Optimization and Performance Analysis of 1×2 and 1×4 MMI Splitters on a Polymer Platform for Board-Level Optical Interconnects

Polymer waveguides are promising for short-reach, board-level optical interconnects due to low-loss propagation and fabrication compatibility. This work presents the design, beam-propagation-method (BPM) simulation, and optimization of step-index polymer multimode-interference (MMI) splitters with 1×2 and 1×4 configurations at λ = 1550 nm. The devices are modeled in RSoft BeamPROP using SUNCONNECT organic–inorganic hybrid polymers (core: NP001L2, n = 1.573; cladding: NP216, n = 1.560). Geometrical parameters of the multimode section and access/output interfaces, including WMMI, LMMI, taper dimensions, and port spacing, are refined via parametric sweeps to obtain clean self-imaging with low loss and uniform splitting. The optimized 1×2 splitter achieves 50%/50% power splitting with excess loss of 0.67 dB (TE) and 0.65 dB (TM) and polarization-dependent loss of 0.02 dB. The optimized 1×4 splitter provides near-uniform splitting (25.05%, 24.95%, 24.95%, 25.05%) with excess loss of 0.33 dB (TE) and 0.34 dB (TM) and polarization-dependent loss of 0.01 dB. These results indicate that compact polymer MMI splitters can provide low-loss and scalable passive fan-out for board-level optical routing.