Observation of Gate-Tunable Coherent Perfect Absorption of Terahertz Radiation in Graphene

Abstract

Abstract:We report experimental observation of electrically-tunable coherent perfect absorption (CPA) of terahertz (THz) radiation in graphene. We develop a reflection-type tunable THz cavity formed by a large-area graphene layer, a metallic reflective electrode and an electrolytic medium in between. Ionic gating in the THz cavity allows us to tune the Fermi energy of graphene up to 1eV and to achieve critical coupling condition at 2.8 THz with absorption of 99%. With the enhanced THz absorption, we were able to measure the Fermi energy dependence of the transport scattering time of highly doped graphene. Furthermore, we demonstrate flexible active THz surfaces that yield large modulation in the THz reflectivity with low insertion losses. We anticipate that the gate-tunable CPA will lead efficient active THz optoelectronics applications.

Controlling phase of microwaves with active graphene surfaces

“…Integrating these thin layers with a metamaterial structure is demonstrated as a good intensity and phase tuning device in IR and THz [19][20][21][22] region. Very recently, we have demonstrated active graphene devices operating in terahertz 23 and microwave frequencies 24 . We integrated electrically tunable graphene as a tunable absorbing layer and showed that these devices can operate as a perfect intensity modulator at their resonance frequencies.…”

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

“…The surface impedance of the graphene layer can be expressed as [20] Z 1 The surface impedance of the graphene layer can be expressed as [20] Z 1…”

“…[2][3][4] Most of these structures, however, were passive devices and incapable of real-time adjustment. [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. [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.…”

“…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. [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. 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.…”

“…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.…”