Abstract-Double-stacked hyperbolic metamaterial waveguide arrays for efficient and broadband terahertz quarter-wave plates

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• Xianmin Ke, 
• Hua Zhu, 
• Junhao Li, 
• Lin Chen & 
• Xun Li

http://www.nature.com/articles/s41598-017-00726-3

We demonstrate how it is possible to achieve weak dispersion in the phase delay between two orthogonal polarization states by using double-stacked hyperbolic metamaterial (HMM) waveguide arrays. The weak dispersion in the phase delay originates from the different signs of phase delay from the two different HMM waveguide arrays. The condition of dispersion-free phase delay for the transmitted waves has been theoretically derived from the transmission matrix as the propagation characteristic of the HMM waveguide is involved. We further reveal that the designed double-stacked HMM waveguide array can function as an efficient quarter-wave plate that enables the conversion of linearly polarized light to circularly polarized light within a broad frequency band. In addition, the bandwidth over which the degree of linear polarization is nearly unity and over which the angle of linear polarization is kept at approximately 45° is basically consistent with the phase bandwidth. This offers a promising approach for developing a practical polarization converter in the terahertz domain.

Abstract-Ultrabroad terahertz bandpass filter by hyperbolic metamaterial waveguide

Ultrabroad terahertz bandpass filter by hyperbolic metamaterial waveguide Xuetong Zhou, Xiang Yin, Tian Zhang, Lin Chen, and Xun Li  »View Author Affiliations

Optics Express, Vol. 23, Issue 9, pp. 11657-11664 (2015)
http://dx.doi.org/10.1364/OE.23.011657

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http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-23-9-11657

We propose and demonstrate an ultrabroad terahertz (THz) bandpass filter (BPF) by integrating two different-sized tapered hyperbolic metamaterial (HMM) waveguides, each of which has wide but different absorption and transmission bands, into a unit cell. With proper structural design of each HMM waveguide to control the absorption and transmission bands, we numerically demonstrate the designed BPF is capable of operating with a broad passband in the THz domain. A typical TM-polarized HMM BPF has a peak transmission of 37% at 3.3 THz with the passband bandwidth of 2.2 THz ranging from 2.97 to 5.17 THz. The co-designed three-dimensional HMM BPF also shows the capability of operating with independence to the polarization of incident light because of the structural symmetry and has sharp bandedge transitions of 22.6 and 17.6 dB/THz to the stop bands, respectively. The presented results here hold great promise for developing practical THz BPF with various applications in THz field.

© 2015 Optical Society of America

Abstract-Plasmonic rainbow trapping by a graphene monolayer on a dielectric layer with a silicon grating substrate

                                                                                                

Schematic of the designed graded plasmonic grating structure (GPGS) for rainbow trapping in the infrared domain. The width of dielectric spacer, w 1 , increases linearly from 10nm to 30nm with an incremental step s.

Lin Chen, Tian Zhang, Xun Li, and Guoping Wang »View Author Affiliations
http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-21-23-28628

Considering the propagation of surface plasmon polaritons (SPPs) supported by a graphene monolayer can be effectively controlled via electrostatic gating, we propose a graphene monolayer on a graded silicon-grating substrate with dielectric spacer as an interlayer for plasmonic rainbow trapping in the infrared domain. Since the dispersive relation of SPPs is dependent on the width of dielectric spacer filling the silicon grating, the guided SPPs at different frequencies can be localized at different positions along the graphene surface, associated with the period of silicon grating. The group velocity of slow SPPs can be made to be several hundred times smaller than light velocity in vacuum. We also predict the capability of completely releasing the trapped SPPs by dynamically tuning the chemical potential of graphene by means of gate voltage. The advantages of such a structure include compact size, wide frequency tunability, and compatibility with current micro/nanofabrication, which holds great promise for applications in graphene-based optoelectronic devices.
© 2013 Optical Society of America