Enhanced spatial terahertz modulation based on graphene metamaterial

Abstract

The plasmonic mode in graphene metamaterial provides a new approach to manipulate terahertz (THz) waves. Graphene-based split ring resonator (SRR) metamaterial is proposed with the capacity for modulating transmitted THz waves under normal and oblique incidence. Here, we theoretically demonstrate that the resonant strength of the dipolar mode can be significantly enhanced by enlarging the arm-width of the SRR and by stacking graphene layers. The principal mechanism of light-matter interaction in graphene metamaterial provides a dynamical modulation based on the controllable graphene Fermi level. This graphene-based design paves the way for a myriad of important THz applications, such as optical modulators, absorbers, polarizers, etc.OCIS Graphene is a promising two-dimensional (2D) material in many fields due to its extraordinary mechanical, thermal, electronic, and optical properties [1][2][3] . Various graphenebased electronics and photonics devices operating in a passive or active mechanism have been demonstrated, such as optical modulators, saturable absorbers, photodetectors, and polarizers [2,4,5] . Particularly, graphene has shown advantages in manipulating terahertz (THz) waves thanks to the controllable interaction between THz waves and graphene by turning the carrier concentration (i.e., Fermi energy) through physical or chemical methods [6] , which could provide a splendid platform for the design of THz devices [7] . Nevertheless, the intensity of interaction between graphene and THz waves is not strong enough for practical applications due to its nonresonant Drudelike behavior [8] . Artificially constructed material (metamaterial) can be introduced for enhanced light-matter interaction. The plasmonic resonance in metamaterials excited by incident light can be tailored by the structure and size [9] , which plays a crucial role in modulation and manipulation of electromagnetic waves. Consequently, the combination of graphene and metamaterial provides promise for THz applications, which bridges the "THz gap" between the far infrared field and microwave region [10,11] . Recently, investigations about graphene metamaterial THz devices have been carried out. For instance, Alaee et al. proposed a perfect absorber by patterning graphene micro-ribbons on a dielectrics-metal layer [12] . Freitag et al. demonstrated a polarization sensitive gate tunable photodetector by patterning graphene microribbons [13] . A pioneering work about a modulator based on a hybrid graphene/metamaterial structure was also proposed, which can modulate the amplitude of THz waves up to 90% with normal incidence [14] . Among the THz applications, a THz modulator is one of the most important devices. Semiconductors were the most used materials for THz applications, however, there still exists some problems in these traditional devices, such as poor modulation depth and strict operation temperature requirements [15,16] . Further improvement for the traditional semiconductors or 2D graphene-based THz modulators is largely needed for prac...

Enhanced absorption and electrical modulation of graphene based on the parity-time symmetry optical structure

“…Its conduction band and valence band meet at the Dirac point. Accordingly, graphene is equivalent to a zero-gap semiconductor with electron mobility exceeding 15,000 cm 2 • V −1 • s −1 at room temperature [1] , which endows graphene excellent electrical and optical properties and prompts a wide range of potential applications in the perfect absorption of optoelectronic devices, optical communication systems, as well as sensing devices [2][3][4][5][6][7][8] . Due to monolayer graphene itself being incapable of exciting surface plasmon resonances, its theoretical absorption efficiency in air is exclusively about 2.3% of the single-pass light [9] , which seriously obstructs its application range and device performance.…”

Graphene-Assisted Narrow Bandwidth Dual-Band Tunable Terahertz Metamaterial Absorber

“…Metamaterial absorbers showcase huge application value in communication, security, detection and other fields, and have increasingly become one of the study hotspots in terahertz region [11][12][13][14][15][16][17][18][19][20]. Landy et al reported a metamaterial absorber with perfect absorption characteristics for the first time [21].…”