Frequency-Reconfigurable Wide-Angle Terahertz Absorbers Using Single- and Double-Layer Decussate Graphene Ribbon Arrays.

Longfang Ye,Fang Zeng,Yong Zhang,Qing Liu,Xiaofan Yang,Xiong Xu

doi:10.3390/nano8100834

Abstract

We propose and numerically demonstrate two novel terahertz absorbers made up of periodic single- and double-layer decussate graphene ribbon arrays. The simulated results show that the proposed absorbers have narrowband near-unity terahertz absorption with ultra-wide frequency reconfiguration and angular stability. By tuning the Fermi level of graphene ribbons, the over 90% absorbance peak frequency of the absorber with single-layer graphene structure can be flexibly adjusted from 6.85 to 9.85 THz for both the transverse magnetic (TM) and transverse electric (TE) polarizations. This absorber with single-layer graphene demonstrates excellent angular stability with the absorbance peaks of the reconfigurable absorption bands remaining over 99.8% in a wide angle of incidence ranging from 0 to 70°. The tuning frequency can be significantly enhanced by using the absorber with double-layer graphene structure from 5.50 to 11.28 THz and 5.62 to 10.65 THz, approaching two octaves under TM and TE polarizations, respectively. The absorbance peaks of the reconfigurable absorption band of this absorber for both polarizations maintain over 70%, even at a large angle of incidence up to 70°. Furthermore, an analytical fitting model is also proposed to accurately predict the absorbance peak frequencies for this variety of absorbers. Benefitting from these attractive properties, the proposed absorber may have great potential applications in tunable terahertz trapping, detecting, sensing, and various terahertz optoelectronic devices.

Highlights

Terahertz waves generally refer to electromagnetic waves with a frequency of 0.1–10 THz
An enhanced angular stability up to 70◦ (50◦) was achieved in that absorber for transverse magnetic (TM) polarized terahertz waves at 0.94 THz, but the insensitive angle of incidence was drastically decreased to 25◦ as the absorption band shifted to the higher-frequency end at 1.08 THz
We propose a new variety of frequency-reconfigurable narrowband near-unity terahertz absorbers with significantly enhanced relative frequency tuning range (RFTR) and angular stability using single/double-layer decussate graphene ribbon arrays (S/DLDGRAs)

Summary

Introduction

Terahertz waves generally refer to electromagnetic waves with a frequency of 0.1–10 THz. An enhanced angular stability up to 70◦ (50◦) was achieved in that absorber for transverse magnetic (TM) (transverse electric, TE) polarized terahertz waves at 0.94 THz, but the insensitive angle of incidence was drastically decreased to 25◦ as the absorption band shifted to the higher-frequency end at 1.08 THz. In addition, dual-band tunable terahertz and mid-infrared MAs with RFTRs of 31.4% and 19.5% were achieved [26,27]. How to achieve tunable graphene-based absorbers with larger RFTR and wider angular stability remains a challenge To address this issue, we propose a new variety of frequency-reconfigurable narrowband near-unity terahertz absorbers with significantly enhanced RFTR and angular stability using single/double-layer decussate graphene ribbon arrays (S/DLDGRAs).

Geometric Configurations of the Absorbers

Findings

Analytical Prediction of the Reconfigurable Absorbance Peak Frequencies