STEP AND GRADED-INDEX CORE-BASED POLYMER MULTIMODE INTERFERENCE SPLITTERS FOR PHOTONIC INTEGRATED CIRCUITS

This paper demonstrates step-index (SI) and graded-index (GI) core-based multimode interference (MMI) splitters realized with polymer materials for photonic integrated circuits (PICs). These SI and GI index-based MMI splitters guide the input light through the multimode waveguide following the self-imaging principles and demonstrate the multiple outputs with the same uniformity when the self-imaging length is obtained. We numerically design and develop (1×5) MMI splitters by using the beam propagation method (BPM), and we use the RSoft CAD BeamPROP solver for the structural design and waveguide characterization. The structures of the SI and GI MMI splitters are optimized by investigating the structural parameters, particularly the width and length of the multimode waveguide and the core spacing between the output ports with the maximum uniform intensity at the self-imaging length. We also compare the structural design and optical properties of the SI and GI MMI waveguides. The excess losses of the SI MMI splitter are 1.09 and 1.12 dB for transverse electric (TE) and transverse magnetic (TM) modes, respectively, while for the GI MMI splitter, the losses are 0.56 dB and 0.55 dB for TE and TM modes, respectively at 1.55 µm. The power splitting efficiency of SI MMI splitters is 77%, and for GI MMI splitters, it is 88%. We also investigate the polarization dependence loss (PDL) for both MMI splitters, and the losses for SI and GI MMI splitters are 0.024 dB and 0.005 dB, respectively.