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

Abstract

has made realistic applications of the THz wave very limited. Among the functional THz devices, perfect absorbers are highly desirable in manipulating the THz wave in a number of important fields.In recent years, extensive efforts have been devoted to perfect THz absorption based on artificial structures, such as metasurfaces. [2][3][4] Most of these structures, however, were passive devices and incapable of real-time adjustment. Graphene, a 2D sheet of hexagonally arranged carbon atoms, has attracted much attention in the past decade due to its extraordinary electronic and optoelectronic properties. [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. 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. At THz frequencies, graphene-based absorbers were also experimentally realized. By integrating monolayer graphene into a classical Salisbury screen structure, perfect THz absorption was achieved. [19][20][21][22] However, the graphene Fermi level needed to realize perfect absorption was very high and the thickness of the absorbers were required to be around λ/4, which is too bulky for optical integration. A broadband, nearly perfect THz absorber based on patterned graphene was also reported [23] with a relatively small electrical tunability. 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. The measured results show that perfect absorption can be achieved with a more lightly doped chemical vapor deposition (CVD) graphene compared to that of the classical Salisbury screen absorber and the modulation depth of absorbance can reach up to 25%. Numerical simulations were performed using commercial full-wave numerical software showing a good agreement with the measurements. Furthermore, we proposed a simple Graphene, as a popular 2D semiconductor, with a carrier concentration that can be extensively tailored by external stimulants, such as electric bias and photoexcitation, is a promising candidate for active optoelectronics. An electrically tunable perfect terahertz absorber is presented by integrating a metallic grating into classical graphene Salisbury screen. The measurement shows that perfect absorption can be achieved for even lightly-doped graphene and a modulation depth up to 25% is realized. Numerical simulation and analytical model based...

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