Monolithic Integration of 2-D Multimode Interference Couplers and Silicon Photonic Wires

A new technology using hydrogen annealing and thermal oxidation is proposed to fabricate a very compact 2-D multimode interference coupler monolithically integrated with two-layer silicon photonic wires. Two devices, a 1 × 1 cross-power coupler and a 1 × 2² power splitter, are presented and characterized. The experimental result shows that a 3-dB transmission bandwidth of 1.1 nm, and the on-chip coupler losses of 8.6 dB and 2.84 dB were accomplished for the 1 × 1 cross-power coupler and the 1 × 2² power splitter. This paper demonstrates the possibility of realizing 3-D photonic integration for silicon-on-insulator lightwave circuits.