Penalties from 2D Grating Coupler Induced Polarization Crosstalk in Silicon Photonic Coherent Transceivers

Silicon photonic two-dimensional grating couplers for C-and O-band dual-polarization coherent transceivers are analyzed with respect to their polarization splitting/combining performance. Due to scattered light in the grating's plane, a linear cross-polarization results. The latter is responsible for a limited polarization split ratio and a polarizations' non-orthogonality. The impact of these two quantities is evaluated by system-level simulations with regard to OSNR penalties in coherent systems. For both C-and O-band, a design modification for reduced penalties is proposed.