Heterogeneously Integrated PLC With Low-Loss Spot-Size Converter and Newly Developed Waveplate PBS for DC-DP-16QAM Receiver

Digital coherent transmission systems with multilevel and multicarrier modulation formats have been moving beyond 100-G systems. In this paper, we report a one-chip 400-G coherent receiver founded on a silica-based planar lightwave circuit (PLC) integration platform. To integrate a polarization beam splitter (PBS), two polarization rotators, four-optical hybrids, and 16 high-speed photodiodes (PDs) in one chip, we employed a 5%-Δ waveguide with a minimum bending radius of 300 μm, and the heterogeneous integration of InP-PDs. To achieve a compact receiver without any degradation in optical passive performance, we also investigated a three-branched spot size converter with a low loss and a high-fabrication tolerance and a waveplate type PBS with a high-polarization extinction ratio. Using these techniques, we fabricated a dual-carrier dual-polarization (DP) 16-level quadrature amplitude modulation (QAM) receiver PLC, and successfully demonstrated 32-Gbaud DP-16QAM signal demodulation for each channel.