Polarization monitoring of photonic components using optical test points

Photonic integrated circuit technology has become a popular design platform for applications ranging from optical communications to biomedical sensing. The testing of these components is often very challenging, typically requiring multiple electrical/optical connections for testing of a single feature. However, these testing schemes typically cannot provide information about the guided mode immediately before or after the feature under test. In particular, any change in polarization state along with the relative loss incurred by a component are important quantities to verify in testing. These figures of merit are typically extrapolated with prior knowledge of the loss within a waveguide, or monitored by integrated sensors. Using engineered scattering elements as optical test points, information regarding the polarization state of light can be gleaned without the need for any other connections beside the input fiber coupler. Observation of these test points is possible using a short-wave infrared microscope with the polarization information discernible with an integrated rotating quarter-wave polarimeter. Placing engineered scattering elements before/after directional couplers, we observe a change in polarization between the input and output states. Additionally, we monitor the relative power splitting between each output branch and compare our findings with designed values.