Design of a graphene-based silicon nitride multimode waveguide-integrated electro-optic modulator

The mode-division (de) multiplexing (MDM) technology is promising to scale the transmission capacity of on-chip optical communications by carrying information on different spatial modes of a multimode waveguide. For the current MDM technology, different spatial modes are first converted to the fundamental mode and then modulated in parallel by individual electro-optic modulators, which may result in a large device footprint and high-power consumption. Here we designed a graphene-based silicon nitride waveguide-integrated spatial mode modulator to individually modulate different spatial modes in a multimode waveguide. Specifically, we utilized the coplanar interaction between patterned graphene layers and propagating light in the multimode waveguide to introduce contrasting phase shifts to different spatial modes. Based on the optimized waveguide configuration, a Mach-Zehnder interferometer modulator is designed. Our study paves the way for the development of high-density on-chip MDM systems for optical interconnects and on-chip optical networks.