Low-loss inverted taper edge coupler in silicon nitride

An inverted lateral taper with one vertical discrete step was designed for a medium confinement silicon nitride waveguide platform in the C-band, as a chip edge coupler, with a predicted insertion loss of 0.58 dB. The design is supported by an extensive study to evaluate the impact of fabrication process variations on the performance of such a coupler. The device was manufactured and measured, showing an insertion loss of 1.47 dB, which was traced back to fabrication process variations as cross-checked with simulations. To the authors' knowledge, the reported edge coupler is the shortest and among the best performing found for silicon nitride platforms.