Compact four-port optical mode router based on direct mode-selective coupling

Mode-division multiplexing has emerged as an effective approach to increase the capacity of on-chip optical interconnects. Efficient routing and add-drop manipulation of different modes are therefore essential for scalable multimode photonic integrated circuits. However, implementing compact mode routers with low loss, low inter-mode crosstalk, and high-speed signal compatibility remains challenging on the silicon photonic platform. In this work, we propose and experimentally demonstrate a compact four-port optical mode router on a silicon-on-insulator platform. The device enables mode-selective and bidirectional add-drop routing for multiple modes by integrating multimode waveguide crossings, multimode waveguide bends, and mode-selective microring resonators. Low-loss and low-crosstalk operation is achieved through carefully designed mode-matching and multimode waveguide engineering. Experimental results show correct routing for three supported modes with inter-mode crosstalk below -15.4 dB and an insertion loss below 6.6 dB. High-speed data transmission at 40 Gbit/s is demonstrated for all routing paths, resulting in an on-chip aggregate data capacity of 480 Gbit/s. The proposed architecture provides a scalable solution for high-capacity mode-division-multiplexed optical interconnects on a silicon photonic platform.