Compact InP-based 1×2 MMI splitter on Si substrate with BCB wafer bonding for membrane photonic circuits

Ultra-low power and compact optical interconnects can be realized with III-V-based membrane photonic integrated circuits (PICs) on Si platform. This study focused design and fabrication of the III-V-based passive components of the PICs, especially, a compact 1×2 multimode interference (MMI) splitter with SiO₂ buried GaInAsP wire structure. The calculated excess loss was as low as 0.28dB in the optimized structure, and the structural tolerance obtained was as low as 0.05dB, when MMI width W_MMI, length L_MMI, output gap Y were changed in range of ± 50 nm. The footprint of the MMI region was only 1.4×1.5 μm². In the spectral range of 1548-1552 nm, the average excess loss measured was around 3dB and the average imbalance between the outputs was 0.5dB allowing the compact size and light splitting function.