of THz pulse can reach up to 42% and 1.0 THz with forward bias of 4.8 V, respectively. The observed bias dependent THz transmission in the BFO/Si heterojunction is well-interpreted by the proposed model: the diffused carriers across the heterojunction are localized in BFO thin film with applied forward bias. Our finding provides great potential for applications in designing all electrical broadband THz modulators.

© 2016 Optical Society of America

Full Article  |  PDF Article

Enhanced optical modulation depth of terahertz waves

http://materialsviews.com/enhanced-optical-modulation-depth-of-terahertz-waves/

The terahertz region of the electromagnetic spectrum (covering ~0.1 – 10 THz corresponding to wavelengths from 3 mm to 30 mm) is a hotbed of scientific and technological activity based, in part, on the unique attributes of radiation at these frequencies. This includes spectroscopic imaging with sufficient spectral and spatial resolution through materials that are opaque at other spectral ranges (e.g. microwave, infrared, or visible) and the promise of short-range high-bit-rate data transfer far beyond existing modalities. To advance beyond demonstration towards low-cost real-world applications requires continued development of devices such as modulators and phase shifters to adeptly control terahertz waves. Indeed, groups around the globe are exploring novel device concepts using metamaterials and plasmonics.

Along these lines, a particularly intriguing terahertz modulator has been created by Dr. Tianlong Wen, Prof. Qiye Wen and their colleagues. They report on a broadband optically-controlled silicon modulator with impressive amplitude modulation accomplished by depositing a single monolayer of gold nanoparticles on the silicon surface. Crucially, the plasmon resonance of the gold nanoparticles strongly enhances carrier generation in the insulating silicon substrate upon optical excitation. This is important because insulating silicon is transparent to THz radiation (modulo Fresnel reflection losses). With sufficient carrier excitation the reflectivity of the silicon increases, leading to a corresponding decrease in the transmission and thereby modulating the THz beam. The plasmonic layer leads to a dramatic improvement of the modulation depth: for 100 mW of incident optical power, the absolute transmission only changes by ~3% for the bare silicon device in comparison to nearly 30% for the device with a plasmonic layer for an order-of-magnitude improvement. Further, in this elegant approach the THz beam is “blind” to the gold nanoparticle layer, meaning that there is no additional insertion loss.

These results represent an interesting example of a multiscale device where an important performance metric is fruitfully augmented using nanoscience. It will be interesting to follow subsequent developments of this idea to see if the incident optical power could be further reduced to achieve a given modulation amplitude. One could also envision, for example, using metamaterials resonant at THz frequencies in conjunction with gold plasmonic particles to further optimize the modulation response.

Abstract-Optically tuned terahertz modulator based on annealed multilayer MoS2

• Yapeng Cao
• , Sheng Gan
• , Zhaoxin Geng
• , Jian Liu
• , Yuping Yang
• , Qiaoling Bao
•  & Hongda Chen

• Scientific Reports 6, Article number: 22899 
• http://www.nature.com/articles/srep22899

Controlling the propagation properties of terahertz waves is very important in terahertz technologies applied in high-speed communication. Therefore a new-type optically tuned terahertz modulator based on multilayer-MoS2 and silicon is experimentally demonstrated. The terahertz transmission could be significantly modulated by changing the power of the pumping laser. With an annealing treatment as a p-doping method, MoS2 on silicon demonstrates a triple enhancement of terahertz modulation depth compared with the bare silicon. This MoS2-based device even exhibited much higher modulation efficiency than the graphene-based device. We also analyzed the mechanism of the modulation enhancement originated from annealed MoS2, and found that it is different from that of graphene-based device. The unique optical modulating properties of the device exhibit tremendous promise for applications in terahertz switch.

Abstract-Flexible terahertz modulator based on coplanar-gate graphene field-effect transistor structure

Jingbo Liu, Pingjian Li, Yuanfu Chen, Xinbo Song, Qi Mao, Yang Wu, Fei Qi, Binjie Zheng, Jiarui He, Hyunsoo Yang, Qiye Wen, and Wanli Zhang

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-41-4-816

The terahertz (THz) modulators, as an essential component of the THz system, have been developed by many efforts until now. However, the development of flexible THz modulators is hindered due to the lack of flexible THz modulating materials. Herein, for the first time to the best of our knowledge, we demonstrated the feasibility of flexible THz modulators based on the coplanar-gate field-effect transistor (FET) structure of ion-gel/graphene/polyethylene terephthalate. The THz transmittance through this THz graphene modulator can be well controlled with a modulation depth up to 22% by tuning the carrier concentration of graphene via electrical gating. Furthermore, because of the integration of high flexibilities of graphene, ion-gel, and polyethylene terephthalate (PET), the proposed THz graphene modulator shows superior flexible performance, where the modulation properties can be maintained almost unchanged, not only under bending deformations, but also before and after bending 1000 times. In addition, due to the unique structure of ion-gel/graphene/PET, the flexible THz graphene modulator has a low insertion loss (1.2 dB). Therefore, this Letter is expected to be beneficial for the potential applications, ranging from the traditional compact THz system to a new flexible THz technology.

© 2016 Optical Society of America

Full Article  |  PDF Article

Abstract-High speed optical modulation of terahertz waves using annealed silicon wafer

Tao Li   Dongxiao Yang   Jian Wang 
http://www.opticsjournal.net/abstract.htm?id=OJ140723000031C0FbIe

Modulation properties of terahertz waves going through a light excited high resistivity silicon wafer are analyzed and measured. Free carrier lifetime of the silicon wafer affects the modulation depth and speed of the terahertz wave. The lifetime is reduced to less than 1 μs by thermal processing for high speed modulation. Experimental results show that the response time and modulation depth of the proposed modulating structure are close to 1 μs and 51%, respectively.