Polarization-Independent Modulator by Partly Tilted Graphene-Induced Electro-Absorption Effect

A polarization-independent graphene-based electro-absorption optical modulator concept is presented. The device is based on a slanted silicon stripe upon which two graphene flakes reside; on this surface, another silicon waveguide is capped, forming a rectangular silicon-graphene waveguide (SGW). Simulation results show that effective mode index of both TE and TM modes in the SGW undergo almost the same variations under different biases across a broad wavelength range. For a 30-μm-long silicon-graphene waveguide, throughout the S, C, and L communication bands, extinction ratio (ER) higher than 20 dB can be obtained by proper choosing of switching points for “ON” and “OFF” states. The ER discrepancy between TE and TM modes is smaller than 2.3 dB, and the polarization dependency is lower than 0.1 dB for “ON” state, which fulfills the requirement of polarization-independent modulation. Calculations show that the 3-dB modulation bandwidth higher than 100 GHz of our modulator is possible.