Graphene-based waveguide modulator for independent control of amplitude and phase

This study presents a highly efficient graphene-based electro-optical phase and amplitude modulator operating at 1550 nm, specifically designed for the TE fundamental mode. A phase difference of π is achieved at a minimum propagation length of 105 μm by applying 7.5 volts, with a V_π·L coefficient of approximately 0.0787 V·cm. By leveraging the unique optical and electrical properties of graphene integrated within a waveguide structure, the device attains a very low insertion loss of only 0.016 dB over 105 μm, enabling effective phase modulation and amplitude control. Additionally, the shortest length at which a 3 dB extinction ratio is reached for amplitude modulation is 13 μm. Circuit model analysis indicates a modulation bandwidth of f_3dB=6.5 GHz and a modulation depth of 99.6% (0.228 dB/µm) for a compact device with a 105 μm waveguide length. Dynamic performance is further validated through eye-diagram simulations at this length, which show an extinction ratio of 11.02 dB at a bit rate of 20 Gbits/s. This graphene-based electro-optic modulator offers a single structure for both phase and amplitude modulation, allowing separate control of these functions via bias voltage.