Design and optimization of optical modulators based on   graphene-on-silicon nitride microring resonators
  In order to overcome the challenge of obtaining high modulation depth due to weak graphene-light interaction, a graphene-on-silicon nitride (SiNx) microring resonator based on graphene's gate-tunable optical conductivity is proposed and studied. Geometrical parameters of graphene-on-SiNx waveguide are systematically analyzed and optimized, yielding a loss tunability of 0.04 dB/{\mu}m and an effective index variation of 0.0022. We explicitly study the interaction between graphene and a 40-{\mu}m-radius microring resonator, where electro-absorptive and electro-refractive modulation are both taken into account. By choosing appropriate graphene coverage and coupling coefficient, a high modulation depth of over 40 dB with large fabrication tolerance is obtained. 
Zeru Wu, Yujie Chen, Tianyou Zhang, Zengkai Shao, Yuanhui Wen, Pengfei   Xu, Yanfeng Zhang, and Siyuan Yu
physics.optics