Automated Photonic Waveguide Loss Measurement Using Out-scattering Light Method

Characterization of optical waveguide propagation loss is fundamental to the practical realization of integrated photonics. Evaluating waveguide performance throughout the fabrication process enables rigorous quality control and rapid fabrication process development and optimization. Conventional measurement techniques such as the cutback and modified cutback methods directly measure the out-coupling light intensity from optical fibers and photonic waveguides of different lengths, and subsequently estimate the waveguide propagation loss. These methods are generally laborious, requiring many measurements for each device. Additionally, they are destructive to the device under test, as in the case of the cutback method, or require specially-designed arrays of various lengths, as in the case of the modified cutback method. In this work, we describe a method utilizing the out-scattering light intensity profile to efficiently assess multiple waveguides non-destructively and in a fully-automated manner to determine the individual waveguide propagation loss and identify faulty waveguide regions. The accuracy of the out-scattering method is validated using traditional modified cutback methods. Moreover, a comparative analysis of the two methods is presented, along with strategies to optimize their performance. This study is performed using Parylene photonic waveguides, which we have recently demonstrated for light delivery into the brain for neural stimulation.