Abstract

Graphene modulators suffer from a poor on-off ratio due to graphene and insulator imperfections, a finite operating temperature and a limited modulation voltage. Modulating the loss in critically coupled resonators was previously demonstrated to allow infinite extinction in the off-state. However, figures of merit combining the influence of MD and IL have not been considered by these works. In a first step it was attempted to optimize the MD/IL ratio of arbitrarily shaped modulators by inverse photonic design. The resulting modulators exhibited an improvement in the MD/IL ratio only for geometries that introduce significant loss in the on-state. These observations adhere to a fundamental limitation for singly coupled resonantors used in the preceding works. The limitation was identified using the analytical expressions for the transmission of an all pass filter ring resonator. As a result the strong extinction in resonant modulators was shown to contribute less than \qty{5}{%} improvement to the relative optical modulation amplitude. The strongly enhanced light matter interaction provides the opportunity to reduce the graphene area per device. By using a computational model of the doping variations in graphene it is shown that reducing the graphene dimensions can have beneficial effects on the switching ratio beyond the limitations stated above. Efforts to evaluate the minimum graphene dimensions and the autocorrelation length of doping variations in graphene, suggest that resonant enhancement has the potential to scale the graphene well below the doping correlation length. Those findings imply that a significant deterioration of the switching behavior can be eliminated. However, further experimental evidence should be collected to support or disprove the conclusions made here.