Numerical investigation of the linearity of graphene-based silicon waveguide modulator

We investigated the linearity of graphene-based silicon waveguide modulators used in microwave photonics links. A theoretical model was developed to systematically analyze the linearity performance for the second-order harmonic distortions (SHD2) and the third-order intermodulation distortions (IMD3). For the graphene-based silicon waveguide electro-absorption (EA) modulator, the distortions were suppressed through bias optimization. As a result, the maximal spurious free dynamic range (SFDR) obtained for SHD2 and IMD3 were 105.9 dB ·Hz^1/2 and 117.8 dB·Hz^2/3, respectively. For the graphene-based silicon waveguide electro-refraction (ER) phase modulator, SHD2 was fully eliminated through the push-pull modulation and quadrature biasing, while the remaining IMD3 term was linearized by the proper adjustment of the bias voltage and phase shifter length to obtain an ultrahigh SFDR of 130 dB ·Hz^2/3. Moreover, the graphene-based silicon waveguide ER modulator is more compact and tolerant to bias errors than a pure silicon modulator. These results reveal that the graphene-based silicon waveguide EA and ER modulators can be potentially utilized in integrated microwave photonics.