In the same year Xing et al adopted graphene-on-Si WGs as mode filters see Figure 6c to suppress the propagation of spurious modes224 which was the key to promote the development of the mode division

In recent years, the demand for high-speed data transmission has increased rapidly, leading to the development of mode division multiplexing optical systems. However, the propagation of spurious modes presents a significant challenge in achieving high-quality data transmission. To address this issue, Xing et al. utilized graphene-on-Si waveguides as mode filters. By selectively tailoring and deploying graphene segments on the waveguide surface, differential absorption of the TE0 (stop) and TE1 (pass) modes was achieved, resulting in the suppression of spurious modes. This mode filter demonstrated high selection ratios, large bandwidth, and low insertion losses, making it an effective solution for stop-mode filtering. Overall, the implementation of graphene films has facilitated the development of mode division multiplexing optical systems, meeting the growing bandwidth demands of modern communication technologies