An All Optical Method for Fabrication Error Measurements in Integrated Photonic Circuits

We propose an optical method to quantify the level of fabrication imperfections in a Silicon On Insulator wafer. The method is based on the use of Side Coupled Integrated Spaced Sequence of Resonators (SCISSOR) as test devices. Fabrication induced fluctuations of the effective index and of the coupling coefficient are mapped by comparing different spectral responses of nominally identical samples taken from different dies in the wafer. Random variations of the resonator's optical path are quantified in terms of standard deviations of normally distribuited variables by finding a statistical correlation with the coupled resonator induced transparency (CRIT) phenomena. We found a strong correlation between CRIT and fabrication errors. This led us to design a SCISSOR based test structure that allows to quantify the degree of local structural imperfections in a fast, accurate and non invasive way. Performances, possible applications and limitations are investigated with the help of transfer matrix simulations.