Broadband, Spectrally Flat, Graphene‐based Terahertz Modulators

Abstract

Advances in the efficient manipulation of terahertz waves are crucial for the further development of terahertz technology, promising applications in many diverse areas, such as biotechnology and spectroscopy, to name just a few. Due to its exceptional electronic and optical properties, graphene is a good candidate for terahertz electro-absorption modulators. However, graphene-based modulators demonstrated to date are limited in bandwidth due to Fabry-Perot oscillations in the modulators' substrate. Here, a novel method is demonstrated to design electrically controlled graphene-based modulators that can achieve broadband and spectrally flat modulation of terahertz beams. In our design, a graphene layer is sandwiched between a dielectric and a slightly doped substrate on a metal reflector. It is shown that the spectral dependence of the electric field intensity at the graphene layer can be dramatically modified by optimizing the structural parameters of the device. In this way, the electric field intensity can be spectrally flat and even compensate for the dispersion of the graphene conductivity, resulting in almost invariant absorption in a wide frequency range. Modulation depths up to 76% can be achieved within a fractional operational bandwidth of over 55%. It is expected that our modulator designs will enable the use of terahertz technology in applications requiring broadband operation.

Family of graphene-assisted resonant surface optical excitations for terahertz devices

“…This value is larger than that of devices based on Fig. 1c 11 12 , and much larger than the experimentally measured values, which are 15% or below, for devices based on SRR or monolayer graphene on a flat substrate 10 13 14 . In this paper, we mainly focus on the devices based on the excitation of graphene SPPs.…”

“…Again, the issue of this type of devices is the large footprint. For a resonance frequency in the sub-THz region, the thickness of the substrate is around 100 μm to few hundred micrometers 10 11 . The operational range is also limited even with a large doping of the graphene sheet.…”

Current-controlled light scattering and asymmetric plasmon propagation in graphene

“…The tunability is achieved by applying a gate voltage that allows the charge carrier density in graphene to be controlled externally [6][7][8] . This opens up many exciting possibilities for creating tunable photonic devices [9][10][11][12] that can potentially help bridge the gap between photonics and electronics 13,14 .…”

All-Optical Graphene-Based Modulation of Surface Plasmon Polaritons via Modulation Instability for Secure Optical Communication

“…Due to its large effective surface, graphene can efficiently support Surface Plasmon Polaritons (SPPs). On this base, several studies represented the proof of concept for designing and fabricating the graphene-based optical modulators from electro-optical to all-optical plasmonic modulators [16,[23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]. A huge nonlinearity can be released in a system containing the multiple graphene sheets embedded inside a dielectric host [21][22].…”