Broadband graphene terahertz modulators enabled by intraband transitions

Abstract

Terahertz technology promises myriad applications including imaging, spectroscopy and communications. However, one major bottleneck at present for advancing this field is the lack of efficient devices to manipulate the terahertz electromagnetic waves. Here we demonstrate that exceptionally efficient broadband modulation of terahertz waves at room temperature can be realized using graphene with extremely low intrinsic signal attenuation. We experimentally achieved more than 2.5 times superior modulation than prior broadband intensity modulators, which is also the first demonstrated graphene-based device enabled solely by intraband transitions. The unique advantages of graphene in comparison to conventional semiconductors are the ease of integration and the extraordinary transport properties of holes, which are as good as those of electrons owing to the symmetric conical band structure of graphene. Given recent progress in graphene-based terahertz emitters and detectors, graphene may offer some interesting solutions for terahertz technologies.

Self-biased reconfigurable graphene stacks for terahertz plasmonics

“…The measured hysteresis behaviour of the sample conductivity, which is mainly related to the charges trapped in the dielectrics surrounding the graphene layers 45 , is not considered in the model. In addition, the extracted values permit estimating a modulation speed of 6.2 kHz for the stack (see Supplementary Note 1), similar to the one found in singlelayer graphene structures 12,46 .…”

“…The characterization of single-layer graphene structures has already been done for microwaves [4][5][6][7] , THz 7-9 and optics 3,10 , and some promising applications such as modulators [11][12][13][14][15][16] , plasmonic waveguides 17,18 and Faraday rotators 19 have been developed. However, the simple implementation and performance of these devices might be hindered by the presence of a gating electrode located close to graphene and the relatively weak control that this approach offers over the conductivity of graphene 11,20 .…”

“…Furthermore, the Coulomb drag of massless fermions has been experimentally measured 27 , while both intra-and interlayer phenomena in structures surrounded by various dielectrics and their influence in the supported in-phase and out-of-phase plasmons have also been considered 28,29 . Potential applications of graphene stacks include modulators 12 , enhanced metasurfaces 30 , antennas 31 , or plasmonic parallel-plate waveguides 18,32 , among many others. Experimentally, graphene stacks have recently been applied to the development of vertical field effect transistors (FET) transistors 33,34 .…”

Graphene-Enhanced Optical Signal Processing

“…The primary mechanism of optical absorption in graphene involves two processes: carrier intraband transitions and interband transitions [25][26][27]. For short wavelengths (that is, infrared and visible range), the graphene optical absorption is determined by interband transitions, whereas for long wavelengths (that is, terahertz range), it is dominated by intraband transitions.…”

A low-voltage high-speed terahertz spatial light modulator using active metamaterial

“…10,15,16 These dynamic metamaterial SLMs are electronically controlled by injecting charges or depleting them in the bulk semiconductor substrate, which is an inherently slow process due to the intrinsically large capacitance of what is essentially a large bulk diode structure. 15,17,18 This results in a slow switching speed and large dynamic power consumption. Moreover, in typical integrated circuit (IC) processes, this large diode needs 15 V-50 V to completely deplete the charges.…”