Low insertion loss and high modulation depth Tunable modulator at Telecommunications Band enable by graphene/hBN multilayer gratings

In this paper, a novel Graphene Plasmonic Grating modulator is composed of four-layer graphene, encapsulated in hBN layers, and merged with a Fabry-Perot (FP) cavity presented. The main aim of graphene in the proposed modulator is to tune the FP cavity's resonant frequencies. The Standing electric field waves induced by the FP interferometer are strongly formed at the top of grating, where the hBN/graphene layers are established. Therefore, propagation surface plasmon polaritons (SPPs) on graphene sheets strongly confines the electric field between the graphene and hBN layer at the top of the gratings, causing the high absorption of the proposed structure and allowing for modification of the optical signals in the telecommunications range wavelengths. An Au electrode keeps transmission light from the proposed structure at zero. Therefore, the incident light is either absorbed or reflected, which gives the proposed modulator another feature since it can operate in both the absorption and reflection modes and can be adjusted to any desired wavelengths. Moreover, the proposed structure can be used as a perfect absorber since its absorption spectra reach a high value of 100 %. A reflection (absorption) type modulator with a central wavelength of $1.55\mu \mathbf{m}$, a modulation depth of 97% (98%), insertion loss of 0.20 dB (0.22 dB), with a gate voltage difference of 0.18 V is designed. In addition, the modulation depth of 97 % for both regimes are evaluated in the wavelength of 1.3 and 1.8 μm, Moreover, numerous modulators with different modulation parameters are designed in any desired wavelength of 1–2 μm simply by adjusting the FP interferometer resonance by electrostatically tuning the graphene chemical potential via gate voltage.