Engineered scattering elements used as optical test points in photonic integrated circuits

. Efficient packaging of fabricated photonic integrated circuits (PICs) has been a daunting task given the breadth of applications and skill required for scalable manufacturing. One particular challenge has been accurately assessing the polarization state at various points in a PIC during the test, assembly, and packaging process. Polarimetric monitoring is necessary for optimizing fiber alignment, for verifying the quality of PIC components and for polarization-related functional testing. We analyze and demonstrate small-footprint engineered scattering elements for polarization monitoring. We find that small scatterers placed above or below a Si or SiN waveguide provide the best polarization integrity in a way that preserves foundry compatibility. The polarization response of these elements along with proper placement provides an optical test point that can be utilized for optimized fiber coupling into waveguides.