Multimode Interference Coupler Integrating Dual 50/50 Splitters and Waveguide Crossing

We present a novel multimode interference coupler (MMI) that integrates two independent 50/50 splitters and an on-chip waveguide crossing into one compact block. With four inputs and four outputs, the outer inputs split evenly to the outer outputs, while the inner inputs split to the inner outputs. This geometry inherently produces a waveguide crossing, removing the need for a separate crossing component. Fabricated devices show broadband 50/50 splitting with <3% imbalance and <0.51% (-23 dB) leakage to unintended outputs from 1530 nm to 1570 nm.