Design of a Graphene-Based Waveguide-Integrated Multimode Phase Modulator

The on-chip mode-division multiplexing (MDM) is an attractive technique to achieve high-capacity optical transmissions by using a single-wavelength carrier. In traditional schemes, multiple channels with a fundamental mode are modulated by parallel arranged electro-optic modulators and then converted to high-order modes. However, the method is usually limited by large device footprints and high energy consumption. In this work, we study a graphene-based waveguide-integrated multimode phase modulator to individually modulate TE0 and TE1 modes in a multimode waveguide device. To be specific, we designed a single layer of graphene narrow strips (GNSs) integrated on the surface of the multimode waveguide device to selectively introduce contrasting phase shifts to different modes. Based on the optimized waveguide structures, a Mach-Zehnder interferometer modulator with different GNS patterns on each arm is designed. Our study is promising to be used in the future high-density on-chip MDM systems for optical interconnects and optical networks.