Low voltage, high modulation depth graphene THz modulator employing Fabry-Perot resonance in a metal/dielectric/graphene sandwich structure

In this article, a novel THz modulator for modulating signals in the frequency range of 0.5-10 THz is designed and numerically investigated with finite difference time domain method. The structure is composed of a graphene layer sandwiched between two complementary metallic gratings. The proposed structure has Fabry-Perot like behavior at which the resonant condition depends on the geometrical parameters of the device and graphene plasmonic mode characteristics. A major advantage of the presented modulator is its capability to function in various regimes such as resonant and non-resonant as well as transmission and reflection. Based on the proposed structure, a broadband modulator for THz signals in the frequency range of 0.5-3 THz is proposed with modulation depth of 90% (36%) at 0.5 THz (3 THz). Insertion loss of the modulator is 1.2 dB. Electro-optic bandwidth is more than 2 GHz depending on the device surface area. In addition to this, several low voltage and relatively narrowband modulators are designed either at central frequencies of 4.5, 5.5, and 6.5 THz with modulation depth of more than 75% and insertion loss of less than 2.5 dB at their central frequency.