An efficient three-waveguide spot size converter using 180nm silicon photonic process node

An efficient silicon three-waveguide spot size converter (SSC) featured by 180nm silicon photonic process node is proposed to deal with the butt coupling between InP-based quantum well laser diode (QW LD) and silicon on insulator (SOI) chip. With two sets of overlapped Si nanotapers employed at input facet of SSC, followed by a central Si waveguide tapered down to 450-nm-wide and 220-nm-high output facet, the coupling efficiency (CE) of mode conversion in transverse electric (TE) mode for a wavelength of 1342nm is calculated. The best coupling loss is 1.18dB at zero deviation and the tolerance of misalignment up to 1-dB loss increase are ±0.6μm for X axis and ±0.4μm for Y axis, respectively. The relatively low-loss transformation achieved by this structure shows less dependance of SiP process node better than 180nm. We also confirm that the coupling loss of three-waveguide SSC will be lower than 0.5dB if 140-nm-wide tip is allowed by more advanced process.