Broadband absorber with periodically sinusoidally-patterned graphene layer in terahertz range

Abstract

We demonstrate that a broadband terahertz absorber with near-unity absorption can be realized using a net-shaped periodically sinusoidally-patterned graphene sheet, placed on a dielectric spacer supported on a metallic reflecting plate. Because of the gradient width modulation of the unit graphene sheet, continuous plasmon resonances can be excited, and therefore broadband terahertz absorption can be achieved. The results show that the absorber's normalized bandwidth of 90% terahertz absorbance is over 65% under normal incidence for both TE and TM polarizations when the graphene chemical potential is set as 0.7 eV. And the broadband absorption is insensitive to the incident angles and the polarizations. The peak absorbance remains more than 70% over a wide range of the incident angles up to 60° for both polarizations. Furthermore, this absorber also has the advantage of flexible tunability via electrostatic doping of graphene sheet, which peak absorbance can be continuously tuned from 14% to 100% by controlling the chemical potential from 0 eV to 0.8 eV. The design scheme is scalable to develop various graphene-based tunable broadband absorbers at other terahertz, infrared, and visible frequencies, which may have promising applications in sensing, detecting, and optoelectronic devices.

Toward Ultimate Control of Terahertz Wave Absorption in Graphene

“…From (13), (14), and (15) we can see that both the freespace impedance and the input impedance of the metasurface substrate change with θ i . Therefore, if perfect absorption is defined at normal incidence, the increase of the incident angle will degrade the absorption level since the matching conditions (9) and (10) are not satisfied anymore.…”

“…For example, under this assumption on mobility, graphene is patterned into different shapes to enable plasmon-induced absorption and realize various functionalities. In particular, full absorption [12], [13] as well as broadband [14], [15] and multiband [16], [17] absorption spectra have been reported. Despite the appeal of these theoretical predictions, it has been very difficult to realize this performance in laboratory.…”

Electrically Tunable Perfect Terahertz Absorber Based on a Graphene Salisbury Screen Hybrid Metasurface

“…[5] As a 2D semiconductor, its electron mobility and Fermi level can be extensively controlled by external stimulants, such as gate voltage [6] and thus its surface conductivity. [24][25][26][27][28][29] However, most studies mainly focused on simulations and calculations. At THz frequencies, graphene-based absorbers were also experimentally realized.…”

“…Therefore, graphene has been a promising candidate for active optoelectronics applications and absorber devices based on demonstrations in the microwave [7,8] and infrared [9][10][11][12][13][14][15][16][17][18] regimes. [24][25][26][27][28][29] However, most studies mainly focused on simulations and calculations. By integrating monolayer graphene into a classical Salisbury screen structure, perfect THz absorption was achieved.…”

“…Besides, theoretical works on graphene-based THz absorbers were proposed. [24][25][26][27][28][29] However, most studies mainly focused on simulations and calculations. Therefore, experimental realization of electrically tunable perfect THz absorption based on lightly-doped and low-quality graphene with deep subwavelength dimensions remains as an unsolved challenge.In this article, we experimentally demonstrate an electrically tunable perfect THz absorber by integrating a metallic grating into a graphene-based Salisbury screen structure.…”