Multimode Switch for Modes E11/E12, E21 on a 640-nm Silicon Photonics Platform Using an Adiabatic Y-Junction–MMI Hybrid: Numerical Study

A multimode switch (MMS) enables efficient multimode optical communication for high-speed data transmission. In this paper, we design and numerically demonstrate a compact 1×2 MMS on a silicon photonic platform with a 640-nm-thick silicon core, which departs from the conventional 220-nm SOI standard to support higher-order guided modes. The device architecture consists of an adiabatic Y-junction coupler with a central straight waveguide section, whose two output branches are connected to a 2×2 multimode interference (MMI) coupler. Thermo-optic phase shifters are integrated to provide dynamic control of the optical path, enabling simultaneous switching of optical states among the E ₁₁ , E ₁₂ , and E ₂₁ modes. Simulation results show that the proposed MMS achieves low insertion loss (< 1.9 dB) and crosstalk below − 16 dB across a 40-nm bandwidth in the C-band (1525–1565 nm). Beyond compactness and low loss, the conceptual design offers reconfigurability and scalability for multifunctional on-chip mode-division multiplexing interconnects, providing promising potential for large-scale photonic integrated circuits in broadband communication applications.