Silicon Photonic Polarization-Multiplexing Nanotaper for Chip-to-Fiber Coupling

We describe the design and operation of a polarization-multiplexed optical coupler that is integrated into a silicon photonic IC. The design is based on a nanotaper, and thus permits broadband edge-based coupling to lensed single-mode fiber. Since it operates adiabatically, the polarization-multiplexing nanotaper exhibits superior performance over an extremely broad bandwidth of 130 nm, and is robust to the fabrication variations that are typical of CMOS processes. Polarization crosstalk is below -30 dB, PDL is within ±0.5 dB, and the insertion loss is comparable to that of a traditional single-polarization nanotaper. We also demonstrate the operation of the polarization-multiplexing nanotaper in a high-speed DP-QPSK test bed.