Abstract-Tunable terahertz wave difference frequency generation in a graphene/AlGaAs surface plasmon waveguide

Tao Chen, Liangling Wang, Lijuan Chen, Jing Wang, Haikun Zhang, and Wei Xia

https://www.osapublishing.org/prj/abstract.cfm?uri=prj-6-3-186

Graphene-based surface plasmon waveguides (SPWs) show high confinement well beyond the diffraction limit at terahertz frequencies. By combining a graphene SPW and nonlinear material, we propose a novel graphene/AlGaAs SPW structure for terahertz wave difference frequency generation (DFG) under near-infrared pumps. The composite waveguide, which supports single-mode operation at terahertz frequencies and guides two pumps by a high-index-contrast AlGaAs/AlO𝑥$\mathrm{AlGaAs}/{\mathrm{AlO}}_x$ structure, can confine terahertz waves tightly and realize good mode field overlap of three waves. The phase-matching condition is satisfied via artificial birefringence in an AlGaAs/AlO𝑥$\mathrm{AlGaAs}/{\mathrm{AlO}}_x$ waveguide together with the tunability of graphene, and the phase-matching terahertz wave frequency varies from 4 to 7 THz when the Fermi energy level of graphene changes from 0.848 to 2.456 eV. Based on the coupled-mode theory, we investigate the power-normalized conversion efficiency for the tunable terahertz wave DFG process by using the finite difference method under continuous wave pumps, where the tunable bandwidth can reach 2 THz with considerable conversion efficiency. To exploit the high peak powers of pulses, we also discuss optical pulse evolutions for pulse-pumped terahertz wave DFG processes.

© 2018 Chinese Laser Press

Abstract-Dynamic tuning of mid-infrared plasmons in graphene–buffer–SiO2–Si nanostructures

Morteza Hajati and Yaser Hajati
https://www.osapublishing.org/josab/abstract.cfm?uri=josab-33-6-1303

Dynamic tuning of the plasmonic properties of graphene-based multilayer nanostructures provides a promising platform for the development of novel optoelectronic devices. In this paper, we numerically demonstrate that inserting an ultrathin dielectric buffer layer between monolayer graphene and a SiO2/Si substrate can result in highly tunable and confined low-loss mid-infrared surface plasmons. The characteristics of surface plasmons in the proposed device can be effectively controlled by changing the permittivity and thickness of the buffer layer, operation frequency, and chemical potential of graphene. In particular, we show that using nanometric buffer materials with dielectric constants lower than that of SiO2 can lead to a low propagation loss with better performance. In contrast, utilizing nanometric buffer materials with dielectric constants higher than that of SiO2 reduce the guided wavelength, resulting in a strong optical confinement. Moreover, increasing the operation frequency (chemical potential) leads to an increase (decrease) in propagation loss in the proposed structure.

© 2016 Optical Society of America

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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.