Design and Modeling of High Efficiency Graphene Intensity/Phase Modulator Based on Ultra-Thin Silicon Strip Waveguide

Abstract

Based on the electro-absorption/electro-refraction effect of graphene, we present a high efficiency intensity/phase modulator by exploiting ultra-thin silicon strip waveguide (UTSSW) structure. Due to the special structure of UTSSW, the propagating transverse electric (TE) mode is less confined to the core of silicon and penetrate deeper into the cladding SiO2 layer, which makes the double-layer graphene closer to the maximum of electric field. The combination of UTSSW structure and double-layer graphene facilitate low insertion loss (IL) together with high modulation efficiency modulator. The graphene intensity/phase modulator performances are comprehensively studied in terms of attenuation, IL, modulation depth (MD), optical operation bandwidth, phase shift, energy per bit (Ebit) consumption, and 3-dB electro-optic bandwidth. With graphene chemical potential μ = 0 eV, the MD is about 0.297 dB/μm, 0.304 dB/μm, 0.306 dB/μm for typical incident light wavelength λ = 1310 nm, 1550 nm, 2000 nm, respectively. When the electro-refraction working region is set between 0.6 eV and 1.0 eV, the $\Delta {\rm{Re}}({{\rm{n}}_{{\rm{eff}}}})$ keeps >6.8 × 10−3 with the wavelength increasing from 1250 nm to 2000 nm, which can be used for phase modulation. The maximum value of $\Delta {\rm{Re}}({{\rm{n}}_{{\rm{eff}}}})$ is 8.055 × 10−3 at incident light wavelength of 1616 nm. The 3-dB electro-optic bandwidth of graphene intensity/phase optical modulator are estimated by using an RC circuit model. Moreover, performances metrics dependence on the distance between the capacitor plates d and the doping level (EF) of transferred graphene are quantitatively analyzed and described. Finally, the quantum capacitance of designed graphene-based intensity modulator with different charged impurity concentration are also discussed when graphene μ = 0 eV and μ = 0.6 eV, respectively.