Abstract-Tunable terahertz hybrid graphene-metal patterns metamaterials

Chenyuyi Shi, Xiaoyong He, Jun Peng, Guina Xiao, Feng Liu, Fangting Lin, Hao Zhang,



https://www.sciencedirect.com/science/article/pii/S0030399218317250

Based on the hybrid metal-graphene structures, we investigated the tunable Fano resonances in the terahertz region, including the effects of graphene Fermi levels, structural parameters, and operation frequencies. The results reveal that an obvious Fano resonance can be observed, the maximum peak value of Fano resonance can reach 0.9711, and its Q-quality factor is more about 20. With the help of the graphene layer, the resonant curves of the proposed structures can be effectively modulated, the frequency modulation depth can reach 60% as the Fermi level changes in the range of 0.1–1.0 eV. In addition, by varying the length of graphene bar in the scope of 10–60 μm, the amplitude modulation depths are about 21.0%. The results are helpful for designing novel graphene-based tunable terahertz devices with high Q factor, e.g. modulators, sensors and antenna.

Abstract-A polarization-insensitive broadband terahertz absorber with a multilayer structure

Hai-Feng Zhang, Jia-Xuan Liu, Jing Yang, Hao Zhang,Hai-Ming Li,


https://www.sciencedirect.com/science/article/pii/S2211379718324306

In this paper, a polarization-insensitive broadband terahertz absorber (PBTA) is presented and demonstrated, which can realize a polarization-insensitive, and broadband perfect absorption in the terahertz regime. By simulation, the polarization-insensitive broadband absorption is over 90%, which runs from 4.904THz to 6.632THz (the relative bandwidth is 29.96%), and the obtained absorption remains a good absorption performance with a wide incident angle for both TE and TM waves. The surface current distributions, power loss densities, electric and magnetic field distributions of such an absorber are investigated to figure out the physical mechanism of such a PBTA. The effects structure parameters on the absorption performance are also studied, which will be a guiding to realize a PBTA. The simulated results show that the proposed multilayer structure can help to design a PBTA.

Abstract-Investigation of graphene-supported tunable asymmetric terahertz metamaterials

Chenyuyi Shi, Xiaoyong He, Feng Liu, Fangting Lin, and Hao Zhang

https://www.osapublishing.org/josab/abstract.cfm?uri=josab-35-3-575

By integrating a graphene layer with asymmetric split-ring metamaterial (MM) metal resonators, we investigated tunable propagation properties in the terahertz regime, including the effects of graphene Fermi levels, structural parameters, and operation frequencies. The results reveal that a sharp inductor-capacitor (LC) resonance can be observed at low frequency for the asymmetric MM structure, and its 𝑄$Q$ factor can reach more than 17.5. With the help of a graphene layer, the optical response is modulated efficiently. For instance, if the Fermi level changes in the range of 0.01–0.3 eV, for the semiconductor MM structure, the modulation depths (MDs) of amplitude and frequency are 27.0% and 43.4%, respectively. In addition, the resonant curves of indium antimonide (InSb) MMs can be modulated by changing the temperature; the amplitude MD is 56.2% as the temperature changes in the range of 350–800 K. The 𝑄$Q$ factor of the InSb MM structure is about 44.6. The results are helpful for designing novel graphene-based tunable terahertz devices, e.g., filters and modulators.

© 2018 Optical Society of America

Abstract-Theoretical Evaluation on Terahertz Source Generator from Ternary Metal Chalcogenides of PbM6Te10 (M = Ga, In)

Wendan Cheng, Chen-Sheng Lin, Hao Zhang, Guo-Liang Chai,

https://pubs.acs.org/doi/abs/10.1021/acs.jpcc.7b10972?journalCode=jpccck

We develop a new method to calculate nonlinear optical susceptibility, and give a definition of the extended figure of merit (EFOM) contributing from optical susceptibility, refractive index and absorptions to evaluate the material intrinsic property. The calculated phonon frequency determines the infrared absorption coefficient and transparent cutoff edge. We calculate the conversion efficiencies of terahertz source generating from chalcogenides PbM6Te10 (M = Ga, In), based on difference frequency generation of optical process in term of the EFOM and experiment parameters. The calculated terahertz light conversion efficiencies of PbGa6Te10 and PbIn6Te10 are in the order of 10-3 to 10-2 at low side of THz wavelengths, and the conversion efficiency of PnIn6Te10 is larger than that of PbGa6Te10 at the same conditions. A small terahertz wavelength and absorption coefficient, and large nonlinear susceptibility, i.e. a large EFOM will result in a large conversion efficiency. These studies give an indication that the chalcogenides with heavy element composites are the desired candidates as terahertz source generation. The present work will give contributions to evaluate and search new NLO materials as terahertz source generation.

Abstract-Theoretical Evaluation of Terahertz Sources Generating From Infrared Nonlinear Optical Materials SnGa4Q7 (Q = S , Se)

http://onlinelibrary.wiley.com/doi/10.1002/cphc.201601128/abstract

We have theoretically evaluated the integrate knowledge, which contribute to conversion efficiency, including the phonon, photon and electron properties of infrared nonlinear optical materials SnGa4Q7 (Q = S, Se) being as terahertz (THz) sources. Specially, we have developed a new formula to calculate susceptibility of difference frequency generation (DFG) optical process. By the characteristics of materials-self properties in the THz region, we find that a larger nonlinear susceptibility or a large figure of merit will result in a large efficiency of THz source by the comparisons between the findings of SnGa4Se7 and SnGa4S7 under the same experimental conditions, and the THz absorption will reduce the efficiency of THz source for the two materials of SnGa4Q7 (Q = S, Se). The efficiency of THz source also depends on the experimental conditions. A large crystal size, strong pump intensity and small THz wavelength will gain large efficiency of THz source based on DFG process. The efficiency is a comprehensive index to evaluate the THz source based on DFG process.

Abstract-Terahertz transmission and sensing properties of microstructured PMMA tube waveguide

Fei Fan, Xuanzhou Zhang, Shanshan Li, Decai Deng, Ning Wang, Hao Zhang, and Shengjiang Chang
https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-23-21-27204&id=330151

A terahertz (THz) tube waveguide with grating structure has been designed, fabricated and characterized as a microstructure waveguide sensor. The resonance and polarization properties of this microstructured tube have been experimentally and theoretically investigated, which indicates that the grating etched on the tube surface has a remarkable modulation effect on the tube resonance and polarization dependence for THz waves. Moreover, a real-time quantitative sensing has been realized based on this tube waveguide in the THz time-domain spectroscopy system. Compared with the bare tube without grating, the grating structure strongly enhances the interaction between THz evanescent field on the tube surface and analytes, improving the sensitivity. This microstructured PMMA THz tube reveals a high sensitivity of 50GHz/μl and precision of larger than 0.125μl with a good linear relationship for THz sensing applications.

© 2015 Optical Society of America

Abstract-Theoretical investigation of semiconductor supported tunable terahertz dielectric loaded surface plasmons waveguides

• Chunlin Liu, 
• Xiaoyong He, 
• Zhenyu Zhao, 
• Hao Zhang, 
• Wangzhou Shi

• Department of Physics, Mathematics & Science College, Shanghai Normal University, No. 100 Guilin Road, Shanghai 200234, PR China

Received 16 April 2015, Revised 12 July 2015, Accepted 21 July 2015, Available online 30 July 2015

http://www.sciencedirect.com/science/article/pii/S0030401815006604

The tunable propagation properties of semiconductor-based dielectric loaded surface plasmons (DLSPs) structures have been theoretically investigated in the THz regime, including the effects of temperature, operation frequency, and the thermo-optic effect of dielectric stripe materials. The results show that the waveguide properties of DLSPs structure can be modulated in a wide range via changing the temperature. For instance, when the temperature is changed in the range of 300–600 K, the modulation depth of propagation length can reach more than 80%. With the increase of refractive index of the dielectric stripe, the modulation depth of the effective indices and propagation lengths increase. In addition, the propagation length and figure of the merit can be improved obviously with the hybrid dielectric stripe structure (by coating Si on the SiO₂ layer). The results are very helpful to design novel waveguide devices, such as modulators, switchers, sensors and polarizers.

Abstract-Terahertz polarization splitter based on orthogonal microstructure dual-core photonic crystal fiber

Shanshan Li, Hao Zhang, Yu Hou, Jinjun Bai, Weiwei Liu, andShengjiang Chang  »View Author Affiliations

A broadband polarization splitter operating in the terahertz (THz) band is proposed based on dual-core photonic crystal fiber with orthogonal microstructure in the core regions. The Index Converse Matching Coupling method is presented to design the THz polarization splitter for the first time, which exhibits several advantages, such as short splitting length, high extinction ratio, low loss, and broad operation bandwidth. By numerical simulation, it has been found that the strong coupling occurs within a frequency range of 0.4–0.7 THz. The operation bandwidth is more than 0.15 THz (equal to 138 μm). The shortest splitting length is only 1.83 cm at 0.4 THz. The extinction ratios for both of x and y polarization are better than −15  dB when the frequency is larger than 0.51 THz. The lowest material absorption loss is only 0.34 dB at 0.4 THz. Moreover, this structure is simple to design and easy to fabricate over its counterparts in the communication band. Our research offers an effective method to design a broadband THz device and would be of significance for future relevant applications

© 2013 Optical Society of America